An expansion joint is a specially designed component of compact dimensions that allows for differential movements between two adjacent components and that maintains the pressure envelope. This joint can be of all-metal construction or be nonmetallic for low-pressure application; it can be discontinuous as in a packed gland (e.g., TEMA P-type head). In this section the discussion on expansion joints is limited to metallic convoluted bellows.

Many years of the suppliers' experience are incorporated in the design and fabrication details of the bellows; however, it is important for the exchanger designer to appreciate the capabilities of the bellows unit so that problems are not unwittingly built into the exchanger. The decision to use bellows should be made at the initial thermal and mechanical design stage of the exchanger. This section gives guidance on the type, application, design, and analysis; it suggests the scope of an exchanger bellows specification and discusses fabrication and operational aspects.