The failure forms of ordinary corrugated pipe mechanical seals are mainly caused by the following sealing failure forms of corrugated pipe mechanical seals and their auxiliary systems currently used.

1. Sealing failure caused by bellows failure or breakage. During the use of corrugated pipes, the stiffness of the mechanical seal or elasticity of the fire pump will gradually decrease, and this phenomenon of reduced elasticity is usually referred to as loss of elasticity. Experiments and practical applications have shown that when the loss of elasticity of the bellows exceeds 18% to 20% of the initial design compression, the entire bellows mechanical seal will leak. The loss of elasticity of the metal bellows machine seal is not obvious when the temperature is below 200 ℃, but when used at high temperatures (over 300 ℃), the pump quickly leaks after driving. When the machine seal used was removed and the Naichi mechanical seal was measured, it was found that the height of the metal bellows component decreased by an average of 2-3mm compared to before installation. The loss of elasticity of corrugated pipes is mainly due to permanent deformation or relaxation of mechanical seals in multi-stage pumps under stress. Another situation is that the working medium crystallizes or solidifies in the gaps of the corrugated pipe, reducing or losing its deformation ability. Therefore, high temperature and load are the main causes of bellows failure [1]. In addition, under high temperature and high compression or contact pressure of the corrugated pipe, the corrugated pipe may break; The higher the temperature and the greater the load, the higher the probability of the corrugated pipe breaking.

2. Sealing failure caused by excessive wear of graphite rings in paired friction pairs. Usually, when the failed machine seal is removed for inspection, it is found that the graphite sealing ring is severely worn. Through analysis and experimentation, it was found that the end face specific pressure of the metal bellows machine seal is affected by the effective diameter of the bellows, which changes with pressure. Due to excessive pressure, the friction of the friction pair is severe, and the graphite ring is excessively worn, causing leakage.

3. Sealing failure caused by surface hot cracking of hard alloy rings in paired friction pairs. After inspection, it was found that the hard alloy ring of the sealing friction pair had many radial cracks of varying thicknesses diverging outward from the center of the hard surface, which were caused by thermal cracking and seal failure. The main cause of hot cracking is excessive local thermal stress, among which the difference in linear expansion coefficients between the hard alloy ring and the ring seat materials, whether to use a weld overlay structure or a monolithic structure, and whether the type, flushing method, and flow rate of the flushing liquid in the sealing cooling flushing system are appropriate may all cause hot cracking of the sealing end face.