Maersk cargo handling

     Chapter and Title A B C D E F Preparation, Inerting, Purging Loading - Various Procedures Transportation, Tank Atmosphere, Inhibitor Discharging, Stripping Tank Cleaning, Heating, Gasfreeing Measuring Instruments A-1 Introduction These guidelines which is the second edition (first edition SEP 1993) are part of the Safety Management System and are the property of: A P Møller Technical Organisation Copenhagen Denmark Copies of this manual or part thereof shall not be made for use outside the vessel without written consent being obtained from the Nautical Department in the Technical Organisation, Copenhagen This manual shall not effect the legal relationship or liability of A.P Møller with or to any third party and neither shall such third party be entitled to rely upon it A.P Møller shall have no liability for technical or editorial errors or omissions in this manual nor for any damage, including but not limited to direct, punitive, incidental or consequential damages resulting from or arising out of its use by A.P Møller’s directors, officers, representatives, owners or others 1.1.Objective employees, agents, The objective of these guidelines is to provide the officers on board with a guide to conduct cargo -handling safely and efficiently The objective is also to give advice and information to recently promoted officers on procedures proven to be safe and efficient by experienced senior officers and to avoid using procedures already proven unsafe and inefficient 1.2.Foreword These guidelines prescribe how the Owners expect officers involved in cargo handling - through organisation and established procedures - to utilise all available information and guidelines as comprehensively as possible, so that the cargo operation is conducted safely and efficiently It is essential that these guidelines are read in conjunction with the manufacturer's instructions and recommendations for the handling of equipment involved, and guidelines or recommendations issued by authorities, I.M.O., National Authorities and Classification Societies 1.3.Document Control and Update "Guidelines for Cargo handling in Maersk Gas Carriers" is a con-trolled document, and any changes in the contents of this manual shall be logged in RECORD OF CHANGES The Master and the Chief Engineer shall have a copy of "GUIDELINES FOR CARGO HANDLING IN MAERSK GAS CARRIERS" available as a personal copy, while the 3rd copy shall be located at the Master’s discretion 1.4.Familiarisation The Master shall ensure that both he and his officers are familiar with "Guidelines for Cargo handling in Maersk Gas Carriers" Before any officer is involved with and responsible for any cargo operation, these guidelines shall be read by that officer 1.5.Updating The guidelines are based on experience collected from all our gas carriers and other sources They are not to be considered complete, as from time to time new products are being introduced in our ships Additionally procedures may change in order to save time or to make cargo operations more safe and efficient This manual is kept updated with ships assistance by reporting to Nautical Department about new procedures with as many details as possible; thus, new sections can be added to the manual when the need arises 1.6 Reporting Prior to any tank cleaning or any special cargo operation the Master shall hold a meeting with the officers involved in the tank cleaning or cargo operation, after which the agreed plan containing all details of the procedure and estimated time required is telexed to Nautical Department Before the operation is initiated the Nautical Department shall be informed of the plan thus making it possible to suggest an alternative procedure if necessary If instructions to perform tank cleaning or other special cargo operation are received after office hours, communication with the Nautical Department shall be by telephone Telephone communication shall be confirmed by telexed from the Nautical Department at earliest opportunity During tank cleaning or other special cargo operations, daily situation reports shall be telexed to the Nautical Department All correspondence concerning cargohandling shall be forwarded with a copy to Gas Tanker Department A-2 Inerting On gas carriers certain requirements to the atmosphere in the cargo tanks have to be met The requirements may refer to the oxygen content, dew point, traces from previous cargo, carbon dioxide, carbon monoxide, sulphur, etc In order to meet some of the requirements, the cargo tanks may be inerted using the vessel's inert gas plant The inert gas on board is produced by burning off Diesel or Gas oil in the Inert gas Generator and thereby reducing the Oxygen content The produced inert gas is subsequently washed, cooled and dried, further on vessels able to produce Nitrogen, the CO2 and the CO produced during the incineration is removed by filtering With inert gas it is possible to reduce the oxygen content and the dew point in the cargo tanks On vessels equipped with CO2-strippers, it is also possible to avoid excessive amounts of carbon dioxide and carbon monoxide, which is normally present in the inert gas produced It may however be necessary to continue