Compressive Axial Force: Pipeline

[JT100]

I know that over a pipeline the effective axial force is compressive (negative), and that it builds up to a constant value over the so called 'anchor length'. The 'anchor point' being the point at which the effective axial force in the pipeline equals the friction between the pipeline and the seabed, and where the pipeline no longer expands. This results in the force profile that most pipeline engineers will be familiar with. I was wondering though, does this force profile include the tie-in spools? As I'd of thought the tie in spools will, in some cases if not all, be in tension?

 

[BigInch]

If you're talking about the "V" tie-in spools I know about, there should be no forces there during installation. The pipeline ends must be free; not forced into position during installation when the spool is set into place and connected. Tie-ins usually include at least two misalignment flanges and ball joint, with a take-up for length variations, and a relatively flexible overall configuration that should not develope significant stresses when under loads.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[JT100]

Thanks BigInch, apologies I was meaning during operation, after tie-in. The effective axial force resulting from pressure and temperature etc.

What do you mean by "V" tie-in spools, are these the vertical tie-in design that tend to be used in deep water?

 

[BigInch]

You need to provide a flexible configuration. Pressure stress in the axial direction will be tension, temperature increase is compression, decrease is tension. Depends on the net, but you need to provide enough flexibility in the tie-in configuratioin so that those stresses will be below allowables.

The tie-in spool I used to use was a swivel flange, a length of pipe, a ball joint, a length of pipe and another swivel joint. Overall length was at least 40 feet and not really a V as the vertex angular rotation was limited to relatively small values. We would lower those with a spreader bar to divers and they would swing it in place and blot it up. They probably have a more expensive way to do it now using a "hydrolock" fitting or something.

As you can see here,

http://www.oilstates.com/fw/main/Deepwater-Pipeline-Products-426.html

http://www.oilstates.com/_filelib/F...ie-InSled.pdf?FileName=Mid-LineTie-InSled.pdf

there are a number of different methods you could use.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[BigInch]

Found it. This page has the misalignment and ball joint fittings,

http://www.oilstates.com/fw/main/Pipeline-Fittings-431.html

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/