The expansion joints are applied to pipelines, which are altering their lengths due to changes in temperature and pressure, as well as to pipe systems, which are subjected to vibrations. There are four different fields in which the expansion joints can be applied:

Heating systems
Power plants

These fields demand expansion joints with superior specifications, high reliability, quality construction and long life expectancy. Metalloviotechniki manufactures expansion joints using bellows, which are supplied by BOA AG.

These bellows consist of many thin stainless steel layers (Drw. 2). The multi-ply expansion joints, contrary to the single-ply ones (Drw. 1), provide great elasticity, noise reduction and a high degree of safety in the case of rupture.

Bellow material
The multi-layered bellows are constructed by high-grade chrome-nickel steel (AISI 321, 316ti), offering a high resistance against aging, temperature, UV-radiation and most of aggressive media. Upon request other stainless steel alloys may be used, for example AISI 309, 310 provide resistance to high temperature conditions and Nickel-based alloy 825 is suitable to resist the sea water corrosion on the bellow.

The end parts of the expansion joints may consist of stainless steel (AISI 304, 316, 321, 309, 310), of mild steel (St37, St60). or of many other materials (Cu, Al, Cu-Sn). These materials can be used for the production of the flanges, whose dimensions are according to the international standards (DIN, ANSI, JIS) or according to the customer's request.

For the protection of the bellow and for a smooth flow of the medium, an internal sleeve should be welded at the expansion joint. This is recommended wherever the following conditions are to be faced:

Abrasive media
Flow velocity of liquids, u > 3 m/s
Flow velocity of air, steam or gas, u > 7 m/s
Big temperature difference

Types of expansion joints
According to the direction of the bellows movement, expansion joints can be classified in the following categories:

Axial expansion joints
Angular, hinged expansion joints
Lateral expansion joints
Universal expansion joints (compensation of axial & lateral movement)
Special Expansion joints
Vibration absorbers