SS stub-in to CS pipe in steam service
SS stub-in to CS pipe in steam service
(OP)
On the advice of a Vendor, we have welded a 316SS piece (essentially pipe) directly into a CS header pipe (DN300 Sch 40) in temperatures operating up to 400degC. Using a 309L electrode.
When we do our finite element analysis of the junction, we see yeilding (at operating temp) local to the weld zone due to dissimilar metal expansion.
This result depends greatly on the assumptions made in the analysis. If the properties of the two materials blend across a wide enough area (ie smooth transition), there is no yeilding. However, if we model the juction as only three material properties (316, 309 & CS with no blending) we get a much higher stress.
Does anyone know how much weld dilution is realistic? Is there a reference that I can use for this?
When we do our finite element analysis of the junction, we see yeilding (at operating temp) local to the weld zone due to dissimilar metal expansion.
This result depends greatly on the assumptions made in the analysis. If the properties of the two materials blend across a wide enough area (ie smooth transition), there is no yeilding. However, if we model the juction as only three material properties (316, 309 & CS with no blending) we get a much higher stress.
Does anyone know how much weld dilution is realistic? Is there a reference that I can use for this?





RE: SS stub-in to CS pipe in steam service
RE: SS stub-in to CS pipe in steam service
The amount of weld metal dilution is based on the welding process. For example, SMAW provides a 30% base metal dilution rate versus GTAW (TIG) that provides about a 40% base metal dilution rate.
The best reference that I am aware of is as follows;
"Pay Attention to Dissimilar Metal Welds - Guidelines for Dissimilar Metal Welding" by Richard Avery. This paper is located at the Nickel Development Institute Web site.
RE: SS stub-in to CS pipe in steam service
I have see people use multiple weld passes in high temp cases to get the blending. You would be better off with a high Ni filler (82) on the CS. You could do this as a local overlay and then weld the 316 to it using 309. Or you could use multiple passes of 82.
Read Avery's paper. There are also some EPRI studies on this, if you have access to them.
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