A hot pipe gets longer, and on a long run that growth has to go somewhere. A pipe expansion joint puts a flexible corrugated bellows between two flanges so the movement is absorbed instead of bending the pipe. Use the buttons to look inside.
An expansion joint is a short section of pipe made to flex. Instead of a rigid length of tube, it has a corrugated metal bellows between two flanges. It is fitted into a pipeline wherever that pipeline is expected to change length, and it gives the unavoidable movement a safe place to happen.
From the outside it looks like a bulging collar with rods around it. The useful detail is the corrugation: the wrinkles in the metal are what let it behave like a spring. Looking inside shows how a solid-looking steel pipe can stretch and squash on demand, and why the rods and sleeve are there.
When a fluid warmer than its surroundings flows through a pipe, the pipe warms up with it. Metals expand as they get hotter, so a long run of pipe grows measurably longer — often by more than the eye would expect.
If both ends of the run are fixed, that extra length has nowhere to go. It either bows the pipe into a curve or pushes hard against the anchors and supports, stressing the whole line. A joint is placed to relieve exactly that.
The corrugated bellows is the flexible element. Because its walls are shaped into folds, it can shorten and lengthen like an accordion. As the pipe grows the bellows squeezes; as it cools it springs back, so the pipe itself never has to bend.
Tie rods run along the outside from one flange to the other. They limit how far the bellows can travel, so it flexes enough for thermal growth but is not over-stretched or pulled apart by pressure. The nuts on the rods set those limits.
A smooth liner sleeve sits inside the bellows, in the path of the fluid. It shields the thin corrugations from the flow, so the stream cannot cause vibration or wear the folds thin from the inside over the years.
Fixed anchors on either side take the push and pull of the line. Working with the joint, they keep the pipe in place while the bellows quietly takes up all the movement the changes of temperature create.
Because metal grows when it is heated. A long pipe run heated by hot fluid gets longer, and if that movement has nowhere to go it bends the pipe or loads its supports. The joint gives the growth somewhere to be absorbed.
The corrugations flex like a spring. As the pipe lengthens the bellows squeezes; as it cools the bellows stretches back. The metal never has to bend, so it is not stressed.
They limit how far the joint can move. The rods run from one flange to the other, so the bellows can flex for thermal growth but cannot be over-stretched by pressure thrust or pulled apart.
The smooth inner sleeve shields the corrugations from the flowing fluid. It keeps the flow from causing vibration or wearing the thin bellows walls from the inside.
Anywhere a hot pipeline changes length or a machine vibrates: district heating, steam lines, pump connections, and long runs between fixed anchors.