GTM-8.3 Gas Tanker Manual
GTM Introduction to Gas Tankers
 Form No.: GTM-8.3
Revision: 01
Date: 15 Oct 2024
Issued by: DPA
Approved by: MD



3. INTRODUCTION TO GAS TANKERS

3.1 DEFINITIONS

The ICS publication “Tanker Safety Guide – Liquefied Gas” is carried on board all managed gas tankers. This publication should be read in conjunction with these operating instructions.

3.2 PHYSICAL PROPERTIES

The physical properties of a liquefied gas depend on its molecular structure. Some compounds have the same molecular formula but a different arrangement within the structure. These different compounds of the same basic substance are called ISOMERS. For example, N-BUTANE x ISO-BUTANE.

The single most important physical property of a liquefied gas is its saturated vapour pressure/temperature relationship. This property governs the design of the containment system suitable for each cargo.

3.3 SOURCES OF IGNITION

Smoking

There are frequently local regulations about smoking which must be rigidly observed. Smoking may be permitted but only under controlled conditions at times and in places specified by the Master.

Personnel when working aboard the ship must not carry matches or more particularly lighters, and the risk of doing so is to be impressed on all.

Portable Electrical Equipment

Only approved Safety torches or hand lamps are to be used.

Portable Electric Equipment self-contained or on extension cables are not to be used in a gas dangerous place or zone as specified in paragraph 2.1 and the IMO IGC code unless the equipment is intrinsically safe.

Portable domestic radios, electronic calculators, tape recorders, and other non-approved battery equipment are not to be used in a gas dangerous place or zone.

Communication Equipment

When berthed, the ship's normal communication equipment is not to be used unless certified safe.

Main radio transmitters are not to be used during cargo operations. This does not apply to permanently and correctly installed VHF equipment or Satellite communication systems.

Hot work, hammering, chipping and power tools

Before any hot work, hammering, chipping, or power tools, including shot blasting, are used, the responsible officer is to examine the area to be worked and satisfy himself that such work can be safely undertaken and a hot work certificate Form SAF 04 issued.

Non-sparking tools are not to be used as they do not significantly reduce the risk of igniting a flammable vapour.

Aluminium paint is not to be smeared across steel. A heavy smear of aluminium on rusty steel if struck can cause an incandescent spark.

Ship to Shore Bonding

On some jetties, this may be required, but it is considered to be of minimal benefit. Cargo hoses and loading arms are to be fitted with an insulating flange to ensure discontinuity between ship and shore.

Auto - Ignition

The vapours from flammable liquids, including fuel and lubricating oil, may ignite if the liquid comes into contact with any surface heated above the auto-ignition temperature, e.g., steam lines, exhaust manifolds, overheated equipment.

Immediate steps are to be taken to rectify any leakage and to remove any soaked rags or other material including lagging.

Static Electricity

Static Electricity can cause sparks capable of igniting a flammable gas.

The cargo system of a gas carrier is electrically bonded to the ship's hull to prevent any build-up of charges. Bonding connections must be maintained in good order.

Steam

A jet of steam may become charged in passing through a nozzle. Steam is not to be injected into a tank compartment or piping system which may contain a flammable mixture.

Carbon Dioxide

Liquid Carbon Dioxide, when released under pressure, may form particles of solid carbon dioxide that may become electrostatically charged. For this reason, it must not be released into tanks or spaces which contain a flammable mixture.

Electrical Equipment / Fittings

All electrical equipment and fittings outside the accommodation and machinery spaces must be intrinsically safe. Damaged electrical fittings must be isolated and not used until they are repaired.

Particular care must be taken to ensure that portable electrical equipment such as radio telephones, pagers, electrical equipment, cameras, etc., are not used in hazardous areas. The batteries for portable equipment must not be changed on the open decks, and strict control to be put in place to ensure that the following are intrinsically safe:

Damaged portable equipment must not be used until it is repaired.

