Fire Case PSV Chatter Risk
Fire Case PSV Chatter Risk
(OP)
I have a new vessel with a range of relief cases. I'm proposing to install a single conventional PSV.
The governing case is gas blow by. For the fire case, the relief load is less than 25% PSV capacity so i believe chatter may be a risk for the fire case (as per guidance in API 521). However, this seems to be a common problem for fire relief.
Do i need to alter my PSV design just to avoid chatter in the fire relief case?
Thanks.
The governing case is gas blow by. For the fire case, the relief load is less than 25% PSV capacity so i believe chatter may be a risk for the fire case (as per guidance in API 521). However, this seems to be a common problem for fire relief.
Do i need to alter my PSV design just to avoid chatter in the fire relief case?
Thanks.





RE: Fire Case PSV Chatter Risk
Best regards, Morten
RE: Fire Case PSV Chatter Risk
Thanks.
RE: Fire Case PSV Chatter Risk
After a significant fire, ALL PRV's will be pulled and rebuilt or replaced - springs may have lost temper, disks may be chattered, etc. Disaster has a very different set of rules than Normal Operations.
RE: Fire Case PSV Chatter Risk
If so, is inlet dP > 3% for fire case, or is inlet dP < 3% for fire case and the PSV will cycle from set pressure to re-seat pressure due to the dynamics of the system/fire? I don't consider the latter, chattering, but one does need to consider the frequency of the chattering.
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: Fire Case PSV Chatter Risk
If I have two credible scenarios that have widely different required rates, then I put two PSV on the vessel--a small one sized for the lower case set around 95% of MAWP, and another one sized for the difference between the required rate for the small case and the required rate for the bigger-flow case set at something like 102% of MAWP. This staged approach results in much smaller valves (less potential for chatter) and better control.
Read Duwe6's post carefully. After a fire you need to be a lot more concerned with assessing what components actually survived than worrying about chatter.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Fire Case PSV Chatter Risk
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: Fire Case PSV Chatter Risk