What is metal bellows expansion joint?

 

 

An expansion joint, also known as a compensator, is a flexible structure installed on a container shell or pipe to compensate for additional stress induced by temperature differences and mechanical vibration.

 

As an elastic compensating element that may be flexibly expanded and contracted, the expansion joint is widely used in a variety of fundamental engineering fields due to its dependable operation, high performance, and compact structure.

 

The expansion joint is classified as either metal or non-metal based on its material.

 

The expansion joint is classified into three forms based on its structural form: elbow, bellows, and sleeve.

 

This article focuses on the metal bellows expansion joint from the aspects of concept, advantages, and application.

 

 

 

A metal bellows expansion joint consists of one or more metal bellows and structural components. It uses the effective expansion and contraction of the working main body bellows to absorb the dimensional changes of pipes and containers caused by thermal expansion and contraction, or compensate for the axial, lateral and angular displacement of pipes and containers.

 

 

 

The metal bellows provide the foundation of the metal bellows expansion joint. Its spring-like construction ensures good flexibility. It might deform variably depending on the working conditions. It absorbs pipeline movement and deformation by twisting and stretching itself, ensuring that the pipeline system continues to operate normally.

 

 

 

Choosing the right material for the metal bellows expansion joint is critical to ensuring its performance and longevity. Metal bellows components are frequently made from austenitic stainless steel and heat-resistant chromium-nickel-inconel alloys.

 

The most popular bellows expansion joints on the market are constructed of stainless steel. Because:

  Stainless steel has a narrow corrosion margin, so the thickness of the expansion joint can be reduced, and the single wave compensation is increased.

  Stainless steel has double the plasticity of carbon steel, which makes it ideal for cold forming.

  For the same service life, the allowed stress amplitude value of stainless steel is around 1.5 times that of carbon steel.

 

  Carbon steel and low alloy bellows expansion joints are suitable for use in environments with temperatures not exceeding 375°C, with a corrosion margin not exceeding 1mm

  Austenitic stainless steel bellows expansion joints are suitable for use in environments with temperatures not exceeding 500°C

  High-grade corrosion-resistant alloy or high-temperature alloy bellows expansion joints can be used in environments with temperatures above 550°C or with chlorides, sulfides, acids, alkalis and other media that are prone to corrosion

 

 Stainless steel grades: AISI 304, AISI 321, AISI 316L, AISI 309S, and AISI 310S

 Heat-resistant chromium-nickel-iron alloys: Incoloy 800/800H (N08800/N08810), Incoloy 825 (N08825), and Incoloy 625 (N06625).

 

 

 

  single axial expansion joint

  universal axial expansion joint

  single tied expansion joint

  universal tied expansion joint

  single external pressurized axial expansion joint

  universal external pressurized axial expansion joint

  single hinged expansion joint

  universal hinged expansion joint

  gimbal expansion joint

 

 

 

  Flanged end

  Weld end

 

 

 

Metal bellows expansion joints can generally absorb three types of displacements.

 

  Axial displacement: The bellows expansion joint compresses or stretches along the pipeline axis

  Lateral displacement: The relative displacement of the two ends of the expansion joint in a direction perpendicular to its axis

  Angular displacement: The bending of the bellows compensates for the angular change of the two ends of the expansion joint relative to the pipeline axis

 

 

 

 

  Sufficient creep stability

  Excellent internal and external corrosion resistance

  High elasticity

  Large compensation

  Long service life

 

 

  Power industry: thermal power generation, nuclear power

  Boilers, steam pipes, turbine systems

  Oil and gas industry

  Chemical industry

  HVAC systems

  Shipbuilding and marine engineering

  Wastewater treatment