Ch16 cargo handling

ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R 16 CARGO HANDLING 16.1 Change of Grade Propane/Butane Propane Loading The term "fully cooled ready to load" means:  The cargo tank bottom is cooled down to a maximum of -39 Celsius and the maximum mean temperature above the mid - depth of the cargo tank, in the range between two thirds and three quarters of the Maximum Allowable Tank Filling Level (MATFL), excluding any temperature indicated in the cargo tank dome vapour space, in no warmer than -25C The cargo tank pressure is to be no more than 70MB on arrival at the berth Butane loading The term "fully cooled ready to load" means:  The cargo tank bottom is cooled down to a maximum of Celsius and the maximum mean temperature above the mid depth of the cargo tank, in the range between two thirds and three quarters of the MATFL and excluding any temperature indicated in the cargo tank dome vapour space, no warmer than + 14C Cargo tank pressure is to be no more than 70 mb on arrival at the berth Changing Propane tanks to Butane There are two possible ways to change two Propane tanks to receive Butane  The first is to be utilised only if there is insufficient Butane retained on board to allow the complete or partial displacement of the propane vapour by Butane vapour The method is to merely puddle heat the Propane liquid heel and to reliquify the resulting excess vapour into the remaining Propane tank, on completion the excess propane can be pumped into the deck pressure vessel, according to the filling table in the cargo operations manual, and ensuring that there is sufficient coolant left in the remaining Propane tank so that it will be fully cooled on arrival Kuwait On completion of this operation the tanks are hot gassed until they are approximately -5 degrees average vapour temperature, the tanks are then ready to load the Butane  The second method must be utilised when there is sufficient Butane retained on board to partially or fully replace the propane atmosphere in the tanks to be changed In this method the Propane heel is puddle heated and, as before, the resultant vapour is reliquified to the remaining Propane tank The tanks are warmed up to approx zero degrees and Butane vapour is then introduced to the bottom of the tanks, the Butane vapour is generated either by liquid through the /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R vaporiser or by puddle heating the Butane heel and thus generating Butane vapour The propane vapour is drawn from the top of the tanks and is reliquified to the remaining Propane tank, the interface between the Propane and Butane is easily detectable b9 monitoring the condensing pressure in the reliquifaction plant or the temperature after the expansion valve It is particularly important that the interface is carefully monitored because if the recovered Propane is heavily contaminated with Butane it will be difficult to fully cool the tanks when they have to be converted back to propane carriage, indeed it is preferable to vent the Propane / Butane mix at the interface rather than save it Once all the Propane has been consolidated in the remaining Propane tank, transfer the available Propane liquid to the pressure vessel by pump Finally the tanks are to be cooled ready to load  It is important that if the pressure vessel does not have sufficient capacity for the quantity of Propane that is recoverable from the tanks, then the excess Propane is retained in the Propane cargo tank If there is a large excess of Propane remaining then the Charterer should be informed of the amount that can be added to the Bill of Lading, but the ship must retain sufficient to convert the two tanks back to Propane and cool them after the completion of the Turkish voyage Changing Butane tanks to Propane  On departure from the discharge port, the heel in the butane tanks to be changed should be puddle heated and the resulting vapour reliquified back to the remaining Butane cargo tank If there is a large amount of Butane recovered, the Charterer should be informed so that they can add the excess to the Bill of Lading  Propane from the pressure vessel is to be passed through the tank to be changed, the Butane is to be removed from the bottom of the tanks, reliquefied and returned to the designated Butane cargo tank, the interface between the Butane and Propane is readily detectable by observing the condensing pressure on the reliquifaction plant or the temperature after the expansion valve If there is insufficient propane in the pressure vessel to fully change the atmosphere of the tanks, then liquid or vapour can be taken from the designated propane cargo tank  When the atmosphere in the tanks has been changed to Propane then Propane liquid, from the reliquifaction plant or by cargo pump is to be sprayed into the top of the tank until it is fully cooled ready for loading  If there is insufficient Propane retained after discharge, either to fully change the atmosphere in the cargo tanks or to fully cool them ready for loading, then the Charterer is to be informed that the ship will require coolant at the load port and that it will have to go off the berth to cool down  In order to avoid having to take coolant, when possible, prior to loading for Turkey the Master is to inform the Charterer of the approximately amount of Propane that the ship will need to retain, to fully prepare the tanks for the next voyage, so that the Bill of Lading can be adjusted /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R accordingly  It must be stressed that if, for any reason, the Master believes that the ship will be unable to fully achieve the required arrival temperatures and pressures, the Ship Managers and Charterer must be informed as early as possible, in order to either arrange coolant or an indemnity against delays due to high tank pressures during loading 16.2 Butadiene Preamble Butadiene and Crude C4 containing Butadiene are very reactive chemicals which during transport may react with itself and form polymers (dimers) and/or react with any oxygen in the cargo system and form highly explosive peroxides Refer to form "Notice Butadiene" Objective To minimise the risk of any unwanted chemical reaction when transporting Butadiene and Crude C4 containing Butadiene Inerting of Cargo Tanks with Nitrogen In order to avoid the formation of peroxides, which besides being highly explosive also acts as a catalyst for polymerisation, the cargo tanks, piping and refrigeration system shall be inerted with nitrogen until the oxygen in the cargo system is reduced to the level required by the shippers Regardless of the requirements by the shippers Butadiene shall not be loaded into a tank containing more than 0.2% oxygen Inhibitor Before leaving the loading port, sufficient inhibitor to prevent the cargo from self-reacting during the voyage must be added to the Butadiene If the inhibitor is added to the cargo during loading, only one tank shall be loaded at a time, and all liquid valves to all other tanks shall be positively confirmed closed when adding the inhibitor in order to ensure that