CTM 9.7	Chemical Tanker Manual CTM Tank Cleaning	Doc No.: CTM 9.7 Revision: 01 Date: 15 Oct 2024 Issued by: DPA Approved by: MD

1. APPLICATION

This document applies to all Chemical Tankers managed by Company.

2. PURPOSE

To specify requirements and instructions for the safe and efficient cleaning of tanks on board chemical tankers operated by COMPANY.

3. RESPONSIBILITY

• Master is responsible for:
  • Approving tank cleaning plan (in consultation with COMPANY Marine Department as required)
  • Overall monitoring of the Tank cleaning operation
  • Reporting Tank cleaning progress to concerned parties (COMPANY, Commercial Operators etc.)
  • Crew Awareness in terms of dangers, precautions & limitations of equipment/materials used
• Chief Officer is in-charge of executing the Tank Cleaning Operation
• Deck Officers and ratings shall assist Chief Officer as instructed
• Chief Engineer is responsible for readiness of Cargo/Tank cleaning pump and supply of steam

4. INTRODUCTION TO TANK CLEANING

4.1 Basic Information

• Enormous variety of chemical and oil products are transported on Chemical tankers
• Thus, next cargo is almost never identical with the previous cargo
• Tank Cleaning is required for cargo quality assurance to avoid contamination
• Type and extent of cleaning is governed by nature and characteristics of:
  • Previous cargo
  • Cargo to be loaded (in particular)

4.2 Requirements

Master/ Chief Officer shall ensure:

• Properly planning of the Tank Cleaning Operation
• Rigorous precautions appropriate to the cargoes involved
• Compliance with guidelines given in Chapter 7 of Tanker Safety Guide (Chemicals)
• Compliance with P&A Manual particularly with respect to:
  • Environmental aspects of removal and disposal of residues from cargo tanks
• Mandatory pre-wash as required by MARPOL Annex II.

5. TANK CLEANING PRINCIPLES

5.1 General

• Type and extent of cleaning is governed by nature and characteristics (physical and chemical) of:
  • Previous cargo
  • Cargo to be loaded (in particular)

5.2 Type of Cargoes

For cleaning purposes, cargoes can be classified into three groups:

• I. Mineral Oils
  • Further divided below as per physical and chemical characteristics -
    • a) Clean Petroleum Product (CPP), e.g. Naphtha, Kerosene, Jet Fuel, etc.
    • b) Lubricating oils
• II. Animal, Fish, and Vegetable Oils and Fats
  • Further divided as per -
    • properties and behaviour when exposed to atmospheric conditions
    • the effect that oxygen has on each product
  • a) Non-drying oils (Iodine value: less than 100)
  • b) Semi-drying oils (Iodine value: 100 ~ 130)
  • c) Drying oils (Iodine value: more than 130)
  • d) Water-soluble products
  
  

  Note:

  • Fats are natural organic products with a freezing point at or below 20oC (86oF) In other respect, they are similar to natural oils.
  
  

  For List of Oils in the 4 groups See section 3 of CTM 9.7 – Appendix 1 – Miscellaneous

  
  

  Coution:

  • Drying or semi-drying oils will adhere to the tank surface in the form of a thin hard (varnish) film if the tank is allowed to become hot or dry.
  
  
• III. Petrochemicals and Solvents

  These include a vast and complex range of commodities such as acids, alkalis, alcohols etc. Some -

  • are similar to petroleum in terms of risks and precautions
  • have enough oxygen to enable them to burn without additional supply from air
  • are very dangerous to handle
  • vapours are very toxic
  • can be absorbed through skin into the bloodstream, and reach vital organs
  • are extremely corrosive such as acids and strong alkalis

5.3 Physical Properties Affecting Cleaning and Key Points for Handling

• I. Water Soluble – Miscible Products
  • Easy to clean with water
  • Solubility of the substances might increase at higher temperatures
• II. High Melting Point
  • Carry out washing as soon as possible after discharge
  • Wash at a temperature of at least 15-20°C above the melting point
  • Avoid ballast water or cold cargoes adjacent to the cargo being cleaned
  • Give special attention to cargo & vapour lines to avoid freezing/solidification
• III. High Viscosity
  • Carry out washing as soon as possible after discharge
  • Wash at higher temperatures
  
  

  Note:

  • Viscosity is proportional to temperature and will decrease at higher temperatures, Exception - Some lube additives and polyols. Wash these at lower temperatures.
  
  
  • Avoid ballast water or cold cargoes adjacent to the cargo being cleaned
  • Give special attention to cargo & vapour lines to avoid freezing/solidification
• IV. Vapour Pressure / Boiling Point
  • Following products can be removed by evaporation or light cleaning –
  • Products with low boiling point and high vapour pressure (higher than 50mbar at 20°C)
  • In case of evaporation, the pre-cleaning can be omitted, however,
  • Flush lines and pumps with fresh water as evaporation may be difficult.
  • Following should never be cleaned by evaporation (ventilation):
  • Products with low vapour pressure
  • Products which leave residues (NVM)
  • Products which contain inhibitors
  • These must be cleaned by water washing and steaming.
  • Cold wash is recommended for first stage of washing.
• V. Flash Point / Flammable Range (CDI 5.3.33)
  • Pre-cleaning temperature must be well below the flash point, and
  • If this is not possible, then exercise care to avoid any source of ignition.
• VI. Specific Gravity
  • Below 1.0 indicates product will float on the water (for a product with limited or no solubility)
  • More than 1.0 indicates that the product will sink.

5.4 Product Characteristics Affecting Cleaning and Key Points for Handling

• I. Polymerising Products
  • Wash tanks, lines, vent lines with cold water as soon as possible after discharge.
  • This is to avoid polymerisation by loss of inhibitor protection.



Coution:

• Hot water wash will result in polymeric residues being left in the tank and lines, which are very difficult to remove.


• II. Reaction with Water

  Coution:

  • Isocynates (MDI or TDI) must never come in contact with water.
  • The reaction produces urethane, which is very difficult to remove.
  
  
  • Wash such products with suitable solvents.
  • Ensure the solvent as well as the equipment used is free of any moisture.
• III. Reaction with Oxygen, Drying Products
  • Drying and Semi Drying vegetable and animal oils react with oxygen to form a varnish-like polymeric film, which is very difficult to remove from bulkheads.

  Coution:

  • Heat increases the speed of reaction.
  
  
  • Carry out initial washing of these products with water at ambient temperature
  • As soon as possible after discharge.
• IV. Evaporation of Volatile Cargoes
  • Cargoes consisting of mixtures with different vapour pressures should not be cleaned by evaporation (ventilation) or prewashed with hot water.

