Bent pipe in lieu of fittings
Bent pipe in lieu of fittings
(OP)
We are having problems locating the proper fittings, especially in larger diameters, for use in hydrofluoric acid service. A106 would seem to indicate that the use of bent pipe is acceptable as long as it meets the material requirements set forth for the pipe specs. My internal inquiries bring about concerns for SCC as a result of the bending process as well as a few other less serious concerns. Thus far I have not been able to find anyone who has used bent piping in HF service. I am not thrilled with the prospect of using seamed fittings. Are any of you aware of bent piping being used in HF acid service, H2S service or other services subject to SCC, SOHIC and such?





RE: Bent pipe in lieu of fittings
What is the concentration and temperature of the hydrofluoric acid?
RE: Bent pipe in lieu of fittings
Concentrations of HF are around 90% while temperatures range from ambient to ~150F. We are dealing with an HF Alkylation unit. I haven't been able to find any specific guidance condoning the use but on the other hand I haven't found anything prohibiting its use either. API-751 doesn't address the issue. The current mindset is that if there is nothing stating it is okay then we are going to assume it is unacceptable.
Would using properly manufactured bent pipe be an worse or provide more potential for problems than using a seamed fitting?
RE: Bent pipe in lieu of fittings
This approach can greatly reduce the number of fittings, and fitting welds in a system and improve overall reliability.
The most common use is for long radius elbows, not much strain and it assures smooth interior surfaces.
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Plymouth Tube
RE: Bent pipe in lieu of fittings
I have seen bent piping in lieu of fittings in catalyst transfer service which for all intents and purposes is not process piping. Failed piping in these locations can typically be replaced without impacting unit throughput.
I see the value of using bent pipe in place of fittings I am just having a hard time finding support to do so.
RE: Bent pipe in lieu of fittings
Can they be made from pipe?
Then follow those rules.
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Plymouth Tube
RE: Bent pipe in lieu of fittings
RE: Bent pipe in lieu of fittings
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Plymouth Tube
RE: Bent pipe in lieu of fittings
Is bent pipe that has been properly fabricated in a manufacturer's shop in accordance with the pertinent pipe codes and in keeping with the customer's material specs any more susceptible to SCC, SOHIC, etc than corresponding forged fitting? A forged fittings is extruded and then pounded into shape. Bent pipe is extruded and then cold or induction bent into shape. If both meet the same carbon content, residual element, carbon equivalent, tensile strength, hardness specs and have undergone heat treatment and the requisite testing such as RT or UT are they for all intents and purposes the same?
RE: Bent pipe in lieu of fittings
RE: Bent pipe in lieu of fittings
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.
RE: Bent pipe in lieu of fittings
That is also my take on the matter. Unfortunately, my take is not the final say. Part of my search is to find code cases or documented instances of the use of bent pipe in hydrocarbon service with particular emphasis on H2S or HF service. We are currently of the mindset that if we haven't seen it we won't use it, even though it is fully accepted within the governing codes, because there maybe something not covered in the codes that will cause a problem. Organizationally, the best way to overcome this reservation is to see proof of use.
RE: Bent pipe in lieu of fittings
http://ballots.api.org/ecs/sc5/ballots/docs/5LIB_b...
RE: Bent pipe in lieu of fittings
Excellent!! I'll have to bring this to the attention of our materials folks. Much appreciated.
RE: Bent pipe in lieu of fittings
From the Nickel Development Institute publication 10-074 regarding materials in hydrofluoric acid, hydrogen fluoride, and fluorine... for carbon steel to resist HIC or other hydrogen-induced phenomena, carbon steel should be low strength, low sulfur grade with a maximum hardness of 22 HRC.....
http://www.nickelinstitute.org/~/Media/Files/Techn...
RE: Bent pipe in lieu of fittings
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.