the inerting with nitrogen supplied by the shore installation, if the inert gas plant is unable to produce sufficiently clean inert gas or nitrogen Regular measurements shall be taken during the inerting, using Servomex and Teledyne oxygen analysers From these measurements, graphs shall be drawn The graphs will clearly indicate the progress of the inerting, thereby enabling early intervention, should the inerting not proceed as planned Furthermore, these graphs will indicate, the time at which the inerting can expect to be completed In order to maintain the best possible stratification the cargo tank pressure shall be kept to a minimum and all tanks shall be inerted in parallel Procedure Before Loading 1.1 Inert gas The inert gas is introduced into the cargo tanks via the loading line (in H- and J- class) and the lower spray line (in the Sclass) The air is vented off through the vapour line, which shall be connected to the vent -stacks 1.2 Nitrogen If the inert gas plant is producing nitrogen, the nitrogen is introduced into the cargo tanks via the vapour and upper spray lines The nitrogen shall be heated in the nitrogen heater before being introduced into the cargo tanks 1.3 Preheating Pipes In order to maintain the stratification as long as possible tanks are opened (not possible on the J-class) The compressors may be inerted during the heating of the pipes 1.4 Inerting Cargo Tanks in Series Inerting cargo tanks in series has proved unsuccessful and should therefore not be used unless under special circumstances, in which case, the Gas Tanker Department will instruct the vessel 1.5 Disconnecting Inert gas Pipeline After inerting is completed, the inert gas deck pipeline shall be disconnected from the supply line from the engine room, as this connection must only be established, when the plant is in operation and inert gas is supplied to deck The times for connecting and for disconnecting shall be entered in the deck log book After Discharging 2.1 Inertgas After the cargo tanks have been heated to the required temperature, inerting is commenced As the vapour from most cargoes is heavier than inert gas, the inert gas is introduced into the top of the cargo tanks through the vapour line and the upper spray line The gas is vented off through the liquid line, which shall be connected to the vent stacks 2.2 Ethylene If inerting after ethylene, the inert gas shall be introduced into the bottom of the tanks though the loading line 2.3 Nitrogen Displacement Discharge If cargo tanks are to be further inerted after Nitrogen Displacement Discharge the inerting shall be performed according to Section E 13 in these Guidelines Inerting with Nitrogen from Shore 3.1 Before Loading The nitrogen shall always be introduced into the cargo tanks via the vapour and upper spray lines In order to ensure the stratification in the cargo tanks the nitrogen shall be heated to approximately 80°C at the manifold, either by using shore heater or vessel's nitrogen heater Nitrogen at higher temperatures may damage the insulating material on the pipelines Unheated nitrogen which may be colder than the atmosphere in the cargo tanks shall also be introduced into the cargo tanks via the vapour and upper spray lines 3.2 Preheating Pipes In order to maintain the stratification for as long as possible, the pipes shall be preheated with heated nitrogen before the valves to the cargo tanks are opened (not possible on the Jclass) The compressors may be inerted during the heating of the pipes 3.3 Rate To ensure stratification, the initial rate shall be approximately 7% of the total volume to be inerted When the oxygen content in the top of the cargo tank is less than 1% the rate is gradually increased to approximately 20-25% of the total volume to be inerted If the supplied quantity is insufficient to maintain a rate of 2025% of the volume to be inerted, the volume shall be reduced accordingly by purging a smaller number of cargo tanks at a time This rate is maintained until maximum 1% oxygen is measured in the bottom of the tanks As the cargo tanks at this stage contain mainly pure nitrogen, no stratification can be expected and the rate is now increased to approximately 50% In order to control the flow into each cargo tank, the cargo tanks may be divided into two systems The nitrogen used to inert first tank(s) shall not be reused to inert the next tank(s) When the cargo tanks are divided into two systems, the pipes shall be heated prior to changing the inerting to the second system 3.4 Stratification If the stratification is disrupted e.g by too high a rate or by changing temperatures, it can often be re-established by stopping the inerting completely for an hour or two Inerting is then resumed at low rate and high temperature The sooner turbulence is detected, the easier stratification may be reestablished 3.5 Compressors and Piping If inerting of compressors and piping has not been completed during heating of pipes, the compressors and piping should be inerted simultaneously with the inerting of the cargo tanks When inerting the compressors, it is important to turn these frequently as otherwise the associated piping will not be inerted 3.6 Change of Compressor Oil If unable to