5.5 The Role of Tank Cleaning Chemicals

The action of chemicals used in tank cleaning can be divided into several different categories:

• I. Solvents
  • These are chemicals which dissolve or solubilize other materials or chemicals.
  • This way residues and deposits are removed from the tank surfaces
• II. Surface Active Agents (Surfactants)
  • These are usually detergents which act to:
  • Reduce the surface tension of a liquid, thus, improving its wetting and cleaning capabilities.
  • They are usually used together with solvents to produce a cleaning solution which aids in the complete removal of tank residues, such as hydrocarbons, liquid chemicals, etc.
• III. Emulsifiers
  • This is a surface-active chemical which assists to form an emulsion of two liquids.
  • One liquid is present as extremely small droplets, such that particles or globules of it are dispersed and suspended in the other.
  • Using this property an emulsifier can remove oily deposits with water.
• IV. Saponifiers
  • This is an alkaline chemical which changes oils and fats into soaps:
  • It converts the fatty compounds into water-soluble materials.
  • These are biodegradable and easily flushed away from the surfaces to which they adhere.
  • Strong alkali solutions (NaOH and KOH) are used as saponifying agents together with a variety of other compounds

5.6 Cleaning Processes and Detergents for Use to Each Product

The following table brings together categories of cargo already described and the applicable processes.

Group	Sub-Group	Cleaning Principle	Detergent
Mineral oils	(A) Clean Petroleum Product (B) Lubricating Oil	Emulsification And / Or Saponification	Unitor: Sea Clean Drew: TC-4 Gyro: Voyage Clean or equivalent Vecom: B-4 If next cargo is Hydrocarbon sensitive, use Hydrocarbon cleaner to remove traces of HC.
Chemicals	(A) High Volatile (B) Low Volatile	Evaporation / Emulsification	As per the property of the cargo. Usually no need for chemical.
Animal, vegetable & fish oils & fats	(A) Drying (B) Semi-dry (C) Non-dry Fatty Acids	Saponification	Gyro: 3025 (Mild Alkaline) Gyro: AVO Liquid or equivalent Unitor: Alkleen Liquid
			In case of any white powder deposits on the tank bulkheads, use: Unitor: Metal Brightner or equivalent Gyro: Rust Cleaner

5.7 Use of Heat

• Heat is a very important factor in the efficiency of almost all tank cleaning operations.
• Heat:
  • Accelerates chemical processes to residues of some products,
  • Dissolves residues, and
  • Reduces viscosity of most oils.
• In tank cleaning, water temperatures are usually defined as follows:
• Cold (Ambient): up to 30°C
• Lukewarm: 30 ~ 35°C
• Warm: 40 ~ 50°C
• Hot: 65 ~ 80°C
• Exceptions - where it is essential to pre-wash with cold water:
• Polymerizing chemicals such as Styrene Monomer
• Drying and semi-drying oils such as Sunflower oil, Soya bean



Note:

• For mineral oils, use cold water prewash if the oil is a kind requiring to be heated on passage.
• Introduction of heat into the stripped tank causes the lighter fractions to evaporate, leaving a waxy residue. If pour point is above 20oC the oil is likely to leave wax deposits.



Coution:

• Many vegetable and mineral oils polymerize on heating, making the residue much more tenacious.
• Risk of polymerization becomes greater, the longer the oil is exposed to air.


• Clean as soon as possible after discharging, with water at ambient temperature

5.8 Coated Tanks

• Tanks to carry chemical cargoes can be made of either
  • stainless steel or
  • mild steel with an inert coating.
• In the latter case, the most widely used coatings are
  • epoxy-based (organic) paints and
  • zinc silicate (inorganic) paints.
• Coating resistance to chemicals varies by type and manufacturer.
• Consult coating resistance guide (or coating manufacturer, if in doubt) when chemical cleaning is to be carried out.
• The most useful criterion is the PH range to which a coating is resistant.
• Coating Manufacturers specify the PH range to which a coating is resistant.

6. TANK CLEANING SYSTEM AND EQUIPMENT

6.1 Tank Cleaning Machines

For efficient cleaning:

• Ensure adequate water pressure and temperature is achieved.
• Assess the maximum number of tank cleaning machines that can be operated at a time considering the pump & heater capacity, and tank cleaning supply pipelines.
• Confirm the satisfactory operation of the machines routinely during the washing.
• For shadow sectors, consider cleaning by hand-spray subsequently.

If using Portable machines:

• Lower in several 'drops' to clean the whole depth of a tank.

6.2 Tank Cleaning Pumps

• Supply water under pressure to the fixed or portable tank cleaning machines using:
  • Either a designated independent tank cleaning pump or
  • A cargo pump
• The rated volume capacity of the pump should be slightly in excess of the total designed discharge of the number of machines to be used simultaneously.
• This excess capacity should be:
  • About 10% - if only one or two machines are used at one time,
  • Can be decreased to 5% - if four or more machines are to be used at once.
• Ensure that the pump:
  • Has an automatic means of limiting the discharge pressure
  • Is provided with a constant-pressure regulator.

6.3 Tank Cleaning Heaters

• The heat exchanger is installed in the water supply line on the discharge side of the pump and should be provided with a by-pass.
• Use the heater and drain cooler in combination so that the heat of the condensate from the heater section may be used to minimize steam consumption.
• Before use, check that the liquid level control and temperature control function is satisfactory.

6.4 Tank Cleaning Main Supply Lines

• Check that the cleaning water lines:
  • Have working pressure of at least 10 kg/cm²
  • Are of sufficient size to carry maximum discharge from pump without excessive pressure loss.
  • Have thermometers & pressure gauges installed both in the pump room and on deck.

6.5 Associated Equipment

In addition to the basic washing system, various accessories are required depending on the extent of the tank.

As an example, the following is a typical checklist of system and equipment requirements to clean a chemical tanker converting from vegetable oil to mineral oil:

• Operational mechanical washing machines
• Quadrant saddles
• Mechanical washing hoses of 15m lengths each or 20m lengths each.
• Spanner wrenches for connecting hoses
• Air hose
• Squeezing paddles
• Six (or three)-cell safety flashlights, with extra batteries or pneumatic lights.
• Clean rags
• Diaphragm pump

7. PRECAUTIONS FOR TANK CLEANING & TANK ATMOSPHERE DURING CLEANING

7.1 General Precautions

Chief Officer shall ensure:

• No unauthorized work is carried out in the way of the cargo space.
• Appropriate personnel are notified of gas freeing or tank cleaning starting.
• All cargo tank lids, tank cleaning hatches, ullage opening, etc., are closed. (Except those in the tanks to be cleaned first)
• Cargo lines not in use are isolated, if possible, and associated valves are closed.
• The valves in common vent systems are properly isolated. This is to prevent the passage of flammable or harmful vapour back to the tank that has been cleaned or gas freed.
• Scuppers are properly plugged.
• Sand or spill trays are in place beneath the manifold connections.