The level of protection provided by explosion-proof or intrinsically safe electrical equipment may be compromised by incorrect maintenance procedures.

Even the simplest repair and maintenance operations must be carried out in strict compliance with the manufacturer’s instructions so that such equipment remains in a safe condition. In particular, regarding lights, where incorrect closing after changing a light bulb could compromise the integrity of light.

Lights and cargo compressors’ electric motors located on weather deck areas must be periodically inspected as per the PMS.

During inspections of electrical equipment or installations, particular attention should be paid to the following:

3.4 PRINCIPLES OF REFRIGERATION

See Appendix I for the basic components in a simple refrigerator.

Cold liquid refrigerant (Liquid Gas Cargo) is evaporated in an evaporator coil (Cargo tank), which being cooler than its surroundings, draws heat to provide the latent heat of vaporisation. The cool vapour is drawn off by a compressor, which raises both the pressure and the temperature of the vapour and passes it to the condenser.

The pressure of the vapour having been increased, the vapour now has a temperature of condensation greater than the temperature of the condenser cooling fluid (sea water).

The vapour is condensed to a high-pressure liquid and the sensible heat of desuperheating the vapour together with the latent heat of condensation is removed via the condenser coolant, which is warmed up in the process.

The high-pressure liquid then passes through an expansion valve to the low-pressure side of the cycle, in doing so flash evaporates to a mixture of cold liquid and vapour. The mixture passes to the evaporator (cargo tank) to continue the cycle.

3.5 CRITICAL TEMPERATURES & PRESSURES

The critical pressure of a gas is the pressure required to compress a gas to its liquid state at its critical temperature.

Critical Temperatures and pressures are listed in the table of Physical Properties (see Appendix I).

For the carriage or storage of ethane or ethylene as a liquid, some additional refrigeration is required, often in the form of a cascade system.

3.6 BASIC THERMODYNAMIC THEORY

Cargo and Deck Officers must be familiar with Basic Thermodynamic Theory. Section 13.4 and A3.5 of the Tanker Safety Guide, Liquefied Gas, deals with the most important points, and these sections are to be read in conjunction with these operating instructions.

3.7 FLAMMABILITY AND EXPLOSION

3.8 TYPES OF GAS CARRIERS

a) Fully Pressurised Ships

These ships are the simplest of all gas carriers in terms of containment systems and cargo-handling equipment and carry their cargoes at ambient temperature. Type C tanks - pressure vessels fabricated in carbon steel with a typical design pressure of 17.5 bar g, corresponding to the vapour pressure of propane at 45°C, must be used. Ships with higher design pressures are in service: 18 bar g is quite common - a few ships can accept up to 20 barg. No thermal insulation or reliquefaction plant is necessary and cargo can be discharged using either pumps or compressors.

Because of their design pressure, tanks are extremely heavy. As a result, fully pressurised ships tend to be small with maximum cargo capabilities of about 4,000m3 and they are used to carry primarily LPG and ammonia. Ballast is carried in double bottoms and in top wing tanks. Because these ships utilise Type C containment systems, no secondary barrier is required and the hold space may be ventilated with air.

b) Semi-refrigerated Ships

These ships are similar to fully pressurised ships in that they incorporate Type C tanks - in this case pressure vessels designed typically for a maximum working pressure of 5.7 barg. The ship's range in size up to 7,500m3 and are primarily used to carry LPG. Compared to fully pressurised ships, a reduction in tank thickness is possible due to the reduced pressure, but at the cost of the addition of refrigeration plant and tank insulation. Tanks on these ships are constructed of steels capable of withstanding temperatures as low as -10°C. They can be cylindrical, conical, spherical, or bi-lobe in shape.

c) Semi-pressurised/fully refrigerated Ships

Constructed in the size range 1,500 to 30,000m3, this type of gas carrier has evolved as the optimum means of transporting the wide variety of gases from LPG and VCM to propylene and butadiene. Like the previous two types of ship, SP/FR gas tankers use Type C pressure vessel tanks and therefore do not require a secondary barrier.

