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Information required prior to loading of a given Chemical Cargo in Bulk:

1. The correct chemical name of the cargo should be provided so that the appropriate data sheet in the Tanker Safety Guide (Chemicals) can be consulted.
2. Quantity in Weight.
3. Required quantity control – Contamination is measured in parts per million (ppm). Thus tanks & pipelines must be practically spotless. Degree of wall-wash required.
4. Specific Gravity – This is required in order that an estimation can be made of the probable volume that the weighed quantity will occupy.
5. Temperature – This is required for two purposes.
   • The loading temperature is used in conjunction with the specific gravity to obtain the probable volume of the particular parcel.
   • The temperature at which the cargo is to be carried will indicate if heating will be required on passage. Some chemicals will solidify or polymerize if a certain temperature is not maintained. Polymerization is a chemical reaction in which small molecules combine into larger or very large molecules, which contain thousand of the original molecules. Thus a free flowing liquid can become a viscous liquid or even solid.
6. Compatibility – Certain chemicals react with other chemicals and thus may not be stowed in adjacent compartments.
7. Tank coating compatibility – The tank coating must be suitable for the proposed cargo.
8. Corrosive Properties – This will also indicate the required tank coating and also possible damage to ship fittings.
9. Electrostatic generation – Some chemicals can accumulate static, the principles which apply to HC cargoes should be applied to chemical static accumulators.
10. Fire & Explosion Data – It has been previously noted that 50 % of the chemicals transported are derived from hydrocarbon oil and thus fire hazards are similar to those which pertain to petroleum products.
11. Toxicity – Chemicals which emit highly toxic vapours requires Closed Ventilation and Ullaging System.
12. The Health Hazard of the particular parcel.
13. Reactivity.
14. Action to be taken in the event of particular emergencies – Most of the above information and additional essential information can be found on the chemical data sheets in the safety guide.

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Publications which are referred to get info Prior to Loading Chemical Cargo:

1. On receipt of the name of the cargo, the certificate of fitness must be checked to verify if the said vessel is allowed to carry that particular cargo as enlisted in the COF.
2. Depending on whether the ship is constructed before / after 01-07-1986. The relevant IBC Code / BCH Code must be consulted. Chapter 17 of the IBC code – contains summary of minimum requirements & various information pertaining to the cargo can be obtained.
3. Additional information can be obtained from the chemical data sheet pertaining to that cargo – found in the ICS (International Chamber of Shipping) publication. Tanker Safety Guide – Chemical in Volume – I, II, III & IV.
4. Also added information can be obtained from USCG system. CHRIS – Chemical Hazard Response Information System, provided for essential decision making during emergencies involving the water transport of the hazardous chemicals.
5. The “Procedure & Arrangement” (P & A) manual which is ship specific, gives information such as tank arrangement, pumping & piping arrangements any special requirements to assists any loading can be obtained.
6. Annex 2 of the MARPOL 73/78 should be referred to obtain discharge criteria & procedure.
7. Paint compatibility guide – to check if the coating in the tank will withstand with particular cargo to load.

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Types of Chemical Tankers:

There are 3 basic types of Chemical Tankers, All 3 types are meant to carry chapter 17 cargoes of IBC code.

Type I ships

• It must be able to survive assumed damage anywhere in their length. Cargo tanks for the most dangerous products should be located outside the extent of the assumed damage and at least 760mm from the ship’s shell. 
• IMO type 1, 2 and 3. Other cargoes, which present a lesser hazard may be carried in tanks next to the hull – (incl diluted slops after tank washings)

See layout below–

• Some of the chemicals carried on type one ships are Chlorosulphonic acid, Dodecyl phenol, Phosphorous yellow/ white, Tricresyl Phosphate (>1% ortho-isomer), Trixylyl Phosphate.
• Maximum tank size is 1250 M3.
• Double side width B/5 or 11.5 mtrs whichever is less.
• DB depth B/15 or 6 mtrs at centre line, but not < 760mm.
• Auto ignition temperature of cargoes <65 deg C.
• Explosive range >50% by volume in air.
• Type 1 offers highest limit of containment.

Type II ships

• If more than 150m in length, must be able to survive assumed damage anywhere in their length; if less than 150m, the ship should survive assumed damage anywhere except when it involves either of the bulkheads bounding machinery spaces located aft. Tanks for Type II cargoes should be located at least 760mm from the ship’s shell and outside the extent of assumed grounding damage.
• Maximum tank size is 3000 M3.
• Capable of stripping tanks <100 litres.
• Auto ignition temp of cargoes <200 deg C.
• Explosive range >40% by volume in air.

Type III ships

• If more than 125m in length, should be capable of surviving assumed damage anywhere in their length except when it involves either of the bulkheads bounding the machinery space.  If less than 125m in length, they should be capable of surviving damage anywhere unless it involves machinery spaces. There is no special requirement for cargo tank location. No limit for size of tank.
• Capable of stripping tanks <300 litres with tolerance of 50 litres.
• Length > 125 m but < 225 m damage anywhere in length except including ER bulkheads.
• Length <125 m damage anywhere in length except machinery space

After 1 January 2007 vegetable oils are carried in chemical tankers complying with the revised IBC Code as a Ship Type-2 (double hull) with COF as Cat Y.

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Chemical Tankers: P & A Manual

• MARPOL Annex II requires that each chemical tanker be provided with a P&A Manual to achieve compliance with the regulations and to be able to demonstrate that compliance has been considered from the earliest design stage. The format of the P&A Manual and its contents must be as specified in MARPOL Annex II Appendix D, and be approved by the flag administration of the ship.

• The P & A Manual is concerned with the marine environmental aspects of cleaning of cargo tanks, and the discharge of cargo residues that may or may not be mixed with a washing medium. The results of the stripping test are recorded in it.

• Ships’ officers should familiarise themselves thoroughly with the P&A Manual, and adhere at all times to operational procedures with respect to cargo handling, tank cleaning, stop handling, residue discharge, ballasting and deballasting. The master is obliged to ensure that the ship does not discharge into the sea any cargo residues, or mixtures of residue with water, unless such discharges are made in full compliance with the operational procedures contained in the P&A Manual, and that the equipment required by the Manual for such discharge is used.
• The P & A Manual, together with the cargo record book and Certificate of Fitness, will be checked by the ship’s own flag administration and by port state control officers in order to confirm full compliance with the requirements of MARPOL Annex II.

• It is now recognised that almost any discharge from a ship into the surrounding environment needs to be carefully considered in advance. Not only are chemical cargo residues, oily water from machinery room bilges and overboard disposal of garbage strictly regulated, but funnel exhausts and ballast water have now been identified as requiring control.

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Cargo Related Documents required on board Chemical Tankers:

Transportation of chemicals by tankers is usually accompanied by considerable documentation. Documentation can be even greater when trading to and from less developed countries. The vessel’s management is presented with a great deal of documentation from parties to the cargo, authorities, etc. Furthermore vessel’s management must also issues papers serving to record evidence, claims etc.

Following are most needed documents:-

1. Deck Log Book
2. Sea Passage Report
3. Port Log
4. Notice of Readiness
5. Dead freight Statement
6. Protest of Difference Between Ship and Shore Figures
7. Pre arrival and Commencement – Cargo Operations Checklist
8. During Loading Ops Checklist
9. Completion of Cargo & Pre-departure Checklist
10. Prior to Use of Vapour Emission Control System Checklist
11. During Discharge Ops Checklist
12. Ullage Report
13. Pumping Record
14. Cargo Heating Report
15. Inert Gas Log
16. Tank Cleaning Record
17. ROB Report
18. Dry receipt
19. Vessel Experience Factor (Load)
20. Cargo Loading Plan
21. Cargo Discharge Plan
22. Chemical & Physical Properties
23. Pressure Log & O2 Log
24. Cargo Hose Record
25. Cargo Sampling Log
26. Tank Cleaning Plan
27. Tank Cleaning Schedule Checklist
28. Monitoring During Cleaning Operations
29. Wall Wash Test Results

Documents provided by the Shipper:-

1. Cargo quality certificate (analysis report)
2. Cargo quantity certificate.
3. Certificate of origin.
4. Cleanliness report.
5. Heating instructions.
6. Inhibitor certificate.
7. Cargo manifest.
8. Vessel’s experience factor.
9. Tank History.
10. Sample receipt.
11. Custom Clearance Reports / Papers

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Diagram, a ‘closed circuit’ loading operation, using a vapour return line on Chemical Tankers under the provision of IBC Code:

Closed loading guideline for various noxious liquid chemicals in bulk:

• Special precautions are necessary onboard a chemical tanker during closed loading of various grade liquid chemicals.
• Closed loading/discharge means loading or discharging with securely closed ullage, sounding and sighting ports. Additionally the venting must be controlled. Vessels equipped with a system such as Skarpenord (pressure gauges in the tanks) or radar ullage systems shall at all times carry out closed loading/unloading procedures for all cargoes. Closed loading should be used at all times unless not possible due to the design of the vessel or trade practices (e.g. vegetable oil trade loading over the top is normal.)
• For gauging e.g. ullaging and sounding closed devices must be used. The level alarm systems must be operated during the entire closed cargo operation. Closed cargo operations must be stopped as soon as any essential system for safe loading or discharging becomes inoperative. Sampling to be carried out with closed sampler whenever possible. When more than one grade of cargoes is loaded, use of same sampler for different grades will contaminate the cargo sample unless the sampler has been thoroughly cleaned.

Gauging, sounding and sampling:

• A closed gauging device penetrates the cargo tank, but is part of a closed system and prevents the cargo or its vapour being released. Examples are the float-type systems, radar systems, electronic probe, magnetic probe and protected sight-glass.
• For sampling and sounding, the Dovianus or Hermetic portable gauging and sampling systems may be used. It is important that sufficient of these devices are carried onboard and maintained in a fully operational and certified calibrated condition. The vessel must fully comply with ISGOTT “Measuring and Sampling Non-Inerted Tanks” and ISGOTT “Measuring and Sampling Inerted Tanks” as applicable.
• Vapour locks, where fitted, are to be calibrated and certified by a recognised cargo inspection company which will also approve the datum level corrections including list and trim corrections for tank volumes. The approval certificate is to be readily available during cargo surveys.

Cargo tank venting:

• Controlled venting must be established if closed cargo operations are required. A controlled tank venting system is a system with pressure and vacuum-relief valves (P/V-valve) fitted on each tank in order to limit the pressure or vacuum in the tank. The P/V valve should operate in such a manner that neither pressure nor vacuum is created in the cargo tank during cargo operations that exceed the tank design parameters.
• Secondary venting system must also be operational Information on maximum loading rates and venting capacities is to be readily available and displayed in the cargo control room.

Vapour emission control system onboard chemical tankers:

• Where required, VEC is to be used and operated in accordance with IBC Code, local regulations, and instructions contained in the vessel’s VEC System Operation Manual and in conjunction with the requirements and provisions of the shore installation.
• Masters and Officers must be aware that significant operational and safety implications are present, as the shore and the ship are effectively joined together as one unit.

