Orientation of Seam Line of welded pipeline 2

[tarekdata]

Dear All Piping expert

we are doing a pipeline and piping work in iraq.

We have pipe 52" API 5L X60 welded oil transfer line. the pipe is welded.

my question : is there any standard or regulation controlling the orientation of pipe's seams " line of longitudinal welding " , by another word can the pipe fitter place and weld the pipes in a way where all of longitudinal weld located at the same polar coordinate " i.e all seam lines are place on top or bottom of line " ? or we have to make an alternative opposition of polar angle of seams ?

Would would be the justification for such regulation " if it exist " from Engineering and corrosion point view ?

 

[SJones]

BS 4515-1:

"When a pipe with one longitudinal seam is used, this seam shall be
located within the top half of the pipe circumference and the
longitudinal seams of adjacent full pipe lengths shall be offset by an
angle of approximately 90º or by a circumferential distance of
approximately 250 mm, whichever is the smaller."

The engineering and corrosion points of view are:

1. Fracture arrest of cracks initiated in the weld zone of the seam
2. The greatest accumulation of liquid water as a corrodent would be expected at the bottom of the pipeline and the seam, being a different material to the pipe body, might give rise to preferential corrosion

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

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

 

[tarekdata]

Dear Sjones,

thanks for reply.

the point of making seam line on the upper part of pipe, see the attached sketch and please confirm the proper angle as per the provided scale on the sketch.

that will work for one spool, what is about the consecutive spool, shall it follow the same angle or I have to turn it CCW by 90 Degree to avoid keeping all spools on the same run.

Is there any Standard regulating this condition ?

 

[zdas04]

The corrosion that SJones talks about is not a small thing. I've had 6 lines that failed due to MIC. 5 of them had the longitudinal weld seam on the bottom of the pipe. The waste products of the microbes seems to have a greater tendency to initiate pitting in the HAZ of the longitudinal weld.

The 90° the code is talking about is satisfied by placing one weld at about 45° CW from the TDC and the next weld about 45° CCW from the TDC. I've never seen a problem with putting all the welds near TDC but I work in gathering systems where we tend to design systems with max stress during operations of less than 20%. In cross country pipelines this would be seen as wasteful and they tend to design much closer to SMYS. In gathering systems we have so little control over the fluids in the line that I think the low stresses are justified. All of the cracking modalities require relatively high stress, so a crack-propagation protection scheme seems to make a lot of sense.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist

 

[tarekdata]

Dear ZDas,

thanks for your feedback , would you please elaborate more about the TDC , the acronym is not well know for myself.

 

[BigInch]

top dead center

I tend to locate seams along what would be the neutral axis of a pipe, if bent in the vertical plane, ideally putting seams at 3 O'clock or 9 O'clock.
If welding sequential pipes, or double longitudinal seamed pipe, I use 3 and 9 O'clock as base lines, but then offset the seams by +15% then -15%, putting weld seams on the first pipe at approximately 4 and 10 O'clock, then the next pipe at approximately 8 and 2 O'clock positions, or visa versa.

 

[LittleInch]

The other point is that when doing this for piping, most people want to avoid cutting into the weld seam when adding fittings such as weldolets or similar items. These tend to be at either 0, 90, 180 or 270 degrees, hence zdas04's +45, -45 degrees from TDC makes sense to me.

For pipelines I agree with BI.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

Between LittleInch and zdas04 you should have all the advice you need- I was going to add LittleInch's point, because I've seen people cut through the weld seam to add fittings at the normal locations many times. Alternating the weld seam between -45 and +45 degrees from top dead centre is your best bet.

 

[Duwe6]

TDC = Top Dead Center, i.e. 12 o'clock.