AISI 4130 material with Weld overlay

[metboss]

Hi All,

Item: Gate Valve (4-1/8"); Applicable code: API 6A.

Material: AISI 4130; Weld overlay: Inco 625 (3mm thickness) inside entire bore.

During UT inspection, defect was found in weld metal and as a part of procedure, our vendor has brought this issue to our attention with their internal NCR. Upon reviewing corrective measures, it is been noted that defective weld surface will be removed entirely till base metal and hardness to be verified.
After that, weld overlay(repair) is going to be performed using “the same conventional WPS which was used for initial production welding process” followed by full furnace PWHT.

My queries are as below:

Does it require any repair specific WPS or the same production welding (used for initial process) WPS can be sued?

MTC reveals that base material(forging) was heat treated in Mill (Q & T). Is there any effect on base material mechanical properties if it is subject to full PWHT in furnace? Or localized PWHT would be suffice?
Is PWHT type (full or localized) is essential variable as per ASME IX?

 

[gtaw]

If at first you don't succeed, try, try again.

There's a lot of information you didn't provide that could help us form an opinion.

Best regards - Al

 

[SJones]

1. No. Yes. See API Spec 6A, 7.5.3.

2. The PWHT temperature should be selected to be lower than the tempering temperature stated on the inspection documents for the forgings. A commonly adopted margin is 30 deg C or more. Normally, when it is known that PWHT will be employed, the forging inspection documents would include mechanical properties after a simulated PWHT cycle resulting from an instruction to the manufacturer to provide the same.

The part probably requires full heat treatment after complete overlay. Local heat treatment of an internal overlay repair would not be practical.

3. No as per QW-407.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.