Use of 4D Bends for 28" topside piping in offshore platform.

[pipexp]

For development of one of oil field in offshore, we are in the process of installing an unmanned well head platform. The well fluid (Mainly gas) from the said unmanned platform is to be transported to a process complex via sub sea pipe line of size 28". During detail engineering for top side modification at the process complex it is found that routing of the pipe line with 5D bend is difficult in the topside of the platform.
Therefore, it has been suggested by the agency involved in the construction of the top side portion of the pipeline that the top side of the pipeline to be routed with minimum 4D bends radius and sub sea portion of the pipeline to be routed with 5D bend.
In my company so far all sub sea pipelines are routed with 5D bends only. Therefore I would like to know your view /suggestion w.r.t to pipeline maintenance concerning the following points:

Pigging of the pipeline with scrapper pig or any other pig with min 4D bend radius.
Intelligent pigging min. 4D bend radius.
Any other pipe line maintenance related problems with use of 4D bend.

Your kind and early response on the above issue shall be highly appreciated.

 

[GregLamberson]

pipexp

As far as intelligent pigging, it all depends on whose pig you use, you'll need to get the specs from them and ask if their pig naviagtes a 4D.

Most utility type pigs (batching, cl;eaning) can pass through a 3D, so 4D should be okay, but the smart pig will be the decider.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Many scrapers will pass a 1.5 D Ell. Its going from the bottom leg of a branch into a Tee that might cause problems. As Greg said, instrument pigs vary. They used to be very long and could not pass <5, but now many are divided into short hinged segments which can navigate quite well smaller radaii, but in any case do check with your service provider.

5D is not usually convenient topsides for process piping, but on the pipeline from the launcher down it normally isn't too much trouble.

http://virtualpipeline.spaces.msn.com

 

[MDSPE]

A 4D bend will no doubt be an induction bend. There are various pitfalls in incorporating a 4D bend into a pipeline intending to be pigged. You will probably need "mother pipe" that will exceed the SMYS of the line pipe so that the post induction tensile strength of the bend will be at least the value of the line pipe. The D/t ratio of the pipe will need to be checked against out of tolerance ovality for pigging and code requirements. Typically specs call for a 5D bend when they should be calling for a MINIMUM bend of 5D since the Induction bend standards typically exceed code requirements for radii of less than 5D. It all has to do with D/t ratio and post bend SMYS. If you furnish the pipe for the 4D bend, make sure you provide enought for them to complete a proto-type bend that will meet your pipeline spec. The ovality issue for the 4D bend may impact certain pigging tools but can probably be accommodated by pigging specialists.

 

[pipexp]

MDSPE(Petroleum)

I have not understood how the SMYS value shall change in 4D bend but not in 5D bend. I think the condition is applicable for both 4D as well as 5D bend. Further, if grain structure does not change after hot induction bend the there is less likely hood of change of SMYS.