Back purging criteria in gtaw welding

[vks1986]

Hello,

For Gtaw of cr-mo steel,

is there back purging required for p11(1% Cr) and P22(2.25%Cr) cr-mo steel
because customer spec. say above 4% Cr required back purging.

At which minimum % of Cr it is required.

 

[metengr]

Typically, no back purging is required for base materials with chromium contents less than 9%.

 

[weldstan]

At one time back purging became standard in the petrochemical industry for P22 alloy, it is now seldom required. Back purging is normally required for 5%Cr-1/2% Mo and greater chrome alloy steels.

 

[gtaw]

If the Owner/customer includes a requirement for a purge in the project specification, it takes precedence over the code since it is more restrictive than the code. The Owner/customer can include more restrictive requirements, but generally, not less restrictive requirements if ASME applies.

If the AWS structural welding code applies, the Engineer, representing the Owner, can modify the code to suit specific project requirements.


Best regards - Al