reduce the content of previous cargo in the compressors after ventilating the oil sump, the oil should be changed The oil should not be changed on request from shippers or receivers unless so specified by the Gas Tanker Department A-4 Purging and cooldown – Gas Carriers with Deck Tanks Preamble Before loading it is necessary to replace the Inert Gas atmosphere with product gas to enable cooling of the cargo and cargo tanks At some installations replacement (Purging) of the atmosphere is performed during loading by use of the vapour return line Purging during loading shall only be performed if the temperature difference between the cargo and the cargo tanks is within the maximum allowed temperature difference (6°C on fully ref gas carriers 15°C on semi-ref gas carriers) otherwise the steel may be stressed beyond design limits Where installations are not equipped with vapour return or not able to deliver vapour to the vessel, it is necessary to load a purge parcel and purge the cargo tanks at sea In order to avoid calling at an additional port for loading a purge parcel, the fully ref gas carriers are equipped with deck tanks for loading and/or storing of purge parcels The larger deck tank of 210 m3 is normally used for storing LPG The smaller deck tank of 60 m3 is normally used for storing ammonia, however, if vessel is not likely to be in the ammonia trade, the tank may be used for storing additional LPG for cooling purposes The semi-ref gas carriers are equipped with a deck tank of 210 m3 only Before purging is commenced a number of conditions have to be taken into consideration, such as: - Number of tanks to be loaded with the product in question - Estimated product loss - Do the deck tanks contain sufficient product to accomplish requirements Purging with LPG and Chemical Gases 1.1 Purge Parcel In order that there is sufficient product to perform a full conditioning of the cargo tanks, as much cargo as possible should be transferred to the deck tank(s) during normal operation in the LPG trade (when changing grades etc.) If possible the large deck tank should always contain Propane 1.1.1 Loading Purge Parcel If the deck tank(s) does not contain sufficient product to perform a full purging of the cargo tanks, additional product shall be loaded either in the deck tank(s) or in a cargo tank if already conditioned 1.2 Purging 1.2.1 Transferring Liquid to the Vaporiser Deck tank pump should be used to transfer the liquid if the deck tank pressure is below bar 1.2.2 Vaporiser Starting procedure for the vaporiser is described in the LPG operation manual 1.2.2.1 Steam Supply During automatic operation the steam supply should be constant This is to prevent any loss of stem pressure which will result in liquid filling the vaporizer and adjacent piping, and in the worst case, rupturing the vaporizer 1.2.3 Flow Direction of Vapour The cargo tanks shall be purged in parallel as this will minimise the flow through each cargo tank and thus increase the stability of the stratification The additional product used for purging in parallel compared to purging in series is marginal Vapour is directed from the vaporiser to the cargo tanks through the liquid filling line Nitrogen or inert gas is removed from the cargo tanks through the vapour lines which shall be connected to the vent stacks with elbows 1.2.4 Pressure In order to maintain the best possible stratification the cargo tank pressure shall be kept to a minimum 1.2.5 Monitoring and Recording It is essential to monitor the progress closely during the entire purging operation with regular measurements taken to ensure uniform distribution of vapour in all tanks From these measurements, graphs shall be drawn The graphs will clearly indicate the progress of the purging, thereby enabling early intervention, should the purging not proceed as planned Furthermore, these graphs will indicate, at which time the purging can expect to be completed When purging with VCM, the Gascope must not be used as the measuring filament of the instrument will be destroyed by VCM vapours 1.2.6 Starting Compressors Before starting the compressors, it is good practice to continue the purging for 15 minutes after 100 % reading is reached 1.2.6.1 Blow off Should the atmosphere in the cargo tanks not be 100 % pure gas, the inert gas/nitrogen may be vented off via the condensers until the top of the cargo tank is 100 % gas 1.3 Cooling On completion of purging, the liquid remaining should be transferred to the liquid line It is then used to cool the cargo tanks via the upper spray line 1.3.1 Pressure If the tank pressure falls too quickly during cooling there may be insufficient pressure to complete the operation Provided there is sufficient liquid in the cargo tanks and the pressure is not above 0.25 bar, the cargo pumps should then be started and liquid circulated through the upper spray line 1.3.2 Temperature 10 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 Nautical Department Tank Cleaning 4.1 Venting off Unpumpable Liquid 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 as described in Guidelines For Cargo Handling In Maersk Gas Carriers, Section E, part E11, 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 