the correct amount of inhibitor is added to each tank Before leaving the loading port a certificate shall be delivered on board stating the following: The name and quantity of the inhibitor added; The date inhibitor was added and the normally expected duration of its effectiveness; The action to be taken should the length of the voyage exceed the effective lifetime of the inhibitor; /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Any temperature limitations affecting the inhibitor If a certificate is not received prior to departure, the Gas tanker Department shall be contacted immediately Transportation Temperature As polymerisation increases with heat, it is important that the cargo is cooled until fully refrigerated as soon as possible, and maintained fully refrigerated during the entire voyage regardless of the discharge temperature Draining Water Depending on the specification Butadiene may contain up to 0.5 per cent water, which besides the risk of freezing the pumps also absorbs the inhibitor, with subsequent risk of polymerisation When the cargo has settled, the cargo tanks are checked for free water by opening the puddle heating/stripping line If no or only a little water is present the tanks are left until the temperature in the sump is close to +1 C Any water contained in the cargo will emerge during cooling and the cargo tanks shall again be checked for water when the temperature in the sump is close to +1 C Small amounts of water are drained overboard by use of an ejector During the draining the soundings shall be closely monitored to avoid any excessive loss of cargo If a large amount of water (more than 100 litres per tank) is either suspected or detected, the Gas tanker Department and the Nautical Department shall be contacted before any draining is commenced Circulating the Cargo during Voyage The inhibitor used in Butadiene and Crude C4 containing Butadiene is normally Tertiary-ButylCatechol (TBC) If too much inhibitor has been added in the loading port, it may be difficult to remove the surplus inhibitor during the subsequent tank cleaning Circulation of the cargo for a few hours each day during the laden voyage reduces the risk of surplus inhibitor sticking to the tank surface Circulation shall be through the upper spray line and filling line Before circulation is performed the precautions mentioned in Section B3 of these Guidelines shall be taken Circulating the Cargo during Discharge /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R During discharge some of the cargo shall be recirculated through the start-up line When the sounding is at about 1.5 metres some of the cargo shall also be circulated through the lower spray lines If performing Nitrogen Displacement Discharge according to Section E13 in these Guidelines, no circulation of cargo shall be performed during discharge Product Washing in the H-class During discharge product washing according to Section E12 in these Guidelines shall be performed Product washing is not to be performed if the vessel is discharging by use of Nitrogen Displacement Discharge according to Section E13 in these Guidelines, in which case a complete methanol wash shall be performed when tank cleaning As the inhibitor does not boil off and the vapour therefore is uninhibited, the risk of polymerisation or formation of peroxides in the refrigeration system is present Cooling of Butadiene Normal Cooling Operation During normal cooling operation the flow of uninhibited liquid through the refrigeration system is constant and the risk of polymerisation or formation of peroxides is therefore minimal Compressor Discharge Temperature The Chemical reaction increases when Butadiene is heated and pressurised and it is therefore important that the compressor discharge temperature and the suction pressure not exceed the values prescribed by the manufacturer, i.e 600C and 2.0 Bar Gauge The Temperature Selector Switch shall be set accordingly before cooling of Butadiene or Crude C4 containing Butadiene is initiated Disconnection of the Refrigeration Plant If the refrigeration plant or a part thereof is taken out of operation and blanked off from the cargo system for a prolonged period, the system in question must be drained and cleaned in a systematic manner in order to positively remove all Butadiene Gas Freeing after Discharge After discharge of Butadiene or Crude C4 containing Butadiene all pipes, compressors, condensers, intermediate coolers, auxiliary manifolds and drain system used for loading and discharging must be drained and cleaned in a systematic manner in order to positively remove all Butadiene thus preventing the formation of peroxides 16.3 Anhydrous Ammonia /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R General Anhydrous (water free) Ammonia (NH)is a gas at ordinary temperatures and pressures It may be liquefied by reducing its temperature to minus 33 0C, or by moderately increasing the pressure above it Anhydrous Ammonia should not be confused with Aqueous Ammonia, which is a solution of Ammonia in water Often Anhydrous Ammonia is simply referred to as Ammonia Ammonia is a common feedstock in the fertiliser industry Properties of Ammonia All persons on board should be familiar with the properties of Ammonia At normal temperature and atmospheric pressure Ammonia is a pungent colourless vapour Under low temperature conditions it may appear as a dense white vapour Ammonia vapour serves as its own warning agent At concentrations of 10 ppm the odour will be detectable by most persons The TLV of Ammonia is 25 ppm Any uncontrolled leakage of Ammonia, especially of li4uid, will release large amounts of harmful vapour which may cause varying degrees of damage to the skin, eyes and respiratory tract Skin contact with liquid will cause skin bums Warm Ammonia vapour at ambient temperature is lighter than air and in the open will disperse by virtue, of its own buoyancy Vapour produced from cold liquid may mix with air however and produce heavier than air mixtures which will stay close to the ground dispersing only when it warms to ambient temperature A concentration of 2500 ppm is rapidly fatal to life The main physical constants of Ammonia are as follows: 1) Atmospheric boiling point -33.30C 2) Freezing point - 77.70C 3) Critical temperature 132.40C 4) Critical pressure 114.25 bar 5) Latent heat (1 atm, minus 330C) 1370.76 J/kg 6) Flammable limits(% by vol in air) 16 – 28 % 7) Auto ignition temperature 6510C At ordinary temperatures and atmospheric pressure Ammonia is a vapour, /~, but by reducing its temperature to its atmospheric boiling point of minus 33.3 50C, it may be stored as a refrigerated liquid /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R The vapours of Ammonia are flammable and bum with a yellow flame forming water vapour and Nitrogen, however, the vapour in air requires a high concentration (16 - 25%) to be flammable and has a high ignition energy requirement (600 times that for propane) and bums with a low combustion energy For these reasons the IMO codes (1994), while requiring full attention to the avoidance of ignition sources, not