The Primary Hazards include:

• The ship loses effective control of the tank atmosphere pressure, and is directly influenced by any changes which may occur within the terminals system.
• Associated pressure sensing devices on the vessel are well maintained.
• It is also essential that individual cargo tank P.V. valves are properly maintained and operate correctly.
• Check that the VECS alarms are correctly set and tested. (Secondary PV alarms are set 5-10% above PV valves setting as per Oil Major Requirements for normal operations).
• Whenever any of these alarms activates during cargo operations, the cargo operations shall be immediately stopped and cause of alarm activation rectified before resuming cargo operations.
• Vessels fitted with a VEC system must have an independent overfill alarm providing audible and visual warning. These are to be tested at the tank to ensure their proper operation prior to commencing loading, unless the system is provided with an electronic self-testing capability. Fixed gauging systems must be maintained in a fully operational condition at all times.
• The ship’s system is to be provided with means to collect and drain condensed vapour, which may have accumulated in the pipelines. Drains must be installed at low points within the ship’s piping system. These drains must be checked clear before each use of the VEC system and on a regular basis when the system is not in use.
• Care must be taken to ensure that no possibility of misconnection of Vapour and Liquid hoses can occur. The ship’s vapour connection is to be clearly identified. The outboard 1.0 metre of piping is to be painted with yellow and red bands (0.1m red, 0.8m yellow, 0.1m red) and marked with the word “Vapour” (not less than 50mm high). The vessel’s presentation flange is to be fitted with a stud to prevent an incorrect connection.
• To prevent electrostatic build up within the vapour return pipe work, all pipe work is electrically bonded to the hull. The integrity of these connections is to be periodically checked.
• VECS manual requirements to complied with respect to loading rate, vapour density, pressure drop etc.
• The full procedures for the use of the VEC system are to be clearly agreed at the pre-transfer meeting between the Terminal Representative and the Chief Officer.

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Typical tank & Piping Arrangement of any one type of Chemical Tanker:

The pipes leading from the cargo tanks to the pumps are termed as bottom lines, from the pump-room up to deck are called risers. The lines on deck are termed as deck lines. The lines which lead from the deck to the tanks are called drop lines. Besides these, there are Crude Oil washing lines on deck (COW lines). The COW main line usually branches off from the main discharge line in the pump-room. It further branches out to the various tanks on deck. There is also a small diameter line (Marpol line) which is used to discharge the last part of the cargo from the ship.

In the cargo tanks, the pipes terminate in a bellmouth. A tank may have two bellmouths – one main and one smaller stripper bellmouth. Alternatively, one bellmouth may serve the purpose of main as well as stripping discharge.

The piping system has evolved over the years to cater to varying cargo requirements. In a product tanker which is designed to carry many grades, we see that there are many more pipes so that many grades can be catered to. In a crude oil tanker, the piping is straightforward and simple.

There are three basic types of pipeline systems:

1. Direct Line system
2. Ring main system
3. Free flow system.

Each system has their uses and is designed to fulfill a need in a particular type of vessel.

Direct Line system:-

It consists of lines running longitudinally in the centre tanks and branching out to bellmouths in the centre and wing tanks. The system is uncomplicated and found on some crude carriers.

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Procedure for Tank Cleaning a Cargo Tank in a Chemical Tanker:

No cleaning can take place unless the mandatory prewash as required by MARPOL is done.

The master must enforce precautions like “no smoking “and “AC on recirc “.  It is important for all on a chemical tanker to know the location of AC fresh air intake, and the Anemometer, to use the relative wind direction to advantage.  Bio accumulative vapours and carcinogenic fumes can enter the engine room via intake vents and cause health problems for the engine staff. It is not all right to say that just the deck crew are exposed to toxic vapors.

Water washing can be done even if the solubility of the chemical in water is low to as much as 0.3%.  such solubility always increases if the water temperature is higher. Hence always try to use wash water at high temperature ( about 25 deg higher than MP after removing cold ballast interface ) unless the cargo being cleaned does not allow it, like drying oils and mineral oils with high paraffin content.  Solidified matter when melted flows away with the stripped out water, it need not be soluble.

Mineral oils with high paraffin content and certain crude oils which require heating during transportation should always be cleaned with ambient wash to prevent evaporation of lighter fractions which would leave a waxy residue on tank bulkheads. 

Drying oils if prewashed with hot water will polymerize. Drying oils must be washed immediately after dischg with ambient water. If they are left to dry polymerization takes place due to reaction with oxygen, and heat increases the reaction speed. This means by removing the air form the tank using Nitrogen this process can be slowed down. By the way, Ambient means upto 35 deg C. Moderate means upto 60 deg. Hot means >60 deg C.

Certain cargoes like acetic acid, benzene, luboils, caustic soda, paraffin, molasses, phenol, DINP, fatty alcohols, HMD , Hitec, WPAC, butyl acrylate , creosote etc  can be hot pre-washed.

However, if you hot prewash Styrene monomer or Acrylic acid polymerization will happen. The hotter the water, the faster the polymerization. Due to condensation of vapour, inhibitor free liquid is formed, as the inhibitor is not volatile. Inhibitor if not removed will affect the PTT test.

When a cargo is fully soluble in water, using tank cleaning chemicals in a mindless manner does more harm than good.

Cleaning the tanks is just not enough. Most often it is the tank appendages which cause huge cargo claims or tank rejection. PV valves, vent lines, fixed pipelines , portable manifold hoses, superstrip lines, sampling and drain cocks, air/ nitrogen/ steam portable connection stubs, pump internals , cofferdams –all can hold contaminant matter. With certain cargoes like LSHW FO even the butterfly valve Teflon seals can trap sludge and discolor the next cargo.

Washing tanks with portable/ fixed Butterworth machines from designated areas may not clean everything. This is why it is important to enter the tank and have a visual check before wasting fresh water and expensive tank cleaning chemicals after high MP cargoes like palm oil fatty acids. As soon as you open the tank dome you get a general idea of shadow areas.

The chief officer must know if the tank corrugations are horizontal or vertical. Horizontal corrugations mean that fixed tank cleaning machines which cannot be given drops are ineffective. Vertical corrugations mean that the position of the Butterworth port is important.

If the previous cargo is strong smelling like Acrylates or Crude Turpentine or MTBE a smell killer can be used. Gaskets emit smell, hence they must be flushed with methanol.

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STAGES OF TANK CLEANING:-

1) Precleaning with sea water:- Pre cleaning is different from MARPOL mandatory Prewash. Tank cleaning machines may have shadow sectors, and this can be rectified for main wash. Nondrying oils and fats can be steamed before the hot water precleaning.

Pre-cleaning is the first cleaning step, without cleaning agents in order to remove the majority of product residue. The cleaning temperature and the temperature of the adjacent tanks are important parameters for successful cleaning. When water is not allowed, pre- cleaning is carried out with a suitable solvent. Pre-cleaning generally takes several hours and the sooner pre-cleaning is done after discharge, the easier it is to remove the product residue. Pre-cleaning is very important, because it is very difficult to obtain a satisfactory result following an initial mistake

2) Main wash with sea water: – Do not attempt to use tank cleaning chemicals unless the cargo clingage is removed.

3) Tank Cleaning Chemical wash: – If cargo is not water soluble or residues remain , the use of  tank cleaning chemicals is justified.  If the previous cargo is not water soluble using a 0.04% detergent wash will be good enough for WW standard ( this is not WALL WASH ).  Graco barrel pump injecting into the tankcleaning line , is the best as the bottom can be kept stripped and tank cleaning chemical is not reused.  Inject at the rate of 2 litres chemical per cubic meter of wash water.  Discharge from both sides of the manifold to Annex 2 UW overboard.

Recirc using spider / octopus will clean dirty areas, but they will also dirty clean areas.  Also if the solvent is volatile it will evaporate. Recirc is more effective after a Graco injection wash. Prevent static charge dangers. Annex 1 mineral oils which are not soluble in water requires a emulsifier/ degreaser wash. Handspray with undiluted chemicals is only for local application, sufficient contact time must be allowed.

Most cleaning agents are additives which are used in combination with water to improve the water solubility of the cargo to be cleaned. Only very few cargoes which cannot be cleaned with water-based systems require a non-water-based solvent as a cleaner (sometimes in combination with an emulsifier).

To neutralize the odor of some chemicals, the use of an odor remover may be recommended in combination with an emulsifier. For most cargoes a variety of cleaning agents are available. Cleaning agents must be IMO-approved. Cleaning concentrations, times and temperatures in the final cleaning steps are recommended in the cleaning guides to achieve a satisfactory result. Cleaning generally takes several hours.

4) Rinsing with sea water:- This is done with tank cleaning machines, the main purpose is to get rid of the residues loosened up by the tank cleaning chemicals.

5) Flushing with fresh water:- This is done with tank cleaning machine using a low throughput, to remove the salt before they dry up . If you anticipate a delay , as your ship does not have a dedicated FW pump or line prevent the salt from drying up by steaming, more so on zinc adsorbent porous surface.

6) Steaming tank and pipelines (to bring level of chlorides down and wash down appendages):- Steaming is the introduction of saturated steam into the tank to evaporate volatile residue (odour removal). The steam will condense on the tank surfaces. The temperature should normally be  as  high as  possible during steaming. This is enhanced if the adjacent tanks (including ballast tanks) are empty Steaming removes traces of volatile substances. The steam must hence be allowed to escape constantly via the PV valve.

If the chloride level of the wash water is too high, the use of steam for removal of chloride is often the only feasible option. Clearly the steam quality depends on the construction of the boiler.  If the steam is used to remove chloride, the wall temperatures should be cool (in contrast to the evaporation method described above) – this results in condensation  and  water  film  running  down  the  tank  walls  to  wash  the chlorides off.

In case of Wall wash , with low chloride specs, for optimal results the chloride content of the water must be less than 0.1 mg/ litre  (distilled water, deionized water, demineralized water by microfiltration).

7) Draining tank sump:- Strip out the tank and the pump stack. Sometimes it will be necessary to use a Wilden pump and sponges to save time.  Mopping reduces drying time if there are water pools on the tank bottom. Make sure no lint is left .

8) Drying tank with ventilation:- While venting please remember that warm moist air condenses on a cold surface.  Ventilation removes water, moisture and odor, which is usually done by forced air circulation.

The advantages are that:

1. It is easy to operate and less training of personnel is required.
2. As there are fewer valves, it takes less time to set up the valve system before commencing a cargo operation.
3. Contamination is unlikely, as it is easy to isolate each section.

The disadvantages are that:

1. The layout is not as versatile.
2. A very rigid system which makes it difficult to plan

Ring-main systems:-

• It is also called the circular system. This type of piping system provides for the handling of several different types of oil. A particular tank can be pumped out either by a direct suction line or through another line by use of a cross-over. The system is very versatile.

• The pipeline system illustrated above in Diagram 1 is better suited to the centre line bulkhead type of ship. Each tank or oil compartment has two suctions — one Direct suction and one Indirect suction. The direct suctions for the port tanks are all on the port cargo line, and feed the port cargo pump.
• The indirect suctions for the port cargo tanks feed the starboard cargo line and the starboard cargo pump. Master valves are provided on each line between the tanks, so as to isolate each tank from the other when necessary.
• This particular vessel is not fitted with a stripping line and pump. This type of pumping system providing for the handling of several different types of oil was a natural development from the earlier types which were only suitable for one grade of oil.
• To drain the oil from the main tanks it was necessary to list first one way, and then the other, so as to keep the strum covered and to help the flow of oil towards the suction.
• Diagram 2 shows a vessel fitted with a Circular Line or Ring Main but adjusted for the twin bulkhead type of vessel.
• This ship is also fitted with a stripping system. Inspection of the pipeline system shows that the pipeline travels around the ship in the wing tanks, crossing over from one side to the other.
• Each wing tank has a suction on the line which passes through it. The centre tanks have two suctions, one on either side leading to the port and starboard lines respectively.
• It will be noted that the master valves provide separation between the tanks as in the earlier system.
• When the level of the oil in any particular tank has fallen to a foot or less, the main pumps are switched to another full tank, and the stripping pump is brought into operation.