Additionally, If tank cleaning or Gas Freeing alongside in Port –

• Permission to operate alongside in port has been granted.
• Shore authorities are advised of the nature of all grades in the previous cargo.
• Conditions are safe on the jetty.
• No unauthorized craft is situated alongside.
• Any authorized craft that is alongside are warned that cleaning is about to start.
• Any necessary hose connections to shore or craft alongside are proper.

7.2 Tank Atmospheres (CDI 5.3.36)

7.2.1 Managing Tank Atmospheres

• The method of tank cleaning will:
  • Depend upon how the atmosphere in the cargo tank is managed
  • Be determined by the equipment fitted to the vessel.
• Verify the volume of oxygen required to create a flammable mixture.
• Tank atmospheres can be inert or non-inert.

7.2.2 Inert Atmosphere

• Achieve a non-flammable atmosphere through the introduction of inert gas.



Note:

• Refer to ISGOTT Section 11.3 for:
• - the requirements for the maintenance of an inert atmosphere and precautions to be observed during washing and the best level of control of an atmosphere during tank washing operations.


• Ensure the volume of oxygen when carrying chemicals is less than that will support combustion (which may be different from the specified 8%).
• In fire triangle terms, this method physically removes and controls the ‘oxygen’ side of the fire triangle.

7.2.3 Non-Inert Atmosphere

• Ensure additional control measures to reduce the risk of operations to as low as reasonably practicable.
• These control measures MUST address two sides of the fire triangle, namely ‘Fuel' and 'Sources of ignition'.
• Relevant procedures as specified below apply to both Annex I and II cargoes, unless otherwise specified.

7.3 Washing in an Inert Atmosphere

• Check the volume of Oxygen required to support combustion, and maintain below the required levels.
• During tank washing operations, measure the atmosphere to ensure the tank remains:
  • Non-flammable and
  • At a positive pressure.



Note:

• For Annex I cargoes, washing should preferably be conducted under inert conditions.


• When portable tank cleaning machines are used:
  

  Note:

  • Tank cleaning holes are open, and air may enter the tanks.
  
  
  • Supply inert gas to the tanks being cleaned to continuously maintain positive pressure and O₂ content less than 8%.
  • Measure the O₂ content in the tanks which are scheduled for washing prior to commencing tank cleaning.
  • If O₂ > 8%, start purging of the tank.

7.4 Washing in a Non-Inert / Undefined Atmosphere

7.4.1 General Requirements

• Refer ISGOTT Section 11.3.5.2 & TSG (C) 7.3.4.
• Only undertake washing in this atmosphere when both:
  • Source of ignition
  • Flammability of the tank atmosphere are controlled.
• Take precautions as specified in the next points to control 'sources of ignition' and 'fuel'.

7.4.2 Before Washing

• Flush the tank bottom with water, using main cargo pumps and lines and then strip.
  Alternatively, use permanent pipework extending the full depth of the tank.



Coution:

• Do not use tank washing machines
• Flush the piping system, including cargo pumps, crossovers, and discharge lines, with water.



Note:

• The flushing water must be disposed of as required by Annex I or II of MARPOL 73/78 as applicable.


• Initial Ventilation:
  • Ventilate the tank to reduce the gas concentration of the atmosphere to 10% or less of LEL.
  • Carry out gas tests at various levels.



Coution:

• Give due consideration to the possible existence of pockets of flammable gas.
• In particular, near mechanical equipment that might generate hot spots, e.g. (submerged) cargo pump impellers.


• Arrange gas freeing process to minimize hazard due to dispersal of flammable and toxic vapours in the atmosphere.



Note:

• Ref to IBC code chapter 8.5. Cargo tank gas-freeing


• For venting of toxic or flammable gas during gas freeing:
  • Only use the vessel’s approved gas freeing outlets.
  • Comply with IBC Code Chapter 8.5 and the ship’s P&A manual.
• Ensure any portable equipment for use is:
  • Intrinsically safe and
  • Tested before use.

IV. Final ventilation
• This can be continued at deck level through cargo tank and Butterworth hatches only when the gas level within the tank has fallen to:
o 30% LEL or less and
o Below TLV
• Only tanks being ventilated may have open hatches.
• Close all deckhouses and stores
• Keep air condition in re-circulation.



• Tank washing may only commence once the tank atmosphere reaches
   o 10% or less of the LFL

7.4.3 During Washing

• Test tank atmosphere during washing:
  • Frequently
  • At various levels inside the tank to monitor the change in LEL %.
• Water may impact gas measuring equipment, thus consider suspending washing to take readings.
• Whenever possible continue mechanical ventilation during washing to provide a free flow of air from one end of the tank to the other.
• Where mechanical ventilation is not possible, increase the frequency of tank atmosphere monitoring.
• Maintain tank atmosphere:
  • Not exceeding 35% LEL.



Coution:

• If gas level reaches 35% LEL at any measured location within a tank, Stop tank washing operations in that individual tank immediately.



Note:

• Washing may be resumed when:
• - Continued ventilation has reduced the gas level, and
• - It is possible to maintain the gas concentration at 10% or less of the LFL.


• If the tank has a venting system that is common to other tanks, isolate the tank to prevent the ingress of gas from other tanks.

7.4.4 Controlling the 'Sources of Ignition' in the Tank - Precautions

• Ensure water throughput does not exceed for:
  • Tank cleaning machine: 60 m³/hr
  • Nozzle: 17.5 m³/hr (per tank)
  • Total per tank: 110 m³/hr
• Do not use re-circulated wash water.
• Heated wash water may be utilized, but discontinue use if gas concentration reaches 35% LEL.
• Keep tank drained during washing. Stop washing to clear any build-up of wash water.

For a Low Flashpoint Product

• A hot wash should ONLY take place after a full (top to bottom) cold wash cycle
• If hot wash water temperature is above 60°C,
  • Increase frequency of gas monitoring If portable washing machines are used
• Before introducing the machine into the tank
  • Make all hose connections,
  • Test for electrical continuity
  • Ensure tank LEL is 10% or less
• Do not break connections until after the machine has been removed from the tank

• Introduce sounding rods and other equipment into the tank utilizing
  • a full depth sounding pipe
• If a full depth-sounding pipe is not fitted -
  • Ensure that any metallic components of the sounding rod or other equipment:
    • are bonded, and securely earthed to the ship before introduction into the tank
    • remains earthed until removed.
• Observe this precaution
  • during washing, and
  • five hours thereafter to allow sufficient time for any mist carrying a static charge to dissipate.

Note:

• If the tank is continuously mechanically ventilated after washing, this period may be reduced to one hour.


