PWHT for dissimilar weld joint 9Cr with 310 austenitic SS 4

[Ibahaa]

hello all,

I meet a case with dissimilar weld joint 9Cr with 310 austenitic SS
I found two approved WPS as follow:
• WPS no.1 filler metal is NiCr-3 with no PWHT (which mean the residual stress in the 9cr will not be eliminated).
• WPS no.2 filler metal is NiCr-3 but PWHT is required (which mean the austenitic SS will susceptible to sensitization).
I take my decision to follow WPS no.2 and perform PWHT at 720 C with 2hr holding time.

After PWHT I perform PMI on the 310 SS side HAZ which showed that the Cr percentage had been reduced from 24% to 18%
If I follow the correct procedure or there is any better procedure to follow.

 

[metengr]

Yes, for this weld joint, I would have used a Ni-base filler metal (Inco 182). First, since the 9 Cr requires PWHT, I would recommend a butter layer (2 pass) across the entire 9Cr weld prep, followed by PWHT. Once this operation is completed, you can complete the weld joint to 310 stainless steel using either Inco 182 filler metal or even 310 stainless steel filler metal with no PWHT.

 

[Ibahaa]

thank you metengr,unfortunately the weld joint was a fillet weld which make it is hard to perform such buttering

 

[metengr]

Not necessarily. I have seen it used for fillet welds. You weld a pad on the 9 Cr, PWHT and complete the remainder of the fillet weld on the pad.

 

[weldstan]

Assuming that the 310 SS is being used at high temperature, sensitization will occur in service. I would also assume that there will be no aqueous media so oxidation is the primary corrosion concern; in which case, sensitization should not be considered as detrimental to service.

Whereas B31.1, B31.3 require PWHT for the weld, why are you considering without PWHT? If this is a repair to an existing system, the Owner may option out of PWHT. Lastly is this P91 or P9 alloy?

 

[fleischfresser]

In the event that the seam is completed with an austenitic-ferritic welding Material (after buttering with Ni-base alloy), a ferrite-free, fully austenitic zone with a high hot cracking tendency would arise in the transition zone due to Ni-absorption from the Ni-based alloy.

That means after buttering you must also use Inco 182 in any case.

Regards - Juergen

 

[Ibahaa]

Thanks for your responce
Finally the correct action to weld using inconil electrode followed by PWHT.
But what is your idea about the decrease of Cr percentage in the SS after PWHT.

 

[metengr]

If you follow the advice provided above the stainless steel will not be subject to PWHT, this was the point about buttering with Ni-base and perfoming the PWHT for the 9 Cr material before completing the weld joint.