Back Purging of P22

Date 12-12-2002 14:32

Back purging for P22 piping will not result in any improvement in the weld. It will be cleaner, but there will not be any mechanical improvement in the strength of the weldment. Im pretty sure there have been some studies done by EPRI in regards to this. So save your argon. I have however, run into specs recently that do require purge with P22 material. I then submit a change to the engineer to delete that requirement. Good luck.

Steve

By korety_k Date 12-13-2002 04:12

where can I find literature in web telling about purging in detail.

Korety

By Weldmedic (*)

Date 12-13-2002 05:12

Try this web site http://www.intercononline.com/welding/ypurge.htm
some useful info...

Steve

By dasimonds (**)

Date 12-14-2002 12:29

So your saying that gross high temperature oxidation in the root pass(sugar) is acceptable?

While P11 has less chrome content, I've seen cases where, due to poor fit up, the formation of sugar was inevitable because of the time the metal was held at welding temperatures trying to fill a gap that was wider than the filler metal.

It has been my experience that the higher the chrome content, the greater the likelihood of bringing these internal root conditions into existence. Also, the choice to purge or not to purge is usually budgetary in nature.

I'd be willing to bet that under magnification, the microstructure of an un-purged, open root, chromium containing material would differ from an identical weld that was purged.
Dale Simonds

By pipewelder_1999 (****)

Date 12-14-2002 12:44

As far as the ASME Boiler and Pressure Vessel Code Sec I goes, root oxidation is not addressed. I may be incorrect and if you have evidence otherwise, let me know the paragraphs.

I've welded P22 material and in most cases the light scale that formed on the interior of the tube was similar to that on SA 210 A1 material.

Your probably very correct about the surface under magnification but as far as fitness for service in many applications, adding purge does increase cost without any added benefit. If there is no benefit for the application and the cost goes up, thats a reduction in quality. At least thats my opinion.

G Austin
www.weldinginspectionsvcs.com

By dasimonds (**)

Date 12-18-2002 01:22

Have you ever seen P22 sugar?

Dale Simonds

By pipewelder_1999 (****)

Date 12-18-2002 03:16

No but I've only looked at it through the gap as I welded tubes and also the RT film.

Have you seen it sugar?

G Austin