require flammable gas' detection in the hold or other spaces of ships carrying Ammonia However, Ammonia must be regarded as a flamn4able cargo All electrical equipment used in the cargo area must be electrically safe Health Hazards At low concentrations in air, Ammonia vapour irritates the eyes, nose and throat Inhalation of high concentrations produces a sensation of suffocation, quickly causes burning of respiratory tracts and may result in death Liquid Ammonia causes severe burns on contact with the skin, while its effect on being swallowed would be to cause severe corrosive action on the mouth, throat and stomach Severe eye damage can be caused by exposure to high gas concentrations or direct contact with liquid Advice on emergency medical treatment for Ammonia is also contained in the IMO Medical First Aid Guide (MFAG), Table 725 A copy of the guide must be available in the medical locker / dispensary Safety Equipment A set of respiratory and eye protection shall be provided for each person on board The number of sets on board must take into account any supernumeraries carried in addition to the articled crew The number of sets on board should not be less than the number of person who are likely to sail on the ship In addition to the foregoing, a further two sets must be located on the bridge for the use of pilots or other persons temporarily on board The respiratory protection must be of a self contained type and have a working duration of at least 15 minutes Filter type respiratory protection is not permitted Emergency escape respiratory protection will normally be stored in the same location as a person's lifejacket Emergency escape respiratory protection shall not be used for fire-fighting or cargo handling purposes Each piece of respiratory equipment shall be marked with this requirement A separate set of tight fitting goggles shall be provided with each emergency escape respiratory protection set unless the design of the 'respiratory equipment face mask also provides suitable eye protection All persons on deck or in the vicinity of the cargo area shall at all times wear, or have immediately available on their person a set of tight fitting eye goggles Goggles shall be worn over the eyes during all high risk operations such as sampling, disconnection of cargo hoses / arms or when there are any leaks or suspected leaks of cargo liquid or vapour At least two decontamination showers and an eye wash shall be maintained in an operational condition at all times Ammonia liquid or vapour are on board The showers and eyewash are to be /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R prominently marked such that there location can easily be identified from all areas on the cargo deck The showers and eyewash shall be constructed and maintained such that they can operated in all ambient temperatures Isolation valves in the showers or eyewash supply line shall be kept open at all times When due to maintenance or other requirements the water supply to the showers or eyewash must be isolated, alternative arrangements for the supply of water to temporary showers and eyewash must be made All persons on deck or in the vicinity of the cargo area shall wear suitable clothing, which will provide them with protection against the effects of a release of Ammonia All protective equipment required by the IMO Gas Code shall be maintained in good operating condition at all times The location of all equipment is to be clearly marked The equipment shall be located in areas where personnel can retrieve and don the equipment in the minimum of time Equipment should not be stored in the vicinity of areas which could be considered at high risk in the event of a leak or spill i.e the manifold area Toxic Gas and Moisture Detection Equipment All instrumentation for monitoring the level of Ammonia in spaces must be maintained in good condition and be operating at all times Ammonia liquid or vapours are on board It should also be possible to monitor the pressure in all hold spaces These items form part of the operational checks detailed in Section All detection equipment calibration shall be checked and all audible I visual alarms and any other systems shall be tested at least monthly A record of all calibration checks and system tests shall be maintained In the event of a toxic gas detection system deficiency, the Master shall be informed All equipment shall be maintained in accordance with the manufacturer's instructions A copy of the instructions shall be maintained on board At least two sets of portable detection equipment shall be maintained in good condition on board A sufficient supply of Ammonia detector tubes shall be available The tubes carried shall all be within their expiry date The portable detection equipment shall be fitted with sample lines of suitable length to enable sampling of remote spaces Solubility Ammonia vapour is extremely soluble in water and will be absorbed rapidly with heat liberated during the solution process, to produce a strong alkaline solution of Ammonium Hydroxide One volume of water may absorb 1000 volumes of Ammonia vapour The introduction of water into tanks containing high concentrations of Ammonia may immediately cause dangerous vacuum conditions unless unrestricted access of air is provided Similarly, the air within the hold spaces around cargo tanks should be maintained in a dry condition, so as to prevent a vacuum forming in the event of a leakage of Ammonia into the space Ammonia is alkaline and Ammonia vapour/air mixtures may cause stress corrosion cracking in any part of the cargo containment system made of Carbon-manganese steel or Nickel steel When any changes are made to any part of the cargo system on board, then any replacement or /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R additional parts must conform to the requirements of the applicable IMO codes and Flag or Class requirements Reactivity Ammonia is highly reactive with Copper Alloys, Aluminium Alloys, Galvanised surfaces, Phenolic Resins, Polyvinyl Chloride,~ Polyesters and Viton Rubbers These are unsuitable for any part of machinery or instrumentation which may be exposed to Ammonia liquid or vapour, even if due to accidental release It can form explosive compounds with Chlorine, Iodine, Bromine, Calcium, Silver Oxide and Silver Hypochlorite and Mercury It is for this reason that instruments containing mercury must not used if Ammonia can come into contact with the Mercury either by design or by accidental release Mild steel, stainless steel, neoprene rubber and polythene are generally suitable Preparing to Load Ammonia When preparing a tank in a gas free condition for the carriage of Ammonia, inert gas from a combustion type inert gas generator must never be used, due to the reaction of Ammonia vapour with the CO2 content of the inert gas The reaction will form carbamates which will cover tank walls and may block sensors and lines also seize pumps The formation of carbamates is to be avoided Inerting prior to the carriage of Ammonia is not required by international conventions, however many terminals may require