Safety Relief Valves

Pressure Relief Valves (PRVs) and Pressure Safety Valves (PSVs) are common in most Oil & Gas installations and protect systems against damaging pressure.

The valve must open quickly enough to control the rising pressure and must also have enough capacity to contain the incident. When the incident causes slow dynamic events the industry is safe using the old, traditional, sizing methods.  But faster events need simulation and surge analysis to be used to accurately specify the relief valves.

This is especially necessary because of the well reported problems of over-sizing spring operated relief valves. This can cause valve chatter and that will damage welds and pipes.

The pressure drop in the pipework leading to the PSV and the backpressure developed in the discharge pipework also have a significant impact to the stability of the operation and need to be studied carefully, which is again, a compelling reason to study the operation of the relief valve either at design stage or when issues occur with operating relief valves.

Spurious operation of relief valves cause problems with most operations. The valve may need re-seating and incidents reports and analysis may be needed. The accuracy of simulation and surge analysis ensures that spurious operation is minimised which is of considerable commercial benefit to operating plants.

The operating speed of ‘pop-action’ and ‘modulating or pilot operated’ safety relief valves is significant and some process conditions may require the faster acting pop-action valve. Studies of the events leading to the operation of the relief valves can help specify which type of safety relief valve to use.

But, some incidents and operations in liquid systems, or in systems that can have slugs of gas and liquid, can cause very rapid transients (Waterhammer) that will be too rapid for conventional relief valves to contain. In these situations, fast-acting, specialist valves are needed and the opening speed required can be determined by surge analysis.

In many process situations the combination of liquid and gas passing through the relief valves can cause very high dynamic loads on the discharge pipework and it is now well accepted that this needs to be studied to avoid damage