What is meant by expansion joint and Where expansion joints are used in refinerieswhythis type joint used now?

Expansion joints are used on long runs (over 100 feet) of pipe or ducts where the expansion of steel will create stress on the pipe or its supports. for every 1 degree change in metal temperature the pipe will expand 6 millionths of a foot per foot of length. on a steam pipe 400 foot long carrying 750 degree steam this expansion would amount to a change in length of the pipe of 1.632 feet. this could tear down the supporting structure if this expansion weren't relieved by an expansion joint every 100 feet.

expansion joints could be flexible corrugated pipe, reinforced rubber sheet, sliding pipe joints, or expansion loops, among other things.