4.3 Inerting without Methanol Wash If no methanol wash is to be performed, the cargo tank pressure is released, initially through all liquid lines used throughout the discharging in order to ensure these are free of liquid If the gas concentration in the cargo tanks is above the lower explosion limit, the cargo tanks are further inerted until the concentration is well below the lower explosion limit, after 85 which the cargo tanks, lines and compressors are vented with air 4.4 Heating of Cargo Tanks If any additional heating of cargo tanks is necessary, this is either done by using the nitrogen heater or by using the cargo compressors If the cargo compressors are used, it is important that the manufacturer's instructions are followed, i.e if the last cargo was butadiene, VCM or ammonia the temperature set point on the compressors shall be adjusted to the correct set point for these cargoes 4.5 Visual Inspection If no visual inspection of cargo tanks is required prior to loading the next cargo, special instructions shall be obtained from Gas Tanker Department 86 F – MEASURING INSTRUMENTS F1 – Standard stock of measuring instruments As of now the gas ships will be supplied with measuring instruments for use during cargo handling according to list below: For measuring: Number Make and Type oxygen Oxopac I oxygen Servomex model 262 A oxygen in low concentration Teledyne model 311 (semi.ref vessels only) gas concentration (ppm) Dräger Multi Gas Detector gas concentration (LEL - %) MSA Combustible Gas Indicator model LV gas concentration (%) Riken interferometer HC17 explosive limits (LEL) Explosiometer model 2E Description of instruments This stock of instruments differs somewhat from what has previously been delivered to the ships There are a number of reasons for this: Dräger Oxopac is an instrument which has proven very reliable and easy to operate in addition to requiring almost no maintenance This instrument should be on board as units with integrated sensor in addition to unit with sensor on a 10 metre long cable Inclusion of Oxopac (and Teledyne) into the standard stock makes it possible to reduce the number of Servomex instruments to one The Servomex oxygen analyser is primarily used when good accuracy is required This instrument is advantageous to use when measuring oxygen concentration in void spaces during transport of e g propylene oxide, and during nitrogen purging cargo tanks before reaching the lowest concentration of typically 0.1% oxygen at which point the accuracy of the instrument is not good enough Additionally, Servomex can be used as a replacement for Teledyne, should that instrument be inoperative The Teledyne which can only be used for measurements of concentrations up to 1% oxygen has been specially purchased 87 for use when conditioning cargo tanks before gas-up This instrument is very accurate and with high sensitivity, thus also making it vulnerable It should in particular be remembered that the cell sensor is destroyed by oxygen making it necessary to purge with pure nitrogen after use The Dräger Multi Gas Detector is mainly used during tank cleaning to check tank atmosphere before opening the tanks to ensure that the threshold limit value is not exceeded while working in the tanks Standard stocks of test tubes differ from one ship class to the other which can be seen from the list found in section F2 Combustible Gas Indicator model LV can be used for measurements of explosive gases in the range up to LEL and measurements of concentrations by volume up to 100% The instrument is delivered calibrated for propane When measuring other gases, the proper response curves must be used to convert value read off from the display to the correct value Purchase of this instrument has made it possible to reduce the number of explosiometers to one Riken Interferometer has for a number of years been absent from the gas carriers but has again been implemented There are a number of advantages to using this instrument as it is easy and quick to operate, requires very little maintenance, and is the only one which is not actually damaged when used for measuring VCM vapours The supplied version can measure in two ranges, 0-6% and 0-30% by volume It is not possible to purchase an interferometer with a range up to 100% by volume for gases other than methane Explosiometer is generally used for checking the atmosphere in enclosed spaces and tanks before entering them for carrying out repairs or cleaning Changes in the standard stock Most of the ships will have for a period of time a stock which differs from the above standard Instruments in the standard stock not presently on board should be ordered It is, however, not the intention that surplus instruments are sent home as they of course can still be used on board 88 Units above standard stock will in connection with returning faulty instruments for servicing be deleted from the ship's stock, and instead be entered into central stock to be used for supplementing other ships' stock as required Instruments returned must be accompanied by Advice Note specifying whether the equipment should be returned to the ship or entered into central stock Cell sensors Oxygen meters by Dräger and Teledyne use