Backing Gas for Chrome Moly Piping

Not logged inAmerican Welding Society Forum

Forum

AWS Website

Help

Topic American Welding Society Services / AWS Learning & Education / Backing Gas for Chrome Moly Piping

By nichols7007 Date 12-17-2010 18:43

I have two qualified ASME Sec IX welding procedures for welding 1.25Cr-.5Mo piping (GTAW/SMAW). One is qualified with a backing gas (100% Argon) and the other without. Both procedures also were qualified with PWHT.

For cost purposes on this project, we would like to use the procedure without backing gas during the welding. What is the risks/cons for weldability for not using backing gas during the root pass welding?

By MBSims

Date 12-17-2010 21:53

I see no problem with this. We have welded many tube and pipe welds in 1.25CrMo and 2.25CrMo without gas backing and not had any problems with RT results or performance of the welds. Backing gas does give a much cleaner and smoother surface. I believe the AWS standard on purging of pipe and tubing states that backing gas is optional for CrMo alloys with less than 5%Cr.

Topic American Welding Society Services / AWS Learning & Education / Backing Gas for Chrome Moly Piping