• During this period, an interface detector of metallic construction may be used
  • if earthed to the ship by means of a clamp or bolted metal connection.

Coution:

• Do not use a metal sounding rod suspended on a fiber rope, even if the end at deck level is fastened to the ship as a rope cannot be relied upon to provide an earthing path.


• A metal rod may be used on the end of a metal tape
  • if earthed to the ship by means of a clamp or bolted metal connection.
• Equipment made entirely of non-metallic materials may, in general, be used,
  • for example, a wooden sounding rod may be suspended on natural fibre rope without earthing

Other Precautions

• Do not use Ropes made of synthetic polymers for lowering equipment into cargo tanks.
• Take measures to guard against ignition from mechanical defect of machinery,
  • e.g. in-tank (submerged) cargo pumps, tank-washing machines, tank gauging equipment etc
• Take Precautions to eliminate the risk of mechanical sparks from metallic objects being dropped into the tank.
  • such as hand tools, sounding rods, sample buckets etc

7.5 Portable Tank Washing Machines and Hoses (CDI 5.3.48 / CDI 5.3.37)

• Ensure the material of portable machines is such that it will not give rise to a spark on contact with the internal structure of a cargo tank.
• The coupling arrangement for the hose is such that effective bonding is established between:
  • Tank washing machine
  • Hoses
  • Fixed tank cleaning water supply line.
• Washing machines are electrically bonded to the water hose by means of a suitable connection or external bonding wire.
• When suspended within a cargo tank, machines are supported by means of a natural fibre rope and not by the water supply hose.

7.6 Portable Hoses for Use with Both Fixed and Portable Tank Washing Machines (CDI 5.3.48)

• Ensure bonding wires are incorporated within all portable tank-washing hoses to ensure electrical continuity.
• Couplings are connected to the hose in such a way that effective bonding is ensured between them.
• Hoses are individually and clearly marked to allow identification.

Note:

• Keep a record showing the date and the result of electrical continuity testing.


• Test all hoses supplied for tank washing machines for electrical continuity in a dry condition prior to use.
• Ensure the resistance in no case exceeds 6 ohms per meter length.

7.7 Tank Cleaning Concurrently with Cargo Handling

• If for any reason this is necessary, consult and have agreement with both:
  • Terminal representative
  • Relevant port authority
• Clearly discuss and agree on the precautions required to be taken with the terminal.

7.8 Free Fall

• Avoid free fall of water, cargo residues, or slops into a tank.
• Maintain liquid level in the slop tank such that the discharge inlets are covered to a depth of at least one metre to avoid splashing.

7.9 Spraying of Solvents and Water (CDI 5.3.36)

• For tanks that contain static accumulator cargoes, always bottom flush before washing with water and/or solvents, unless the tank is kept in an inert condition.

7.10 Use of Chemicals in Tank Cleaning Wash Water (CDI 5.5.32, 5.3.35, 5.3.37, 5.3.38)

• Check if possible reactivity with cargoes in concern may result in toxic or flammable vapour.
• The Chief Officer must make personnel involved in the cleaning operations aware of the Threshold Limit Value (TLV) of the product.
• Use detector tubes for detecting the presence of specific gases and vapours in tanks.



Coution:

• For tank cleaning chemicals which are capable of producing a flammable atmosphere - Only use when the tank has been inerted or gas freed.


• Flammable tank cleaning chemicals/agents may only be used through fixed or portable machines.
• Toxic tank cleaning chemicals/agents may only be used through fixed machines under closed conditions.

Note:

• Chemical additives used for tank cleaning of cargo tanks shall be approved for use by IMO. See Annex 10 of MEPC.2/Circ. Series circular related to Provisional categorization of liquid substances.



Note:

• For Further Reference
• See Regulation 13.5.2 of the MARPOL Annex II
• MEPC.1/Circ.590 – Revised Tank Cleaning Additive Guidance Note and Reporting Form


• All solutions using approved cleaning additives shall be:
  • Discharged at sea as per Marpol Annex II requirements, for pollution category of the additive.
  • Discharged to an ashore facility as the case may be.

7.11 Use of Chemicals for Local Cleaning of Tanks (CDI 5.3.36)

• Some products may be used for the local cleaning of tank bulkheads and blind spots by hand wiping, provided:
  • The amount of tank cleaning chemical used is small.
  • Personnel entering the tank observe all enclosed space entry requirements.
  • Any manufacturer's instructions for the use of these products are followed.
  • Personnel are familiar with MSDS and emergency procedures.

7.12 Cleaning of a Cargo Tank Which Has Contained a Toxic / Flammable Product (CDI 5.3.33)

• The responsible officer shall supervise all tank cleaning and gas freeing operations and ensure the following:
  • Take precautions appropriate to each individual chemical's characteristics, such as toxicity, corrosiveness, and reactivity.
  • Personnel must wear appropriate PPE as per the properties of the cargo. Ref MSDS and FOM-10 Manual.
  • Take all normal safety precautions. (No smoking, accommodation ventilation on recirculation, etc.)
  • Consider wind strength and direction before allowing ventilation.
  • To avoid a build-up of explosive or toxic vapors on deck, limit the amount of gas to be escaped from the tanks.
  • Never open and ventilate several tanks at the same time.
  • Reduce emissions to the water to the absolute minimum.
  • Operate all on-board facilities as per P&A Manual to reduce the residues during unloading.
  • Keep accommodation ventilation in recirculation mode during the operation.

Tank Cleaning Steps

8.1 Typical Steps

A typical tank cleaning operation generally consists of the following steps:

• Planning
• Pre-cleaning
• Final Cleaning
• Ventilation and Drying of tanks
• Verification of tank cleanliness

8.2 Planning

Cargo cleaning should be well-planned in advance of operations. Consider the following factors:

• The physical properties and characteristics of the last cargoes
• The next cargo to be loaded
• Surrounding conditions such as:
  • Outside temperature
  • Seawater temperature
  • Weather
  • Adjacent cargo
  • Ballast temperatures
• The capabilities and restrictions of available equipment:
  • Tank cleaning machines (with particular attention to shadow sectors)
  • Pumps and heaters
• Location of cleaning hatches
• Type and condition of tank coatings (SUS or MS coated tanks)
• Available cleaning time

8.3 Pre-cleaning (CDI 5.5.31)

• Always carry out pre-cleaning with fixed or portable tank cleaning machines, using sea or fresh water as the cleaning medium.
• Do not use recirculated water for pre-cleaning due to the risk of static generation.
• Pre-clean immediately after the tank has been emptied and before any residues can oxidize, polymerize, or solidify.
• For oils or polymerizing chemicals, use cold water (sea or fresh).
• For oils with high pour points, use water 10-15°C higher than the pour point.
• Avoid introducing chemical additives into tanks containing a flammable atmosphere.
• During pre-cleaning, move portable tank cleaning machines frequently, both horizontally and vertically, to ensure that all surfaces are reached.
• After pre-cleaning, inspect the tank to assess the cleaning level and whether further cleaning is required.
• Pay particular attention to tank bottoms and shadow areas.

