Thermal Expansion of underground cross-country pipelines

[IFTI]

Would appreciate your help on below question:

How we can compensate thermal expansion/contraction of cross-country pipelines,
1) when right-of-way is ALSO one of the constraints and
2) When there is no right-of-way limitation.

Is there a way to compensate through installation of expansion joints & expansion bellows (in concrete culverts, where a visual inspection of both is possible at least)?

Thanks for the feedback.

 

[alchemon]

What is the fluid you are moving and operating conditions of the fluid?

Also - when you say “cross country” what do you mean. Is the thing running from Texas to Canada? Or are you asking about a specific area (say southeastern US) etc?

 

[LittleInch]

Is this a general or specific question?

Needs more information on this and your knowledge and experience.

Normally you don't build below ground expansion loops.

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

 

[1503-44]

Normally no "compensation" of thermal expansion stress is required for all products typically transported via underground cross country pipelines. When pipe is straigh, it is fully restrained by up and downstream pipe segments. Problems may be introduced where such is not the case, or where soil cohesive strength varies radically, or some unusual pipe configuration is needed that might cause misalignment of pipes. In that case you may need to provide expansion possibilities by extra means, such as when crossing active fault lines, where pipe might be buried in loose sand, surrounded by a styrofoam-type material, or the crossing made above ground. I have designed cross country cold (-30C) liquid ammonia pipelines, where tension introduced by lower op temperatures, created higher combined stresses, to be placed inside a culvert type assembly, entirely free of soil, and long molten sulfur pipelines placed entirely on piperack structures and with typical expansion loops, but those pipelines are far from the usual case.

In any case, when you see high thermal stress in your calculations, the only effective solution is to provide flexibility that reduces that stress. Increasing wall thickness only increases the associated thermal forces, so that quickly becomes counterproductive and requires massive anchor blocks whereeveryoucannotkeep pipe relatively straight, in both horizontal and vertical planes.

 

[KevinNZ]

I have seen a number of buried hot water pipelines with vertical expansion loops above ground.

 

[saplanti]

Change of direction underground is the general practice. However this may need to be supported by pipe stress analysis depending on the temperature difference between construction and operation.

 

[IFTI]

Sorry for late reply.
This is actually a very general question in regards to movement of DITBIT (Diluted Bitumen), in areas where the ambient temperature drop below - 29 degree C during extreme cold (i.e., Northern USA or Southern Canada) or vice versa.
With building expansion loops for underground pipelines, i mean not to construct it underground but vertical expansion loops in the section of pipeline exposed to atmosphere and inside concrete vaults. From piping layout point of view, My understanding is that the bends or change in direction can also accommodate some of the thermal expansion of underground pipe. Would like to know another means of taking care of expansion. Thanks.

 

[LittleInch]

Well you need to give us something here in terms of installed temps vs operating temps.

What you can do depends hugely on route and number of bends, pipe soil friction properties, external coating, Design pressures, wall thicknesses as well as temperature difference.

I've usually found that once you get much above about 60 to 70C temp difference between installed and operating you run into serious issues at bends and end movements.

Many DILBIT high temp lines raise the installed temp by running hot water through directly before burial and compaction to "lock in" the expansion stress.

Hover vertical AG bends on a buried line also cause big issues. At the buried A/G interface practice shows this is a major corrosion hot spot as the CP becomes ineffective 10-20cm below the surface, but there is repeated movement and hence damage to coatings. Now instead of two locations where this could happen you now have dozens. Plus the pigs don't like it much.

You do get below ground vaults or expansion boxes, either air filled or foam packed to allow for the expansion. How these work over time is not clear as once you bury it you can't see it no more! Again these can become corrosion hotspots as CP is less effective in most of these and/or they fill with water and sand etc.

Some fault crossings designed to allow movement use LECA -

https://www.leca.co.uk/lecar/lecar-lightweight-aggregate-characteristics/

or similar "non cohesive" backfill.

but really try not to put in anchor blocks. They can become enormous if you're not careful.

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

 

[1503-44]

What is important is to realize that air temp is different than the temp of a buried pipe with oil flowing inside. I dont think you will have such low temperatures in the pipe or dilbit itself, certainly not when flowing. You may even be heating the soil a little. Even if pumping stops for several days the line will still stay warm, but it certainly could eventually cool to earth temp if shut down for extended times.

Anyway try to get a handle on minimum underground temperatures.

Pipelining dilbit in Canada's cold weather is not a new thing. Do you know of anything different that is complicating things here?