Emergency Shutdowns on Cargo Systems
Emergency Shutdown (ESD) systems have been a requirement of the IMO IGC Code for the carriage of liquefied gases in bulk for a long time.
An ESD system is basically a link between the ship and the terminal. It can be automatically activated either by pre-defined conditions, such as high tank levels or high pressure, or manually activated by an emergency button.
Once activated, by either party or an abnormal condition, then a series of events starts to return the cargo system to a static condition so that any remedial action can be taken in a timely and safe manner. This includes the structured closing of valves both onboard and ashore and the tripping of pumps and compressors.
This safety system works well on gas carriers but would it work on a conventional tanker? Is there even a need for it? We must ask ourselves: how many times do we read about the overfilling of cargo tanks because cargo tank ullages were not properly monitored? Or when a ship desperately tries to contact the terminal to stop pumping?
A recent paper co-published by the Oil Companies Marine Forum (OCIMF) and the Chemical Distribution Institute (CDI) discusses the subject of emergency shutdown systems for oil and chemical tankers.
The main recommendation is that linked ESD systems should be used for oil and chemical transfers, including ship-to-ship (STS) transfers.
What is more, one of the core recommendations is the requirement for shut down of cargo transfers in abnormal conditions, such as high tank level, high or low tank pressures, fire or gas detection or excessive movement in relation to cargo manifold.
Another key feature of any ESD system is the ability to stop the cargo operation safely. No party either on board or at shore, should have to shut a valve against a full flow of incoming liquid. A system that links the ship and shore can allow either party to activate a pre-defined and controlled shutdown procedure. This process aims to protect the system against unacceptable pressure surges and brings the transfer operation to a static condition safely.
Whilst the current ESD system on liquefied gas carriers is well established, one of the biggest flaws is the lack of standardisation. The type of umbilical connection is dependent on the terminal and a gas carrier may have to carry and be familiar with a number of different connections to be accepted into a port.
OCIMF and CDI propose a standard 5-pin twist connector, offering a degree of standardisation. This should enable any tanker to berth at any terminal and be linked with the ability to transmit a signal from ship to terminal or vice versa.
If these recommendations become widely adopted, then hopefully we will see an end to overfilling of cargo tanks. This in turn should reduce the risk of oil spills from tankers during cargo operations.
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