8.4 Final Cleaning

8.4.1 Steps in Final Cleaning

The steps involved in final cleaning are:

• Butterworth washing (tank washing with seawater/fresh water & detergents)
• Detergent wash (recirculation, injection, spraying of detergent)
• Rinsing (with seawater/fresh water)
• Flushing (with fresh water)
• Steaming (not suitable for tanks containing flammable atmospheres)
• Draining (removing the last traces of liquids)
• Ventilation (airing and gas freeing)
• Drying (ventilating, deodorizing, and drying)

8.4.2 Butterworth Washing

• Typically done using seawater, which is an efficient cleanser.
• Water can be heated to improve effectiveness.
• The cleaning time will depend on the cargo being removed, the cargo to be loaded, and the temperature of the cleaning solution.

Coution:

• Consider - maximum temperature restriction due to cargo tank coating - Effect of hot water wash on the adjacent tanks.


• After cooling, inspect the tank thoroughly, especially hidden spots.
• If traces of cargo remain, continue cleaning, and ensure shadow areas are cleaned by hand using detergent or other cleaning agents.

8.4.3 Detergent Wash - General

The methods for detergent washing have specific advantages and limitations:

• Recirculation (Open system)
• Recirculation (Closed system)
• Hand spraying
• Injection

8.4.4 Detergent Wash - Recirculation Method

• A chemical solution is prepared in one tank, circulated through the tank to be cleaned, and stripped back into the detergent solution tank.
• Ensure the solution is at the right temperature; if required, heat using tank heating coils.
• If time is short, live steam may be injected for faster cleaning, although it is more expensive.
• Dispose of cleaning washings and chemicals according to MARPOL Annex I or Annex II as appropriate.

8.4.5 Detergent Wash - Hand Spray Method (CDI 5.3.36)

• Use air-operated drum pumps and hand spray guns to spray the cleaning solution onto bulkheads, frames, and stringers.

Coution:

• Check manufacturer recommendation for maximum allowed concentration of the cleaner on to the coating through Product Data Sheet.
  Check with coating manufacturer if in doubt.


• After a predetermined time, wash the tanks with water using washing machines.

8.4.6 Rinsing

• Rinse tanks immediately after the cleaning operation and once residues and slops have been stripped.
• Use tank cleaning machines and hot or warm freshwater/seawater.
• Continue rinsing until no traces of cleaning detergent remain.

8.4.7 Flushing

• If seawater is used for rinsing, flush the tanks with freshwater immediately afterward.
• Flushing can be done using cleaning machines or by hand-washing with hoses fitted with special nozzles.

8.4.8 Steaming (CDI 5.5.33)

Procedure

• Keep tank vents open • Inject Steam into the tank via either:        o cargo manifold, drop line or        o steaming adopter pipe fitted to tank cleaning hatch cover

Precautions Prior to Steaming:

• Check steam hoses before use to ensure continuity and ensure they are free from any foreign matter (oil or water).
• Verify that the atmosphere is gas-free before introducing steam.

Note:

• Record the same in CHEM 08


• Consider the nature of the cargo in adjacent tanks.

Coution:

• Never carry out steaming in the cargo tank when any cargo sensitive to heat is stowed in the adjacent tanks.

Precautions During Steaming:

• Monitor the tank temperature remotely to avoid exceeding 60°C.

Note:

• If it does, stop steaming and resumed only after the tank temperature drops to a suitable level.


• Regularly strip the tanks during steaming.
• Ensure there are no sources of ignition in the cargo tank.
• Do not carry out any hot work during steaming operations.
• Keep tank dome or purge pipe vent slightly open to avoid excessive pressure buildup in the cargo tank.

8.4.9 Line Blowing and Draining

• Drain the tanks, lines, and pumps completely.
• Remove drain plugs and blow the lines with compressed air, ensuring they are free from oil, rust particles, debris, or previous cargo.
• At each stage, briefly open the drain valve, allowing sufficient time for the pressure to build up.
• Once confirmed empty, blow the entire line back into the tank.
• Inspect the manifold visually after opening the blanks on both sides to ensure it is free from contaminants.

• Exercise due care to prevalent weather conditions as sea sprays can easily contaminate the cargo lines.

8.5 Drying

• Ventilate and dry the tanks thoroughly.
• Inspect for any remaining residues, and remove them by wiping with rags.
• Drain any remaining liquid into a bucket.
• Do not leave water residues in the bottom or pump wells.
• Use air fans to dry the tank completely, and mop up any remaining moisture as soon as possible.
• When entering tanks, wear shoe covers or wrap clean, lint-free rags around shoes.
• Leave valves and plugs open until a surveyor has inspected the tank.

8.6 Verification of Cleaning

• Visually inspect the tank after cleaning.
• Inspect areas like the undersides of heating coils, behind ladders, and behind securing clamps/bolts for pipelines.
• Tighten any loose nuts on heating coil clamps and repair any broken connections on ladders.
• Check pipelines, valves, and flange openings for cleanliness.
• If the next cargo requires high purity, perform a Wall Wash Test (WWT).

Note:

• If the tank walls of SUS tanks are discoloured or show rust stains, it may be necessary to carry out pickling or passivation.


• For detailed procedures on Wall Wash Tests, refer to CTM 9.7 – Appendix 2.

9 Gas Freeing (CDI 5.3.47)

Also see Section 7.4

9.1 General

• Before gas freeing, assess what type of vapours can be expected (flammable, toxic, and/or corrosive).
• Carry out venting of toxic and flammable gas through the vessel’s approved gas freeing outlets.
• Portable or permanent venting trunks can be used as gas freeing outlets:
  • Only as per IBC 8.5
  • If listed in the P&A Manual
• Ensure no escape of cargo vapours occurs at deck level before the concentration within the tank has fallen:
  • Below 30% LFL
  • Below the relevant TLV
• Final clearance of the vapour mixture can continue at tank deck level through other larger deck openings.
• To calculate the maximum number of tanks that can be gas freed/vented together, refer to:
  • Vapour control system manual
  • P&A manual
• For cargoes mentioned as fit for ventilation in the vessel’s P&A Manual:
  • Bottom flush may be considered
  • Vent the tank by the approved venting system until LEL < 30% and toxicity < TLV
• Once TLV and LEL are within range, remaining venting can be carried out at deck level.
• If the tanks are connected by a common venting system, isolate each tank to prevent the transfer of gas to or from other tanks.