The tanks are made either from low temperature steels to provide for carriage of -48°C which is suitable for most LPG and chemical gas cargoes or from special alloys which allow the carriage of ethylene at -104°C. The SP/FR ship's flexible cargo-handling system is designed to be able to load from, or discharge to, both pressurised and refrigerated storage facilities.

d) Fully Refrigerated LPG Ships

Fully refrigerated ships carry their cargoes at approximately atmospheric pressure and are generally designed to transport large quantities of LPG and ammonia. Four different cargo containment systems have been used in FR ships: independent tanks with double hull, independent tanks with single side shell but double bottom and hopper tanks, integral tanks, and semi-membrane tanks, both these latter having a double hull. The most widely used arrangement is the independent tank with single side shell with the tank itself a Type A prismatic free-standing unit capable of withstanding a maximum working pressure of 0.7 barg.

The tanks are constructed of low-temperature steels to permit carriage temperatures as low as -48°C. FR ships range in size from 10,000 to 100,000m3.

e) Ethylene Ships

Ethylene ships tend to be built for specific trades and have capacities ranging from 1000 to 30,000m3. This gas is normally carried fully refrigerated at its atmospheric pressure boiling point of -104°C. If type C pressure vessel tanks are used, no secondary barrier is required; Type B tanks require a partial secondary barrier; Type A tanks require a full secondary barrier and because of the cargo carriage temperature of -104°C the hull cannot be used as a secondary barrier, so in this case a separate secondary barrier must be fitted.

Thermal insulation and a high capacity reliquefaction plant is fitted on this type of vessel. Many ethylene carriers can also carry LPG cargoes thus increasing their versatility. Ballast is carried in the double bottom and wing ballast tanks and a complete double hull is required for all cargoes carried below -55°C whether the tanks be of Type A, B, or C.

3.9 COMMUNICATIONS

3.10 CARGO INFORMATION

3.11 GENERAL PRECAUTIONS AT LOADING/DISCHARGE BERTH

a) Moorings

The safe mooring of a vessel requires close co-operation between the ship and the shore. The principles of good mooring, including the dangers associated with mixed moorings, is to be understood by ships personnel. Particular attention must be given to the correct application of winch brakes as well as the maintenance of moorings, winch brakes, and associated equipment.

b) Craft Alongside

Unauthorised craft are to be prohibited from securing alongside the ship.

c) Dispersal of Vented Cargo Vapours

Any cargo vapour, whether toxic or flammable, is to be vented to atmosphere with extreme caution, taking account of regulations and weather conditions.

d) Openings in Deckhouses and Superstructures

It is essential that the accommodation is kept under positive pressure to prevent the entry of Hydrocarbon Vapours.

3.12 WEATHER PRECAUTIONS

a) Wind Conditions

If there is little wind movement, vapour may persist on deck. When there is a wind, it may, in crossing a deckhouse or structure, create a low pressure on the lee side thereby causing vapour to be carried towards the deckhouse or structure.

b) Electrical Storms

Cargo operations involving the venting of flammable cargoes should be stopped during electrical storms in the immediate vicinity of the ship.

If a vent mast is struck by lightning during venting operations, ignition can occur. To extinguish the flame the source of fuel should be isolated and, if possible, inert gas should be injected into the vent mast. Venting should not be resumed until the temperature at the mast head has returned to normal.

