Bend to Bend welding without straight length

[nanil]

For an 8” 2500# pipeline (API 5L X60), we have made cold bends of 40D. For bending we have considered min 1.5m straight length at the start and end of bends during bending.
However due to site alignment requirement, we will have to cut the 1.5m straight length and weld the cold bends directly at one location. Is this permissible. Please advise. I checked ASME B31.8 & API 1104 but could not find a direct reference to this.

 

[LittleInch]

There's no such thing as a class 2500 pipeline, you have a pipeline worth a high design pressure.

Anyway, yes this is permissible but you might have issues with the pipeline ovality if you cut it back too far.

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[0707]

ovality and stress relieve of cold bends

luis

 

[alchemon]

CFR 192.313 covers the bending requirements for field bending of regulated gas pipelines.

 

[LittleInch]

SO what does it say wrt the lenght of the unbent tangent?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[alchemon]

It does not specify a minimum tangent. This is more a function of bending equipment to be used anyhow. It does indicate that you can bend a circumferential weld provided that the weld is NDT.

 

[nanil]

Thank you everyone for the responses. To add, our client has specified that the start or end of the bend shall not be any closer than 1.5 m from the pipe end or within 1 m of a girth weld. Means there should be minimum 1m from the bend portion to the weld.
Is there any specific code reference to this requirement? Is it only to avoid ovality?

 

[LittleInch]

N Amil,

There's no code reference I've ever seen, but it is simply custom and practice to avoid any ovality issues and also for cold bends you need a straight length for the machine to work, so cutting back 1m would just be a waste of pipe normally. Someone might be worried about the work hardening that occurs when you bend the pipe, but nowadays that shouldn't be an issue.

for an 8" pipe, you should be able to cut back to 300mm from the end of the bend without an issue.

If you have a particular situation requiring a shorter tangent length then you will need to apply for a deviation to the specification for that location and argue it out with the client. that will put some onus on them to come up with an alternative if you can't fit it in.

Why can't you use a formed bend in this instance at 5D?

If that's the only alternative then express that to the client saying we can do this or we can do that. But that will be more expensive and take longer. What do you want to do??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nanil]

Thank you @littleInch. We have already done the cold bending with 1.5m tangent length. Because of alignment issues at one location at site we have to cut down the straight length. Best way as you said would be to get the deviation discussed and approved with client. But prior to that, i wanted to be sure about any Code requirement.

 

[LittleInch]

One thing to add into the procedure is to do some accurate ovality measurements along the bend before you cut it back, however there may be some cold springing of the pipe if you cut it back too far.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[alchemon]

N_Anil, I agree with the suggestion to use preformed bend(s) (aka a fitting) here instead. The simplest solution will be to cut the line back on both ends, and drop in the fittings and pipe length. Trim the fittings back slightly as required. And then field coat.

Who is going to verify the ovality/cold springing/etc.? We can discuss it all we want here but what will the guys in the field do to make it fit? Are you going to sit out on site to make sure it is done properly? We have also uncovered one of the reason that fittings were invented - the area is too tight to bend. I would pitch the client on that as being the best solution, and then have the Contractor price up a change order to make it work.