9.2 Using Permanently Installed Fans

• Where cargo tanks are gas freed by permanently installed fans, air is introduced into the cargo tank through the cargo lines.
• Drain the entire line system thoroughly before venting:
  • To avoid obstruction of airflow
  • To prevent water or cargo residues from being blown into a cargo tank
• Close & secure valves on systems, other than those required for ventilation.

9.3 Using Portable Fans

• If portable ventilation equipment is used to blow air into a tank, keep tank openings closed until work on that tank is about to commence.
• Only use fans that are water, hydraulically, or pneumatically driven.
• Ensure the fan construction materials are such that no hazard of incendiary sparking arises if the impeller touches the inside of the casing.
• Ensure protective guards are in place to prevent accidental contact with fan blades.
• Place fans and ventilation openings so that all parts of the tank being ventilated are effectively and equally gas freed.
• Locate fans as remotely as possible from ventilation outlets.
• Ensure an effective electrical bond exists between the fan and the deck.

9.4 Accommodation/Engine Room Ventilation

• The wind direction may cause cargo vapours to pass near air intakes for accommodation spaces or engine room ventilation.
• Adjust the central air conditioning or mechanical ventilation system intakes to prevent the entry of gas, if possible, by using recirculation of air within the spaces.

9.5 Gas Measurement

• Take final gas measurements when:
  • The tank appears to have been gas freed, and
  • All mechanical ventilation has stopped, and
  • A period of about ten minutes has elapsed before taking the measurement (this allows relatively stable conditions to develop within the tank space).
• Make the tests at several levels:
  • Where the tank is subdivided by a wash bulkhead, in each compartment of the tank
  • In large compartments, at widely separated positions
• If satisfactory gas readings are not obtained:
  • Check the tank for cargo residues, and
  • Resume ventilation.

9.6 On Completion of Gas Freeing and Tank Washing

• Carefully check the gas venting system.
• Pay particular attention to the efficient working of P/V valves and any high velocity vent valves.
• Check and clean flame screens, if fitted on the valves or vent risers, as necessary.
• Check gas vent risers and their drains to ensure that they are free of any blockage.
• Ensure no unsuspected dangerous pockets remain by inspecting:
  • All equipment that has been used
  • Enclosed or partially enclosed spaces that can retain or contain cargo residues or vapours
• Areas where cargo traces may remain include:
  • Cargo lines
  • Cargo valves
  • Cargo pumps
  • Stripping lines and valves
  • Venting lines and P/V valves
  • Vapour return lines
  • Ullaging or sounding arrangements
  • Heating coils
  • Cargo handling equipment storage rooms
  • Protective clothing storage rooms
  • Cargo sample storage rooms

10 Reasons for Tank Survey Failures

Tank surveys may fail for a number of reasons. The most typical ones are listed below:

• Wet tank bottom, sides, or top (condensation)
• Film of residues adhered to the tank surfaces
• Bleeding of oil from slits or cracks in tank coating
• Dried or hard residues on beams, heating coils, frames, inside loading pipes, and submerged cargo pumps or suction bell mouths
• Odour
• Sediment remaining on the bottom, especially beneath lightning holes and heating coils
• Negative results from the wall wash test (wipe test) with reagents

11. Consumables for Cleaning

Master/Chief Officer shall ensure:

• Sufficient kinds and quantities of consumables are available on board to perform tank cleaning efficiently, such as cleaning detergents, solvents, wiping rags, dry cells.
• The remaining quantities are checked and recorded properly after cleaning operation.
• Requisition for replenishment is made well in advance to arrival at the port of supply to:
  • Vessel Manager & Marine Superintendent, or
  • Commercial Operator (if the tank cleaning consumables are arranged by them as per agreement)
• Consumables are:
  • Kept on board in a safe place, and
  • Stored as per manufacturer’s recommendation.

12. Prewash & Control of Effluent Discharge (CDI 5.5.16)

12.1 General

The purpose of the required prewash is to reduce the amount of cargo remaining in the tank and piping system by flushing mainly the tank bottom, the sump, the pump, and the pipelines with the prewashing water.

• Follow the guidelines provided in the ship’s Procedures and Administration (P&A) Manual regarding:
  • Slop Discharge Procedure (SDP) and
  • Cargo Discharge Procedure (CDP)
• When required, a mandatory pre-wash of the ship’s tanks must be witnessed by a competent authority of the Port State / government surveyor.

Note:

• Enter details of such washings in Cargo Record Book and ensure it is endorsed by the PSC / government surveyor.


• Chief Officer shall exercise proper control over the discharge of effluent from the cleaning operation.

12.2 Vessel within Special Area

No discharges into the sea of residues of Noxious Liquid Substances, or mixtures containing such substances, are allowed within the special area.

• Antarctic Area (the sea area south of latitude 60°S)

12.3 Vessel Outside Special Area

Category X:

• Discharge to sea - Not permitted.
• Prewash (as per P & A Manual) – Required.
• Washings - Discharged to reception facilities prior to departure from unloading port.
• Cargo record book - Must be endorsed by a Government Surveyor on completion.
• Any water subsequently added to the tank - May be discharged through the underwater outlet when the vessel is:
  • Proceeding at 7 knots or more,
  • More than 12 miles off land, and
  • In a water depth of 25 m or more.

Category Y:

• Solidifying or high viscosity category Y residues
  • Discharge to sea - not permitted.
  • Prewash (as per P & A Manual) – Required.
  • Washings - Discharged to reception facilities prior to departure from unloading port.
  • Cargo record book - Must be endorsed by a Government Surveyor on completion.
  • Any water subsequently added to the tank - May be discharged to the sea as specified in the P & A manual.
• Non-solidifying or low viscosity category Y residue tank washings
  • May be discharged to the sea as specified in the P & A manual.

For the purpose of this rule, the definition of solidifying or high viscosity cargo shall be taken as follows:

• Solidifying substance: Any substance having a melting point less than 15°C whose unloading temperature is less than 5°C above that temperature, or
• Any substance having a melting point equal to or greater than 15°C whose unloading temperature is less than 10°C above that temperature.
• High viscosity substance: Any substance in Category X or Y, having a viscosity equal to or greater than 50 mPas at the unloading temperature.

Category Z:

• If the cargo has been discharged as per the P&A Manual, then the wash water may be discharged to the sea as specified in the P&A manual.

13. Tank Cleaning After Drydocking

13.1 General

In addition to the inspection to confirm successful completion of the work immediately after finishing dry dock work, or just after sailing, actions as listed in the below points have to be performed.

13.2 Inspection of Cargo Tanks

Chief Officer shall inspect all the cargo tanks to identify and remove any abnormality or any foreign matter left behind.

