Dear Mr. Diehl,

Thank you for answer.
Yes, the majority of the calculation follows 75-WA/FE-23 "Steam Flow through Safety Valve Vent Pipes" by H. E. Brandmaier and M. E. Knebel.

However, it’s not the case of "transient pressure"; the article says "…it is assumed that transient effects due to piping valve opening are small…".
It would be interesting to understand the assumption made for transient case, because in "closed" flare systems it is the only true component. For me, it make more sense to consider the article "Simplified analysis of steamhammer pipe supports loads", by E.C. Goodling.


Just a comment, not related to the "transient" subject.
It is interesting to see that the Brandmaier and Knebel’s article was subject to criticism in the "Discussion" section, by G.S.Liao, Bechtel Power Corp. Mr. Liao’s discussion makes sense and, trying to answer, the article authors concluded in "Author’s Closure" section: "It is unfortunate that published test data do not exist against which to compare the calculated data". The modern software, like AFT Arrow, are successfully applied in industry- including Power applications- and don’t consider any supersonic underexpanded free supersonic jets.
Of course, nothing wrong to consider article method. We may keep in mind that is just an acceptable Fluid Mechanics model, but isn’t the only one.

My best regards,