Free-flow system:-

• In this system, the oil flows freely into the aft most tanks when the interconnecting gate valves are opened.
• Main suction bellmouths in a full free flow tanker will only be provided in the aft tanks. However, each tank is generally provided with a small stripping line.
• This system has the distinct advantage of having lesser and less complicated piping system in the tanks and is suitable for large tankers which usually do not carry many grades of oil.
• Obviously, the flexibility of operations is comparatively less as compared to other piping systems. Some ships are also designed as part free flow i.e. free flow system only between certain tanks, which is a hybrid or cross between a full free flow system and a ring main system.

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Phosphoric Acid Discharge & Tank Cleaning:

• For all cargo operations including stripping & tank cleaning procedures always refer to ship’s P & A manual.
• Phosphoric Acid is normally carried in rubber lined or Stainless Steel Tanks.
• Phosphoric Acid is generally carried on a “Type 3” Chemical tanker.

IMO Ship Type 3:- is a Chemical Tanker intended to transport products with sufficiently severe environmental & safety hazards. These products require a moderate degree of containment to increase survival capability in a damaged condition. There is no filling restrictions for chemicals assigned to Ship Type 3.

Some of the properties of Phosphoric acid is listed below:-

Pollutant Category: Z

Sp. Gravity:- 1.685 @ 25^OC (Water =1 )

Vapour Pressure: 0.3 k Pa (@ 20^OC)

Vapour Density: 3.4 (Air = 1)

• Easily soluble in hot water. Soluble in cold water.
• Very hazardous in case of skin contact (irritant), of eye contact (irritant) of ingestion.
• Phosphoric Acid is non-flammable.
• Reacts with metals to liberate flammable hydrogen gas.
• Minor corrosive effect on bronze. Sever corrosive effect on brass, corrosive to ferrous metals & alloys.
• Polymerization will not occur.

Tank Cleaning:-

• Ensure the prewash after dischg is with fresh water. Then use sea water till the pH is 7. Immediately after that wash again with fresh water to remove all chlorides from tank. This is crucial to avoid elephant skin.
• Any sediment at the bottom of tank can only be removed with more pure phosphoric acid like crude oil wash. It will take a long time to kew machine the cement off the bottom. So keep some good clean pac in 200 drums for this manual effort.
• Have a look at the first empty tank. If the sediment is too much –it is usual to recirc at end of discharge of each tank.
• Acid/sea water mixture remaining in lines and stainless steel hoses will soon result in pittings.
• For Stainless Steel (SS) Tanks: – After the tanks are thoroughly/finally cleaned, passivate the tanks with Nitric Acid as the Phosphoric destroys the passive oxide coating on the stainless.
• Category Z:- Noxious Liquid Substances which, if discharged into the sea from tank cleaning or deballasting operations, are deemed to present a minor hazard to either marine resources or human health and therefore justify less stringent restrictions on the quality and quantity of the discharge into the marine environment.
• Every ship constructed on or after 1 July 1986 but before 1 June 2007 shall be provided with a pumping & piping arrangements to ensure that each tank is certified for the carriage of substances in Cat X or Y does not retain a quantity of residue in excess of 900 ltrs in the tank of its associated piping.
• Similarly each tank certified for the carriage of substances in Cat Z does not retain a residue of quantity in excess of 300 ltrs in the tanks and associated piping.

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Discharge Criteria for Tank wash residues into Sea:-

• Underwater discharge criteria are applicable to all ships built after 1 Jan 2007.
• If outside any S.A. (Special Area)
  • Discharge tank washing 12 NM from Nearest land.
  • Depth of water must be more than 25 mt.
  • Speed of ship must be more than 7 kmts.
• S.A. designated for Annex II cargoes is Antartic Region.
• Discharge of tank washings is not permitted in the Baltic Region.

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IBC Code: Integral tank:

Ans:- Integral tanks: Integral Tank means a cargo-containment envelope which forms part of the ship’s hull and which may be stressed in the same manner and by the same loads which stress the contiguous hull structure and which is normally essential to the structural completeness of the ship’s hull.

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IBC Code: Gravity tank. (July-18)

Ans:- Gravity tank: Gravity tank means a tank having a design pressure not greater than C). 7 bar gauge at the top of the tank. A gravity tank may be independent or integral. A gravity tank should be constructed and tested according to recognized standards, taking account of the temperature of carriage and relative density of the cargo.

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IBC Code: Pressure tank. (July-18)

Ans:- Pressure tank: Pressure tank means a tank having a design pressure greater than 0.7 bar gauge. A pressure tank should be an independent tank and should be of a configuration permitting the application of pressure-vessel design criteria according to recognized standards.

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Hazards involved with Tank Cleaning in Type 1 Chemical Tankers:

A Hazard is a physical situation with a potential for human injury, damage to property, damage to the environment, to capital investment or some combination of these. Hazards can be identified through a review of the Physical Properties and Product Characteristics of the product to be cleaned.

• Fire & Explosion Three elements are necessary to create a fire: Fuel, an Oxidiser (usually air) and a Source of Ignition (energy). In theory, ignition is not possible, if any one of the 3 is eliminated. Most cleaning operations will be carried out in tanks that are filled with air, thus the oxidiser is present in most cases, unless the tank is inerted. Fuel as far as tank cleaning is concerned could be the product itself, if this product has a low flash point, or a flammable cleaning solvent. Under certain circumstances even substances with a high flash point can be ignited and must thus be considered as a fuel (mist). During many tank cleaning operations the atmosphere in the tank must be considered as flammable because the product to be cleaned is flammable and inertisation is not possible. Under these circumstances the only way to guarantee that an explosion cannot occur during cleaning is to make certain that there is no source of ignition. A potential source of ignition during tank cleaning is Electrostatic discharge. Especially during water spraying electrostatic charges could be induced.
• Undesired reactions Polymerization (Depletion of inhibitor or excessively high temperature) Saponification (Creation of hard soap forming a layer on the tank requiring acid cleaning or even removal by Hydroblasting) Drying/Hardening (Formation of hard debris that is no longer soluble, requiring treatment with a Solvent) Reaction with water (Violent reaction of an Isocyanate after Pre-Cleaning with water)
• Corrosion – Corrosive substances destroy human tissue on contact (e.g. skin, eyes and mucous membranes in the mouth and respiratory tract) Metal or other material used in ship construction could be corroded at an excessive rate.
• Overexposure to toxic substances (Death of operator after wiping Phenol residues by tank entry without wearing a full chemical suit and SCBA [self-contained breathing apparatus])
• Asphyxiation – Oxygen deficiency (Entry into a tank with an inert gas atmosphere)
• Emissions
• To the air: As always when ventilating, special care must be taken to prevent the risk of explosion (flammable products) or with regard to toxic vapors. All normal safety precautions must be taken. (No smoking, accommodation ventilation on recirculation etc.) The wind strength and wind direction must also be a decisive parameter for the Master to allow ventilation. To avoid a buildup of explosive or toxic vapors on deck the amount of gas to be escaped from the tanks should be limited. Never open and ventilate several tanks at the same time.
• To the water: Emissions to the water should be reduced to the absolute minimum. All on-board facilities must be operated carefully according to the P&A Manual to reduce the residues during unloading. All regulations, especially MARPOL I and II, must be followed strictly.

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Certificate Of Fitness (COF) on Chemical Tankers:

• An International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk shall be issued after an initial or renewal survey to a chemical tanker engaged in international voyages which comply with the relevant provisions of the Code.
• Classification society issues the certificate of fitness on behalf of the administration.
• An International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk shall be issued for a period specified by the Administration which shall not exceed 5 years.
• All ships will get a new COF after 1.1.07, considering IBC code and Marpol rules are revised as on 1.1.07.  IMO has decided that Chemical carriers can carry COF or NLS, not both.
• Ships with COF can carry IBC code chapter 17 XYZ cargoes also —–  while NLS certificated ships an carry IBC code Chapter 18, Category Z and  OS cargoes only.
• For ships carrying IBC code chapter “Other Substances” OS, there is no need for COF, they require only NLS certificate.
• COF is a certificate issued by Flag administration confirming that the structure, equipment and materials used in the construction of the chemical tanker are in compliance to carry a given list of chemicals and it gives the conditions of carriage.
• Upon receipt of cargo loading instructions, all products are to be checked against the Certificate of Fitness. Any irregularities are to be reported immediately to the chemical operator. However, it must be understood that this by itself is not enough. The tank lining resistance tables must be consulted and only if both agree can the chemical be considered to be loaded.
• Since new chemicals are being manufactured and re-evaluated for safe sea carriage regularly it may be possible that some chemical is not included in the COF list. In such a case permission may be obtained from flag administration or their representative for this particular chemical and attached to the COF as an addendum.
• The issuance of an Addendum to CoF may be done immediately based on the Tripartite Agreement. The submission of data and evaluation by GESAMP and ESPH may come afterwards.

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Cargo tank coatings can be categorized into two main groups:

Inorganic coatings – zinc silicates and ethyl silicate types.

Generally, the life of this coating is proportional to the thickness of the coat. This coating is one-layer coating, comprising of inorganic silicates pigmented with high percentage of zinc powder.

Organic coatings – epoxy and modified epoxy systems.

This type of coating consists an organic resin system, which form strong chemical bonds between the resin molecules. Those types of coating have the ability to resist in more strong acids or alkalis than inorganic coatings. And they tend to absorb significant quantities of cargo and contamination problems can occurs.

Coating Systems and Types:

Numerous types of coating have been used for cargo tank service in sea trades. Some of these coating have stopped to being used. And more reliable and flexible coating has been developed. Typical coating system can be categorized as Zinc and Epoxy coating

Zinc Silicates:- Zinc silicates are formulation of zinc powder plus organic or inorganic binder, and designed to be porous films, which can create problem in the tank cleaning process especially when vessel carry non-volatile cargoes.

Main Characteristic:

• Not resistant to strong acid or bases, including sea water which has a slow weakening effect
• High resistance and tolerance to aromatic hydrocarbon solvent, alcohols and ketones
• Volatile cargoes are desorbed very fast, and retain non-volatile oil like cargoes.
• Residues can result in contamination of next or after next cargo

Epoxy:

Generally suitable for the carriage of alkalis, animals fats and vegetable oils but they have limited resistance to aromatics such as benzene and toluene, alcohols such as ethanol and methanol

Main Characteristic:

• Resistant to most strong acids and bases
• Do not retain oil like cargoes. Solvent cargoes are absorbed
• Water wash before thorough ventilation and desorption of residues could result in serious damage of the coating
• Residues can result in contamination of next or after next cargo
• Suitable for carriage of animal fats and vegetable oils provided the free fatty acid content of 5%.

