Longitudinal seam visa-vis helical seam welded pipe 2

[pipexp]

Can any body suggest advantage and disadvantage of Longitudinal seam visa-vis helical seam welded pipe because I am in fix to decied between this two with API-5L pipe. Further, I would like to know what should be preffered between this two. Please suggest.

 

[acedude]

The manufacturing differences are quite different and well documented in the literiture. Howewver, I believe your query relates to the advantages or disadvantages between the two.

One of the few or only advantage of sprial welded line pipe (and the reason for its emergence) is that it is generally less cost, and it can be produced at large diameters, at significantly less cost than longitudinal seamed line pipe.

The disadvantages of spiral welded line pipe are more significant, and have been a focus of considerable research and debate within the Industry for many years. Of most importance and concern is that the quality of the spiral weld can vary considerably amoungst manufacturers worldwide. The most agreed concern is the existance of stress concentrations in the spiral weld, since spiral welded pipe is not cold expanded during the manufacturing process.

In addition, the various design codes require that a joint factor be applied when computing the wall thickness based on internal pressure. The joint factor is dependent upon the material specification, and the "welding" procedure/method used to make the continous spiral weld (i.e. ERW, SAW, etc.)during manufacture.

Each Operating Company generally has their own position regarding use of spiral welded pipe on their projects. Some oil companies do not allow use spiral welded pipe for higher pressure service due to the poor past performance and experience with this type of pipe. Some Companies do not allow use of spiral welded pipe for "on-plot" piping/portions of pipelines inside facilities areas, but may allow use of it "off plot" outside the facilities plot limit boundaries.

There has always been two positions regarding the use of spiral welded line pipe. The people interested and driven by economics will promote the use of this line pipe (since it can be significantly less expensive), while the engineers are very cautious regarding the use of such pipe. I very much belong to the later group, since I have experienced the results of spiral welded pipe failures, resulting fires inside plant facilities, attributed to seam failure of spiral weld.

In addition, it is pointed out that that the maximum shear stress for restrained (buried) hot oil spiral welded pipe segments occurs along the spiral weld, who's orientaion is very close to a 45 degree angle to the pipe springline. This means that if there is significant shut-down and start up events of the line during the operational life, It is certain that fatigue of the spiral weld can be a consideration.

 

[unclesyd]

Here is some good information on Spiralweld pipe that mirrors some of the above information. You will notice that this company only references it's use in various types of water service. There is also some very good information on design, handling, and installation at this site.

Though we have considerable Spiralweld pipe in service it is limited mainly to return water line service.

http://www.acipco.com/aswp/

 

[DrillerNic]

I'd agree- spiral welded pipe is seen as a 'cheap & cheerful' option. With good QA/QC at the mill it can be used for lower risk pipelines- oil say, rather than gas, say.

 

[grampi1]

Use of Spiral in sour service in generally discouraged as it has historically had more problems than straight seam.

Use in oil and gas buried transmission pipelines is all about weld quality and NDE. We have used in oil and know others that have used in gas.

Spiral is great at very large diameters, but typically wall will not be able to fabricate as thick as in LSAW mfg, so this can be a limit.

Spiral is generally discouraged in any service involving axial fatigue loading.

 

[SJones]

Most of Europe's gas is piped through SAWH (helically welded SAW) pipe. Issues with SAWH are issues that can apply to any pipe manufacturing process if the wrong mill is selected to supply. TWI produced a report on the state of the art for spiral welded pipe which is available to industrial members. If you want some increased confidence in the pipe, try staring with ISO 3183-3 as the specification, instead of API 5L, and then audit potential mills using experienced engineers as well as quality personnel in the audit team.

See also:

http://www.google.com/custom?domain...000000;GFNT:0000FF;GIMP:0000FF;FORID:1;&hl=en

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/