Safety valve rupture disc

It is a relief set-up in which a rupture disc is installed directly upstream of a safety valve. The disc seals the relief branch during normal operation and keeps the process medium away from the valve. When the pressure reaches the burst pressure, the disc opens and the safety valve lifts to relieve the excess. Once the pressure has dropped, the valve closes again and limits the loss of medium. The disc then has to be replaced before the arrangement is complete again. The small space between disc and valve must be monitored for pressure. A burst indicator tells you when the disc has opened. Together these parts form one relief system that needs to be looked after as a whole.

A rising pressure in the interspace usually means that medium is getting past the disc without the disc having burst. The most common causes are a pinhole from corrosion, a crack from fatigue or a leaking seal in the holder. Temperature effects on trapped gas can also raise the pressure. Because a disc responds to the pressure difference across it, the disc will now open at a higher process pressure than intended. The protected equipment could exceed its intended relief pressure before anything opens. The valve is also no longer fully isolated from the medium. Treat such a reading as a reason to investigate promptly and to plan a disc replacement. Do not simply vent it and carry on without finding the cause.

An excess flow valve lets small leakage escape from the space between disc and valve. That prevents pressure from building up behind the disc. When the disc bursts, the large flow closes the excess flow valve. The medium is then directed to the safety valve rather than out through the vent. This keeps the interspace at atmospheric pressure without constant manual attention. It is only suitable where the leaking medium can be vented safely. For toxic or hazardous media, a pressure switch or transmitter with an alarm is often preferred. Our holders can be supplied with leak detection ports as the connection point for such devices.

Yes, the safety valve still needs inspection, testing and overhaul according to your site regime and the regulations. The disc does not replace that maintenance. What changes is the condition of the valve, because it is no longer wetted by the process medium. Corrosion and deposits on the seat and internals are therefore much less of a problem. When the valve is removed, the disc and holder should be checked at the same time. We advise fitting a new disc whenever the assembly has been opened. The holder is designed for reuse and usually only needs visual inspection. The interspace monitoring and burst indicator should be tested before start-up.

A burst alarm means that the disc has opened and the safety valve is now exposed to the medium. The first step is to bring the process to a safe state. Next, the cause of the overpressure has to be found. The safety valve should be treated as exposed and checked before it goes back into service. The disc is then replaced with a new one of the correct specification. The holder, seals, interspace monitoring and burst indicator are checked and reset. A short instruction per tag in the control room helps operators respond quickly and consistently. Keeping spare discs in stock keeps the downtime as short as possible.

We advise against reinstalling a disc that has been removed from its holder. Handling during removal and storage can damage the disc. A damaged disc must never be installed, because even small defects can change the burst pressure. Such damage is not always visible to the eye. Fitting a new disc is a small effort compared to the consequences of a disc that opens at the wrong pressure. That is why we recommend planning a new disc for every opening of the assembly. Keep spare discs with the correct burst pressure, material and size in stock. The holder itself can be reused after inspection.

The clearest sign is pressure in the interspace between disc and valve. A gauge that reads above zero, or a pressure switch or transmitter that alarms, points to a leak. Without interspace monitoring, a leaking disc can remain unnoticed for a long time. Signs of process medium at the valve inlet during maintenance also indicate that the disc has not been tight. A burst indicator will not always detect a small leak, because the disc has not opened. That is why interspace monitoring and burst detection complement each other. If you suspect a leak, plan a disc replacement and check the holder seals. Tell us what you found so we can check whether the disc selection still fits the process.

We supply the disc side of the arrangement as exclusive STRIKO agent for the Benelux. That includes replacement rupture discs matched to your tag, medium, temperature and burst pressure. We also supply holders, which can be fitted with leak detection ports for interspace monitoring. Burst detection with electrical or magnetic sensing and fail-safe design can be added to the disc or holder. Holders come with material certificates, pressure calculations, inspection reports and traceability. For a quick answer, send us the valve tag, the existing disc data, the medium and the operating conditions. Tell us as well how the interspace is monitored today. Mail your data to sales@dutchvalvevision.com or call +31 (0)70-2210560.