Coatings are required for any cargo tank which constructed from mild steel. Most of BLT Chembulk Group modern chemical fleet is SUS cargo tank. SUS are good materials for chemical tanks, because of their ability to create a passive layer on their surface. This passive layer is mainly consisted by chromium oxide, which is very resistant to corrosive environment.

However, in some environments like strong hot acids, chloride solutions and generally solutions which contain halogens, the passive film can break down locally and new film formulation can be disrupted. Generally, SUS is considered to be the ideal material of construction because it’s non-corrosive and easy to clean.

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Hazards associated with Carriage of Chemicals:

• FLAMMABILITY:
  • Vapour given off by a flammable liquid will burn when ignited provided it is mixed with certain proportions of air, or more accurately with the oxygen in air. But if there is too little or too much vapour compared to the air, so that the vapour-and-air mixture is either too lean or too rich, it will not burn. The limiting proportions, expressed as a percentage by volume of flammable vapour in air, are known as the lower flammable limit (LFL) and the upper flammable limit (UFL), and the zone, in between is the flammable range (see Definitions for further details).
  • In addition, a flammable liquid must itself be at or above a temperature high enough for it to give off sufficient vapour for ignition to occur. This temperature is known as the flash point. Some cargoes evolve flammable vapour at ambient temperatures, others only at higher temperatures or when heated. Safe handling procedures depend upon the flammability characteristics of each product. Non-combustible cargoes are those which do not evolve flammable vapours
  • Volatile and Non Volatile Cargoes.
  • If a cargo is being handled at a temperature within 10C of its flashpoint, it should be considered volatile.
  • Therefore a cargo with a flashpoint of 80C should be considered volatile if handled at a temperature of 70C or above.

• HEALTH HAZARDS:
  • Toxic means the same as poisonous. Toxicity is the ability of a substance, when inhaled, ingested, or absorbed by the skin, to cause damage to living tissue, impairment of the central nervous system, severe illness or, in extreme cases, death. The amounts of exposure required to produce these results vary widely with the nature of the substance and the duration of exposure to it.
  • Acute poisoning occurs when a large dose is received by exposure to high concentrations of a short duration, i.e. a single brief exposure. Chronic poisoning occurs through exposure to low concentrations over a long period of time, i.e. repeated or prolonged exposures. Prevention of exposure is achieved through a combination of cargo containment, which prevents toxic fumes or liquid from contaminating the workplace, and the use of personal protective equipment (PPE)
  • Suffocation: suffocation is unconsciousness caused by lack of oxygen, Any vapour may cause suffocation, whether toxic or not, simply by excluding oxygen in air. Danger areas include cargo tanks, void spaces and cargo pumprooms. But the atmosphere of a compartment may also be oxygen-deficient through natural causes, such as decomposition or putrefaction of organic cargo
  • Anaesthesia: Certain vapours cause loss of consciousness due to their effect on the nervous system. In addition, anaesthetic vapours may or may not be toxic.
  • Additional health hazards: Additional health hazards may be presented by non-cargo materials used on board during cargo handling. One hazard is that of frostbite from liquid nitrogen stored on board for use as atmosphere control in cargo tanks. Full advice on dealing with frostbite is contained in the MFAG. Another hazard is that of burns from accidental contact with equipment used while handling heated cargoes.

• REACTIVITY
  • Self Reaction:
    • The most common form of self-reaction is polymerisation. Polymerisation generally results in the conversion of gases or liquids into viscous liquids or solids. It may be a slow, natural process which only degrades the product without posing any safety hazards to the ship or the crew, or it may be a rapid, exothermic reaction evolving large amounts of heat and gases. Heat produced by the process can accelerate it. Such a reaction is called a run-off polymerisation that poses a serious danger to both the ship and its personnel. Products that are susceptible to polymerisation are normally transported with added inhibitors to prevent the onset of the reaction.
    • An inhibited cargo certificate should be provided to the ship before a cargo is carried. The action to be taken in case of a polymerisation situation occurring while the cargo is on board should be covered by the ship’s emergency contingency plan.
  • Reaction with water: Certain cargoes react with water in a way that could pose a danger to both the ship and its personnel. Toxic gases may be evolved. The most noticeable examples are the isocyanates; such cargoes are carried under dry and inert condition. Other cargoes react with water in a slow way that poses no safety hazard, but the reaction may produce small amounts of chemicals that can damage equipment or tank materials, or can cause oxygen depletion.
  • Reaction with air: Certain chemical cargoes, mostly ethers, may react with oxygen in air or in the chemical to form unstable oxygen compounds (peroxides) which, if allowed to build up, could cause an explosion. Such cargoes can be either inhibited by an anti-oxidant or carried under inert conditions.
  • Reaction with other cargoes: Some cargoes react dangerously with one another. Such cargoes should be stowed away from each other (not in adjacent tanks) and prevented from mixing by using separate loading, discharging and venting systems. When planning the cargo stowage, the master must use a recognised compatibility guide to ensure that cargoes stowed adjacent to each other are compatible.
  • Reaction with other materials: The materials used in construction of the cargo systems must be compatible with the cargo to be carried, and care must be taken to ensure that no incompatible materials are used or introduced during maintenance (e.g. by the material used for replacing gaskets). Some materials may trigger a self-reaction within the product. In other cases, reaction with certain alloys will be non-hazardous to ship or crew, but can impair the commercial quality of the cargo or render it unusable.

• CORROSIVENESS:
  • Acids, anhydrides and alkalis are among the most commonly carried corrosive substances. They can rapidly destroy human tissue and cause irreparable damage. They can also corrode normal ship construction materials, and create a safety hazard for a ship. Acids in particular react with most metals, evolving hydrogen gas which is highly flammable. The IMO Codes address this, and care should be taken to ensure that unsuitable materials are not included in the cargo system. Personnel likely to be exposed to these products should wear suitable personal protective equipment.

• PUTREFACTION:
  • Most animal and vegetable oils undergo decomposition over time, a natural process known as putrefaction (going off), that generates obnoxious and toxic vapours and depletes the oxygen in the tank. Tanks that have contained such products must be carefully ventilated and the atmosphere tested prior to tank entry.
  • It must not be assumed that all vapours produced by cargoes liable to putrefaction will in fact be due to putrefaction; some may not be obvious, either through smell or appearance of the cargo. Carbon monoxide (CO), for instance, is colourless and odourless and can be produced when a vegetable or animal oil is overheated.
  • Vapour given off by a flammable liquid will burn when ignited provided it is mixed with certain proportions of air, or more accurately with the oxygen in air. But if there is too little or too much vapour compared to the air, so that the vapour-and-air mixture is either too lean or too rich, it will not burn. The limiting proportions, expressed as a percentage by volume of flammable vapour in air, are known as the lower flammable limit (LFL) and the upper flammable limit (UFL), and the zone, in between is the flammable range (see Definitions for further details).
  • In addition, a flammable liquid must itself be at or above a temperature high enough for it to give off sufficient vapour for ignition to occur. This temperature is known as the flash point. Some cargoes evolve flammable vapour at ambient temperatures, others only at higher temperatures or when heated. Safe handling procedures depend upon the flammability characteristics of each product. Non-combustible cargoes are those which do not evolve flammable vapours
  • Volatile and Non Volatile Cargoes.
  • If a cargo is being handled at a temperature within 10C of its flashpoint, it should be considered volatile.
  • Therefore a cargo with a flashpoint of 80C should be considered volatile if handled at a temperature of 70C or above.

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Contents of Procedure and Arrangements (P & A) Manual as required under Annex II of Marpol 73/78:

MARPOL Annex II requires that each ship which is certified for the carriage of Noxious Liquid Substances in bulk shall be provided with a Procedures and Arrangements Manual. Scope of this plan is to provide the arrangements and equipment required to enable compliance with MARPOL Annex II. Plan is developed in line with IMO Legislation. Approval by the Administration or a Recognised Organisation (RO) on behalf of the Administration is mandatory.

Indicative Contents:

• Main Features of Marpol 73/78, Annex II
• Description of The Ship’s Equipment And Arrangements
• Cargo Unloading Procedures And Tank Stripping
• Procedures Relating To The Cleaning of Cargo Tanks, The Discharge of Residues, Ballasting And Deballasting
• Flow Diagrams & Drawings
• Heating requirement of cargo
• Control of heating system
• Method of temperature measurement
• Stripping requirement for the ship
• Cleaning & disposal procedure
• Prewash procedure
• Prewash for solidifying substances
• Minimum quantity of water to be used
• Required duration of prewash
• Ventilation procedure

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Table showing Control of Discharge of Category X, Y & Z NLS as per Marpol Annex II:

Marpol Annex II – Discharge Criteria:-

Category	BCH Ships Constructed before 31/7/1986	Existing IBC Constructed from 31/7/1986 but before 1/1/2007	New Buildings Constructed from 1/1/2007	Ships Other than Chemical Tankers Constructed before 1/1/2007
X	Pre-Wash Strip to 350 Litres 12 mile 25m water depth 7 knots, en-route	Pre-Wash Strip to 150 Litres 12 mile 25m water depth 7 knots en-route	Pre-Wash Strip to 75 Litres 12 mile 25m water depth 7 knots, en-route	Carriage Prohibited
Y	Pre-Wash for Solidifying for high viscosity substances Strip to 350 Litres 12 mile 25m water depth 7 knots, en-route	Pre-Wash for solidifying for high viscosity substances Strip to 150 Litres 12 mile 25m water depth 7 knots, en-route	Pre-Wash for solidifying for high viscosity substances Strip to 75 Litres 12 mile 25m water depth 7 knots, en-route	Carriage Prohibited
Z	Strip to 950 Litres 12 mile 25m water depth 7 knots, en-route	Strip to 350 Litres 12 mile 25m water depth 7 knots, en-route	Strip to 75 Litres 12 mile 25m water depth 7 knots, en-route	Strip to Maximum Extent 12 mile 25m water depth 7 knots, en-route
OS	No carriage Requirements	No Carriage Requirements	No Carriage Requirements
Underwater Discharge Required	Only X and Y cargoes	Only X and Y cargoes	X, Y and Z cargoes

WRT to above table, discharge of residues of category X for ship constructed before 31 July 1986.

• Stripping to 350 Ltrs
• Pre-Washed
• The resulting residues to be discharged to the reception facility.
• The concentration of substance in effluent must be at or less than 0.1% by weight.
• Ship proceeding enroute with speed of atleast 7 kts.
• More than 12 NM from nearest land.
• Depth of water not less than 25 mtrs.
• Discharge is made below the water line.
• P & A Manual shall be referred.

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Contents of SMPEP manual and who approves it:

SMPEP (Shipboard Marine Pollution Emergency Plan):

Background

MARPOL Annex II Regulation 17 requires every chemical tanker of 150 GT and above to carry a SMPEP. Scope of this plan is to provide guidance on the actions to be taken if a spill of oil or noxious liquid substance has occurred or is likely to occur. The plan is in line with IMO MEPC. 54(32), MEPC. 86(44) and the SMPEP guidelines in Resolution MEPC. 85(44). Plan Approval by the Administration or a Recognised Organisation (RO) on behalf of the Administration is mandatory.