tanks to be inert prior to loading Ammonia When inerting is required, Nitrogen must be used If loading into a gas free tank, liquid Ammonia should never be sprayed into the tank containing air as there is a risk of creating a static charge which could produce a source of ignition and also the conditions for stress corrosion cracking due to the presence of oxygen In order to minimise the risk of Ammonia stress corrosion cracking in tanks constructed of Garbo-manganese or Nickel steel it is advisable to keep the dissolved oxygen content below 2.5 ppm w/w This can best be achieved by reducing the average oxygen content in the tanks prior to the introduction of liquid Ammonia to less than the values given as a function of the carriage temperature in Table below Temperature -300C and below -200C - 100C 00C Oxygen (% vlv) 0.90 0.50 0.28 0.16 /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL +100C +200C +300C Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R 0.10 0.05 0.03 /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 10 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R vapour pressure is well above the pressure in the shore tanks, upon which cooling of tank is stopped and all condensate and vapour valves closed Vapour from tank I is returned to shore via the vapour return until the tank pressure is slightly above the pressure in shore tanks The above procedure is continued until the vapour in tank I is pure VCM, upon which cooling of tank is initiated simultaneously with the cooling of tank Topping Up As the cargo is cooled and the capacity thereby increased, the cargo tanks shall be topped up frequently until all tanks are loaded to capacity or until the shore installation stops the loading 16.5 Loading of Warm Propane in the Semi–Refrigerated Vessels Loading of "warm" propane, particularly with a high ethane concentration, is an operation which requires the full operational capacity of the ship's compressor units and aux motor or generators in order to ensure the shortest possible loading time In the semi-refrigerated gas carriers, the compressor units are designed for cooling of propane containing a maximum of 2.5% ethane in the liquid phase without any problems These gas carriers have been loading several cargoes of warm propane containing from to 8% ethane in the liquid phase Particularly during the initial loading stage such high ethane contents may create problems as ethane content of for example 6% in the liquid phase can produce an ethane contents of 25% in the vapour phase In order to obtain a satisfactory loading rate, the following general recommendations are given for the semi-ref vessels: Initially, the loading rate must be low, and the compressors shall be started up as quickly as possible The temperature in the tanks shall be lowered to below-i 00C and the loading rate adjusted so as to maintain the temperature at highest -100C The loading rate shall, while closely monitoring the tank pressure, be gradually increased in line with the increasing load on the compressors It is preferable to maintain a condenser pressure of 20 bar in order to obtain maximum cooling effect The condenser pressure can be adjusted by blowing off vapours containing ethane to the tanks through the lower spray lines in order to keep the ethane trapped in the liquid The loading rate can be adjusted to correspond to the compressors capacity by throttling the liquid line valve on the tank domes so as to maintain tank temperatures below -100C /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 15 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Note the fact that the heavy load on the compressors will generate intense heat in the electric-motor room Owners must be consulted if problems are encountered 16.6 Loading and sampling of Propylene Oxide Initially the shore line and the vessel's liquid line shall be filled with propylene oxide Valves on the dome/tank shall be kept closed until an analysis has been made of the propylene oxide contained in the lines If this analysis is not satisfactory the propylene oxide shall be returned to the shore installation by means of nitrogen pressure from shore If the analysis is satisfactory the loading is commenced and metre of propylene oxide is loaded into the tank(s) The cargo is circulated for hour after loading, after which, samples of the tank contents are taken If these samples are satisfactory loading continues until completed After completion of loading the cargo is again circulated for hour after which samples are taken again As the boiling point of propylene oxide is approximately 34 0C an overpressure has to be created in the tanks by means of nitrogen supplied from the shore installation The tanks are generally pressurised to about bar overpressure After departure from the loading port during the first few days the overpressure will decrease to approximately 0.5 bar as the nitrogen is absorbed into the liquid Some cargo receivers will only accept the ship arriving with a limited overpressure in the cargo tanks, normally about 0.1 bar The overpressure must therefore be reduced during the voyage While reducing the overpressure, it must be ensured that nitrogen is not added to the tanks from the ship's nitrogen battery through the reduction valve After the pressure has stabilised reduction of it can be started It is recommended to halve the overpressure and then close the tanks until next morning The overpressure will then have increased to almost the same level as before blowing off The overpressure is halved again This procedure is continued until the required overpressure has been reached The process of reducing the overpressure should be adjusted to terminate close to the end of the voyage Thus it is ensured that potential leaks from the cargo tanks not require the addition of nitrogen from the battery to maintain the tank overpressure See also IGC Code 17.20 /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 16 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL 16.7 Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Inhibitor Where a cargo, such as butadiene or VCM, is carried which requires the addition of an inhibitor it is essential that the ship is fully aware of the manner in which the inhibitor is added to the cargo and the amount added The inhibitor may be added either in the tanks ashore or it may be added at the ship's manifold during loading If the inhibitor is added at the ship's manifold care should be taken to ensure that during the process of adding inhibitor, cargo is only loaded into the tank for which the inhibitor amount is intended Before loading the master shall require that the shipper provides the ship with a certificate prior to departure containing the following information: Name and amount of inhibitor added Instead of amount the concentration in ppm can be stated Date inhibitor was added and the duration of its effectiveness Any temperature limitations affecting the duration of the inhibitor Any action to be taken should the length of the voyage exceed the effective lifetime of the inhibitor See: CS Tanker Safety