Why do gas pipelines run straight for a few hundred metres/yards then do a bit of a U-bend, straight run for a bit, then another U-bend etc. Why the bend? No valves or anything where the bend is.
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There is a phenomenon in fluid systems called “water hammer”. It is named because it was studied in water systems, but it exists in all fluid systems. When water is moving, it has momentum, and that momentum is based on velocity. The higher the velocity, the higher the momentum, and the more severe the water hammer if a pressure transient were to occur.
Additionally, these piping systems are subjected to a wide range of temperatures, and will expand and contract with the temperature. If the piping were completely straight, and it expanded, it would have to buckle somewhere to accommodate the added length, and if it contracted it would put a lot of stress on the flanged connections.
To mitigate these effects, engineers put the bends in there. The zig zag shape gives the piping some room to move for thermal expansion and contraction so it can flex instead of break, and breaking up the long runs of straight pipe reduce the flow velocity and shorten each individual run of pipe to minimize the severity of water hammer transients.
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