Pigging through different pipe thickness 1

[MechP]

Greetings all,
I'm having the following issue with a piggable pipeline:
The pipeline has been designed in accordance with ASME B31.4, however the location of the launching and reciever traps has been designed in accordance to ASME B31.3. The piping class indicates that for the pipeline the pipe specification should be API 5L X42 SCH STD. For the lines in the location of the traps the pipe should be ASTM A53 Gr. B SCH XS. The limit between both classes is projected with a flanged joint (one flange SCH XS the other SCH STD, same 300 class), so there is a change in the inside pipe diameter from 7.981" to 7.625", i.e. a change in thickness of 1.78" (4.52 mm).
I understand that a change in thickness in piggable pipelines shouldn't be an issue and is not unusual, but generally this takes place in a welded joint where a smooth 30° transition can be done.
My question is, for the receiving trap, is it a problem to have a sharp change in thickness such as that in this flanged joint? Has anyone had any experience with such transitions in piggable lines?
Thank you

 

[1503-44]

The diameter difference is 0.36" Change in the wall is 0.36/2 = 0.18" Yes that is 4.52mm.

That will be OK.

If those mm were cm, then there would be trouble.
If you can get the pipe welded together, don't worry about the pigs.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[LittleInch]

First off, whoever designed those pig traps to B31.3 should never design another pipeline ever again. All pipeline codes extend to the pig trap to avoid this exact issue.

You want to avoid a sharp edge. It can rip cups and also intelligent pigs don't like it.

Normally you machine a 1:4 slope on the inside of the thicker flange to match the larger ID.

At 8" it's not so bad, but bigger lines you definetly need to do this if someone has made this error in design.

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

 

[1503-44]

ISO maximum wall difference and weld joint design requirements here.

https://pin.it/4pzkrxl

Agree with LittleInch.

As for the pig trap, specify both pressure locks and ASME VIII stamp for the closure. Only the closure.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[SJones]

Still not getting this set up, and terminology "lines in the location of". These should be two B16.5 300 class rated flanges going together - where is the "sharp lip" given the tapering requirements of 31.3, 31.4, 16.5? Should have done the whole trap to ASME VIII and specified the required ID of the two barrels with the minor matching that of the pipeline.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[LittleInch]

Should have done the whole trap to ASME VIII and specified the required ID of the two barrels with the minor matching that of the pipeline

Sorry, but No, NO and NO again.

ASME VIII is the last code you want to use for a pig trap. All the pipeline codes cover pig traps very well and there is no reason to change it to some other code.

So sure you could in theory stipulate the ID of the minor barrel to be the same as the pipeline, but then you end with non standard pipe as the thickness is greater than the pipeline codes, you need to get an AI and approval to the PV codes, you then need to inspect it like a PV and it ends up costing 4 times what it would if you just designed it, perfectly legitimately in in accordance with >90% of all pig traps all over the world for zero advantage. IMHO.

The sharp lip is between the bore of the flange machined to one thickness of pipe and the flange machined to a thinner bit of pipe.

In this instance it's pretty small, but larger ODs and pressures it can become quite large and has been know to rip pig cups and sensors off an intelligent pig.

Don't know why someone has changed from X42 to A53 grade B. It all smacks of a piping engineer designing a pipeline inside a fence boundary or some other artificial point on the incoming pipeline. That hasn't ever worked well IME.

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

 

[1503-44]

A53 is for plumbing and HVAC.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[SJones]

Sorry, but No, NO and NO again

Try telling that to BP. Nearly every pipeline project I've been on ends up with a pressure vessel because the trap manufacturers cannot deal with the materials specifications, or the pipeline welding specifications of Operators, or DNV if that is the pipeline code. They would have to be qualifying welding procedures out of their ears every time. As to AIs and approvals - depends what part of the world you are in.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[LittleInch]

Offshore they may end up with something like that, but the vast majority of traps onshore can be made to the pipeline code.

Also depends who they ask to make it....

A pressure vessel is still to be avoided for a pig trap design if at all possible.

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

 

[1503-44]

.4 or .8 everywhere on pipelines.
For everything.
Redline every piece of B31.3 you find.


A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[MechP]

Thank you all for your comments,
My understanding is that the change in class was agreed with the client due to delivery times of fittings such as the barred tees, elbows and flanges associated to both traps.
Poor project planning I suppose.

 

[GD2]

Different customers specifies differently for the pig traps.
As Steve Jones says BP applies ASME Sec VIII, other applies Pipeline Codes and some uses the Facility Piping Code.
While ASME Sec VIII is rare, majority of the traps follow Pipeline Code or Facility Code, depending on the Spec Break, which usually happens at the fence line through a transition piece.

I would say from design perspective all codes will work. It's a pressure design. the common design is the Closure that requires ASME Sec VIII.

In the current configuration, all it can happen is the likelihood of damage to the pig due to the ID mismatch.

Obviously, all pigs have a clearance with the barrel ID but it will be ideal, if the Sch XS flange is given a smooth taper (by onsite machining) to prevent any damage to the pigging tools.

GDD
Canada

 

[1503-44]

The problem with pipelines and B31.3 is that .3 only addresses pipe design and that's only about 10% of the work.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.