Crack in alloy steel flange

[SukhpalSingh]

low alloy steel flange (2.25% Cr) was welded to carbon steel pipe (ASTM A106) by mistake and the welding was done by E7018 electrode. after that, we have noticed a longtudinal crack in HAZ of flange (low alloy side). I know the hydrogen with martensite microstructure of low alloy steel after welding can cause such crack, but I want to ask about what are the additional reasons that contribute in this failure.

 

[HakiNoir]

I assume you welded with A106-P1 WPS! In my opinion, there wouldn't be too many other factors. You could weld P22 with 7018 and to CS but perhaps with a P11 butter layer, proper preheat and PWHT. See here also:

http://www.eng-tips.com/viewthread.cfm?qid=365137

In addition to what you said, depend on the flange and pipe position and weight,there could be more stress on the brittle side of the weldment. Also, you have to keep this in mind during PWHT. This might happen to CS part at the P22 PWHT temp.

 

[metengr]

Most likely lack of preheat caused the defect either from delayed cracking or excessive restraint. I have seen this problem with lack of preheat on relatively thick (>25mm) 2.25% Cr - 1% Mo steel components.

 

[SukhpalSingh]

Thank you for replaying, but can the difference in mechanical properties between filler metal and base metal cause such failure?

 

[metengr]

In this case, I doubt it. Tensile strength mismatch can result in a metallurgical notch effect causing low fatigue strength.

 

[racookpe1978]

Replace the flange, replace the welder supervisor, replace the weld.