DUPLEX COLD BENDING 1

[GabrieleB]

Have anyone had experience with Duplex Cold Bending.
I'm working on a pipeline engineering with duplex pipe (S31803) 6"/4" thick. 4.8mm.I have to specify a limit angle for the cold bending on site. Some people has experience with 15°, someone else with 30°. There is also Company like SHELL that prohibit the cold bending of duplex.
Obviously there is a lot of parameters that influence the feasibility of this process. very important is also beending speed and method of bending. A this phase (engineering)is not possible to give an answer but rather a good practicse.
In my opinion 15° could be feasibile, but have to be considered that high pressure condition (96 barg) and very very low thickness do not permit high margine on thinning or wrinkling. Waiting for your experience on this matter.

 

[Guest102023]

15° of bending could be acceptable or it could not.

The relevant parameter here is % strain, the only thing the metal understands. You need to follow ASTM and the construction Code and any technical specifications.

 

[SJones]

Assuming that the pipe will have cathodic protection, then the end user may very well have a strong aversion to cold bending.

https://exchange.dnv.com/Publishing/Codes/download.asp?url=2008-10/rp-f112.pdf

And, if the transported fluid also contains H2S, then they may have a really strong aversion.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[austsa]

Depends on max fibre elongation and whether you plan to do subsequent heat treatment.

 

[TWP]

piping under internal pressure has to be designed per piping design code. pipe design to comply with all design code requirements incl fabrication (incl bending). So, in first instance you must comply with piping design code bending requirements. Rather severe for S31803. In addition to this perhaps Sour service requirement apply (as per ISO 15156-2; former NACE MR0175). Bending results in strain hardening (hardness increases!).

Strain at bend outer radius (extrados) has nothing to do with bending angle; only depending on bend radius.
Doesn't matter whether bending angle is 1, 15 or 30 degr.

I always follow the requirements per piping design code ASME B31.3 + limits per ISO 15156-2 for Sour service (H2S).
I wouldn't bend in case of Sour service unless hardness is surely below ISO 15156-2 limits.
No Sour service > apply rules of ASME B31.3 (cold bending rules).
My advise is to apply a relative large bend radius; as large as possible.
Min. radius recommended 3,5 * OD pipe (if allowed by piping design code of course)

Be aware; pipe bends must be engineered as required per design code(s).


good luck