Situation
For most of the components in use in chemical plants, such as vessels, columns, piping, valves, seals, hoses, and expansion joints, industry Recognized and Generally Accepted Good Engineering Practices (RAGAGEPs) concerning life cycle and integrity issues exist. Of interest for this article are expansion joints, which often receive less attention than other components in piping systems. Expansion joints, also called compensators or bellows, normally compress rather than expand and provide the necessary stress relief from thermal and mechanical forces, such as movements and vibrations during normal operations. The most commonly used expansion joints are either elastomeric with wire or fabric reinforcements or made of polytetrafluoroethylene (PTFE), a common fluoropolymer used for corrosion mitigation. Major chemical producers have banned the use of PTFE bellows in their plants due to poor reliability, inability to inspect, and numerous failures. Others use them when there is no other option available. However, the correct use of properly manufactured and designed bellows together with correctly qualifying fabricators/suppliers can provide significant advantages for plant design. Such bellows can even increase plant safety and reliability when isolating stress from sensitive equipment like graphite heat exchangers.
Problem
Unlike PTFE-lined piping, PTFE expansion joints have no external support or boundary protection. This shortcoming has led to catastrophic failures resulting in safety, health, and environmental incidents. Failures of PTFE expansion joints have been from both deficiencies in manufacturing and issues related to improper installation or application.
