Monitoring of cargo tank pressure/vacuum valves - safety alert

There have been a number of reports recently on problems and safety alerts associated with the possible malfunctioning of pressure/vacuum (p/v) valves onboard tankers.

During the last week of September the Singapore Maritime and Port Authority (MPA) issued a Circular reminding Masters to maintain cargo tank p/v valves and monitor their operation during cargo operations to ensure they are working effectively. This advice was linked to a recent incident where a valve malfunction apparently caused excess pressure in a wing tank. The excessive pressure, coupled with a defective weld, caused the centre bulkhead to deflect toward the adjacent centre tank. Damage to the centre tank then caused the main deck to tear downwards and the tank top to also tear open.

INTERTANKO has also seen a Class NK Technical Information note giving the same advice to masters over the need for maintenance of p/v valves. The Class NK note came as a result of a number of repeated incidents on chemical tankers where structural damage was caused by the malfunction of a named type of high velocity release valve. There is also more anecdotal information that some Administrations have either banned or placed limitations on loading rates for some p/v valve suppliers' products due to apparently erroneous testing and certification by Class Societies.

This is an alarming situation since the ISO 15364 standard states that it is the operator's responsibility to ensure that p/v valves are suitable for the intended purpose. We would therefore urge tanker operators to closely monitor the operation of p/v valves on their ships. INTERTANKO will continue to investigate this issue and revert.

We do not believe that tanker owners are responsible for the installation of improperly- certified p/v valves. If all this anecdotal information is substantiated by the facts, we cannot agree that a tanker operator can ensure the proper operation of p/v valves when these valves are not of the correct design, which, in turn, creates circumstances of either poor drainage from the valve or incorrect opening/closing properties.

Contact: Dragos Rauta