Acceptance criteria for defects on machined areas of valve castings

[Santhosh5974]

Many a times we find surface breaking defects in castings after machining at the valve manufacturer location.

These castings would have been radiographically tested(only critical area as per B16.34) and accepted with 3.2 certification.

What is the acceptance criteria for relevant indications noticed during PT/MPT on machined surfaces of castings?
Is it allowed to repair such defects, revealed by surface NDE after final machining, by welding at valve manufacturer's place? Will it affect the 3.2 certification issued by the foundry and endorsed by TPI?

 

[gerhardl]

In my opinion (and this is an opinion only): surface repairs will not generally be accepted for 'qualified valves'.

Reasons are several: surface repair will involve cleaning (grinding?)and welding, which again might have weakening effects on larger areas and general structure other than effected. A surface fault could also indicate deeper cracks and faults not found either by machining or radiographics.

If surface defects often (many times?) are found after the valve bodies have passed radigraphic, visual and other tests, this would obviously raise the question of the foundry's general quality level, including all manufacturing and QA procedures and practice.

Some end users excludes in their valve specifications surface defect repaired valves for some or all applications.

Other end users have special requirements for which type of parts/repairs to be accepted, usually with extra documentation and tests requirements, very often including welding procedures, repair procedures requiring among other thing certified welders etc. etc.

For common castings for cheaper-end valves the sensible thing would be to return/not accept any casting fault, but yes, some factories repairs some surface defaults for some valves.

I doubt a general answer can be given without including the end users of the specific valve.

 

[MattC1234]

I agree with gerhardl.....

This is too difficult to say. It depends on the customer, the application, the pressure class, where the defect is, how big it is in terms of surface area but also in terms of the depth of the defect.

If the defect is ever more than 1/4 wall thickness then it should be scrapped as a general rule!

 

[PAN]

In view of a client, I tend to reject the valve especially for welded repair. However, we have to consider in detail for each specific case.

 

[SJones]

MSS SP-53?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04