special cell sensors but this is not the case with Servomex which employs another measuring principle These cell sensors deteriorate gradually, mainly when used but also when stored Consequently, it will not serve any purpose to carry any spares in stock on board Instead, new sensors for replacing worn out ones should be ordered as late as possible but naturally early enough to ensure that the instruments are not rendered unusable As delivery times can often be difficult to predict there will possibly be instances when sensors are received before those in instruments have to be replaced, but only applying this procedure prevents the purchase of sensors which by reason of obsolescence are never going to be used Dräger test tubes Test tubes which are used with the Dräger Multi Gas Detector also have a limited lifetime It has, however, been established that these tubes generally function flawlessly after their lifetime has expired, especially if they have been stored in a refrigerator Consequently, it is not necessary to discard tubes past their expiry date; they can be used during the initial inerting and gas freeing, preserving the new tubes for the final measurements Service and maintenance Previously, the standard procedure was to send explosiometers and gas scopes home for servicing annually This procedure was abolished in June 1991 because of frequent unsatisfactory outcome Instead, it was made the ship management's responsibility to check the instruments by means of the MSA Test kit 89 These instruments must therefore be maintained on board and only returned for repair if required Records of calibration, test and servicing of all instruments shall be maintained on board 90 F2 – Standard stock of Draeger test tubes Preamble Before cargo tanks are entered after tank cleaning it is necessary to ensure that the atmosphere in the cargo tanks is safe for entering Further some shippers require that the remaining con-tent of the previous cargo loaded is known prior to loading the next cargo Objective To ensure that the gas tankers have sufficient stock of Dräger test tubes on board to measure the atmosphere after tank cleaning when carrying the most common cargoes Procedure Ordering The standard stock should as far as possible be maintained and supplements should be ordered in as good time as possible in order to avoid expensive air-freight Lifetime of Test Tubes The manufacturer normally guarantees a tube lifetime of years The tubes may however be used beyond their guaranteed lifetime, provided they are stored in a refrigerator Tubes beyond their expiry date may be used for initial measurements while tubes inside valid lifetime shall be used for final and conclusive measurements Test Tubes outside Standard Stock After tank cleaning of certain cargoes the need for tubes not included in the standard stock may arise These tubes which are not part of the standard stock should be ordered as soon as the need is known in a quantity deemed necessary Standard Stock semi-ref Class: Packages Description Order no/Standard Tubes/pkg Ammonia 2/a 2-30 ppm n=5 67 33231302515 10 Ammonia 5/a 1-14 ppm n=50, 5-70 ppm n=10, 50-700 ppm n=1 CH 20501302519 10 Butadiene 10/a-D1,3-40 ppm Diffusion 1-8 hours 81 01161302529 10 91 Carbon Dioxide 0.01%/a 100-3000 ppm n=10 (vessels with N2system only) CH 30801315662 10 Carbon Dioxide 0.1%/a0.1-1.2 vol% n=5, 0.5-6.0 vol% n=1 CH 23501302521 10 H-type1 S-type Carbon Monoxide 2/a 2-60 ppm n=10,10-300 ppm n=2 67 33051315663 10 Chloroprene 5/aIsoprene 10-30 ppm n=3 67 18901302498 10 Ethylene Oxide 1/a (Propylene Oxide) 4-60 ppm n=20 (Double tube) 67 28961302514 2x5 Hydrocarbons 0.1%/bn-Butane 1000-8000 ppm n=3 to 5Propane 0.5-1.3 vol% n=7 to 15 CH 26101302523 10 H-type4 S-type Alcohol 25/a (Methanol)25-5000 ppm n=10 81 01631315664 10 Olefine 0.05%/aButadiene 0.04-1.3 vol% n=1 to 201-Butene 0.04-1.3 vol% n=1 to 20 CH 31201302527 10 Vinyl Chloride 0.5/b0.5-5 ppm n=5, 5-30 ppm n=1 81 01721 10 Vinyl Chloride 100/a100-3000 ppm n=1 to 18 CH 19601302503 10 Standard Stock Fully Ref.-class: Packages Description Order no/Standard Tubes/pkg Ammonia 2/a 2-30 ppm n=5 67 33231302515 10 Ammonia 5/a 1-14 ppm n=50, 5-70 ppm n=10, 50-700 ppm n=1 CH 20501302519 10 Carbon Dioxide 0.1%/a0.1-1.2 vol% n=5, 0.5-6.0 vol% n=1 CH 23501302521 10 Carbon Monoxide 2/a 2-60 ppm n=10,10-300 ppm n=2 67 33051315663 10 Hydrocarbons 0.1%/bn-Butane 1000-8000 ppm n=3 to 5Propane 0.5-1.3 vol% n=7 to 15 CH 26101302523 10 Standard Stock VLGC: Packages Description Order no/Standard Tubes/pkg Carbon Dioxide 0.1%/a0.1-1.2 vol% n=5, 0.5-6.0 vol% n=1 CH 23501302521 10 Carbon Monoxide 2/a 2-60 ppm n=10,10-300 ppm n=2 67 33051315663 10 92 Hydrocarbons 0.1%/bn-Butane 1000-8000 ppm n=3 to 5Propane 0.5-1.3 vol% n=7 to 15 CH 26101302523 10 93 F3 – 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 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 water's 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 94 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 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 95 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 96 F4 – Combustible gas indicator This instrument is designed for measuring concentrations of flammable