Reject/Accept of punch marks on SS line

[MaterialGrad]

A visual inspection was done on a 12" SCH 40 (10.31mm thick) stainless steel pipe for possible damage. I was asked to investigate if punch marks(+/- 1mm deep) measured on pipe will be detrimental. No fatigue stresses are predicted for this line. Punch marks were introduced to start welding of smaller line to the 12"line. Location of this tie in has now been changed.

API 5L states that a discontinuity should not be more than 12.5% of the pipe wall thickness. Hence any discontinuity more than 1.29mm is not allowed and line should be scrapped.

My concern is the measured thickness is VERY close to the max allowable thickness of this discontinouity. At what point can i say we should reject/accept this pipe?

Thanks in advance

 

[Goahead]

If the discontinuity passes the code requirement it is acceptable. However, if you are concerned with possible harm to the structure, you could consider if reducing the sharpness of the punch marks is feasible by carefully controlled radius grinding. Welding on top of this would be acceptable?

http://www.welding-advisers.com/

 

[GregLamberson]

MaterialGrad

What code governs your facility and what is the service, MAOP, Op temp, etc?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[stanweld]

API 5L does not apply for stainless steel pipe. It applies to the manufacturer of steel line pipe. It does not apply to pipeline fabrications.

 

[EdStainless]

My first thought is to ask what the actual wall thickness is, is it SCH40 or 40S?
In either case I wouldn't be too concerned about punch marks unless they are deep and very sharp. There are probably tooling and handling marks in the surface deeper than these.

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