Induction Bends in 42" ASME B31.8 Pipeline
Induction Bends in 42" ASME B31.8 Pipeline
(OP)
Which standards actually apply for the dimensional tolerances of the OD at the ends of induction bends to be used in an ASME B 31.8 42" pipeline?
API 5L (43rd ed.) table 8 gives tolerances for the OD of pipe-ends, which are quite tight. I can see that these tolerances ar fine for straight pipe, but I would have thought that more leeway for induction bends would be acceptable because of the manufacturing process of these bends.
ASME B16.9 (wrought butt welding fittings) give more comfortable tolerances (table 2). But induction bends are not wrought, are they?
The bends in question were first manufactured as longitudinally welded pipe according to API 5L. Then they were bent by the induction process. Due to the bending process, the wall thickness will decrease on the extrados side and increase on the intrados side. As per industry standard, the initial pipe had a slightly heavier wall to allow for the thinning of the extrados wall upon bending. I would naturally have thought that the tight API 5L tolerance would not apply anymore for the finished bend.
Follow on questions are: why do wrought fittings get a laxer bevel end OD tolerance than other fittings and what effect does the difference in the two tolerances have on the field welding process?
Thank you in advance for your input.
API 5L (43rd ed.) table 8 gives tolerances for the OD of pipe-ends, which are quite tight. I can see that these tolerances ar fine for straight pipe, but I would have thought that more leeway for induction bends would be acceptable because of the manufacturing process of these bends.
ASME B16.9 (wrought butt welding fittings) give more comfortable tolerances (table 2). But induction bends are not wrought, are they?
The bends in question were first manufactured as longitudinally welded pipe according to API 5L. Then they were bent by the induction process. Due to the bending process, the wall thickness will decrease on the extrados side and increase on the intrados side. As per industry standard, the initial pipe had a slightly heavier wall to allow for the thinning of the extrados wall upon bending. I would naturally have thought that the tight API 5L tolerance would not apply anymore for the finished bend.
Follow on questions are: why do wrought fittings get a laxer bevel end OD tolerance than other fittings and what effect does the difference in the two tolerances have on the field welding process?
Thank you in advance for your input.





RE: Induction Bends in 42" ASME B31.8 Pipeline
I've never really thought past the obvious about the rest, perhaps its the same logic.
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RE: Induction Bends in 42" ASME B31.8 Pipeline
RE: Induction Bends in 42" ASME B31.8 Pipeline
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RE: Induction Bends in 42" ASME B31.8 Pipeline
RE: Induction Bends in 42" ASME B31.8 Pipeline
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RE: Induction Bends in 42" ASME B31.8 Pipeline
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Induction Bends in 42" ASME B31.8 Pipeline
Which leads me to a real problem. The factory has delivered bends which are therefore out of tolerance (based on measurements out in the field), but equivalent to the other wrought fittings (e.g. barred T's). I can now advise to continue to weld up and to perform extra welding quality control, or to pare the bends down at the bevel (would be about 2 mm and a process which I have not investigated yet), or to say treat them like the barred T's which have a wider tolerance.
RE: Induction Bends in 42" ASME B31.8 Pipeline
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RE: Induction Bends in 42" ASME B31.8 Pipeline
RE: Induction Bends in 42" ASME B31.8 Pipeline
With so many pieces, it might be better to try to find a shop and do them there rather than in the field. Shop rates are cheaper than field rates and QC is much better.
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