gases The model currently in use having a digital display is reliable and readout of the measured concentration is less ambiguous than was often the case using the previous model with analogue display Concentration read off from the display is only valid for the gas for which the instrument has been calibrated, normally propane It is possible to calibrate the instrument to other gases but the procedure is not suitable for performing on board Instead, response curves for measuring volume-percent for other gases have been issued; concentration read off is referenced to the vertical axis and the concentration in volume-percent appropriate for the measured gas is read off from the horizontal axis Attached are response curves to be used when measuring the following gases: Ammonia Butadiene Butane But-1-ene Ethylene Hydrogen Methane Propane Propylene Note: that even though the instrument is calibrated for propane a response curve must still be used as at concentrations above about 60% it will gradually show less than the actual concentration VCM It is not possible to use this instrument for measuring VCM as it does not react to VCM vapours Additionally, the measuring filament will be destroyed by VCM Enclosure: graph sheets and cover page Records of testing, calibration and servicing of the instrument shall be maintained on board 97 F5 – Explosimeter All gas carriers have been equipped with MSA explosimeter model 2E in order to enable fast and easy determination of presence of flammable gases The scale on the explosimeter goes from 0-100% of lower explosion limit (LEL) MSA Calibration Test Kit is supplied for checking the explosimeter The test kit consists of a pressure vessel with test gas composed of approximately 40% LEL methane in air Spangas for the gas indicator cannot be used directly as this gas has been mixed with nitrogen in the pressure vessel and the explosimeter does not work in an inerted atmosphere The pressure vessel contains sufficient gas for about 20 testings The calibrating procedure can be read from the instructions delivered with the calibrating equipment Additionally, graphs are delivered with the instructions showing acceptable instrument readings while introducing test gas to the explosimeter Control and use of explosimeter The explosimeter must be checked regularly using the above mentioned test Checks must also be carried out prior to using the instrument for a series of measurements before tank inspection or repair work in cargo and ballast tanks and void spaces The chief officer and other deck officers must be fully confident with using and maintaining the explosimeter and the calibrating equipment In order to achieve reliable measurements and calibrations it is necessary that the instruction material delivered with the equipment is closely followed Records of calibration, testing and servicing of the explosimeter shall be maintained on board Guidelines for using Explosimeter Rubber suction bellows and sample tube is attached to the explosimeter 98 The explosimeter and tube are flushed with fresh air Use pump strokes plus stroke per metre sample tube Lift the locking pin and turn the "On"-switch ¼ turn clockwise The instrument pointer deflects and settles around zero The scale is illuminated Suck fresh air through the instrument using the number of strokes as described above Turn the switch to make the pointer indicate zero The open end of the tube is placed where a sample is to be drawn from The sample is sucked into the instrument using the rubber bellows and with the number of strokes as above If sucking water into the instrument is at risk, the liquid trap delivered with the explosimeter must be used When drawing samples from tanks with overpressure it must be ensured that the flow is limited in order to prevent damage to the instrument It may be possible to collect a sample in a balloon from the test kit and then suck the sample from the balloon into the instrument Maintenance The explosimeter and calibrating equipment should be stored in the deck office or cargo control room together with other portable instruments The chief officer is responsible for the care of the instrument being in accordance with the instructions To prevent malfunction it is important that the instrument and ancillary equipment is cleaned after use, and that batteries are removed if the instrument is not going to be used for some time Reasons for malfunctions - The most frequent reasons for malfunctions are: The instrument is damaged by leaking batteries Dirty and clogged cotton filters Clogged lead filters Water in the measuring filament 99 ... the cargo heater should be used in order to cool the cargo The cargo heater must be pressure tested according to Section E in General Rules for Maersk Gas Carriers 2.2 Removing Nitrogen from Cargo. .. temperature and the cargo tank temperature is outside the maximum allowed limit, and it is impossible to load via the cargo heater and heat the cargo to within the maximum allowed limit, the cargo tanks... liquid to the cargo heater, vapour to cargo tank No Starboard can only be directed through the liquid line, as the condensate line is used to supply liquid from cargo tank No to the cargo heater