Indicative Contents

• Reporting Requirements
• Steps To Control Discharge
• National And Local Co-Ordination
• Additional Information
• List Of Coastal State Contacts
• List Of Ship Interest Contacts
• Summary of Flow Chart And Checklists
• IΜΟ Resolution A.851(20)
• Vessel Specific Information

Info/Plans Required

• Ship Specific Information (Questionnaire to be submitted)
• General Arrangement Plan
• Capacity Plan
• Midship Section
• Lines Plan
• Tank Tables
• Benefits
• Master will have guidance with respect to the steps to be taken when a pollution incident has occurred or is likely to occur.
• All latest legislation and contact information will be included
• Easy reporting procedure for initial and follow up report (with examples)
• Quick and simple response with actions guide and responsible personnel
• Media handling guidance

We will ensure

• Full compliance with national and international regulations and common marine practice
• Real life documentation addressed to senior officers and crew onboard
• Full integration of any client specific requirements
• Full support provided after development in line with our Document Support Policy

Sketch and Explanation on Inert Gas of an Oil Tanker:

Inert gas system is the most important integrated system for oil tankers for safe operation of the ship.

Inert gas is the gas which contains insufficient oxygen (normally less then 8 %) to suppress combustion of flammable hydrocarbon gases.

Inert gas system spreads the inert gas over the oil cargo hydrocarbon mixture which increases the lower explosion limit LEL (lower concentration at which the vapors can be ignited), simultaneously decreasing the Higher explosion limit HEL (Higher concentration at which vapor explodes). When the concentration reaches around 10 %, an atmosphere is created inside tank in which hydrocarbon vapors cannot burn. The concentration of inert gas is kept around 5% as a safety limit.

Components and description of IG system:

The following components are used in a typical inert gas system in oil tankers:

1. Exhaust gases source: inert gas source is taken from exhaust uptakes of boiler or main engine as contains flue gases in it.
2. Inert gas isolating valve: It serve as the supply valve from uptake to the rest of the system isolating both the systems when not in use.
3. Scrubbing tower: Flue gas enters the scrub tower from bottom and passes through a series of water spray and baffle plates to cool, clean and moist the gases. The SO2 level decreases up to 90% and gas becomes clear of soot.
4. Demister: Normally made of polypropylene, it is used to absorb moisture and water from the treated flue gas.
5. Gas Blower: Normally two types of fan blowers are used, a steam driven turbine blower for I.G operation and an electrically driven blower for topping up purpose.
6. I.G pressure regulating valve: The pressure within the tanks varies with the property of oil and atmospheric condition. To control this variation and to avoid overheating of blower fan, a pressure regulator valve is attached after blower discharge which re-circulates the excess gas back to scrubbing tower.
7. Deck seal: Purpose of the deck seal is to stop the gases to return back which are coming from the blower to cargo tanks. Normally wet type deck seals are used. A demister is fitted to absorb the moisture carried away by the gases.
8. Mechanical non return valve: It is an additional non return mechanical device inline with deck seal.
9. Deck isolating valve: The engine room system can be isolated fully with the deck system with the help of this valve.
10. Pressure Vacuum (PV) breaker: The PV breaker helps in controlling the over or under pressurization of cargo tanks. The PV breaker vent is fitted with flame trap to avoid fire to ignite when loading or discharging operation is going on when in port.
11.  Cargo tank isolating valves: A vessel has numbers of cargo holds and each hold is provided with an isolating valve. The valve controls the flow of inert gas to hold and is operated only by a responsible officer in the vessel.
12.  Mast riser: Mast riser is used to maintain a positive pressure of inert gas at the time of loading of cargo and during the loading time it is kept open to avoid pressurization of cargo tank.

Safety and alarm system: The Inert gas plant is provided with various safety features to safeguard the tank and its own machinery.

Following are various alarms (with Shutdown) incorporated in the Inert Gas plant on board ship:

• High Level in scrubber leads to alarm and shutdown of blower and scrubber tower.
• Low pressure sea water supply (approx. 0.7 bar) to scrubber tower leads to alarm and shutdown of blower.
• Low pressure sea water supply (approx. 1.5 bar) to deck seal leads to alarm and shutdown of blower.
• High inert gas temperature (approx. 70 deg C) leads to alarm and shutdown of blower.
• Low pressure in line after blower (approx. 250mm wg) leads to alarm and shutdown of blower.
• Oxygen content high (8%) leads to alarm and shutdown of gas delivery to deck.
• Low level in deck seal leads to alarm and shutdown of gas delivery to deck.
• Power failure leads to alarm and shutdown of blower and scrubber tower.
• Emergency stop leads to alarm and shutdown of blower and scrubber tower.

Following are various alarms incorporated in the Inert Gas plant:

• Scrubber low level
• Deck seal High level
• Low O2 Content (1%)
• High O2 Content (5%)
• Low lube oil pressure alarm

Working of Inert Gas Plant:

The basis of inert gas production in the IG plant is the flue gas generated from the ship’s boiler. The high temperature gas mixture from the boiler uptake is treated in an inert gas plant which cleans, cools and supplies the inert gas to the individual tanks via PV valves and breakers to ensure safety of tank structure and atmosphere.

The system can be divided in to two basic groups:

a) A production plant to produce inert gas and deliver it under pressure, by means of blower(s), to the cargo tanks.

b) A distribution system to control the passage of inert gas into the appropriate cargo tanks at the required time.

Brief working procedure:

1. Boiler uptake gases are drawn to the scrubber unit via flue gas isolating valve(s) to the scrubber unit.
2. In the scrubber unit the gas is cooled, cleaned and dried before being supplied in to the tanks.
3. Motor driven inert gas blowers supplies the treated gas from scrubber tower to the tanks through. They are mounted on rubber vibration absorbers and isolated from the piping by rubber expansion bellows.
4. Regulation of gas quantity delivered to deck is taken care of by the gas control valves and the deck pressure is managed by pressure controller. If the deck pressure is lower than the set point the output signal will be raised to open the valve more, and vice versa if the deck pressure is lower than the set-point. These valves will then work in cooperation to keep both the deck pressure / blower pressure at their respective set point without starving or overfeeding the circuit.
5. Before entering the deck line, the gas passes through the deck water seal which also acts as non-return valve automatically preventing the back-flow of explosive gases from the cargo tanks.
6. After the deck seal the inert gas relief is mounted to balance built-up deck water seal pressure when the system is shut down. In case of a failure of both the deck seal and the non-return valve, the relief valve will vent the gases flowing from the cargo tank into the atmosphere.
7. The oxygen analyser which is fitted after the blower separates the “production” and “distribution” components of the plant and analyzes the oxygen content of the gas and if it is more than 8%, it alarms and shut downs the plant.

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Features of flammability diagram with respect of following: Purging:

• When it is required to gas free a tank after washing, it should first be purged with inert gas to reduce the hydrocarbon content to 2% or less by volume so that during the subsequent gas freeing no portion of the tank atmosphere is brought within the flammable range.
• The tank may then be gas freed.
• The hydrocarbon content must be measured with an appropriate meter designed to measure the percentage of hydrocarbon gas in an oxygen deficient atmosphere.
• The usual flammable gas indicator is not suitable for this purpose.
• If the dilution method of purging is used, it should be carried out with the inert gas system set for maximum capacity to give maximum turbulence within the tank.
• If the displacement method is used, the gas inlet velocity should be lower to prevent undue turbulence.

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Features of flammability diagram with respect of following: Inerting

• Before the inert gas system is put into service the tests required by the operations manual or manufacturer’s instructions should be carried out. The fixed oxygen analyser and recorder should be tested and proved in good order. Portable oxygen and hydrocarbon meters should also be prepared and tested.
• When inerting empty tanks which are gas free, for example following a dry-docking or tank entry, inert gas should be introduced through the distribution system while venting the air in the tank to the atmosphere.
• This operation should continue until the oxygen content throughout the tank is not more than 8% by volume.
• The oxygen level will not thereafter increase if a positive pressure is maintained by using the inert gas system to introduce additional inert gas when necessary.
• If the tank is not gas free, the precautions against static electricity given in Section 10.6.7 of ISGOTT should be taken.
• When all tanks have been inerted they should be kept common with the inert gas main and the system pressurised with a minimum positive pressure of at least 100mm water gauge.

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Features of flammability diagram with respect of following: Gas Freeing:

• In a gas freeing operation air is delivered into the tank, where it mixes with the existing tank atmosphere and also tends to mix together any layers that may be present.
• The resultant mixture is expelled to the outside atmosphere. Because the process is one of continuous dilution with the air, the highest hydrocarbon concentration is vented at the beginning of gas freeing and decreases thereafter.
• For example, on a non-inerted ship, gas freeing of a motor gasoline tank that has been battened down can give initial concentrations as high as 40% by volume, but in most circumstances the concentration in the vented gas is much lower, even at the start of the operations.
• On inerted ships, where purging to remove hydrocarbon vapour before gas freeing is a requirement, even the initial concentration will be low, 2% by volume or less.

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Functions and maintenances of cargo related equipments on oil tankers using sketches and diagrams: Pressure Vacuum Valve (P/V Valve):

Working:-

• The main components of this system are fixed washing machines which are fed from a 200 mm main line on upper deck.
• The washing fluid is supplied by any of the cargo oil pumps via a riser line from the pump discharge cross-over line.
• In the pump room, there is a steam heated washing water heater which is connected to the riser line in a by-pass arrangement with the water side isolated by means of stop valves and spectacle flanges.
• These flanges may be in open position only when required for hot water washing. The rated heating capacity is 280 m³h of sea water from 20^OC to 80^OC.
• During all washing, the pressure in the main line should be maintained at minimum 8.5 bar at the aft end in order to ensure satisfactory operating conditions also for the forward-most washing machines.
• A pressure less than 7.5 would considerably reduce the effectiveness of the washing operations. For pressure monitoring, there is fixed pressure gauge at the aft end of the main line as well as a boss for a portable pressure gauge at the forward end of the main line.

In order to ensure the correct functioning of PV valves the following should always be complied with:

• PV valves should be serviced and calibrated according to classification society requirements;
• Prior to loading and discharging, PV valves should be checked to ensure they function as designed;
• During cargo operations the correct functioning of PV valves should be monitored; and
• Pressure sensors fitted as the secondary system as a back up to the primary vent system should be checked to ensure that they function as designed and, where provided, that the alarms are correctly set.

Setting PV alarms:- High pressure alarms and low pressure alarms must be set to:

• Activate additional safety or other alarm systems;
• Support maintenance of correct positive inert gas pressure in tanks;
• Prevent air intake to tanks; and
• Comply with regulations.

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Working of a Pressure Vacuum Breaker (PV Breaker):

Pressure Vacuum Breaker or usually known as PV Breaker is a safety measure used in the IG line on deck.

The major functions of a PV Breaker are:-

• Abnormal rise of Pressure in Cargo tanks when loaded specified rate of gas outlets.
• Abnormal rise of Pressure in Cargo tanks when cargo is unloaded beyond specified rate of the inert gas blower.
• Abnormal rise or drop of pressure in cargo tanks when the breather valve does not operate properly for the fluctuation of the pressure in cargo tanks due to variation in atmospheric and sea water temperatures.

Operation:-

• When Pressure Rises: – When the pressure in the cargo oil tanks rise, the seal liquid rises in the inner pipe. At this time , if the pressure beyond the specific capacity of the breaker, the seal liquid will push out of the pipe to let the pressure inside the be out.

