DIB-1 Valve Cavity Relief

Question

DIB-1 Valve Cavity Relief

Bozzy09 (Petroleum)

(OP)

28 Aug 20 18:49

Do DIB-1 valves ALWAYS require a means of relieving cavity pressure (either automatically or manually as per API 6D)? My confusion is, for liquid service there should always be an LRK as thermal expansion is likely, but in gas service, is a means of relief required? API 6D is kind of vague as it says if fluid trapping in the cavity is possible (which is always the case with any valve?), and what if it is a CSA valve? My understanding is that due to the DPE seats it must have some means of relief (auto or otherwise) in case u/s seat fails for whatever reason.

Thanks

LittleInch (Petroleum) · Answer 1 · 2020-08-28 19:09:49

What's an LRK?

If the valve is in gas service and you can show that from max operating pressure the gas can't create pressure bother than the valve design pressure die to temperature increase then no, I don't believe it needs a pressure relief. But liquid yes.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

HitokiriAoshi (Mechanical) · Answer 2 · 2020-08-28 21:35:35

Cavity relief is a default requirement if trapping of fluid is required, UNLESS OTHERWISE AGREED. This does not care if it's liquid or gas, it's just that for liquid, it's faster for the trapped pressure to build up due to lack of compressibility.

Thus, the answer is NO, it's not always required, but it's highly desirable.

Luke | Valve Hax | https://valvehax.com/

Bozzy09 (Petroleum) · Answer 3 · 2020-09-11 20:00:31

Thanks guys. Hitokiri you are correct the 'unless otherwise agreed' clause exempts gas (as does the compressibility of gas as you would have to overpressure piping to overpressure valve cavity...) - classic vague code where they say fluid but gas is essentially always exempt.

Hitokiri, there are lots of issues we are experiencing associated with tubing (namely tubing relief commonly occuring and the valve becoming essentailly a DBB afterwards as pressure is required on both sides of the seat to hold and oftgen the tubing is being ran to the incorrect side; U/S vs. D/S confusion, tubing freezing, plugging, leaking etc.) so we are trying to avoid DIB-1 valves as they don't add any value in standard applications/operations when the relief tubing is either piped u/s or d/s..

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