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Guidelines for Cutting Out and Returning a Pipe Segment

Guidelines for Cutting Out and Returning a Pipe Segment

Guidelines for Cutting Out and Returning a Pipe Segment

(OP)
We are planning to perform some short temporary cut-outs in 12" sch 160 carbon steel pipe, which was not previously stress relieved.
My concern is the unlocking of residual stresses by cutting in close proximity to an existing weld, causing ovality.
What are the recommended guidelines for avoiding this problem in heavy wall pipe? I am expecting it will be expressed in terms of a minimum number of diameters distance.
Thanks in advance.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Guidelines for Cutting Out and Returning a Pipe Segment

Schedule 160 is a thick-walled pipe.
I have never seen pipe that small a diameter "ovalize" from residual stress from welding. Self-weight at 12 inch diameter is much smaller than the strength of the pipe. (Think instead of a 44 or 72 inch diameter pipe only 1/2 inch thick. Do you see how the self-ovalizing will happen on thin-walled, large diameter pipe instead?)

Now, the opposite? Pipes showing significant movement when cut due to relief of fabrication and fitting up stress? Yes, you should expect such movement - it could be compression or expansion or moment (rotation loads), or a combination of all three - when cutting the pipe. You might be lucky and see no movement. But you should expect the sudden movement when the pipe is cut.

RE: Guidelines for Cutting Out and Returning a Pipe Segment

(OP)
Thanks racookpe1978,
I expect movements upon severing, and we can manage those. And with two cuts we gain a degree of freedom when refitting the segment.
Ovalization of heavy wall pipe is more difficult to suppress without fairly extreme measures.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Guidelines for Cutting Out and Returning a Pipe Segment

I think I would attach a heavy friction clamp around the pipe some distance away from the cut.
Tighten the clamp firmly and then tack weld the clamp to the OD of the pipe. This should act as a kind of strong back holding the pipe diameter securely. You can then attach other rigging to the clamp and beam holding the pipe from excessive movement when you finish cutting. Just a suggestion.

RE: Guidelines for Cutting Out and Returning a Pipe Segment

(OP)
Thanks for the suggestions Tmoose.
I'll present them to my team.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Guidelines for Cutting Out and Returning a Pipe Segment

If it is only to prevent ovalizing, and you don't care about relative rotation, you can weld two half-circles on the pipe that stays. After welding in the pup piece, grind away, PT/MT and done.

Size of the "collar" to be determined, and placed at a short, but reasonable distance away from the cut of course.

I've done this on much thinner tubes, no idea if this is feasonable on a sch.160...

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