316SS stub-in to CS pipe @ 400degC

[scotty36]

Has anyone used a "hydratect" fitting before? It is a level switch used for steam service. The physical connection relies on stubbing the fitting into the steam header. The problem is that the only option offered by our vendor is 316SS and our header material is CS. We used a 309L electrode.

Our finite element analysis of the junction shows yield stresses at the weld boundary due to differential thermal expansion.

The hydratect fitting is a proprietary item, and the Vendor says "no problem". I have consulted experienced steam engineers also and they say "no problem". Yet I look at the FEA and I see a potential problem. We are currently working on a solution.

My question is for those with steam experience - what is your experince with welding SS in to CS? In particular do you see local yielding as an issue given that it will only happen once?

 

[PAN]

You may consider AWS A5.4, E309Mo instead of E309L.

I may not reply to your specific question. However, the use of Inconel electrode should be a good choice for high temperature service.


What SMAW rod for 316SS to A36 structural?
thread725-92847

 

[moltenmetal]

The experts who frequent the corrosion forum would be more knowledgeable in this area, but I personally would be worried about intergranular corrosion in carbon-to-austenitic stainless steel welds at 400 C under significant stress. I'd be consulting a metallurgist for sure on this one.

 

[bvi]

If you are calculating thermal stress, the appropriate criteria would be a twice yield type allowable stress, a primary plus secondary stress allowable. See Section VIII, Div 2, Appendix 4 for guidance on this.

Carbon to Stainless welds are commonly used as high as 700F, typically without problems. At the higher temperatures, inconel weld metal is used to blend the coefficients of thermal expansion. Inconel as a coeffficient of thermal expansion between carbon steel and stainless steel.