High pressure piping backout requirements
High pressure piping backout requirements
(OP)
While most welded pipe joint designs have a requirement for backout at fit-up, I need to know if it is required to maintain that requirement after weld completion and where this is written.





RE: High pressure piping backout requirements
RE: High pressure piping backout requirements
In my opinion, looking for the "Gap" after welding by RT is an excess cost. No code I am aware of addresses this as a required inspection. A properly fitup socket weld would usually contract in a manner that would leave a smaller gap or no visible gap.
I have seen perfectly good socket welds cut out that were mistakenly interpreted during RT of an adjacent butt joint with no engineer or inspector argument. There is no code requirement or acceptance criteria for this in ASME Sec I, Sec VIII, B31.1, B31.3.
Gerald Austin
Iuka, Mississippi
http://www.weldinginspectionsvcs.com
RE: High pressure piping backout requirements
RE: High pressure piping backout requirements
Design Data Commercial Construction Codes
ANSI. ASME
Military Std. NAVSEA - 250- 1500
Military Std. 278
Military Std. 22
All our Therminol (vaporized/liquid) piping 2 1/2" and under used socket welds with a 1/16" gap verified by RT. Along with the gap requirement all fillet welds were 2 pass, 6010 + 7018 on old pipe with all 7018 on new piping.
RE: High pressure piping backout requirements
Many codes refer to bottoming clearances on sockets welds. I worked a few years under the codes you mention above and do not recall any RT requirements for verification of bottoming clearance.
Does your company do this as an internal requirement or is it specified somewhere? It seems like an excess cost.
Gerald Austin
Iuka, Mississippi
http://www.weldinginspectionsvcs.com
RE: High pressure piping backout requirements
RE: High pressure piping backout requirements
I will try to get the piping standard we used and see if there is a reference to any particular code/standard. I do remember early on that the gap requirement was reinforced by several incidents at a competitor's plant and later two incidents at a sister site. All our piping internal standards were at or mostly above code requirements even though we were not a Code state and there no incentives other than the commitment to have piping systems you could live with and not worry.
You are correct when you mention the added cost. When we had an internal RT Crew and most of the piping was bent on a slab eliminating fittings the cost was negligible. When we went to RT by contract and low bid contractors, instead of resident, the cost was raised considerable and quality went south. We had started to lower the % RT requirements when we discovered the welder/fitter quality was terrible, not only could the welder not weld, but the fitters were using the sockets as a crutch. While we were attacking this problem the permissible reportable spill was lowered by 90%. Also with any vaporized DP/DPO heating medium there was ever present danger of a vapor or mist explosion or fire a big problem as the majority of the piping was located in an occupied building. Our piping standards also require a vacuum, pneumatic pressure test, and He Leak test prior to commission.
I still say that RT is not the cost it’s the rework that drives the cost escalation. It was our group’s
opinion why should we lower our piping standards, proven, to the lowest common denominator of the industry.
RE: High pressure piping backout requirements
You are correct regarding socket welds. In the power industry, we fabricate socket welds most of the time for external piping and we have never performed an RT. There is no code requirement for volumetric inspection of socket welds (fillet welds).
Using a scribed line works well or using a water soluble gap-a-let contraction ring assures proper clearance for socket welds.