3.13 ENGINE AND BOILER ROOM PRECAUTIONS

a) Combustion Equipment

Boiler tubes, uptakes, exhaust manifolds, and combustion equipment are to be maintained in good condition as a precaution against funnel fires and sparks. In the event of a funnel fire, or if sparks are emitted from the funnel, cargo operations are to be stopped and, at sea, the course is to be altered as soon as possible to prevent sparks falling onto the tank deck.

b) Blowing Boiler Tubes

Funnel uptakes and boiler tubes are not to be blown in port. At sea they are only to be blown in conditions where soot will be blown clear of the tank deck.

c) Flammable Liquids

Flammable liquids or other volatile liquids for cleaning or other purposes are to be kept in closed, unbreakable, and correctly labelled containers in a suitable compartment when not in use. Direct skin contact with cleaning liquids is to be avoided. Cleaning liquids should preferably be non-flammable and non-toxic.

d) Oil Spillage and Leakage

Oil spillage and leakages are to be avoided and the floor plates are to be kept clean.

e) Fuel and Lubricating Oil

Fuel or lubricating oils can be ignited by contact with hot surfaces even in the absence of an external flame or spark. Care is to be taken to ensure that fuel or lubricating oil does not touch hot surfaces; if leakage causes oil to spray or fall onto a hot surface, the source of oil is to be isolated immediately.

f) Cargo Vapour

Care is to be taken to ensure that cargo vapour does not enter the engine or boiler room from any source.

If, as a result of malfunction of equipment, explosion, collision, or grounding damage, cargo vapour is likely to enter the machinery space, immediate consideration is to be given to its possible effect on the operation of any equipment. Any necessary action is to be taken; e.g. isolating the source, closing access doors, hatches, and skylights, shutting down auxiliary and main machinery, evacuation.

Apart from the obvious hazards, diesel engines are liable to over-speed and destroy themselves if flammable vapour is present in the air supply, even at concentrations well below the lower flammable limit (LFL).

3.14 GALLEY PRECAUTIONS

The interpretation of this section may be subject to local regulations.

Galley stoves are not to be used when the Master considers that an undue hazard exists. Galley personnel are to be made aware of the potential dangers from galley equipment and of the safeguards to be taken:

While berthed, galley stoves and cooking appliances with non-immersed elements, such as electric hot-plates and toasters, may be used in galleys, pantries, and accommodation subject to the agreement of the Master and the terminal representative that no hazard exists. Any doors or ports opening directly onto or overlooking the deck are to be kept shut.

Galley stoves and cooking appliances with non-immersed elements are not to be in use in the galley when the stern cargo line (where fitted) is in use. Cookers and other equipment heated by steam may be used at all times.

3.15 CARGO MACHINERY ROOM PRECAUTIONS

Cargo vapour may be present in the compressor room and a gas detection system is installed to warn of its presence. Some ships can carry cargoes (e.g. ammonia and LPG) whose vapours are either lighter or heavier than air; in such cases gas detectors are fitted at high and low levels and the relevant detectors are to be used for the cargo carried.

Ventilation systems are provided to disperse any vapour that may collect in the compressor room. The supply and exhaust ducts are fitted with supply openings at high and low levels and the respective flaps are to be open/closed depending on the cargo carried. The space is to be ventilated for at least ten minutes before cargo operations begin and throughout their duration. If liquid or vapour leakage is suspected cargo operations should be stopped, space ventilated, and leakage rectified. Ventilation systems are to be maintained carefully; if the fans fitted are of a non-sparking design, it must be ensured that their design features are not impaired in any way.

Lighting systems in the cargo machinery room may be certified safe, and it is essential to ensure that these are properly maintained. If additional lighting is required this is to be of a suitable safe type.

Means such as gas-tight bulkhead gland seals and air lock doors are provided to ensure that cargo vapour does not enter the cargo machinery electric motor rooms. Care is to be taken to ensure that these function correctly and are maintained properly.

Electric motors for driving cargo compressors are normally separated from those spaces by a gas-tight bulkhead or deck. However, the IMO code permits, where operational or structural requirements are such as to make it impossible to fit gas-tight bulkheads, that electric motors of the following certified safety type may be installed:

3.16 TRIM, STABILITY, STRESS AND READINESS TO MOVE

During discharge, loading, and ballasting operations the ship must at all times be adequately stable and in good trim to allow for departure at short notice in the event of an emergency.