• Foreign matter liable to be left behind includes:
  • Seizing wires used for staging,
  • Small tools such as brooms, brushes, scrapers, etc.,
  • Consumable items such as sandpaper, plastic masking sheets, and gum tapes used for masking outfitting,
  • Grit used for sandblasting,
  • Paint dusts,
  • Nuts from heating coil U-clamps, etc.
• Likely places where foreign matter is likely to be left behind include:
  • Every nook and corner, especially shadow areas,
  • Beneath or behind heating coils and their supporting angles,
  • On the longitudinal frames, supporting angles, brackets, and face plates,
  • Inside cargo pump or beneath its bell mouth,
  • On the upper surface of corrugated bulkheads.

13.3 Curing of Coating

• Chief Officer shall, before starting any work in a cargo tank which has been recoated, confirm the curing of the coating.
• For proper curing of coating, ensure:
  • The tank is ventilated mechanically with a duct extended to the bottom to discharge the vapour of the solvent being exhausted from the coating, and
  • The ambient temperature in the tank is high enough.
• For detailed procedure for proper curing and curing period, refer to Paint Maker's instructions.

13.4 Pre-Cleaning Before Start of Usual Tank Cleaning

13.4.1 Main Principle

• Clean any recoated cargo tank in both of the following ways before cleaning for loading the next cargo.

13.4.2 Dry Cleaning

• Carry out this cleaning after the coating has cured to a sufficient hardness not to be damaged by usual cleaning work.
• Blow with compressed air to remove foreign matter as far as practicable safely.
  • Tank interior surfaces,
  • Especially upper surfaces of longitudinal members and horizontally corrugated bulkheads,
  • Blow through cargo line and vent lines with compressed air towards the tank to remove foreign matter remaining inside.
• To remove foreign matter remaining in slits or gaps among heating coils, their supports, and U bolts:
  • Loosen and clean the U bolts by air blowing or vacuum cleaner.

13.4.3 Washing by Hand Hose or Tank Cleaning Machine

• Wet cleaning may be started after the coating has cured sufficiently to endure wet cleaning.
• To remove any remaining foreign matter before the start of tank cleaning for loading the next cargo:
  • Wash all tank interior surfaces by spraying fresh water with a hand hose or tank cleaning machines.
  • Discharge water out of the tank by portable diaphragm pump.
  • Completely remove the foreign matter accumulated at the bottom of the tank.

14. Cleaning of Tank Recoated with Zinc Coating

• Dust of coating material will affect the result of the wall wash test and, therefore, the dust must be removed.
• Repeated thorough air blowing of the tank surfaces and continuous mechanical ventilation will be effective in removing the dusts.
• Tank cleaning procedure:
  • Flush the vent line with water by hand hose from the vent head for at least 30 minutes.
  • Wash the tank surfaces by spraying warm fresh water by hand hose, especially the surfaces shaded by internal structural members or outfitting.
  • Butterworth with cold fresh water for 0.5 to 1 hour.
  • Butterworth with hot fresh water for 1.5 to 2 hours.

15. Cleaning of Tank Recoated with Epoxy Coating

• Before starting cleaning a tank with epoxy coating, ensure it has cured as per the instruction of the Paint Maker.
• In a cold climate, warming the tank by supplying steam slightly to the heating coils shall facilitate the curing; however:
  • Keep ambient temperature in the tank below 40°C.
  • Ensure sufficient continuous or intermittent mechanical ventilation of the tank for proper curing.
• After proper curing of the coating and after confirming the tank is safe to enter:
  • Test the coating by wall wash for permanganate time to ascertain the progress of curing.
  • Strong smell of solvent exhausted from the coating generally means insufficient curing.

Tank Cleaning Procedure:

• Flush the vent line with fresh water by hand hose from the vent head for at least 30 minutes.
• Butterworth with hot seawater for 3 hours (Pressure should be kept as per the recommendations given in the P&A Manual).
• Butterworth with hot fresh water for 1 hour.
• Steam for 2 hours. Steam condensate shall be drained out of the tank at every 30 minutes. The temperature of the tank shall not be raised above 65°C throughout the steaming period.
• Dry the tank immediately after steaming, by draining quickly and ventilating mechanically with duct extended to the bottom as long as possible.
• When fine chemicals are to be loaded, the above cleaning is better carried out after curing of coating as long as possible.
• If strong smell still exists in the tank after tank cleaning, the following procedure should be repeated several times:
  • Steam for 1 to 1.5 hours.
  • Dry the tank by draining quickly and ventilating mechanically with duct extended to the bottom for at least 5 hours.

16. Cleaning of Heating Coils

Cargo Leaks

In the case of cargo leaks into heating coils, take the following actions:

• Cargo Soluble in Water

• Flush the coil with warm fresh water for 1 to 2 hours continuously.
• Blow out/drain by compressed air and check the odour of cargoes carried by the water to identify the kind of cargo.
• Blow out drain by compressed air.

• Cargo Not Soluble in Water

• Flush the coil with cold fresh water.
• Clean the coil using the cleaning method applied to the tank itself.

• Cargoes Liable to Solidify/Polymerize in Heating Coils

• Master shall report to Marine Superintendent if leakage of such cargo is found.

17. Tank Materials and Coatings

17.1 General

• Avoid filling cargo tanks with cargoes which may adversely affect them.
• Minimize the detrimental effect which may be caused by:
  • Ballast water
  • Mechanical damage

17.2 Prevention of Mechanical Damage to Tank Surface

• Avoid scratching the surface of stainless steel tanks, as scratches may seriously impair the resistance of the material due to corrosive attack by aggressive cargoes.
• When entering stainless steel and coated tanks:
  • Wear soft-soled shoes with a disposable shoe cover.
  • Lower the required tools in a sack or bag to prevent damage due to falling off.
• Ensure equipment for mopping, etc., including buckets and scoops, is of rubber, plastic, or other soft materials.
• When positioning portable tank washing machines, take care to ensure that they do not knock against tank sides or structure.

17.3 Stainless Steel Tanks

17.3.1 General

• Check the compatibility of the stainless steel with the cargo at the time of planning cargo stowage.
• Strictly control the use of salt water when tank cleaning. Fresh water, hot or cold, does not affect the stainless steel provided that it is relatively chloride-free.
• Ensure stainless steel tanks contain only fresh water except in emergencies.

17.3.2 Avoiding Corrosion of Stainless Steel by Sea Water

• Pitting is likely to occur if stainless steel is left in prolonged contact with static seawater, particularly at crevices. The possibility of pitting increases if the pH of seawater is reduced from its normal level of about 8, especially when acidic cargoes have been loaded.
• Ensure the following:
  • Such tanks are emptied of water as soon as tank cleaning is commenced.
  • Any seawater mixed with acid does not stay in the tank for a long time.

