The degradation of metal vessels properties working under pressure during a long term use

Mechanical properties and metal structure of all-metal gas tanks made of medium-carbon steel after different periods of service have been studied. It has been observed that the duration of the service does not significantly influence on the strength of the metal tanks, but it leads to some reduction of plasticity and toughness decrease. It has been observed that toughness degradation appears after 25-30 years of tanks exploitation. At testing of the Menazhe and Sharp specimen it was also found out that temperature dependence of metal tanks toughness varies with the service life. It has been noted that the metal microstructure does not change under continuous operation. Therefore the decrease in properties after long-term use of the cylinders was caused by the metal substructure. Exploration of the mechanism and kinetics of the substructure changes requires special studies. On the strength of these data the need to improve the existing methods of periodic inspection (as a function of service time) of all-metal steel cylinders, as well as set-ting limits of the life-span of these vessels has been shown