The information contained in the ship's Loading and Stability Booklet is to be taken into account. Care is to be taken to ensure that the distribution of cargo and ballast at no time creates excessive stress on the hull; stress measuring devices if fitted, are to be used to verify this. While berthed at a terminal the ship's boilers, main engines, steering machinery, and other essential equipment is normally to be kept ready to permit the ship to move from the berth at short notice.

Repairs and other work which may immobilise the ship must not be undertaken at a berth without prior written agreement of the terminal. It may also be necessary to obtain permission from the local port Authority before carrying out such repairs or work.

3.17 HELICOPTERS

Helicopters must not be landed on board liquefied gas carriers unless they have the approval of the Administration, and on an approved landing area. In special circumstances "hovering" for the purposes of personnel and/or stores may be permitted. In either of the above cases, operators must comply with the safety measures and procedures required and the advice contained in the ICS Guide to Helicopter/Ship Operations must be taken into account.

3.18 CHEMICAL PROPERTIES

Chemical compounds with the same chemical structure are often known by different names. The alternative names given to the same compound are called synonyms. The table below gives a list of the synonyms of the liquefied gases against each common name and its simple formula. The more complex compounds tend to have a larger number of synonyms than the simple compounds.

Synonyms of Liquefied Gases
Common Name Simple Formula Synonyms
Methane CH4 Fire damp; marsh gas; natural gas; LNG
Ethane C2H6 Bimethyl; dimethyl; methyl methane
Propane C3H8 -
n-Butane C4H10 Normal butane
i-Butane C4H10 Iso-butane; 2-methylpropane
Ethylene C2H4 Ethene
Propylene C3H6 Propene
a-Butylene C4H8 But-1-ene; ethyl ethylene
 - Butylene C4H8 But-2-ene; dimethyl ethylene; pseudo butylene
y-Butylene C4H8 Isobutene; 2-methylprop-2 -ene
Butadiene C4H6 b.d.; bivinyl; 1,3 butadiene; butadiene 1-3; bivinyl; biethylene; erythrene; vinyl ethylene
Isoprene C5H8 3-methyl - 1,3 butadiene; 2-methyl - 1,3 butadiene; 2-methylbutadiene - 1,3
Vinyl chloride monomer CH2CHC1 Chloroethene; chloroethylene; VCM
Ethylene oxide C2H4O Dimethylene oxide; EO; 1,2 epoxyethane; oxirane
Propylene oxide C3H6O 1,2 epoxy propane; methyl oxirane; propene oxide
Ammonia NH3 Anhydrous ammonia; ammonia gas; liquefied ammonia; liquid ammonia

Note: Commercial propane contains some butane; similarly, commercial butane contains some propane. Both may contain impurities such as ethane and pentane, depending on their permitted commercial specification.

Saturated Hydrocarbons

The saturated hydrocarbons methane, ethane, propane, and butane are all colourless and odourless liquids under normal conditions of carriage.

They are all flammable gases and will burn in air and/or oxygen to produce carbon dioxide and water vapour. As they are chemically non-reactive, they do not present chemical compatibility problems with materials commonly used in handling. In the presence of moisture, however, the saturated hydrocarbons may form hydrates.

Sulphur compounds such as mercaptans are often added as odourisers prior to sale to aid the detection of these vapours. This process is referred to as "stenching". Mercaptans are considered to be hazardous in some forms and must be handled with care when on board the vessel.

Unsaturated Hydrocarbons

The unsaturated hydrocarbons ethylene, propylene, butylene, butadiene, and isoprene are colourless liquids with a faint, sweetish characteristic odour. They are, like the saturated hydrocarbons, all flammable in air and/or oxygen, producing carbon dioxide and water vapour. They are chemically more reactive than the saturated hydrocarbons and may react dangerously with chlorine. Ethylene, propylene, and butylene do not present chemical compatibility problems with materials of construction, whereas butadiene and isoprene, each having two pairs of double bonds, are by far the most chemically reactive within this family group. They may react with air to form peroxides which are unstable and tend to induce polymerisation. Butadiene is incompatible in the chemical sense with copper, silver, mercury, magnesium, aluminium, and monel. Butadiene streams often contain traces of acetylene which can react to form explosive acetylides with brass and copper.