• When Pressure drops: – When the pressure in the cargo oil tanks fall, the seal liquid rises in the outer pipe. If the pressure beyond the specific capacity of the breaker, the seal liquid is drown into the cargo oil tanks, and atmospheric air will be inhaled in the tank.

How to ensure that P/V Breaker is protecting the cargo tanks effectively:

• Every inert gas system is required to be fitted with one or more pressure/vacuum breakers or other approved devices. These are designed to protect the cargo tanks against excessive pressure or vacuum and must therefore be kept in perfect working order by regular maintenance in accordance with the manufacturer’s instructions.
• When these are liquid filled it is important to ensure that the correct fluid is used and the correct level maintained for the density of the liquid used. The level can normally only be checked when there is no pressure in the inert gas deck main. Evaporation, condensation and possible ingress or sea water must be taken into consideration when checking the liquid condition, density and level.
• In heavy weather, the pressure surge caused by the motion of the liquid in the cargo tanks may cause the liquid in the pressure/vacuum breaker to be blown out. When cold weather conditions are expected, liquid filled breakers must be checked to ensure that the liquid is suitable for low temperature use, and if necessary anti-freeze is to be added.
• The P/V breaker(s) are to be clearly marked with their high pressure and vacuum opening pressures and also with the type and volumetric concentration of antifreeze (if water filled type), and minimum operating temperature.

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Pressure Vacuum Valve or PV Valve:

• Moderate pressures of 0.24 bar acting on large surfaces in liquid cargo tanks are sufficient to cause damage and rupture.
• The pressure on each unit of area multiplied by the total area gives a large loading on the underside of the top of a tank or other surface, which may then buckle or the metal plate may be torn.
• Similarly, pressure drop within a tank can cause damage due to greater atmospheric pressure on the outside.

• Pressure vacuum valve or pv valve in the ventilation system will prevent either over or under pressure. They are set usually so that tank pressure of about 0.14 bar will lift the main valve (The smaller valve will lift along with it) and release excess pressure. The vapour passes to atmosphere through a gauze flame trap. Drop in tank pressure compared with that of the outside atmosphere will make the small valve open downwards to equalize internal pressure with that outside.
• Pressure vacuum valve or pv valve can relieve moderate changes in tank pressure due to variations in temperature and vapour quantity. A drop towards vacuum conditions as the result of the condensation of steam will also be handled by the valve. Rapid pressure rise due to an explosion would not be relieved.
• The fast rate at which a tank is filled while loading produces a very rapid expulsion of the previous contents (vapour and inert gas). The pressure vacuum valve is not designed as a filling vent and neither should the tank hatch be left open. The latter method of venting can cause an accumulation of flammable vapours at deck level. Tanks should be vented while filling, through mast head vents or through special high velocity vents.

Use & Limitations of Draeger tubes on Oil Tankers:

Multigas Detector or Draeger Multiple detector:

• This is used to detect the presence of a variety of toxic gases inside the compartment.
• They work on the principle of chemical absorption of the gas to be detected by a re-agent which gets discoloured.
• A sample of the atmosphere is drawn into a tube containing crystals of the reagent.
• The tube is graduated and the level of discolouration indicates the concentration of the vapour in the sample.
• The amount of air drawn through the tube must be exactly the same each time, to ensure this the bellows must be fully compressed and allowed to expand to the full limit of the limiter chain.
• The tubes have a shelf life of two years.
• Both ends of the tube are broken before use and one end is fitted into the pump head.
• Different tubes are used for detection of different gases.

Use & Limitations of Explosimeter on Oil Tankers:

It is used for the detection and measurement of combustible gases and vapour. It depends for its operation on the heat developed by the actual combustion of the flammable portion of the sample. The sample is drawn over a heated filament which forms one arm of a balanced Wheatstone’s bridge circuit.

        The current for the circuit is provided by six standard dry cells. Combustible gas in the sample is burnt on the filament. Thus its temperature is raised and its resistance increases in proportion to the amount of combustible gas burnt i.e. in proportion to the amount of combustible gas in the sample. The circuit is now unbalanced which causes a deflection of the meter. The scale is graduated in percentage of the lower explosive limit. The scale is graduated in percentage of the lower explosive limit. The initial balance of the circuit is achieved in fresh air with the meter at zero by adjustment of a rheostat R, in the figure.

The Limitations of the Explosimeter are:-

• As the explosimeter only indicates the presence of flammable gases and vapours it may be dangerous to enter the compartment as no indication of toxicity is given or sufficiency of oxygen.
• A compartment which is initially safe may be rendered unsafe by future operations e.g. stirring or handling bottom sludge in a crude oil tank. Hence, frequent tests are required while the work in progress.
• If a compartment having a high boiling point liquid is heated by welding or other processes the vapour concentration will increase and such an atmosphere which originally showed a low concentration vapour may now be rendered explosive.
• When testing at a high temperature some of the vapour may condense in the sampling tube of the instrument, so only a small concentrate of vapour will be indicated by the instrument.
• As the instrument depends on combustion of the flammable portion of the sample it cannot detect in a steam or inert atmosphere due to the absence of O₂. In the case of inerted tanks of vessels carrying crude or refined petroleum products an instrument called a tankscope has been specially designed to detect and measure the concentration of hydro carbon vapour in the absence of oxygen.

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Use & Limitations of Tank Scope on Oil Tankers:

Diagram same as Explosimeter

• This is used to detect the presence of a variety of toxic gases inside the compartment.
• They work on the principle of chemical absorption of the gas to be detected by a re-agent which gets discoloured.
• A sample of the atmosphere is drawn into a tube containing crystals of the reagent.
• The tube is graduated and the level of discolouration indicates the concentration of the vapour in the sample.
• The amount of air drawn through the tube must be exactly the same each time to ensure this the bellows must be fully compressed and allowed to expand to the full limit of the limiter chain.
• The tubes have a shelf life of two years. Both ends of the tube are broken before use and one end is fitted into the pump head.
• Different tubes are used for detection of different gases.

Use & Limitations of Oxygen Analyzer on Oil Tankers:

The instrument is used to check the O₂ content of the atmosphere within a tank or other confined space. Samples of the atmosphere are drawn by means of a rubber aspirator bulb and passed over a sensor.

The sensor is the most important part of the instrument and can be of various types:

• Paragmagnetic Sensor:-
• The magnetic properties of oxygen is used to deflect a light, metal body suspended in a magnetic field. When the gas is drawn through the cell, the suspended body experiences a force proportional to the magnetism of the gas. An equal and opposing force is produced by an electric current passing through a coil would round the suspended body. This equalizing current is proportional to the magnetic force of the gas which depends on its O₂ content.
• Electrolytic Sensor:-
• In this type of oxygen is passed into an electrolytic cell causing a current to flow between two electrodes separated in a liquid electrolyte. The current flow between the electrodes is directly proportional to the O₂ concentration in the sample. In this type, certain gases may affect the sensor or poison the electrolyte giving rise to false readings.
• Chemical absorption liquid:- in this type a known volume of the sample gas is brought into contact with a measured volume of a liquid which absorbs O₂ causing a change in its volume. The change in volume is a measure of the O₂ content of the sample.
• Limitations:-
• Can only measure O₂ content.
• Regular calculation prior every use.

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Properties of Oxygen Analyzer:

These analyzers come in various makes and models and we will be studying about one such analyzer namely the continuous reading type analyzer.

The main property of oxygen which helps in its detection and measurement of its percentage in the given sample of air is that of Para-magnetism. Basically this means that oxygen gets attracted towards a magnetic field. The set up for measuring oxygen content using this property can be understood from the image shown below.

Hazards of Petroleum with Reference to:-

Toxicity:

ISGOTT 1.2 – Toxicity:- Toxicity is the degree to which a substance or mixture of substances can harm humans or animals.

Toxic substances can affect humans in four main ways: by being swallowed (ingestion); through skin contact; through the lungs (inhalation) and through the eyes.

Ingestion:

Petroleum has low oral toxicity, but when swallowed it causes acute discomfort and nausea. There is then a possibility that liquid petroleum may be drawn into the lungs during vomiting and this can have serious consequences, especially with higher volatility products, such as gasolines and kerosenes.

Skin Contact:

Many petroleum products, especially the more volatile ones, cause skin irritation and remove essential oils from the skin, leading to dermatitis. They are also irritating to the eyes. Certain heavier oils can cause serious skin disorders on repeated and prolonged contact.

Direct contact with petroleum should always be avoided by wearing the appropriate protective equipment, especially impermeable gloves and goggles.

Petroleum Gases:

Comparatively small quantities of petroleum gas, when inhaled, can cause symptoms of diminished responsibility and dizziness similar to drunkenness, with headache and irritation of the eyes. The inhalation of a sufficient quantity can be fatal.

These symptoms can occur at concentrations well below the Lower Flammable Limit.

However, petroleum gases vary in their physiological effects and human tolerance to these effects also varies widely. It should not be assumed that because conditions can be tolerated the gas concentration is within safe limits.

The smell of petroleum gas mixtures is very variable and in some cases the gases may dull the sense of smell. The impairment of smell is especially likely, and particularly serious, if the mixture contains hydrogen sulphide.

The absence of smell should never be taken to indicate the absence of gas.

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Primary & Secondary means of Venting on Oil Tankers:

Primary means of Venting : Vessels utilising a common gas / vapour system as the “primary means of venting” which is isolated from a cargo tank by a valve, or other means, which is shut due to the normal operation of the vessel (such as in the case of a vessel carrying parcel cargo with non-compatible vapours) are not in compliance with the requirements of SOLAS Reg. II-2/4.5.3 unless they have a second independent means of venting which cannot be isolated from the cargo tank.

Secondary means of Venting: (Reg. II-2/4.5.3.2.2) Where the arrangements are combined with other cargo tanks, either stop valves or other acceptable means shall be provided to isolate each cargo tank. Where stop valves are fitted, they shall be provided with locking arrangements which shall be under the control of the responsible ship’s officer. There shall be a clear visual indication of the operational status of the valves or other acceptable means. Where tanks have been isolated, it shall be ensured that relevant isolating valves are opened before cargo loading or ballasting or discharging of those tanks is commenced. Any isolation must continue to permit the flow caused by thermal variations in a cargo tank in accordance with regulation 11.6.1.1.

