CHIRP has recently received several reports relating to pressure surges in pipelines during tanker operations. The following reports show various scenarios where pressure surges can occur.
What did the reporter tell us?
One company noted an increase in loss of cargo containment incidents due to over pressurisation of pipelines during cargo operations, the incidents occurring during changeover of cargo tanks, blowing through cargo lines, and restarting cargo operations after a stoppage. Analysis showed common factors are incorrect cargo line-up, inadequate ship/shore communication, and inadequate supervision.
Another incident occurred during a topping–off operation on a tanker where communication with the terminal failed.
Finally, whilst discharging, the manifold watch heard a change of flow and also observed a pressure increase, immediately reporting this to the Cargo Control Room. The Officer of the Watch simultaneously noted an increase in pressure and suspended the discharge. The terminal informed the vessel that the pressure increase was due to an uncontrolled closing of an automatic shore line valve.
The lessons to be learnt
Any pressure surge carries a high risk of causing damage to a pipeline and pollution.
Cargo operations should be monitored closely and effectively, with any change in flow pressure being reported and investigated. If any doubt exists, transfer rates should be reduced or transfers suspended until the causes are investigated and obviated.
Personnel involved in cargo operations should be fully aware of cargo line-up, tank changeover and blowing-through procedures.
Communications between all participants including terminals should be pre-tested and are vital at all times, particularly at critical stages of an operation such as topping off.
Full compliance with the ISGOTT ship shore safety checklist including repeat checks where required are important, as are thorough cargo planning and understanding of the planned operation by all personnel. Procedures for any valve manipulation should be checked prior to operation, and a responsible officer should double check cargo valve settings before starting/restarting of cargo operations.