Water is soluble in butadiene, particularly at elevated temperatures. The figures quoted are for the purpose of illustration only. On cooling water-saturated butadiene, the solubility of the water decreases, and water will separate out as droplets which will settle as a layer on the bottom of the tank. For instance, on cooling water-saturated butadiene from +15°C to +5°C approximately 100 ppm of free water would separate out. On this basis, for a 1,000m³ tank, 100cc of free water would need to be drained from the bottom of the tank. On further cooling to below 0°C, this layer of water would increase in depth and freeze.

Chemical Gases

The chemical gases commonly transported in liquefied gas carriers are ammonia, vinyl chloride monomer, ethylene oxide, propylene oxide, and chlorine. Since these gases do not belong to one particular family, their chemical properties vary.

Liquid ammonia is a colourless alkaline liquid with a pungent odour. The vapours of ammonia are flammable and burn with a yellow flame forming water vapour and nitrogen, however, the vapour in air requires a high concentration (16-25 per cent) to be flammable, has a high ignition energy requirement (600 times that for propane) and burns with low combustion energy. For these reasons, the IMO Codes, while requiring full attention to the avoidance of ignition sources, do not require flammable gas detection in the hold or interbarrier spaces of carrying ships. Nevertheless, ammonia must always be regarded as a flammable cargo.

Ammonia is also toxic and highly reactive. It can form explosive compounds with mercury, chlorine, iodine, bromine, calcium, silver oxide, and silver hypochlorite. Ammonia vapour is extremely soluble in water and will be absorbed rapidly and exothermically to produce a strongly alkaline solution of ammonium hydroxide. One volume of water will absorb approximately 200 volumes of ammonia vapour. For this reason, it is extremely undesirable to introduce water into a tank containing ammonia vapour as this can result in vacuum condition rapidly developing within the tank.

Since ammonia is alkaline, ammonia vapour/air mixtures may cause stress corrosion. Because of its highly reactive nature, copper alloys, aluminium alloys, galvanised surfaces, phenolic resins, polyvinyl chloride, polyesters, and viton rubbers are unsuitable for ammonia service. Mild steel, stainless steel, neoprene rubber, and polythene are, however, suitable.

Vinyl chloride monomer (VCM) is a colourless liquid with a characteristic sweet odour. It is highly reactive, though not with water, and may polymerise in the presence of oxygen, heat, and light. Its vapours are both toxic and flammable. Aluminium alloys, copper, silver, mercury, and magnesium are unsuitable for vinyl chloride service. Steels are, however, chemically compatible.

Ethylene oxide and propylene oxide are colourless liquids with an ether-like odour. They are flammable, toxic, and highly reactive. Both polymerise, ethylene oxide more readily than propylene oxide, particularly in the presence of air or impurities. Both gases may react dangerously with ammonia.

Cast iron, mercury, aluminium alloys, copper and alloys of copper, silver and its alloys, magnesium, and some stainless steels are unsuitable for the handling of ethylene oxide. Mild steel and certain other stainless steels are suitable as materials of construction for both ethylene and propylene oxides.

N.B. NITROGEN PADDING IS REQUIRED

Chlorine is a yellow liquid which evolves a green vapour. It has a pungent and irritating odour. It is highly toxic but is non-flammable though it should be noted that chlorine can support combustion of other flammable materials in much the same way as oxygen. It is soluble in water forming a highly corrosive acid solution and can form dangerous reactions with all the other liquefied gases. In the moist condition, because of its corrosivity, it is difficult to contain. Dry chlorine is compatible with mild steel, stainless steel, monel, and copper. Chlorine is very soluble in caustic soda solution which can be used to absorb chlorine vapour.

