Radiography before/after PWHT 1

[InspEngr]

I've briefly looked in B31.1 and Section I and I think the answer is no; however, I'm going to ask just in case.

For P1 material (drums and tubes) where PWHT is being performed, is the requisite RT required to be performed after PWHT?

In my opinion, RT should be performed prior to PWHT for info and required after PWHT (in case an otherwise acceptable defect "opens up" from the heat cycle). Our internal documents reflect this (and have for many years) but I haven't been able to determine if it's a code requirement or not. From what I've seen so far it isn't.

I found in B31.3 that for P3, P4, and P5 (I think those are the materials), NDT is required to be performed after PWHT.

Anyway, if you know for sure that it is or isn't your help would be appreciated. It would be even more appreciated if you could point me to the relevant sections of the code.

-InspEngr

 

[metengr]

InspEngr;
This is an interesting topic. In the Power industry we deal with the ASME B&PV codes Section I and ASME B31.1 for field weld repairs. The only requirement for RT is that it shall be performed in accordance with Code guidelines (Table 136.4 in B31.1 and Table PW-11 in Section I). Both Section I and B31.1 do not get into process detail - that is left between the owner and the manufacturer/repair organization.

The ASME B31.1 Power piping code and Section I have been around for many years and are design by analysis codes and thru experience. For us, RT before or after PWHT is not that significant because we use the following options;

1). if the RT will be shot before PWHT, the contractor shall be required to perform an RT of the root/hot pass or after 1/4 of the weld joint thickness is deposited, depending on thickness. Once the weld is completed, an RT is shot before PWHT, which is for Code requirements. After PWHT, a wet fluorescent MT is mandated by us or by Code. This is the key, because if you develop cracks as a result of hydrogen pick-up or excessive joint restraint, which can somtimes occur in heavier wall Cr-Mo piping, the cracks propagate to the OD surface and will reveal themselves on a surface exam.

2). if the RT will be shot after PWHT, we still mandate a wet fluorescent MT surface examination for the reason given above, or as required by Code. We do not require a contractor to perform an RT of the completed weld before PWHT for "information" because this costs money and affects production schedule. We have on occasion required a root/hot pass or 1/4 completed weld joint RT, but not always.If the contractor still wants an info shot of the weld before PWHT it is at their cost, not ours. We have found that contractors will tend to pay more attention to detail if they only shoot one RT after PWHT. Nobody wants to have to repair and perform a second PWHT.

 

[InspEngr]

Thanks metengr,
At our refinery, we "require" the RT to be done after PWHT. If an RT is done prior, it is at the contractors expense. Most contractors we've worked with will shoot RT prior because, as you alluded, they don't want to get bit and have to perform a repair and then re-PWHT. From our standpoint, the one we're interested in is after PWHT. I hadn't heard of performing MT after PWHT to check for cracking due to H2 pickup. Nor had I heard of RT'ing at 1/4 completion or after root/hot pass. Perhaps this is particular to the Power Industry Sect. I and B31.1?

I'm more familiar with B31.3 and Sect. VIII. However, we are having a Sect. I Fired Boiler built and the project engineer did not include our site-specific (versus corporate) specs in the bid package (pre/post PWHT RT is just one of the issues).

You've answered my basic question, though. RT pre/post PWHT is not specified.

Thanks again,
InspEngr

 

[nur12]

http://www.eng-tips.com/viewthread.cfm?SQID=83340&SPID=404&newpid=404&page=1

You may find this thread helpful.

Regards.

 

[llpcode]

ANSI B31.3 and ASME Section III contain specific requirements for certain P-number materials...

The other construction codes are silent on this issue.

However, since delayed cracking can occur after PWHT, it is better to perform RT after at least 72 hours have passed.

 

[bmoorthy]

Drums as per B 31.3/31.1?

I think reference to ASME Sec VIII Div 1 would be appropriate for Drums and ASME/ANSI B 31.3 for Piping.

For CS, LAS, NDT can be performed prior to PWHT. To perform NDT after PWHT is not mandatory. Usually these requirements are specified in te purchase spec (UOP, Stone and Webster, Chevron, EIL, Shell). Even these guys generally do not insist RT after PWHT for CS (P1) Mtl. FOR low Alloy steel, UT or RT is generally called for by UOP.

I remember comparing NDT requirement amongst the various ASME Sections (Long time back) and i found ASME SEC 1 to be less stringent as compared to ASME Sec VIII.

 

[bvi]

For B31.3, when RT is required to be performed by Code, it is required to be done after PWHT. RT testing prior to PWHT would be an optional additional examination. Some folks do this to make sure the joint will pass RT prior to doing the PWHT.