P91 butt joint with SS316 permanent backing ring

[pandithan]

Expert
Pl see the sketch attached and it is being used in steam line
Ur inputs on whether these joint configuration recommended in P91 welding
If so what is the welding procedure to be followed

 

[metengr]

For a dissimilar metal weld (DMW) joint to Grade 91, I would use a transition piece of Incoloy 800/800H between the Grade 91 and 316ss. The linear coefficient expansion differences between Grade 91 and 316ss are too large, and will cause cracking problems from thermal/mechanical loads in service.

 

[weldstan]

Agree with metengr. We have used this method to preclude cracking of former direct P91 to 316 welds with great success. Original welds failed within 5 startup cycles.