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Differentiate between PV valve & PV Breaker:

PV VALVE	P/V BREAKER
Connected On Tank Top Of individual Cargo Tank	Connected To Main Inert Gas Line
1 or 2 per tank	1 on main IG line
Mechanical Type	Gravity Type ( Liquid)
PRESSURE :+1400 mmaq	PRESSURE :+2100 mmaq
VACCUM : -350mmaq	VACCUM : -700 mmaq
Primary Means Of Protection	Secondary Means Of Pretection
Requires Regular Maintenance	Less Maintenance
Fixed Set-Point	SET POINT CANBE INCREASED OR DECREASED
Automatic Self-Closing Checklifts	Automatic Self-Closing Checklifts NOT AVAILABLE
Check Lift AVAILABLE TO CHECK THE OPERATIONAL CONDITION	WATER LEVEL GAUGE AVAILABLE TO CHECK THE PRESSURE& VACCUM SETTING
System Failure May Occur	100% Reliable
No extra precaution in cold climate	Antifreeze  required in cold climate

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Precautions to be taken on an Oil Tanker during Loading, Discharging and Tank Cleaning against Static Electricity Hazard:

• The following are essential only when loading static accumulator oils (conductivity < 50 pS/m): Restrict initial loading rates, when splashing and surface turbulence occur, to flow rates less than 1 meter/second (volume flow rate conversions available).
• Adequate inlet coverage’s are: side or horizontal entrance- 0.6 meter; downward pointing inlet- twice the inlet diameter.
• ISGOTT %B7 Loading rate conversions appear both in ISGOTT and Texaco. %B7 Restrict initial unloading rates to shore installations also, as long as inlets in the shore tank are not covered with liquid. The inlet fill pipe should discharge near the bottom of the tank. NFPA 77 %B7 Keep water and other impurities out of the incoming cargo stream as much as possible.
• Extra care with loading and unloading rates when presence of impurities (e.g., water, sulfur, metals) is suspected is essential. ISGOTT, NFPA 77 %B7 Avoid pumping entrained gases with cargo.
• NFPA 77 %B7 Degassing (to <20% of LFL at tank bottom) or inerting a ship’s tank eliminates loading rate restrictions due to static electricity. Texaco %B7 Reduced pumping speeds are used for discharge of slops and other “mixed-phase flow” (some ballast) to shore tanks.
• Prevention of charge accumulation – recommended by ISGOTT /NFPA 77.

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The following safety precautions have been developed to prevent the accumulation of static charge:

• Antistatic additives:- These additives raise the conductivity of a static accumulator; one specification calls for a minimum of 100 pS/m.
• ISGOTT Treatment is required for these fuels in Canada:- The Canadian General Standards Board specifies minimum conductivity of 50 pS/m for static accumulating fuels, especially aviation fuels .
• API 2003 recommends that these additives be introduced at the beginning of the “distribution train”, and notes that their positive effect may be reduced by repeated shipments or passage through clay filters. Safety precautions for the handling of static accumulating oils have historically been waived for those treated with antistatic additives.
• These precautions have, however, recently been extended to residual oils and oils treated with anti-static additive to raise conductivity above 50 pS/m (May 1991 amendment to ISGOTT).
• Space is too small to give full details. You can get ample literature / case histories of such accidents from published journals and published symposium. Basically, this problem can be a great extent mitigarted if:
• A firm earthing connection exists between tank top to bottom on all sides (four quandrantss), measurement of earthing measuremens once in 6 months to meet both Indian Electricity regulations, as well Indian Petrolem and over all for API construction code requirements, firm earthing at all jump-over points(especially piping joints in and out of tanks).
• Allowing enough settling time betwenn tank loading and allow time for tank discharge (i.e, withdrawal of naphtha), good lightning arrestor at the top of the tanks and the continuity of the same will help you to avoid major catastrophy in naphtha storage tanks – inspie of unpreventable static electric discharge.
• As a precaution, do not load the tank too fast or take fuel discharge during severe lightning time.

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Dirty Ballast:

• This intermitted discharge is composed of the seawater taken into, and discharged from empty fuel tanks to maintain the stability of the vessel. The seawater is brought into these tanks for the purpose of improving the stability of a vessel during rough sea conditions.
• Prior to taking on the seawater as ballast, fuel in the tank to be ballasted is transferred to another fuel tank or holding tank to prevent contaminating the fuel with seawater.
• Some residual fuel remains in the tank and mixes with the seawater to form dirty ballast.
• Dirty ballast systems are configured differently from Compensated ballast and Clean ballast systems.
  • Compensated ballast systems continuously replace fuel with seawater in a system of tanks as the fuel is consumed.
  • Clean ballast systems have tanks that carry only ballast water and are never in contact with fuel.
• In a dirty ballast system, water is added to a fuel tank after most of the fuel is removed.
• Thirty Coast Guard vessels generate dirty ballast as a discharge incidental to normal vessel operations. These Coast Guard vessels do so because their size and design do not allow for a sufficient volume of clean ballast tanks.
• The larger of these vessels discharge the dirty ballast at distances beyond 12 n.m. from shore, while the smaller vessels discharge the dirty ballast between 3 and 12 n.m. from shore. Coast Guard vessels monitor the dirty ballast discharge with an oil content monitor. If the dirty ballast exceeds 15 parts per million (ppm) oil, it is treated in an oil-water separator prior to discharge.

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Cloud Point:

In the petroleum industry, cloud point refers to the temperature below which wax in diesel or bio-wax in bio-diesels form a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines. The wax also accumulates on cold surfaces (e.g. pipeline or heat exchanger fouling) and forms an emulsion with water. Therefore, cloud point indicates the tendency of the oil to plug filters or small orifices at cold operating temperatures.

In crude or heavy oils, cloud point is synonymous with wax appearance temperature (WAT) and wax precipitation temperature (WPT).

The cloud point of a nonionic surfactant or glycol solution is the temperature where the mixture starts to phase separate and two phases appear, thus becoming cloudy. This behavior is characteristic of non-ionic surfactants containing polyoxyethylene chains, which exhibit reverse solubility versus temperature behavior in water and therefore “cloud out” at some point as the temperature is raised. Glycols demonstrating this behavior are known as “cloud-point glycols” and are used as shale inhibitors (see Talk). The cloud point is affected by salinity, being generally lower in more saline fluids.

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Spiked Crude Oil:

• “Spiked crude oil” (also called “enriched” or “tailored” crude) is crude oil, which has had hydrocarbons, added in gas or liquid form.
• The spiked crude may contain rather large amounts of added hydrocarbons and therefore emit heavy gasses under certain conditions (during loading, crude oil washing, discharging).

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Sour Crude:

• Sour crude oil is crude oil containing a high amount of the impurity sulfur. It is common to find crude oil containing some impurities. When the total sulfur level in the oil is more than 0.5% the oil is called “sour”.
• The impurities need to be removed before this lower-quality crude can be refined into petrol, thereby increasing the cost of processing. This results in a higher-priced gasoline than that made from sweet crude oil.
• Current environmental regulations in the United States strictly limit the sulfur content in refined fuels such as diesel and gasoline.
• The majority of the sulfur in crude oil occurs bonded to carbon atoms, with a small amount occurring as elemental sulfur in solution and as hydrogen sulfide gas. Sour oil can be toxic and corrosive, especially when the oil contains higher levels of hydrogen sulfide, which is a breathing hazard. At low concentrations the gas gives the oil the smell of rotting eggs. For safety reasons, sour crude oil needs to be stabilized by having hydrogen sulfide gas (H₂S) removed from it before being transported by oil tankers.

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Pour Point:

• The pour point is the lowest temperature at which a marine fuel oil can be handled without excessive amounts of wax crystals forming out of solution.
• At a lower temperature the fuel will gel, thereby preventing flow.

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Precautions you will observe while loading Crude Oil having very high Concentration of Hydrogen Sulphide:

Bunker fuels containing high H₂S concentrations may be supplied without advice being passed to the tanker beforehand. Tanker’s personnel should always be alert to the possible presence of H₂S in bunker fuel and be prepared to take suitable precautions if it is present.

• Before loading bunkers, the tanker should communicate with the supplier to ascertain whether the fuel to be loaded is likely to have any H₂S content.
• The design of bunker tank vents and their location makes managing the exposure to personnel more difficult, as closed loading and venting cannot usually be implemented.
• If bunkering with fuel containing H₂S above the TLV-TWA cannot be avoided, procedures should be in place to monitor and control the access of personnel to exposure areas.
• Ventilation to lower the concentration of vapour in the ullage space and in specific areas where vapours may accumulate should be carried out as soon as practicable.
• Even after the tank has been ventilated to reduce the concentration to an acceptable level, subsequent transfer, heating and agitation of the fuel within a tank may cause the concentration to reappear.
• Periodic monitoring of the concentration of H₂S should be continued until the bunker tank is refilled with a fuel oil not containing H₂S.

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Sketch Wet Type “Deck Seal” & the required water level is maintained:

• The seal is kept full using a continuously running seal water pump which may be backed up with a crossover from a secondary system as required.
• Should the pressure on the downstream side exceed the upstream side the water is pushed up the inlet pipe.
• The height of this pipe ensures that the head pressure generated is greater than either the pressure release valve or any water seals.

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Sketch High Velocity (HV) vent valve fitted in Cargo Oil Tanks:

• Tank vapours can be released and sent clear of the decks during loading through large, high velocity vent.
• The type shown above has a moving orifice, held down by a counter weight to seal around the bottom of a fixed cone.
• Pressure build up in the tank, as filling proceeds, causes the moving orifice to lift.
• The small gap between orifice lip and fixed cone gives high velocity to the emitted vapour.
• It is directed upwards with an estimated velocity of 30 meters per second.
• Air drawn in by the ejector effect dilutes the plume.

• The conical flame screen fixed to the moving orifice to give protection against flame travel will, like the moving parts, require periodic cleaning to remove gummy deposit.
• The cover is closed (as shown) when the vessel is on passage. A simpler design of a high velocity vent, having two weighted flaps which are pushed open by the pressure build up to achieve a similar nozzle effect.

Precautions to be taken on an Oil Tanker during loading/ discharging against Static Electric Hazard:

• Restrict initial loading rates, when splashing and surface turbulence occur, to flow rates less than 1 meter/second (volume flow rate conversions available). Adequate inlet coverage’s are: side or horizontal entrance- 0.6 meter; downward pointing inlet- twice the inlet diameter. ISGOTT
• Loading rate conversions appear both in ISGOTT and Texaco.
• Restrict initial unloading rates to shore installations also, as long as inlets in the shore tank are not covered with liquid. The inlet fill pipe should discharge near the bottom of the tank. NFPA 77
• Keep water and other impurities out of the incoming cargo stream as much as possible. Extra care with loading and unloading rates when presence of impurities (e.g., water, sulfur, metals) is suspected is essential. ISGOTT, NFPA 77
• Avoid pumping entrained gases with cargo. NFPA 77
• Degassing (to <20% of LFL at tank bottom) or inerting a ship’s tank eliminates loading raterestrictions due to static electricity.
• Reduced pumping speeds are used for discharge of slops and other “mixed-phase flow” (some ballast) to shore tanks.

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International Safety Guide for Tankers and Terminals – ISGOTT

• This Guide makes recommendations for tanker and terminal personnel on the safe carriage and handling of crude oil and petroleum products on tankers and at terminals.
• It was first published in 1978 by combining the contents of the ‘Tanker Safety Guide (Petroleum)’ published by the International Chamber of Shipping (ICS) and the ‘International Oil Tanker and Terminal Safety Guide’ published on behalf of the Oil Companies International Marine Forum (OCIMF).
• This latest edition takes account of recent changes in recommended operating procedures, particularly those prompted by the introduction of the International Safety Management (ISM) Code, which became mandatory for tankers on 1st July 1998.
• One of the purposes of the Guide is therefore to provide information that will assist companies in the development of a Safety Management System to meet the requirements of the ISM Code.
• This guide does not provide a definitive description of how tanker and terminal operations are conducted. It does provide guidance and examples of how certain aspects of tanker and terminal operations may be managed.
• Effective management of risk demands processes and controls that can quickly adapt to change. Therefore the guidance given is, in many cases, intentionally non prescriptive and alternative procedures may be adopted by some operators in the management of their operations.
• These alternative procedures may exceed the recommendations contained in this guide.
• Where an operator has adopted alternative procedures, they should follow a risk based management process that must incorporate systems for identifying and assessing the risks and for demonstrating how they are managed. For shipboard operations, this course of action must satisfy the requirements of the ISM Code.
• It should be borne in mind that, in all cases, the advice in the guide is subject to any local or national terminal regulations that may be applicable, and those concerned should ensure that they are aware of any such requirements.
• It is recommended that a copy of the guide be kept — and used — on board every tanker and in every terminal to provide advice on operational procedures and the shared responsibility for port operations.

