Why do bellows expansion joints fail?
Release time:
2021-05-27
The reason why bellows expansion joints are widely used in many industries is that, in addition to their outstanding compensation capability, reliability is the key factor for bellows expansion joints. However, reliability is ensured through multiple stages—including planning and manufacturing—and neglecting any one of these stages can lead to a reduced service life or even failure of the expansion joint.
By analyzing the failure causes of bellows expansion joints from most manufacturers, we found that failures during operation mainly manifest as corrosion-induced leaks and unstable deformation, with corrosion-related failures being more common.
An anatomical analysis of corroded bellows reveals that corrosion failures generally fall into two categories: pitting corrosion and stress-corrosion cracking. Among these, chloride-ion-induced stress-corrosion cracking accounts for approximately 95% of all corrosion-related failures. Therefore, by correctly selecting the manufacturing materials and structural design of bellows, reasonably planning waveform parameters and fatigue life, and ensuring equipment quality, we can significantly enhance the safety and reliability of bellows compensators.
The compensation capacity of a bellows compensator depends on its fatigue life. The higher the fatigue life, the smaller the compensation capacity per bellows wave. To reduce costs and increase the compensation capacity per wave, the lower the fatigue life, the greater the meridional bending stress induced in the bellows due to displacement, and the higher the induced stress in the rubber compensator, significantly compromising the stability of the bellows. When the bellows are designed for a short service life, not only are the radial induced stresses high, but so are the circumferential stresses, causing the bellows components to rapidly enter plastic deformation and ultimately leading to bellows failure.
The selection of data for bellows compensators is also appropriate. In addition to the working medium, operating temperature, and external environment, the choice of material for the bellows should also take into account the possibility of stress corrosion, as well as the impact of water treatment agents and pipeline cleaning agents on the material. On this basis, and considering the welding formation of the bellows material and the cost-performance ratio of the material, we can optimize the working conditions and select suitable materials for manufacturing bellows that meet practical requirements.
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