Guide Liquefied Gas Appendix I A.I.6, Appendix A.1.7, Appendix 10 and Appendix 11 IMO Gas Carrier Codes A.328 (IX) § 17.10 and A.329 (IX) §17.8 and USCG 46 CFR § 164.1818 Above information nos to are to be included in departure telex to the owners 16.8 Nitrogen Displacement Discharge Preamble When discharging liquefied gases, a substantial amount of cargo will remain in the cargo tanks in the form of vapour and unpumpable liquid, which during subsequent tank cleaning will be vented off to the atmosphere and is time consuming /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 17 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Objective To optimise the discharged quantity and minimise air pollution and time consumption for subsequent tank cleaning by displacing the atmosphere in the cargo tanks with Nitrogen during discharge To stop the liquid from boiling and releasing vapour by introducing the nitrogen into the tanks with a relatively high pressure To enable continued cooling and maintain partly discharged cargo fully refrigerated, by using Nitrogen Displacement Discharge on cargo tanks to be completely discharged only Procedure: Before Arriving at Discharge Port The cargo to be discharged shall be fully refrigerated prior to arrival Nitrogen Displacement Discharge shall only be performed when the cargo is compatible with the nitrogen/inert gas produced by the vessel 1.1 Inert gas Plant The Inert gas Plant shall be tested in nitrogen mode if inhibited cargoes are to be discharged or in inert gas mode if regular lpg-cargoes are to be discharged, and the C02-strippers and dryer filters shall be regenerated and ready for use 1.2 Gas Detector The gas detector including the unit mounted for testing the inert gas line shall be tested according to the manufacturers manual 1.3 Non-return Valves All non-return valves on the inert gas line including valves at the crossover between cargo tank domes and inert gas lines shall be checked 1.4 Automatic Pressure Valve The automatic pressure valve on the inert gas plant shall be adjusted and tested to the required cargo tank pressure 1.5 Permission /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 18 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Before Nitrogen Displacement Discharge is commenced the Nautical Department shall be contacted in order to receive permission and instruction The Nautical Department will in co-operation with the gas tanker department investigate if the shippers and receivers will accept Nitrogen Displacement Discharge prior to the vessel's arrival to the discharge port 1.6 Swing Elbows The swing elbows connecting the inert gas line to the vapour system on the cargo tanks shall be inserted Discharging 2.1 Start Up of Inert gas Plant The inert gas plant is started before discharging is commenced The plant may be set to producing either inert gas or nitrogen depending on the cargo to be discharged When inhibited cargoes are to be discharged the inert gas plant shall always be in nitrogen mode, and the oxygen concentration shall be kept as low as possible, however, in order to keep the CO and C02 content within acceptable limits, the inert gas plant shall always be operated within the design capacity of the inert gas plant 2.2 Pressuring Cargo Tanks When the nitrogen plant is running and the requested quality has been reached, the valves to the cargo tanks are opened and the entire system is pressurised with nitrogen/inert gas If the cargo tank is already partly discharged, the nitrogen is introduced into the tank a few hours prior to arrival at the berth Initially the nitrogen shall be introduced into the tank at a low rate in order to maintain the stratification between the nitrogen and the cargo 2.3 Calculation of Cargo When the cargo tanks are pressurised prior to arrival, the vapour shall be calculated either as Nitrogen or by using the temperature on the liquid as reference temperature 2.4 Pressure throughout Discharge In order to keep the cargo from boiling and releasing vapour, the pressure in the cargo tanks shall be no less than I Bar above the vapour pressure of the cargo at the present cargo temperature throughout the discharging /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 19 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R If the capacity of the inert gas plant is insufficient to maintain above mentioned pressure, the discharge rate is decreased until the pressure can be maintained accordingly Stripping When the tank discharge is completed, the remaining liquid is either transferred to shore via the stripping line or transferred to another cargo tank 3.1 Stripping to Shore If the remaining liquid is to be transferred to shore, the cargo tank pressure shall be as high as possible when completing discharging This may require that the set point of the automatic pressure valve on the inert gas plant is increased to 0.5 Bar below the cargo tank safety relieve valves set point When discharging in the United States, the cargo tank safety relieve valves shall be fitted with the USCG approved set point 3.2 Escaping Nitrogen Care should be taken to avoid any unwanted nitrogen escaping to the shore during stripping, and in order to monitor the amount of nitrogen in the liquid, a sight glass should be mounted on the manifold 3.3 Stripping to another Cargo Tank If the remaining liquid is to be transferred to another tank, it shall be ensured that the pressure in the receiving tank is minimum 1.5 Bar less than the pressure in the tanks to be stripped If two tank sets are to be discharged in the same port, it may be required to discharge one tank set first and then transfer the remaining liquid to the second tank set before pressurising the second tank set N.B No cargo must be transferred from one tank to another without permission from the Operations Department Tank Cleaning 4.1 Venting off Unpumpable Liquid /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 20 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Should cargo tanks not have been properly stripped after completion of discharge, the tank pressure is maintained and the remaining liquid is pressed out of the cargo tanks and vented off through the vaporiser/cargo heater and vent stacks when the vessel is at sea 4.2 Methanol Wash If methanol washing is to be performed, the cargo tank pressure is maintained The cargo lines are vented through with pressure from the cargo tanks until no gas can be detected If any gas is detected in the cargo tanks, the cargo tanks are further inerted until no gas can be detected before the methanol wash is performed 16.9 Pumping Cargo Overboard During tank cleaning at sea, it is necessary to evacuate the remaining liquid heel, before inerting is initiated As is well known the procedure is to heat up the liquid heel thereby vaporising it in preparation to replace it with inert gas Another method has at times been employed Especially when dealing with large amounts of liquid, a hose can be connected on the manifold and the liquid heel can then be pumped directly overboard The time required for tank cleaning is then reduced considerably