3.19 Tank Inspections

Cargo tanks must undergo internal inspections during dry-docking and when a particular tank requires gas freeing for repairs. Other tanks, including ballast and void spaces, should be inspected on a 12-month cycle to assess the condition of steelwork, pipework, fittings, and coatings. To ensure consistency and uniformity in reporting, the "Condition Evaluation & Maintenance of Tanker Structures" publication should be referred to before starting any inspection. Additionally, a pocket-sized copy of the LR publication "Tank Coatings Condition Guide" is provided on board to help assess the condition of the tanks.

The officer performing the inspection must complete and report their findings on Form TEC 25, and any defects should be reported promptly for budgeting and scheduling repairs. Where possible, photographic evidence should support the report, but only intrinsically safe cameras should be used. If there is any doubt about the camera’s suitability, the management office must be informed.

Particular attention should be given to cleaning up any debris left in the cargo tanks after repairs, as it can damage filters, pumps, and valves at both ship and shore installations. Accumulated water should also be removed to prevent the formation of hydrates.

In cases where the standard six-month inspection cycle is impractical due to specific ship designs or trading patterns, an alternative inspection schedule must be agreed upon with the fleet cell and documented.

3.20 Cargo Pipeline Inspection / Test Procedure

Cargo pipelines require regular inspection and testing, with any defects immediately reported to the management office. The condition of pipelines on semi-refrigerated LPG carriers is difficult to assess due to insulation materials, but the following procedures should be adhered to:

a) Checks During Loading / Discharging

  1. A complete visual check of all pipelines should be performed during cooling operations and the initial cargo transfer. Special attention should be given to areas where the pipes are insulated. If a leak is suspected, the insulation in the affected area must be removed immediately.
  2. Cargo checklist GAS 02 or GAS 03 (as applicable) should be completed before cargo operations begin.
  3. Cooling of all pipes should be performed in accordance with the onboard cool-down procedures (refer to Section 13 of the procedures).
  4. Regular checks should be carried out during cargo operations.

b) Annual Checks

At least once every 12 months, ship staff should conduct a thorough visual examination of the cargo and process pipelines, valves (including pressure relief and drainage valves), piping anchor supports, fittings, liquid/vapor hoses, and expansion bellows. A pressure test should also be conducted following a cargo changeover, particularly if the cargo system has been modified to alter tank segregation.

The pressure test should be conducted at a minimum of the designed maximum working pressure for the pipeline. The preferred medium for testing is cargo, rather than nitrogen, due to the large quantities of pressurizing medium required on larger vessels. The system should be checked for leaks, and if any deficiencies are identified, the management office must be notified immediately. If a leak is suspected, the insulation should be removed in the immediate area of the leak.

Prior to testing, the settings for the line pressure safety valves must be confirmed. The test pressure should not exceed 85% of the safety valve activation pressure. The inspection and testing routines should be logged in the PMS onboard, and records should be maintained and up-to-date. A risk assessment should be conducted before performing the test, and a Critical Operations Checklist (SAF16) should be developed following SEP Chapter 6.

c) Test Procedure in Dry-dock

During dry-docking, all cargo and process piping systems, including valves, actuators, and compensators, should be opened for examination as deemed necessary by the Class Surveyor to assess the condition of the pipes. A recognized shore-based company should be employed to carry out this inspection, and insulation may need to be removed and replaced.

If there is any doubt about the integrity of the piping based on visual examination, and if deemed necessary by the Class Surveyor, a pressure test to 1.25 times the Maximum Allowable Relief Valve Setting (MARVS) should be conducted on the suspect pipe section. After reassembly and repairs, the entire piping system should be pressure-tested to a minimum of the designated working pressure, and checks should be made for leaks. Safety procedures for pressure testing should be discussed and documented during the Daily Safety Meeting, and all ship staff should be briefed before testing begins.