API 521 - Piping included or not fire case

[jamesbanda]

Dear experts.

I've been told that within API521 for fire case you need to include the pipework. So during a project at Front end design you estimte the pipeing area and prior building it you recalculate based on the 3d model.

These steps seem overly complex to me and considering the theory by which relief valves are based on (eg fire height) etc a resonable assumption would seem more approprate.

I checked API 521 the only reference i could find was a comment releating to everything in the fire zone and nothing specific for piping.

So is it really that essential to measure iso's for fire cases.

 

[ggordil]

I add 15% additional wetted area to account for piping. This is based on a standard that one of our clients uses. If the piping is large, meaning 12" and above, I would try to do some more precise calculations.

 

[CMA010]

In the following article 10 to 15% additional wetted area is recommended to account for piping: Fire, vessels and the pressure relief valve, W. Y. Wong, Chemical Engineering Magazine, May 2000.

 

[CJKruger]

If the client did not have any standards, I have added 10% in the past.

 

[skearse]

I typically use 10-15%, depending on the size and quantity of piping. If it's an existing installation, I try to get a reasonable estimate of pipe from the vessel to the first isolation valve (fire case assumes that the vessel is blocked in).

 

[jamesbanda]

thanks for the comments. I've not read anything that states you should check the area v isometric diagrams at 75%+piping modelling.

I think that is a level of detail to far. Use decent assumptions (Eg10-15% extra) and thats sufficient,.