Nothing in National or International regulations prohibits this procedure However, certain limitations may be imposed on the amount that can be pumped overboard, and likewise restrictions for special products concerning the degree of dilution, least distance from shore, least water depth, and least speed are imposed during pumping overboard These restrictions can be found in the ships' Procedures and Arrangement Manuals Overboard discharge of a large amount of liquid at sea results the liquid naturally evaporated rapidly when leaving the pipe connected on the manifold and on this occasion resulted in the ship particularly the aft part containing fans for both accommodation and engine room - being engulfed in a cloud of gas It is very probable that this cloud was explosive The danger for the ship and crew during discharge overboard is obvious It is not possible to manoeuvre a ship without thrusters away from a cloud of gas by going astern For all cargoes except ammonia the gas cloud settles on the surface of the water and the ship can thus enter the gas cloud It has for the above reasons been decided that this procedure must not be applied in any of our gas carriers The procedure can and must necessarily be used when evacuating the tanks of products which cannot be vaporised, as for example propylene oxide, various acids, and LPG with boiling point above ambient When pumping out propylene oxide, acids, and other products having boiling point /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 21 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R well above ambient, naturally the risk of explosion or fire will not be present This danger is possible when pumping out LPG having boiling point above, but close to ambient Monitoring of the gas concentration at the aft part of the ship must therefore be performed in the latter case Pumping must be stopped immediately, should the gas concentration rise above Lower Explosion Limit (LEL) On the other hand, draining overboard of deck piping, including filters and collector tanks, is considered warrantable for all cargo grades Thus, draining the liquid left in the deck piping into the tanks, where it would have to be vaporised together with the unpumpable liquid heel can be avoided When draining pipelines etc., constant monitoring of the gas concentration must be performed at the aft part of the ship, and draining must be stopped immediately if the gas concentration rises above LEL Draining can be resumed when gas cannot be traced at the aft part of the ship The prohibition against pumping overboard will in certain cases result in considerable increases in time needed for tank cleaning It is, however, the Owners' opinion that this inconvenience must be accepted as being inevitable considering the risks involved Emergency Discharge of Cargo at Sea (Jettisoning) Emergency procedure for emergency discharge of cargo reference is made to the Tanker Safety Guide Liquefied Gas 16.10 LPG Freeze Valve An LPG freeze valve is used for tracing water in LPG cargoes The ships are equipped with a freeze valve made by Seiscor The freeze valve is used during loading if there is any suspicion that the cargo contains water Equipment A pipe bend has been supplied with the valve making it possible to mount it in a horizontal position as prescribed on the manifold drain cock's flange In addition to the freeze valve, a clean, dry cloth and a stop watch are required for taking measurements Protective measures Using this measuring equipment involves the emission of LPG into the air, therefore a protective mask should be worn For environmental and health reasons the freeze valve must not be used for testing on products with low Threshold Limit Value (TLV), e.g VCM and butadiene /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 22 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R Description The freeze valve is designed for measuring water content in propane and propane type products The working principle is freezing of the water contents by expansion causing a temperature drop Consequently, it is not suitable for measuring water content in products which contain anti-freeze additives, although it is possible to see an indication of water presence in such products Neither is it possible to measure the water content in products at temperatures below waters freezing point The freeze valve is equipped with a control cock at the exhaust opening This cock can be set to flush and to test position In the flush position, the entire valve is cleared of any remains by blowing through a sample of the product to be tested, thereby ensuring a representative sample When the outlet cock is switched to test position, the flowing liquid will expand through it and the thereby created temperature drop will make any water in the sample freeze to ice which will block the cock and stop the flow Measurable concentrations With this equipment tests have shown that it is possible to trace water in concentrations from approximately 14 ppm to about 93 ppm Generally, concentrations from 14 to 26 ppm will be indicated by the outlet cock freezing time exceeding minutes A water concentration of about 49 ppm will freeze up the cock in approximately 18 seconds, while a concentration of about 93 ppm will make the cock freeze up in approximately seconds An accurate determination of the water content is achieved by a number of consecutive measurements which should not deviate by more than plus or minus 10 percent from each other When freezing times are less than minute, an average from 7-8 measurements should be calculated, while at freezing times up to about minutes, measurements will suffice If freezing times exceed minutes it can be assumed that the water concentration is too low to be determined accurately using this equipment To reach a reliable result, it is important to open the outlet cock to flush position for about 15 seconds in order to ensure that all formations of ice are thawed Remaining ice will lead to shorter freezing times during the following tests, erroneously indicating higher water contents The liquid pressure at the freeze valve inlet must not exceed 6.9 bars above the liquid's present vapour pressure Guidance for use The freeze valve is mounted on the flange of the drain cock on the manifold to be used for loading, by means of the matching pipe bend, thus fixing it in a horizontal position The drain cock is opened and the outlet cock on the freeze valve is opened to flow position which is parallel to the main valve body /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 23 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R The freeze valve is flushed for 30-60 seconds The outlet cock on the freeze valve is set to test position (perpendicular to the main valve body) for 2-3 seconds Points and are repeated until the area around the outlet aperture has been covered with frost Turn the cock to test position and start the stop watch As this is the first measurement it is to be regarded as unreliable and not used for anything but comparison with the following measurements The moment the