For contents please refer to ISGOTT (Latest Edition)

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Slop Tanks:

Marpol Annex I- Regulations for the Prevention of Pollution by Oil

Chapter 4 – Requirements for the cargo area of oil tankers. Part A – Construction.

Regulation 29 – Slop tanks

1. Subject to the provisions of paragraph 4 of regulation 3 of this Annex, oil tankers of 150 gross tonnage and above shall be provided with slop tank arrangements in accordance with the requirements of paragraphs 2.1 to 2.3 of this regulation. In oil tankers delivered on or before 31 December 1979, as defined in regulation 1.28.1, any cargo tank may be as a slop tank.

2.1 Adequate means shall be provided for cleaning the cargo tanks and transferring the dirty ballast residue and tank washings from the cargo tanks into a slop tank approved by the Administration.

2.2 In this system arrangements shall be provided to transfer the oily waste into a slop tank or combination of slop tanks in such a way that any effluent discharged into the sea will be such as to comply with the provisions of regulation 34 of this Annex.

2.3 The arrangements of the slop tank or combination of slop tanks shall have a capacity necessary to retain the slop generated by tank washings, oil residues and dirty ballast residues. The total capacity of the slop tank or tanks shall not be less than 3 per cent of the oil-carrying capacity of the ship, except that the Administration may accept:

1} 2% for such oil tankers where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for eductors, without the introduction of additional water into the system;

2} 2% where segregated ballast tanks or dedicated clean ballast tanks are provided in accordance with regulation 18 of this Annex, or where a cargo tank cleaning system using crude oil washing is fitted in accordance with regulation 33 of this Annex. This capacity may be further reduced to 1.5% for such oil tankers where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for eductors, without the introduction of additional water into the system; and

3} 1% for combination carriers where oil cargo is only carried in tanks with smooth walls. This capacity may be further reduced to 0.8% where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for eductors, without the introduction of additional water into the system.

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Tank Cleaning, Purging and Gas free Operation for tankers:

Responsibility: –

• The Chief Officer is in charge of and shall supervise as the person in charge of the Tank Cleaning, Hydrocarbon Gas (HC) Purging, Gas Freeing & Re-Inerting operations.
• He shall ensure that all activities carried out during such operations are in compliance with the latest edition ICS/OCIMF International Safety Guide for Oil Tankers and Terminals (ISGOTT).

Gas-Freeing for Cargo Tank entry:-

• Cargo Tank entry shall not be permitted unless the Oxygen Content is 21% and the hydrocarbon vapor content is less than 1% of the Lower Flammable Level (LFL).
• Follow company’s “Procedure for Entry into Enclosed Spaces” with related permits.
• If the previous cargo contains Hydrogen Sulfide (H2S) or other toxic contaminants which could evolve toxic gases (eg benzene, toluene, Mercaptans, etc), the tank should be checked for such gases. Refer to “Guidelines for Toxic Gases Hazards”.
• Carrying out “Hot Work” inside Tanks within the ‘Dangerous Area’ need special caution as per “Procedures for Hot Work” and carry out preparation accordingly.

Gas-Freeing or Purging for the Reception of Cargo:-

• If the intention of Gas-Freeing or Purging operations is to prevent the next cargo to be loaded from contamination due to the previous cargo oil hydrocarbon gas, use the gas content indicated by the Charterer as standard, but go on with the operations mentioned in (2) of Article 1 until the LFL decreases down to 40% or under.

Safety Precautions:-

• For the operations to be followed, (Tank cleaning, HC Gas Purging, Gas Freeing and Re-Inerting), the Chief Officer shall carry out the following precautions. Detailed guidance on preparations and safety precautions are also described within relevant sections of ISGOTT.
• Have persons engaged in the operations observe the necessary precautions as described in this section and the “Precautions during Gas-freeing Operations”. Complete the necessary sections of “Tank Cleaning, Purging and Gas Freeing Checklist” to confirm safety strictly at the appropriate time.
• Tank Preparation And Atmosphere Control During Operations.

Non Flammable Atmosphere:-

• On Tankers using the inert gas systems, the Chief Officer shall carry out the operations mentioned in Article 1 and should maintain the cargo tanks in a “Non Flammable” condition at all times.
• Refer to the “Flammability composition diagram- Hydrocarbon Gas/Inert/Air Gas Mixtures” from the ISGOTT. i.e. at no time should the atmosphere in the tank be allowed to enter the flammable range, as mentioned therein.
• Pyrophoric hazards on chemical reaction with Hydrogen Sulfide Gas Pyrophoric Iron Sulphide, forms when Hydrogen Sulfide Gas (normally present in most crude) reacts with rusted surfaces in the absence of oxygen (Inert conditions) inside cargo tanks.
• These substances, can heat to incandescence on contact with air. This risk is minimized, by following the correct purging procedure.
• Such procedures serve as a general guidance for the preparation procedures required and may differ as per ship type.

Atmosphere Control during Tank Cleaning Operations:-

• Tank atmospheres can be any of the following, However, ships fitted with an inert gas system, shall carry out the operations under the Inerted Condition, unless otherwise as instructed: It should be met with atmosphere containing less than 8% oxygen, and tank pressure of minimum 200 mmAq. Refer details to “ISGOTT”

Inerted Tanks:-

• An atmosphere made incapable of burning by the introduction of inert gas and the resultant reduction of the overall oxygen content. For the purposes of this procedure, the oxygen content of the tank atmosphere should not exceed 8% by volume.
• This is a condition where the tank atmosphere is known to be at it’s the lowest risk of explosion by virtue of its atmosphere being maintained at all times Non-Flammable through the introduction of inert gas and the resultant reduction of the overall oxygen content in any part of any cargo tank to a level not exceeding 8% by Volume, while being under positive pressure at all times.

Purging with Inert Gas (IG) :-

• For reduction in hydrocarbon (HC) content in tank atmosphere for Cargo  Vapor contamination reasons:
  • After tank cleaning operations the cargo tanks may be purged with inert gas to reduce the concentration of the hydrocarbon gas inside the tank atmosphere.
• Follow the procedures as laid out in the operation and equipment manual.
• Purge pipes, with proper flame screens shall be fitted, where provided.
• Carry out the operations of replacing the tank atmosphere by introducing IG of which oxygen content is 5% by Volume or less into the tanks.
• Go on with purging by IG until the hydrocarbon content reduces to the required / desired level.

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Segregated Ballast:

Annex I- Regulations for the Prevention of Pollution by Oil

Chapter 4 – Requirements for the cargo area of oil tankers

Part A – Construction

Regulation 18 – Segregated ballast tanks

Oil tankers of 20,000 tonnes deadweight and above delivered after 1 June 1982

• Every crude oil tanker of 20,000 tonnes deadweight and above and every product carrier of 30,000 tonnes deadweight and above delivered after 1 June 1982, as defined in regulation 1.28.4, shall be provided with segregated ballast tanks and shall comply with paragraphs 2, 3 and 4, or 5 as appropriate, of this regulation.
  • The capacity of the segregated ballast tanks shall be so determined that the ship may operate safely on ballast voyages without recourse to the use of cargo tanks for water ballast except as provided for in paragraph 3 or 4 of this regulation. In all cases, however, the capacity of segregated ballast tanks shall be at least such that, in any ballast condition at any part of the voyage, including the conditions consisting of lightweight plus segregated ballast only, the ship’s draughts and trim can meet the following requirements:
    • the moulded draught amidships (dm) in metres (without taking into account any ship’s deformation) shall not be less than:

                dm = 2.0 + 0.02L

• the draughts at the forward and after perpendiculars shall correspond to those determined by the draught amidships (dm) as specified in paragraph 2.1 of this regulation, in association with the trim by the stern of not greater than 0.015L; and
  • in any case the draught at the after perpendicular shall not be less than that which is necessary to obtain full immersion of the propeller(s).

• In no case shall ballast water be carried in cargo tanks, except:

1. the opinion of the master, it is necessary to carry additional ballast water in cargo tanks for the safety of the ship; and
2. in exceptional cases where the particular character of the operation of an oil tanker renders it necessary to carry ballast water in excess of the quantity required under paragraph 2 of this regulation, provided that such operation of the oil tanker falls under the category of exceptional cases as established by the Organization.

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Reid Vapour Pressure:

Reid Vapour Pressure (RVP) is measured by ASTM D-323 testing method. The sample is placed in a chamber at a constant temperature of 100^oF. RVP is slightly lower than the True Vapour Pressure (TVP) at 100^oF.

• The volatility characteristics of petroleum fuels are very important especially for gasolines. Motor and aviation gasolines are manufactured as liquids but they are consumed in the vapor phase.
• Consequently, gasoline volatility must be high enough to assure acceptable engine start-up, warm-up, acceleration and throttle response under normal driving (or flying) conditions.
• On the other hand, the maximum volatility of a gasoline must be restricted to avoid vapor lock, vaporization losses, air pollution, and unsafe storage and handling.
• The volatility considerations for other transportation fuels like kerosene and diesel are, to some extent, similar to those for gasoline.
• The Reid vapor pressure (RVP) is frequently used as an indication of volatility of liquid hydrocarbons.
• It is not equivalent to the true vapor pressure. In general, RVP is lower than the true vapor pressure due to some small sample vaporization and the presence of water vapor and air in the confined space.
• The apparatus and procedures for determining the RVP are standardized and specified in ASTM method D-323 and IP-402 [1]. The Reid vapor pressure test is widely used as a criterion for blending gasoline and other petroleum products.
• Once RVP of a fuel is known the methods provided in the API-TDB [2] can be used to estimate true vapor pressure of a fuel or a crude oil at any desired temperature.
• True vapor pressure is an important thermodynamic property related to volatility and phase equilibrium calculations.

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Hazards of Petroleum with Reference to:- Gas Density

ISGOTT – 2.3 :- DENSITY OF HYDROCARBON GASES:

The densities of the gas mixtures evolved from the normal petroleum liquids, when undiluted with air, are all greater than the density of air. Layering effects are therefore encountered in cargo handling operations and can give rise to hazardous situations.

The following table gives gas densities relative to air for the three pure hydrocarbon gases, propane, butane and pentane, which represent roughly the gas mixtures that are produced respectively by crude oils, by motor or aviation gasolines and by natural gasolines. These figures are not significantly changed if inert gas is substituted for air.

It will be seen that the density of the undiluted gas from a product such as motor gasoline is likely to be about twice that of air, and that from a typical crude oil about 1.5 times. These high densities, and the layering effects that result from them, are only significant while the gas remains concentrated. As it is diluted with air, the density of the gas/air mixture from all three types of cargo approaches that of air and, at the lower flammable limit, is indistinguishable from it.