Expansion joint Expansion joint can also be called pipe expansion joint, compensator, expansion. Expansion joint is divided into: corrugated expansion joint, sleeve expansion joint, square natural compensation expansion joint and other major types, 1. Compensation for expansion deformation caused by heating of absorption pipeline in axial, lateral and angular directions. 2. Absorb equipment vibration to reduce the influence of equipment vibration on pipeline. 3. The amount of deformation of pipelines by absorbing earthquake and subsidence. Because of the heat expansion and cold contraction of the pipe, so for the pipe, it is necessary to produce the stress and push tension of the pipe wall; The stress on the wall of the pipe affects the strength of the pipe, and the push and pull force increases. The fixed bracket of the pipe should be made large to withstand the push and pull force generated by the pipe expansion. Therefore, the variable opening method compensated by the ductile iron pipe mechanical joint fittings is used to reduce the stress and thrust of the pipe wall. The expansion joint is mainly used to compensate the expansion deformation caused by the temperature change of the pipeline, and also to compensate the length of the pipeline due to the installation and adjustment. It is mainly divided into three structural forms: wholesale elbow expansion joint, bellows expansion joint and casing expansion joint.