liquid ceases to flow, stop the watch Freezing is indicated by frost rolling over the lip of the testing orifice The orifice is wiped clean with a clean, dry cloth The cock is opened to flow position and is kept open for approximately 15 seconds, permitting all ice to thaw Points to are to be repeated while recording all freezing times until consecutive measurements not deviate more than plus or minus 10 percent Freezing times of less than minute require 7-8 measurements within the same interval to achieve a reliable result Reporting The Gas tanker Department must be notified if measurements indicate freezing times at or below 18 seconds corresponding to 49 ppm of water in the cargo Under certain conditions special instructions will be given quoting other limits for when reports have to be submitted 16.11 Stripping of Cargo Tanks in the Fully Refrigerated Vessels The tanks are prismatic and the tank bottom constructed parallel to the ship's bottom Aft of the suction well it is, however, slightly sloped The ship will therefore have to be trimmed astern and be given a heel to enable better liquid flow to the pump sump The trim should be 1.5-2.0 metres astern This is supported by the trim correction in the sounding tables for the cargo tanks, which for tanks 1, 3, and is largest at a trim of metres, while for tank it is largest at 1.5 metres At these trims the best flow to the pump sump is achieved, considering that no liquid should be trapped aft of the sump As the sump is situated at the centre bulkhead, the heel is not critical Taking care to avoid damage to the shell plating, by the bilge keel touching the dock, heels of approximately degrees can be regarded as recommended In order to avoid accumulation of large amounts of liquid in the thwartship manifold line, stripping of starboard and port tank halves must be planned, so stripping is finished in the seaward tank half As the cargo is carried fully refrigerated, the tank pressure will be bar absolute on the surface of /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 24 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R the liquid When the liquid level reaches the pump during discharge, the dynamic properties of the liquid flow will accelerate the boiling, which will make the pump cavitate as the liquid thus mixes with vapour This process can be delayed by gradually closing the discharge valve to maintain a stable discharge pressure, as is usual practice The discharge pressure is maintained until the automatic low current relay on the electric motor for the pump is activated It has been established by tests with fresh water that a discharge pressure of 16.2 bars is necessary to avoid cavitation of the pump This is the discharge pressure when handling water with a density of 1.000 Discharging gas cargoes at lower densities, the discharge pressure must be calculated to match the actual cargo density To avoid the pump cavitating, adjusting the discharge valve should begin at a sounding of approximately 250 mm By maintaining the back pressure accurately it can then be ensured that the pump continues discharging, until the level reaches the pump suction At a sounding of 100 mm (or when the float touches bottom), discharging is switched to go through the 1" bypass line The discharge valve is closed at this time The pump manufacturer Svaneh0j prescribes a positioning of the pump 50 mm -0/+10 mm above the bottom of the pump sump It has been observed that the deepwell pumps are mounted 120 - 150 mm over the bottom of the pump sumps This makes it necessary to begin the stripping earlier in this ship The rather high positioning of the pump will naturally contribute to a comparatively larger amount of liquid left in the tanks after stripping With a back pressure as mentioned above, the discharge rate will be considerably reduced It is, however, necessary to maintain this back pressure in order to avoid cavitation, as discharging during this phase is often impossible to restart, should the pump stop due to loss of suction The liquid level, at which the boil off starts, can be reduced further by increasing the tank pressure, as a higher pressure requires a temperature above that of the liquids actual temperature before the boiling begins The result will be a more effective stripping of the cargo tanks while the amount of vapour is increased some As the safety valves will open at an overpressure of 0.28 bars an overpressure of about 0.1 bar is recommended This is achieved by directing some of the cargo to the vaporiser and via the vapour lines return the vaporised liquid to the tanks During discharge against a low pressure the tank pressure must be maintained throughout the entire discharge as the vaporising is relatively slow when the vaporiser is supplied with liquid at a low pressure It will not be possible to determine the liquid level by using the level indicators after the stripping has finished It is, however, possible to determine if any liquid is present in the tanks by opening the cock to the lower test pipe: if any gas streams out it means that liquid is not covering the pipe's bottom opening Usually liquid is generally only present in the pump sump, if the stripping has been performed with the above mentioned trim and heel Although stripping with an overpressure and back pressure as described above is relatively slow, the /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 25 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R following heating and vaporising of remaining liquid will be much faster and the loss of cargo will be minimised 16.12Number of Cooled Cargoes Allowed to be Carried in the Semi Refrigerated Vessels The semi-refrigerated vessels are equipped with a total of cargo cooling units enabling them to carry up to two cooled cargoes simultaneously Reference is made to International Gas Carrier Code (IGC code) rule 7.2.2.1 , excerpt of which is: Quote "Where two or more refrigerated cargoes which may react chemically in a dangerous manner are carried simultaneously special consideration should be given to the refrigeration systems to avoid the possibility of mixing cargoes For the carnage of such cargoes, separate refrigeration systems, each complete with a stand-by unit as specified in 7.2.1, should be provided for each cargo." Unquote The relevant excerpts of 7.2.1 are: Quote "A stand-by unit should consist of a compressor with its driving motor control system and any necessary fittings to permit operation independently of the normal service units." and "Separate piping systems are not required." Unquote Consequently, it is permissible to load and carry not more than two cooled cargoes, which for safety reasons are not allowed to be mixed, simultaneously The vessels may, however, carry more than two cooled cargoes simultaneously providing some of the cargoes may be mixed without jeopardising safety, e.g loading BTD in tank and CC4 in tank which could be cooled by the same compressors, although not at the same time Mixing BTD and CC4 will not impair safety but will of course mean that some of the contents of one commodity enters the other