Resistance to Flow Method for Rupture Disks in Two-Phase Flow Service

[CJC0117]

Does anybody know if the Resistance to Flow Method explained in Appendix E of API 520 Part 1 can be used to verify the capacity of rupture disk in two-phase flow service? The equations API uses are compressible flow equations from Crane Technical Paper No. 410.

I'm thinking that two-phase flow would be considered compressible flow, so then the method could be used. The only difference would be that you would use the specific volume of the two-phase mixture instead of just the vapor. Is this right? Could anyone offer any suggestions about what method they use for rupture disk rating/sizing in the case of two-phase flow? Thanks.

 

[Latexman]

You are correct. My company considers the Homogeneous Equilibrium Model as an industry best practice and uses HEM for two-phase flow in relief device sizing/rating.

Good luck,
Latexman

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[PaoloPemi]

I agree with Latexman,
a procedure for sizing a PSV / Rupture Disk for two phase flow based on HEM assumption (homogeneous equilibrium, no slip) generally gives conservative, safe values,
for some cases you may consider HNE or NHNE or introduce corrections for example for high viscosity fluids.
For HEM you may consider a simplified approach (see API Omega) or rigorous available in some simulators.
B.T.W. I utilize regularly the Excel page distributed with Prode Properties and I have posted examples in this forum, good luck.

 

[CMA010]

No you can't use the method for vapour flow for a two-phase flow. However, you can try to use the method for two-phase flow given in API 521, § 7.3.1.3.5

 

[CJC0117]

Thanks for the replies and sorry for the late reply. There's no question in my mind that I should use an HEM approach, because it is easier and more conservative than other approaches, and recommended by DIERS and API. I was just wondering if I could implement HEM into the Resistance to Flow Method developed by Crane and discussed in API 520. I've been looking into it further, and I've come to the conclusion that this method should not be used because in the derivation of the formulas, ideal gas assumptions are made to obtain a Pressure-Volume relationship, and I doubt a two-phase mixture should be modeled as an ideal gas. I read through the 1996 article "Easily Size Relief Devices and Piping for Two-Phase Flow" by J.C. Leung. It was insightful and included many design charts based on the omega method (and also analytical equations including the one mentioned by CMA010 that appears in API 521), however, I'd like to implement a numerical integration method, as recommended in the article and the DIERS project manual for complex piping (i.e. long pipes with expansions and contractions) because many of the RD systems I am trying to re-rate are like this. The DIERS project manual references another DIERS publication called "Emergency Relief Systems for Runaway Chemical Reactions and Storage Vessels: A Summary of Multiphase Flow Methods" that should have an example of how this is done. I've requested the book and I'm waiting for it now. Hopefully it will elucidate the problem for me.