SRV under rupture disk
SRV under rupture disk
(OP)
Do you guys know if it is legal to have a spring pressure relief valve just before a rupture disk. The set pressure of the SRV would be lower than the one of the rupture disk
Thanks for your help on this one
Thanks for your help on this one





RE: SRV under rupture disk
Usually, if both are used, the rupture disk is below (before) the relief valve.
Regards,
SNORGY.
RE: SRV under rupture disk
Are both on the main line -or- is the RD in the PSV discharge ?
As Snorgy said if in the PSV discharge it is WRONG.
But if both are on the main line the PSV could be acting as sentinel valve to take minor upsets to prevent blowing the RD.
RE: SRV under rupture disk
Thanks you both for your help
Bragamor
RE: SRV under rupture disk
RE: SRV under rupture disk
Normal useage is to put the RD just below [inboard of] the PSV, to keep the PSV from experiencing corrosive fumes or solids that might accumulate and plus the PSV. In an overpressure event, the RD blows, the PSV relieves; then the RD is replaced and the PSV is cleaned and reset.
RE: SRV under rupture disk
Rupture disks are sometimes installed in the tailpipe of a PSV to protect the valve from moisture or corrosive vapors.
That's possibly what you're looking at here. I can't think of any other reason for putting a disk on the downstream side of a PSV. In such cases I always suggest a minimally low burst pressure for the disk so that it bursts immediately after the valve opens. However, if there's a reason for setting the PSV at a lower pressure than the disk, you could do so. You just have to make sure that the relief system opens at or below MAWP and you have to account for the open disk in you outlet pressure drop calculation.
RE: SRV under rupture disk
--Mike--
RE: SRV under rupture disk
Rupture disk downstream of PSV outlet, in the actual PSV tail pipe, is acceptable per UG-127 (a)(3)(c) and footnote 54.
Don't know why one would want to do that in any ordinary instance.
Regards,
SNORGY.
RE: SRV under rupture disk
Except for the scenario that MikeClay mentioned (multiple credible scenarios, the PSV is sized for the small one set below 110% of MAWP and the rupture disk is set a bit higher for a larger credible scenario) a PSV and RD in parallel set at the same value is generally an indication of unqualified idiots doing "engineering" with their middle-school education. (A RD under a PSV to protect the PSV from corrosive fluids is quite reasonable, but I don't think that is what we're talking about. I don't agree that a RD in the PSV tail pipe is a great way to keep rain off the PSV, a rain cap is cheeper).
David
RE: SRV under rupture disk
Or should it be slightly higher to prevent premature rupture and possible contamination/damage to PSV?
Thanks!
RE: SRV under rupture disk
Good Engineering Practice = 5 to 10% below the PRV
NEVER above the MAWP
RE: SRV under rupture disk