This, however, is purely a commercial problem, as total segregation cannot be expected NB: Connecting the standby cooling unit to a tank or pair of tanks by means of hoses is a violation of the rules 16.13 Heating Times, Cargo tanks /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 26 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R The gas carriers may receive load orders for LPG to be loaded into tanks already containing LPG, e g butane into propane heel Such orders can be given in order to avoid losses, typically in the range of 45 tons, when the cargoes are compatible and ROB does not degrade cargo to be loaded, which seldom will be the case with pure hydrocarbons Expenses and time used in connection with tank cleaning is naturally also considerably reduced In these cases, requirements for conditioning will often be liquid free and under a certain overpressure, for example 0.25 bars making it possible to draw vapour-samples before loading the next cargo Previously, limitations were imposed on the rate at which the tanks' temperatures were allowed to change Later investigations have revealed that these limitations were not correct In reality, no limitations expressed in degrees C per hour exist, but the tanks' temperatures should as far as possible be evenly distributed throughout the tank in order to avoid too high stresses in the tank steel Procedure To minimise time consumption for heating and vaporising of liquid heel the following procedure is applied: Semi-ref vessels If on the semi-ref vessels, butane is to be loaded at 00C into propane vapour, the cargo tanks after vaporising of liquid heel shall be heated to approximately -200C by routing warm vapour from compressors into the tanks through all spray-lines An even distribution of heat in the tanks is ensured using this method The ships' compressors and associated piping to the tanks are constructed so that changes in temperature will occur at a moderate pace It is therefore possible to concentrate on vaporising liquid heel and thence heat up the cargo tanks to a minimum temperature suitable for the next cargo The reason for heating up to 200C below loading temperature is that loading is commenced on the cooling down-line and immediately after on the upper and lower spray-lines Loading through spray-lines will cool the cargo, typically around 100C Part of the loaded quantity will after passage through spray-lines and vaporisation recondense and collect in the bottom of the tank Most often, a rapid lowering of temperature in the pumpsump can be observed This must not be taken as an indication that loading through the liquid filling-line can commence, as the tank bottom would then be filled rapidly over the length of the tank with liquid too cold compared with the tank steel thereby risking too high stresses on account of temperature difference Tank steel not covered by liquid will be considerably warmer as cooling of tank steel above the sump will only take place by exchanging heat between vapour and steel As vapour owing to the /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 27 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R limited mass in comparison to the liquid in the sump will only be able to draw scanty amounts of heat from the steel, this will naturally cool down at a slower rate than steel in the sump As more liquid is formed the temperature will stabilise and attain loading temperature and loading through the liquid-line can be started slowly and increased to full rate in relatively short time Loading in the fully ref vessels can therefore be commenced on the liquid filling-line directly Loading is commenced slowly, govemed by the degree of opening of the valve which is increased slowly When the temperature is stabilised close to the cargo temperature, the valve can be fully opened General When the temperature in the pumpsump has been stabilised near the loading temperature (possibly by slowly introducing liquid through the liquid filling line after the pumpsump has been filled with recondensed cargo) loading of liquid is commenced and by gradually opening the valve on the liquid line, full loading rate can soon be achieved It is a rule never to be departed from that during the initial loading to monitor the temperatures closely in order to as far as possible distribute the temperature changes evenly over the tank steel Note that it will not be possible to avoid a rapid lowering of temperature at the pumpsump unless the cargo in the beginning is introduced at an unrealistically low rate The rapid lowering of temperature can, however, be limited to the area around the pumpsump The comparatively little amount of liquid settling in and around the sump will therefore only cause a rapid temperature change over this limited area 16.13Loading at Moerdijk For loading of Butadiene or Propylene at Moerdijk you will be requested to extend the liquid and vapour manifolds down to main deck level This is due to the fact that the shore chicksan can not reach our manifold on the top of deck house For this operation we have one 8" s-bend with 10" 300 ASA flange and 8”-10" reducer stored at the Shell terminal at Moerdijk The connection point ( s-bend to chicksan ) will be some 50 cm above the main deck We have fabricated an expansion screw rod ( turnbuckle principle ) with platform down and cradle up ( this same as threaded support bar / rod used in chicksan supports) and landed and stored in Moerdijk for all Zodiac LPG vessels /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 28 of 29 ZODIAC MARITIME AGENCIES LTD GAS OPERATIONS MANUAL Form Issue Date Approved : : : : GOM 002 05-05-02 M.J.R For loading at Moersijk a vapour recovery line will be required as well We have supplied the terminal with m cryogenic flexible hose to connect shore vapour chicksan with the ship's vapour manifold on the main deck level To extend the vapour manifold down our ships are equipped with 8" and 10" s-bends stored on the top of deck house After loading the s bend has to be cleared of cargo - nitrogen blown to the vessel We must be sure that the S- bend is clear of cargo before disconnection Closed sampling must always be used at this terminal - the vessel is fitted with quick couplings for this purpose The arrangements must be totally secure and safe before cargo operations begin and cargo must be immediately stopped in the event of chicksan movement /storage1/vhost/convert.123doc.vn/data_temp/document/sgs1554800585-1959494-15548005857450/sgs1554800585.doc Page 29 of 29 ... ensure that the cargo intake at Rafnes is optimised by initiating cooling of the cargo as soon as possible Inerting with Nitrogen Prior to commencing loading in a cargo tank, the cargo tank shall... order to keep the cargo from boiling and releasing vapour, the pressure in the cargo tanks shall be no less than I Bar above the vapour pressure of the cargo at the present cargo temperature... water is colder than the product in the shore tanks, loading via the cargo heater should be used in order to cool the cargo The cargo heater must be pressure tested well in advance of arrival by