PWHT

Date 06-01-2005 08:19

Absolutely!! If a component or pipe has received PWHT and you perform additional welding, then yes you must perform PWHT again.
However, you may perform localized PWHT.

By chall

Date 06-01-2005 11:44

If the governing standard is the National Board Inspection Code, there are several repair methods that may be used as an alternative to performing PWHT.

All the methods have additional requirements that include things like NDE (pre & post weld), elevated preheat, filler metal requirements, welding technique, strict PQR requirements, (just to name a few). Furthermore, it is expected that both your AI and the client (and their in service inspector) agree to the application of the alternative repair method.

As a rule, the alternative method is only allowed when it is impractical to perform PWHT. It is up to the repair firm to determine what is impractical.

Charles

By NDTIII

Date 06-01-2005 12:12

You are correct Charles. I am assuming Mohammed is working to ASME B31.3, where it states in paragraph 331.2 Where warranted by experience or knowledge of service conditions, alternative methods of heat treatment or exceptions may be adopted as provided in para. 331.2.1 and 331.2.2.
However, para 331.2.2 (a) states where provisions less stringent than those in para. 331 are specified, the designer must demonstrate to the
owner's satisfaction the adequacy of those provisions by comparable service experience, considering service temperature and its effects, frequency and intensity of thermal cycling, etc.
In addition, appropriate tests shall be conducted, including WPS qualification tests.
So if you intend to delete the PWHT requirements, you must have the appropriate WPS and a PQR to support it.
It would be easier, faster and probably cheaper to perform localized PWHT.

By chall

Date 06-01-2005 12:16

I am woefully delinquent in my knowledge of B31.3. We are generally involved in Section I and B31.1. For some reason, many of our customers specify B31.1 even though a more appropriate standard is B31.3.

Thanks for the lesson.
Charles

By G.S.Crisi (****)

Date 06-01-2005 19:36

You're not the only one, Charles.
Back in my days of erector engineer, I'd been in charge of the erection of the piping of two power plants, one within an oil refinery owned by Petrobras (the Brazilian state oil company), and the other one within a pulp and paper mill owned by a Japanese company.

In the first case, the piping was designed to B31.3. Petrobras' argument was that, although the piping belonged to a power plant, it was located within an oil refinery, and so B31.3 was the applicable Code.
In the second case, the piping was designed to B31.1. The Japanesemen's argument was that, although the piping was located within a paper mill, it belonged to a power plant, and so B31.1 was the applicable code.

Well, this happened some 15 years ago and both piping systems are still in service; none of them blew up, which indicates that both codes are good.

Giovanni S. Crisi
Sao Paulo - Brazil

By NDTIII

Date 06-02-2005 03:28

You brought up a good point. Pipelines usually fall under API-1104 and of course the refineries under B31.3.
The trunk lines coming into the plant fall under B31.3.
If the pipe at the first isolation valve is over 19mm, it requires PWHT on the plant side of the valve but not on the pipeline side.
All due to code jurisdiction.

By chall

Date 06-02-2005 12:22

Oh boy, don't get me started on 1104 vs the ASME standards. The differences boggle the mind when you consider that they all address welding.

Charles

By NDTIII

Date 06-02-2005 13:05

I hear you Charles, but it is a fact of life. The code of jurisdiction governs what gets what
The bottom line is I think Mohammed should perform localized PWHT as a minimum. Particularly if he is using P-No.s 3, 4 or 5 materials and it is in MEA service.

By Arnie Corpuz (*)

Date 08-02-2005 09:14

Guys correct me if I'm wrong, first of all you cannot weld on a PWHT treated equipment unless you have an approved welding procedure simulating the condition. You may come up with a welding procedure that does not require PWHT based on the outcome of mechanical testing or you may come up with a welding procedure that requires PWHT. But based in my previous experience we always come up with approved welding procedure requiring PWHT regardless of the thickness of the external attachement.

Regards,

Arnie

By chall

Date 08-02-2005 10:26

I believe you are correct. If you did PWHT during the PQR you must do the PWHT during any welding that the PQR supports.

Where there is latitude in the construction code, we generally run more than one PQR. We run a PQR that supports the maximum thickness without PWHT, and additional PQRs to support the thicknesses above (requiring PWHT). We would also run a PQR at a lower thickness with PWHT in case it is a code or customer requirement.

Charles