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Deck seal & non return check valves & tank gauging for Chemical tankers

On vessels fitted with an inert gas system it is a requirement to maintain a positive seal between the cargo tanks and the inert gas generation plant this is usually accomplished by the use of a non - return valve and a Deck Water Seal. The water seal and non-return valve ensure that the cargo tank atmosphere cannot leak back to the engine room or inert gas generator.

In vessels fitted with a Venturi type “Dry” deck water seal, particular care must be taken with inspections of the Venturi non return valves and/or orifice plates, as applicable, to ensure that there is no corrosion or damage which would allow excessive carryover of water into the inert gas piping system and cargo tanks.

Chemical tanker at sea

Filters in the system must be removed regularly for inspection and repair if necessary. When vessels are trading in cold weather areas it is essential that deck seal heating systems are checked as being operational.

When vessel is not gas free, including when there is a presence of flammable slops onboard, the deck seal pump shall be kept operational on a continuous basis and all alarm systems relating to the pump pressure, or level of water in deck seal, shall be kept in full operation.

Deck seals and non-return valves shall be opened up for inspection of all internal parts, venturies etc. as per PMS.

Tank gauging

The components of all cargo and ballast tank level gauging equipment are to be operationally tested prior to every cargo operation and inspected, cleaned and calibrated as required, according to the maker’s instructions at least every six months. If the vessel is to load a static accumulator cargo in a non-inert atmosphere the fixed tank gauging system must be in full working order prior to cargo operations.

Comparison readings between fixed and portable gauging systems should be taken at regular intervals throughout the loading / discharging periods in order to ascertain any discrepancies between the systems.

If the vessel is loading a static accumulator cargo, the vessel must comply with the measuring and sampling requirements contained within ISGOTT “Measuring and Sampling Non-Inerted Tanks” (Currently 11.8.2) and ISGOTT “Measuring and Sampling Inerted Tanks” (currently 11.8.3) as applicable.

More info:

Useful publications

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Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.

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