Dears,
I have noticed various confusions about the fact that API 520 language mainly focuses on built up backpressure being the main driver for selecting the type of PSVs in comparision to the allowable accumalation for the various contingencies and whether we have multiple relieve devices i.e. section 5.3.3.
However, API at the same time considers superimposed backpressure not as strong as the built up backpressure to drive selecting the PSV type, this is mainly due to the fact that superimposed backpressure can be compensated for conventional PSVs via CTDP or if it causes subcritical flow (due to being too large) can be corrected in the PSV selected area (section 5.6.5).
Therefore, do you agree that built up backpressure is the main driver for PSV type selection since in any means if superimposed backpressure is highly variable we would anyways not consider conventional.
Thanks