Abstract: Spent acid treatment unit is featured by large pipe diameter, high temperature and extremely low allowable stress on equipment nozzle. With the compact layout of the unit, it is unable to absorb the thermal expansion displacement of the pipeline through natural compensation, so expansion joints need to be installed in the pipeline system to reduce the pipeline stress. This article introduces the relevant standards and applications of expansion joints, and lists the common types of expansion joints and the types of absorption displacement. Taking the typical pipeline system in the unit as an example, this article compares the design schemes of expansion joints. It is concluded that the use of single gimbal hinged expansion joint in pairs is superior to the use of double tied expansion joint in reducing the equipment nozzle stress. The calculation of blind plate force and the design of expansion joint piping support are discussed.

Key words: spent acid treatment unit, metallic expansion joint, allowable stress on nozzle, blind plate force