Localized PWHT for pressure vessel

[starships]

Greetings

We're doing repair work for pressure vessel as per EN 13445.
Repair work means "cutting deep dent-damaged area and re-welding with new plate as square size".

After re-welding, localized PWHT as per client's requirement has been planned. But, we're worried about deformation during and/or PWHT. Because, this vessel will be subject to the localized PWHT only for damaged area (3.4m X 5.8m) as per EN standard not entire circumference.

Vessel specification is as below.
- Design code : EN 13445
- Material : P355 NL1
- Thickness : 33mm(existing) / 35mm(new plate to be welded)
- Inside diameter : 7,210mm
- PWHT Temp. : 550-600

Our concern is deformation that may be happened during and/or after PWHT.
To avoid any problem, we've searched for proper manner such as reinforcement inside, but nobody makes it sure.
What is the best method to avoid deformation? And, if using reinforcement, is it available?

 

[metengr]

You do not mention the location on the vessel where the flush patch plate will be installed. If you have concern regarding distortion during PWHT it will be in the form of local buckling from creep deformation. You may need a local creep buckling analysis to demonstrate that stresses causing by vessel weight/support and temperature differential during PWHT will not result in local creep deformation.

 

[TGS4]

I would recommend following the procedures and practices in WRC 452. I am aware that the EN standard permits "bull-eye"-type local PWHT, but that is not really good engineering practice. If you do, however, WRC 452 provides some recommendations on how to do that properly. metengr has also provided you with the failure modes of concern, so that you may investigate them on your own.

 

[stanweld]

Is this a vertical or horizontal vessel? If vertical, where is the repair located? What is the height? Will the PWHT be don insitu or will the vessel be relocated horizontally?
Distortion can be minimized with proper application of PWHT.

 

[metengr]

You may find this article interesting

http://www.ultragen.com/doc/tech-articles/en/Article1_V3N2_JI_IRI_PWHT.pdf

 

[starships]

This is the horizontal-type vessel containing Liquefied Petroleum Gas.
Length (From T.L to T.L) is 52,800mm.
There are two repair locations. One is located at the bottom of vessel and, another is located on the side of vessel. Both locations are so far on the vessel (Approximately, 30,0000mm).
Dimension of both repair areas is almost same.

We've been doing stress analysis to measure the distortion during PWHT, but it's not easy job. Distortion on few areas has been predicted after preliminary analysis. To minimize distortion, proper method of PWHT is required.