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Chemical compatibilities of liquefied gases - LPG tanker procedure

Compatible cargoes are those substances which can be loaded consecutively without prior need to gas free the tanks. However, care must be taken to fully comply with Charter Party, shippers or other stated requirements for the cargo changeover, as these may require more stringent procedures.
On completion of the discharge the amount of liquid stripped from the tanks will depend on the information available on the next cargo. If no prior information is received then normal stripping will be carried out manually.



The conditions then required in the cargo tanks for loading the next grade of cargo will depend on the degree of contamination acceptable to the shippers/charterers between the last cargo and the next. If the degree of contamination is of no importance, it may only be necessary to retain the remaining liquid and maintain the cargo tank temperatures on the ballast passage by use of the reliquefaction plant. If contamination has to be kept to a minimum it may be necessary to remove the remaining liquid in the sumps by boiling off and by venting the remaining vapour to atmosphere whilst on passage.

It is emphasised that the final decision depends on the requirements of the charterer/shipper and the required maximum level of contamination.


Liquid vaporising of residues

The deepwell pumps can normally be used to remove liquid residues, but if the level is not sufficient for them to operate satisfactorily the residues can be cleared by drawing vapour from the tank, heating it in the LPG compressor or vaporiser, and returning it to the tank sump through the stripping line or the puddle heating line. The warm vapour heats the liquid collected in the sump which quickly vaporises. An increase in the temperature of the tank sump signals the completion of vaporisation.

THIS PROCEDURE MUST NOT BE HURRIED. During boiling off it is important to obtain a positive temperature reading on the sump thermometer. Any subsequent drop in temperature indicates that liquid may still be present hence it is important to monitor the temperature even after the flow of hot gas has stopped.


Fig:Chemical compatibilities of liquefied gases ; X = incompatible

Note: Reference should be made to the Data Sheets above to the ICS Tanker Safety Guide (Liquefied Gas) (Ref. 12.2.2) for details of chemical compatibility.



Related Information:

1. LPG cargo loading special guideline



2. Tackling fire onboard LNG & LPG ships



3. Detail guideline for Ballast operation at sea by LPG carrier



4. Handling cargo related documents for LPG carrier



5. Cargo sampling procedure for liquefied gas cargo



6. Cargo measurement and calculation guideline for LPG carriers



7. Handling Propylene oxide, Ethylene oxide mixtures



8. Special characteristics of Vinyl Chloride Monomer & Butadiene

1. Various type LPG tanker - Design characteristics and usability



2. LPG tanker cargo work equipments & product line system



3. LPG tanker cargo pipe line inspection and testing guideline



4. Carriage of LPG cargo at sea & safety guideline



5. LPG reliquefaction plant safety guideline



6. Preparations for LPG cargo discharging, pumping & stripping guideline



7. Preparations for loading compatible cargo onboard LPG tanker



8. Preparation for changing different grade cargo or drydocking -LPG tanker guideline



9. Cargo tank inerting prior to gassing up - LPG tanker procedure



10. LPG cargo tank purging & safety guideline



11. LPG cargo tank cooling safety procedure



12. LPG cargo loading special guideline



13. Tackling fire onboard LNG & LPG ships



14. Detail guideline for Ballast operation at sea by LPG carrier



15. Handling cargo related documents for LPG carrier



16. Cargo sampling procedure for liquefied gas cargo



17. Cargo measurement and calculation guideline for LPG carriers



18. Handling Propylene oxide, Ethylene oxide mixtures



19. Special characteristics of Vinyl Chloride Monomer & Butadiene

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