Dissimilar metal welding with 316 SS wire 1

[MechEgrBDJ]

I currently have a project where we are welding 304 ss and 316 ss to carbon steel. This is a lower temp application so I specified a WPS with 309 filler. After PMI on several of the weld it was discovered the wire was marked 309 but was actually 316 ss. What potential problems do I have with these welds?

 

[stanweld]

A martensitic or partial martensitic microstructure could result depending on weld metal dilution. Cracking could result. Depending on service, stress corrosion cracking could also result.

 

[MechEgrBDJ]

Thanks for the information Stan. Maybe it would help me if we start with another question. What properties does the 309 fillerr have that make it the preferred choice for dissimilar welds? My understanding is that when joining dissimilar metal you need an over alloyed filler, at least for cs to ss. Can anyone elaborate further? Chromium depletion after diluting with base metal? Also what part does the ferrite content play in this scenario? These welds are on pipe with different services ranging from steam to nat gas. Thanks.

 

[stanweld]

The higher chromium content of the 309 filler metal assures an austenitic/ferritic microstructure when diluted with carbon and low alloy steels.

 

[metengr]

Agree with stanweld. You should be using a better matched wire to the 316 stainless steel base metal, not 309.

 

[strider6]

You should use the shaeffler diagram to understand the final microstrucuture of the weld:

http://www.dacapo.com/filer/schaeffler_diagram.pdf

http://www.gietech.be/LinkClick.aspx?fileticket=HJmiFOYi0RA=&tabid=111&mid=539

hope this help

S



Corrosion & Rust Prevention Control

 

[metengr]

After PMI on several of the weld it was discovered the wire was marked 309 but was actually 316 ss.

I find this hard to believe. Are you sure about the above? Did you run bead on plate using the so-called mislabeled 309 rod using PMI to confirm a 316 stainless steel composition? Otherwise, the PMI results may be misleading if you are testing completed butt welds. I have seen strange PMI results from folks that were not qualified to operate an alloy analyzer. If 316 stainless steel filler metal was used by accident, I believe someone just picked up a wrong can of filler metal.

 

[stanweld]

Could the filler metal have been ER309LMo?

 

[MechEgrBDJ]

Thank you for all your posts. The Schaeffler diagram was a big help once I figured out how to account for dilution of both base metals. Based on the prediction of the final weldment, I don't believe there is a martensitic micro structure, but the ferrite percentage is low enough to be a concern so welds are being repaired. Actually, this was a spool of FCAW wire that was mislabeled by the manufacturer.

 

[stanweld]

WAs mislabeling by a major manufacturer or repackager?