It is my understanding that we can perform a Butt Weld on (2) lengths of pipe to be qualified for all fillet welds within the thickness range of the pipe. Correct?
Yes, you are correct kind of because fillet welds will fall in to unlimited thickness with a groove weld qualification.
Also being that the assembly is pipe to flange, would the pipe to pipe butt weld be an acceptable coupon sample if the pipe material is the same material as the assembly? The customer did not provide any code detail in there documentation and we have had a tough time with clear guidance, this is a biopharm app, so we are following Section IX.
Depends on if the flange is the same material as the pipe. If you can qualify your procedure with the exact same materials that will be used in production, that will be just fine. Some people will try and go the cheaper route and use a cheaper material that falls into the same material class or p-number as the material to be used in production.
Hope that helps ya out!
Kix