Why do pipelines have U shaped bends every now and then?

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Wouldn’t that make impossible for “pigs” to go trough resist flow, make cavitation acumulate grime and other piping problems?

Surely they have a reason to be but I have no idea what it is

In: Engineering

Its exactly what you said it does.it keeps dirt and junk away in the bend instead of going even further and causing an even bigger mess

As the horizontal pipes expand and contract with temperature changes the U sections can flex to absorb the length changes.

What you describe sounds like a water trap. Every sewage pipe have a water trap before it is exposed to the inside of a house. As the name suggest these trap water so that there is no contact between the air in the sewage pipe and the air in the living space. This ensures that the smelly gasses from the sewage will not seep into the living space and make it smell like sewage. These water traps is usually detachable so that if you need to maintain the sewage line you can remove the water trap.

The metal pipe expands when it gets warm and contract when getting cold. So the U bend is there so when the part in between expand or contract the pipe there can bend a bit. The alternative is that you need to make the pipes thicker and the stand along stronger to hold them in place.

It might make pumping a bit harder but is make construction a lot cheaper

On a long bridge, you will see a [Expansion_joints](https://en.wikipedia.org/wiki/Expansion_joint) with meral on the road and a small gap that exist there for the same reason of expansion and contraction.

As somebody that has worked in the design and construction for the Oil and Gas industry in Canada for years, I can say that /u/old_liberal is correct. These are for thermal expansion. You may understand that some items increase or decrease in size as the temperature changes.

This also happens with steel, and is captured with ‘bends’ or larger elbows (usually 3x or 5x the diameter of the pipe). This will permit the ‘pigs’ to still pass through the pipeline to either clean or inspect (most inspection pigs would require a minimum 5D bend (5x diameter of pipe).

Let me know if you have other questions, as I no longer work in O&G but I still enjoy the design of the systems.