Chromium burn out (oxidisation)

By mark hughes Date 10-27-2004 03:23

Within ASME B31.3 Table 341.3.2 for acceptance evaluation of radiography, chromium burn out (oxidisation) of root passes (for piping welded from one side only),it is not included within the defect types.
1. Can this be classified as one of the defects addressed such as lack of fusion, or
2. Is it required to be addressed in the specific contract engineering specifications. By stipulating no chromium burn out, % of oxygen allowed in back purge during welding of root pass and or subsequent passes to which thickness and or required colour of completed root pass from inside.

By MBSims

Date 10-28-2004 03:48

My experience has been that use of purging gas on root passes is governed by the contract specifications and not by piping codes. This is a corrosion resistance issue depending on the properties of the fluid in contact with the root and not normally an issue for mechanical properties. Oxidation would not be considered a "lack of fusion" type defect or fit into the defect types in the B31.3 NDE acceptance criteria.

By pipewelder_1999 (****)

Date 10-28-2004 14:10

I don't believe any of the ASME codes address this. Many always take it for granted that if it's stainless its purged. Or protected by some other means. I would like to know if there have been any root oxidation failures in boiler tubes. It sure is a pain to purge or solar flux them. I really like the flux coated rods though.

Have a good one

Gerald Austin

By ssbn727 (*****)

Date 10-31-2004 10:55

I'm wondering what the EPRI has to say about this issue... Hmmm.
Must be some real colorful radiographs in order to tell whether or not there's "oxidisation" in or is it on the surface of the root side of the weld and, to what extent...

"Boris, where's that confounded scope???"

Are we talking Duplex stainless here because if we are, then the contractor spec's should require in parameters, the percentage amount of oxygen allowed for use as the purging gas (Argon purity tolerances in ppm's would be even better). It should also stipulate purge monitoring procedures. I did'nt say must!!!

Respectfully,
SSBN727 Run Silent... Run Deep!!!

By rodofgod (**)

Date 11-10-2004 23:23

Hi All!

Interesting Subject! Not having access to any 'standards' at the moment, I'd have thought this subject would be covered by 'essential variables'!
However, I may be wrong!

Regards

By pipewelder_1999 (****)

Date 11-10-2004 23:37

Deletion of backing gas is an essential variable for both procedure and performance qualification. The actual codes do not address an acceptance criteria for root oxidation for production welds.

Neither is it addressed for acceptance of a performance qualification test.

A little sugar never hurt nobody :)

Have a nice day

Gerald Austin

By Jim Hughes (***)

Date 11-26-2004 19:28

Sugar (oxidation) can be detected by x-ray. It will show up as a rounded indication or as a density issue. With B31.3 were the code is used in Chemical plants and Nuclear waist clean up, sugar can have a very adverse affect because, for instance Cyanides attack sugar (oxidation) and the heat affective zone. Esspecially with 300 series S.S. Thats why sec. IX list essential and non-essential variables.
Hope that helps
JPH
Welding Engineer

By pipewelder_1999 (****)

Date 11-27-2004 00:57

Hello JPH,

I understand the detrimental effects under specific service conditions. Does B31.3 address this as far as acceptance criteria? I have never seen it but may have missed it. Isn't this usually addressed in project specific documents ?

Have a good day

Gerald Austin
http://www.weldinginspectionsvcs.com