field pipelines expansion and flexibility 2

[somacast]

Hello,

The actual case is that some LPGs are being pumped through long pipelines running above ground mostly, and has some buried sections under roads, runs like that for about 20 kilometers, so the majority of the pipelines are exposed, its been there for many years and being well maintained and provided the required CP, the pipes are rested on sleepers every 10 meters approximately, and anchored every 200 meters approximately, and also anchored before and after every road buried sections.

The issue is that the pipes (6 inch and smaller pipes) are expanding freely, and snaking up in shape, such that they hit each other at some points, I was reading through B31.8 but I think I was unable to locate a criteria, I have seen other pipes in field (crude oil pipes) which are provided with a stopper ring surrounding the pipe welded to each sleeper support with about 1 inch on each side gap only, but is it safe to restrict the pipes like that?

The system and plant have been in place for over 29 years now, I have attached examples of some of the excessive locations, the original layout is zigzagged to accommodate expansions but it doesn't seem to be good enough, they try to align them every now and then but they do move again .. also I have attached a small section from google maps to show the zigzag design used.

any thoughts , advises please?

Thanks

 

[somacast]

second attachment

 

[1503-44]

Small diameter (4-12") pipes on sleepers need to be supported at 6-7m maximums to prevent excessive vertical deflections. 4" diameter or less will not usually span more than 3-4m.

There is no requirement to prevent snaking and it is usually not harmful as long as stresses remain below allowable stresses and any stresses due to contact with other objects is not severe. The good thing is that snaking keeps any compressive stresses (normally due to thermal expansion) lower than the axial stress that it took to buckle them from the straight position, but some secondary bending stress will be induced by their new curvature. You can use the degree of curvature to get an idea of the new approximate bending stress.

It doesn't look pretty, but as long as they are not popping up in the middle of the roads, they will probably continue to serve well for a considerable time. The Mideast deserts are full of pipelines that are laid above ground, many directly on the surface without sleepers.

BTW CP is not effective for above ground portions of pipelines. Keep those painted well. Pay attention to possible corrosion where they are buried, especially near the air/ground interface and even more so if the area gets wet. Also pay attention to corrosion and abrasion under the pipes at the sleeper supports.

Provided bending stresses are not too high, for now the short story is, "If it ain't broke, don't fix it." Let them snake around until you can't stand to look at them any longer, or until one pipe starts pushing around the next one.



“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

You don't say what temperature range these pipes are exposed to - just solar radiation?

When it comes to above ground pipes you have two options - you can do it "properly" and create pipe runs with supports with defined expansion loops, kind of like this

Or you can just lay the on the ground with a few sleepers to stop them rusting away underneath and let them find their own place to go when they expand in the midday heat, like errr yours. Agree with ax1e - 10m spacing is long for pipes 6" and smaller. The dip on the smaller ones will be visible when looking along the length but in practice might act as a set of miniature expansion loops.

Which is best?
Define best - the proper way needs a lot of civil works to create a fixed plane and has lots of expensive supports, your example is cheap and cheerful but might result in excess stress / buckle of the pipe.

The biggest risk is that when the pipes expand they fall off the support or otherwise get in a posiiton where they can't return to their previous position as they caught on something. The lines shuffle about a bit then next time the expansion gets worse and worse.

It's called ratcheting or pipeline walking.

Oh and unless each of your buried crossings has isolation joints on either side, this pipeline most definelty does NOT have Cathodic Protection. Also don't really know what your anchors are for or doing. Doesn't sound like a great idea to me.

Those minor zig zags are possible worse than nothing. Often you find the highest stress is at bends of about 15 degrees. Those nes posted will do nothing to relieve stress or expansion.

But they've survived 29 years and if someone goes and inspects them regularly and occasionally goes and moves them around a bit - might be ok. Looks terrible though and it can be hard to know when is the pipe actually yielding as it is bent and when is it still in the elastic zone.

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