2 replies to this topic

[pleckner]

I'm sure you're going to get another answer to this, possible one that involves elasticity calculations for springs, etc. But, being practical:

1. That's why all PSVs must be serviced at least once per year as part of any Process Safety Management program. I would never let a valve go longer than one year before being serviced and I'll bet that's what the manufacturer will tell you.

2. And speaking of the manufacturer, if you want a realistic answer to your exact question, get the model number (and serial number) of your valve and ask the manufacturer!! They'll be very happy to tell you.

3. If the valve had ever opened because of a relief, it should be serviced as soon as possible afterwards and not wait for the yearly turn-around.

And to the general readership of this forum:

We get a lot of very specific questions about the mechanics of relief valves (and other relieving devices) on this forum and that is good, but please don't rule out talking to the people who make them. They won't bite! And after talking to the manufacturer, it would be great if you shared what they say to the rest of us as well. We're all here to learn.

[proinwv]

First the chances of such a spring becoming weak are remote, if the installation has not been modified or the setting changed to one above the spring's published range because springs are not intended to be designed or operated outside of their elastic limit.

Over temperature could reduce the installed load, or otherwise damage the spring.

Contact with corrosives could cause surface damage leading to failure.

Failure by fatigue is unlikely, as the valves rarely operate anywhere near their fatigue limits.

As previously stated, the valve manufacturer is the first resource for information. Also, they can test the spring against it's design specs. Alternatively, a third party can test the spring, but the design specs should be known.

Regards