SS Pipe for UREA Systems containing Ammonia Vapor?

[749KDV]

It seems as if the industry standard is to use carbon steel for piping in UREA systems containing ammonia vapor (Constituents are: Ammonia vapor containing approx. 23% water vapor at a max design pressure of 80 psig @ 400 deg. F) Has anyone ever experienced SS (either 304L or 316) pipe being used in these type systems? If so, how does one justify that SCC is not an issue at the weld joints if field welds are not post weld heat treated?
Thanks in advance.

 

[BenThayer]

take a look at some of the ammonia scc threads. I have never heard of anyone doing a pwht on stainless steel for ammonia/water systems.

when you say ammonia water systems for urea, I assume that you are running a recycle type process such as UTI or STAMICARBON or SNAMPROGETTI process right?

I think that 316L would be the ideal choice since however good your process runs, an upset can result in urea and or carbamate getting places you would rather they didn't.

Unless it is a very major project, do the stainless. IF you know you will not have any source of corrosives from the process, you should not need to do the PWHT for a 23% water mixture since you are well over the 0.2% water that typically requires PWHT. ammonia scc is typically a problem for solutions that are less than 0.2% water. Be careful that you do not have any zones in the process that can see effectively 100% ammonia vapor or you could still have ammonia scc (only if you are using carbon steel, not if using SS).