1 1/4" Axial Expansion Joint Screwed BSPP VS9843Screwed BSPP, Stainless Steel Bellow, Aluminium Outer Cover, Steel Connections Rated PN10, Temperature 80C to 427C. An expansion joint is used to absorb thermal expansion or contraction of pipes, ducts, or vessels caused by temperature changes. When a pipe or duct undergoes a temperature change, it expands or contracts in length, and if the system is rigidly fixed, this movement can cause damage or failure of the system.