Note:

• In order to conserve the corrosion resistance throughout the lifetime of the vessel, it is necessary to retain the passive layer on the steel surface.


• o This may be done by applying correct procedure for tank cleaning as described below:
  • Continue the pumping out process without disruption.
  • Use the maximum quantity of seawater to minimize the drop in pH from the acidic mixture.
  • Continue tank cleaning normally, without stopping washing until the tank is cleaned.
  • Perform final rinsing with fresh water immediately after seawater cleaning.
  • Do not leave seawater in prolonged static contact with stainless steel.
  • Any seawater kept for shorter periods must be kept at temperatures not higher than 50°C.
  • Dry the tank at the earliest.
• Ballasting of SUS tanks with seawater should be avoided as far as possible, only to be used in dire emergency.



Warning:

• Ballasting of Stainless-Steel tanks is discouraged and in case of any requirements/instructions from charterers/operators, contact Vessel Tech Manager/ Marine Superintendent immediately.
• Owners will be informed on this requirement through Office.

For details on the care of Stainless steel See CTM 9.7 – Appendix 3 - Corrosion in Chemical Tanker and Care of Stainless Steel Tanks

17.4 Passivation of Stainless Steel

17.4.1 General

• New stainless steel normally shines in appearance and is said to be active. It is susceptible to reaction with certain cargoes and seawater.
• Stainless steel needs to be passivated before use by treating the surface with nitric acid, forming a thin chrome oxide film on the surface that gives a dull appearance.
• Stainless steel can become active due to mechanical damage or aggressive cargoes like phosphoric and sulfuric acids.
• During tank inspection, examine stainless steel tanks and fittings for shiny areas, which indicate that the steel is active. These areas need to be passivated.

17.4.2 Passivity Test

• Assess the overall condition of the tank every 12 months or after 3 voyages of aggressive acids like phosphoric and sulfuric.
• Inspect to ensure the presence of the passive chromium oxide film on the stainless steel.
• If required, use a passivity meter or palladium chloride test kit to check the surfaces.
• Passivity meter readings:
  • Less than 30mV - active surface.
  • 30mV ~ 60mV - incomplete protective oxide film.
  • More than 60mV and stable or rising - passive surface.
• Palladium chloride test:
  • If the passivity meter cannot be used, the palladium chloride test is an alternative.
  • Use a solution of 0.5 g palladium chloride per 100 ml with 5 ml concentrated hydrochloric acid.
  • Apply a drop of the solution to the surface and wait three minutes.
  • Observe the color:
    • No color change: PASSIVE.
    • Black discoloration: ACTIVE.
    • Grey discoloration: doubtful.

17.5 Coated Tanks

17.5.1 General

• Ensure


• coated tanks are compatible with the cargo to be carried.



Note:

• For detailed information on compatibility of cargoes and coating materials, refer to coating compatibility lists supplied by the paint manufacturers


• After discharging certain aggressive cargoes, the tank coating must be cured for a period as designed by the paint manufacturer before loading the next cargo.
• Tank cleaning chemicals should not be used if they adversely affect the tank coatings.
• Dirty slops or washings should not be stowed in coated tanks unless the cargo contaminant is compatible with the coating.

17.5.2 Zinc Silicate Coatings

• Zinc silicate coatings withstand intermittent exposure to fresh and salt water, but continuous immersion will reduce the life of the coating.
• Do not ballast zinc silicate tanks unless absolutely necessary.
• Suitable cargoes for zinc silicate coatings include alcohols, amines (dry), aldehydes, animal oils and fats (FFA below 2.5%), hydrocarbons, and vegetable oils (FFA below 2.5%).
• Unsuitable for acids, alkalis, vegetable and animal oils and fats with an FFA over 2.5%, unless advised by the manufacturer.

17.5.3 Epoxy Coatings

• Epoxy coatings are suitable for both fresh and salt-water ballast.
• Suitable cargoes for epoxy coatings include alkalis (low grade), amines, glycols, hydrocarbons, vegetable oils (FFA below 5%), and alcohols (with restrictions).
• Unsuitable for acids, aldehydes, animal oils and fats (FFA 5% and above), cyanohydrins, esters, halocarbons, and ketones.

17.5.4 Polyurethane Coatings

• Polyurethane coatings have compatibility similar to epoxy coatings and also some solvents compatible with zinc silicate coatings. Always refer to the coating compatibility list for specific cargoes.

17.5.5 Phenolic Epoxy Coatings

• Phenolic epoxy coatings have resistance similar to epoxy coatings, but with a wider range of chemicals and fewer restrictions.
• Refer to the coating compatibility list for specific cargoes.

17.6 Inspection and Maintenance of Tank Coatings

• The Chief Officer shall inspect coated tanks regularly, at least once every 12 months or after each voyage with aggressive acids.
• Any abnormalities found must be reported to the Master, who will inform the Marine Superintendent.
• Inspection records should be made in the COMPANY E25 Cargo Tank Inspection form.

17.7 Repair of Tank Coatings

• Carry out maintenance and repairs of coatings at every possible opportunity.
• In coated tanks follow coating manufacturer’s instructions with regard to surface preparation, application of coatings and curing time
• In general, give due consideration to the following issues while performing maintenance and repair:

• De-rust the surface thoroughly. (If possible, to a SA 2.5 standard)
• Smoothen the edges by using a disc grinder.
• Wipe bare metal with methanol/thinner prior to the application of the first coat.
• Apply coating by a hand brush and not by roller.
• Keep overlap of the surrounding area to a bare minimum.
• Control humidity in the tank to be in accordance with the manufacturer’s instructions.
• Epoxy coatings require low relative humidity (dry air).
• Consider running ventilation fans in conjunction with steam to heating coils. Cracking open the valve is a good way to raise the air temperature and reduce relative humidity.
• Zinc Silicate coatings may require high humidity at the time of application and during curing. A steam hose lowered into the tank with the valve cracked open raises the relative humidity in the tank.
• Ensure sufficient coats are given to obtain the necessary dry film thickness.
• 100 microns for zinc and...
• 300 micron for epoxies

• Allow Sufficient curing time.

18. Referenced Forms and Checklists

• COMPANY Form E25 - Cargo Tanks Inspection (Stainless Steel Tanks)

19. Appendices

• CTM 9.7 A1 Miscellaneous
• CTM 9.7 A2 Wall Wash Tests
• CTM 9.7 A3 Corrosion in Chemical Tankers and Care of Stainless Steel Tanks
• CTM 9.7 A4 Care & Maintenance of Zinc Silicate Coatings
• CTM 9.7 A5 Aggressive Cargoes in Epoxy Coated Cargo Tanks