Comments on Pressure Relief System Design

I would like to draw your attention to a few points on the November 2008 article, Pressure Relief System Design (pp. 40–45): 1. Pressure drop and pressure loss: The inlet pressure “drop” that the author refers to under Relief system piping is non-recoverable pressure loss, and does not include a “drop” in pressure due to elevation increase. It should be labeled as a pressure loss rather than a pressure drop as the author has specified elsewhere. It may sound trivial, but such errors are not uncommon. The 3% rule is code-mandated and should be followed. However, any excess above this can still be defended in some circumstances in the court of law, but only by an expert analysis. 2a. Bursting of rupture disk: In the penultimate paragraph, when a rupture disk is used in series with a relief valve, the author writes: “… the disk would never burst”. The rupture disk (as well as a conventional relief valve) is a differential pressure device. So the disk will burst when the difference between the upstream pressure and the downstream pressure of the disk equals the burst pressure of the disk (or the set pressure of a conventional relief valve). The other point to remember is that the pressure…