This alert advises dutyholders of an incident involving failure of a bursting disc on the shell side of a shell and tube heat exchanger, which led to an inability to flare gas safely on an offshore installation.
The purpose of this alert is to advise dutyholders of the incident at an early stage so that lessons can be learned and appropriate action taken by dutyholders to avoid a similar incident.
A bursting disc protecting the seawater side (shell side) of a high pressure (HP) gas intercooler suffered a low pressure (LP), in-service failure. This resulted in an uncontrolled flow of seawater into a platform flare system.
The intercooler had two pairs of bursting discs each with inter-disc space pressure sensors and tell-tale velocity check valves.
It appears that that following sequence of events occurred:-
It should be noted that it was not possible to monitor the actual liquid level in the HP flare KO drum once the level was above the high-high trip.
Once both flare drums were full of water there was no clear path to either flare and any event leading to the flaring of gas at this stage could have resulted in the release of hydrocarbon gas with potentially very serious consequences.
This incident highlights the need for dutyholders to be aware of the potential for impairment of the flare and relief system from the uncontrolled flow of cooling water / cooling medium into the flare knock-out drum as a result of bursting disc rupture.
It also highlights the need for dutyholders to ensure that bursting disc rupture will initiate measures to ensure isolation of the cooling water / cooling medium supply (and return where appropriate) to the protected item of equipment, so that the integrity of the flare and relief system is not compromised.
The main relevant legal requirements include:
There are legal duties on both the owner and the operator of the plant.
Any queries relating to this alert should be addressed to:Team Leader – OSD 3.1 Process integrity
This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice.