X-Ray after PWHT
X-Ray after PWHT
(OP)
Are X-Rays of the Welds required after PWHT? I thought that they are required because you need to check the integrity of the welds and the properties. One of our QC guys do not think this is the case. Thanks...





RE: X-Ray after PWHT
Generally speaking, all qualitative NDT should be performed AFTER PWHT!This is because defects can arise due to the heat treatment or other factors arising from the stress/strain associated with PWHT. However, it is quite common to perform x-ray or UT before PWHT to ensure that the weld is clear of welding defects before another thermal cycle is performed on the weld!
Regards
RE: X-Ray after PWHT
Nondestructive testing (NDT) requirements, like RT (X-ray) are typically found in the Code of Construction for the vessel. If you are fabricating this vessel to ASME B&PV Code, Section VIII, Div 1 requirements you need to review Part UW for NDT requirements. In most cases, NDT is required based on service conditions, wall thickness and weld joint configuration.
If RT is not specified by Code, you do not need to perform it.
RE: X-Ray after PWHT
If your question relates to RT after PWHT, this is a different matter from my answer above. The Code implies that RT shall be performed AFTER fabrication of the vessel. Some folks interpret this to mean that after welding, if an RT is shot, this satisfies Code requirement for RT. The Code really does not specifically state or require a post weld treatment RT. It is implied. Other Construction Codes like Power Piping do have specific requirements for post weld RT.
I would follow good engineering practice or judgment and consider after fabrication to mean after post weld heat treatment.
RE: X-Ray after PWHT
RE: X-Ray after PWHT
RE: X-Ray after PWHT
The key word is fabricated. Heat treatment either pre or post weld is still considered a stage of weld fabrication.
RE: X-Ray after PWHT
RE: X-Ray after PWHT
RE: X-Ray after PWHT
Remember the term "construction" would infer design and "fabrication" does not.
Both of you guys make great points and I agree with metengr's position because it makes the most sense. That is why having a proven WPS and competent Welders and Welding Operators will pay off when the dust settles.
Usuually the "Inspector" would help make the final decision for you.
RE: X-Ray after PWHT
European Codes however require that NDE is performed after PWHT.
RE: X-Ray after PWHT
RE: X-Ray after PWHT
This is the practice we uses in the Oil and Gas sector. I have found that it is common across the globe.
When PWHT is specified due to either 1. Process reasons such as in sour service, Hydrogen Service, etc., or 2. By Code due to thickness per UCS, all final acceptance NDE shall be performed after final PWHT. The reason is already explained well by Rodofgod above. Code do not require this but this is "standard industry practice" with NO exceptions permitted.
This forces the "good and skilled" fabricators to quote inclusive in their price to perform either RT or UT of welds before PWHT. Purpose is to use the results as the baseline and self-assurance to ensure welds are sound before it goes into the oven. This is how things are done in the oil and gas industries.
RE: X-Ray after PWHT
I have absolutely no problem with what you are saying although double NDE is certainly not standard industry practice in my part of the world. On the contrary, most fabricators will not include this unless it’s specified up front and you have to pay for it.
RE: X-Ray after PWHT
Although many codes do not specify RT after PWHT, many client specifications call for a surface detection method like MT or PT to be applied after PWHT.Otherwise RT could become a very expensive affair.
RE: X-Ray after PWHT
I used to receive the comment that PWHT may be a cause of "surface crack". MT or PT after PWHT as qualitypro's comment is recommended instead of RT/TOFD after PWHT.
RE: X-Ray after PWHT
The key word is fabricated. Heat treatment either pre or post weld is still considered a stage of weld fabrication."
I think this is a fallacy in argument- if "fabricated" here includes heat treatment, then it isn't "fabricated by welding"- it's "fabricated by welding and heat treating". IE, I think that interpretation puts more meaning in the term than is intended, which makes the phrase disagree with itself.
Maybe some of you guys can clue me in here- but I was under the impression that the main flaws that might be worsened or caused by stress relief would be cracks- but that xray is primarily aimed at other types of flaws.
RE: X-Ray after PWHT
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: X-Ray after PWHT
RE: X-Ray after PWHT
RE: X-Ray after PWHT
So, let the "smart" buyer beware. Codes and Standards provide MINIMUM guidelines for NDT to assure safe operation. One can always exceed the minimum Code requirements for NDT.
RE: X-Ray after PWHT
I'm with Metengr. Codes set minimum standards and sometimes reflect the loudest voice on the committee and not necessarily the best practice. In the petrochem plant I work in, we exceed code requirements often - due to the experience of Oil and Gas world wide.
Standards tend to lag well behind new best practices.
In the case of the original posters question, we double up NDE when PWHT is involved. On really critical vessels, we'll pay for both RT and UT of welds. Interestingly, we've not found many reworks - but I think that's more down to the welder knowing he's not going to be able to hide anything and so does a good job. [why they just don't do a good job in the first place is beyond me!]
Cheers
Rob