The effect of environmental media on the fatigue life of bellows compensators
The effect of environmental media on the fatigue life of bellows compensators
Bellows compensators are commonly used in heating systems for steam and high temperature water. Dead zones, condensation and deposition give chloride ions the opportunity to concentrate and easily cause corrosion fatigue damage to austenitic stainless steel.
When corrosive media are present, the expansion of the bellows is reduced. Cross-sectional fatigue life. Therefore, the influence of environmental factors should be considered when designing the fatigue life of corrugated compensators. It is not enough to focus only on mechanical loads. Measures should be taken in material selection and structure. When selecting materials, suitable materials should be selected according to the actual working medium. Experimental research should be conducted on the corrosion fatigue performance of expansion joints in important parts.
When multi-layer expansion joint structure is used, the inner layer can be made of materials with good corrosion resistance. If the working temperature is not too high, the inner layer can be lined with engineering plastics. In the process, austenitic stainless steel compensators are used to reduce the concentration of chloride ions and adequate deoxygenation process. In the structure, some occasions can consider the use of external pressure jacket type expansion joint structure. This allows the extractive fluid to be discharged through the lower discharge valve without accumulating and concentrating on the surface of the expansion joint. In view of the commonly used steel bellows expansion joint corrosion fatigue for brittle damage, should try to use multi-layer bellows compensator, because only the inner layer in contact with the medium, sudden failure will not occur.
As the dangerous section of the expansion joint is in the local high strain cycle conditions, it is not appropriate to use the post-forming heat treatment process to reduce the forming stress, or by changing the wall thickness to eliminate the corrosion fatigue crack. The location of the corrosion fatigue crack is the same as the fatigue crack in the air, both in the location of higher stress. Single-layer expansion joints appear near the trough of the medium wave, and corrosion fatigue cracks appear on the side in contact with the medium. The measurement method of corrosion potential value is simple and reliable, which helps the experimenter to understand the whole process of bellows crack sprouting, expansion and penetration in the fatigue test.
