I'm a little confused. The heading suggests three base metals, but your question seems to indicate two. Can you provide a little more information? Joint type for example.
I have been told that to weld a pipe butt dissimilar 2% Cr Mo TO A106 Carbon Steel is not possible so you have to weld 2%CrMo to 1 1/4 %Cr Mo then to A106 Carbon Steel.
Is this correct or do I only have to run a procedure 2% CrMo to A106. The material is P22 I think to P11 Carbon.
I am using Union 1 Crmo 910 GTAW and the SMAW has slipped my mind at the moment.
No, this is not the case. Most likely, someone was thinking if this being a dissimilar metal weld due to the difference in Cr between the Grade 22 material (2.25% Cr-1% Mo) that is being welded to carbon steel.
To qualify this procedure, all you really need is one weld coupon consisting of Grade 22 material (ASME P-No 5A) welded to SA 106 carbon steel (ASME P-No 1). You have several choices for filler metal - you can use carbon steel E 7018), or you can use an E 8018 B2 (1.25% Cr- 1/2 % Mo) or you can use E9018 B3 (2.25% Cr-1% Mo).
Normally, when you are welding low alloy steels to carbon steel that have greater than 3% Cr in difference, this would be more of a true dissimilar metal weld that would require possible use of a safe end that contains a chromium content in between the high and low alloy materials or careful selection of filler metal to reduce carbon migration of the steel containing lower chromium content.
It is no problem to weld 2 1/4Cr-1Mo directly to CS and pass the PQR tests. The problem is that you have to do a PWHT at the temperature required for P22 . This temperature can be to high for CS and as such destroy the long term properties of the CS. You will not always notice this when making the PQR. For that reason sometimes a butter layer of 1 1/4Cr-1/2Mo is made on the P22 , PWHT at high temperature and then weld the P11 to CS with PWHT at lower temperature. In that case you need 2 PQR s or simulate the whole procedure in 1 PQR.
Also be aware that a Procedure qualification test of P22 welded to itself qualifies for welding P-No. 5A to P-No. 5A, P-No. 4, P-No. 3 or P-No. 1. So, the PQR doesn't necessarily have to be A106 welded to P22.
