In conclusion, under the working pressure, the circumferential assembly gap at the root of the weld will lead to a stress concentration of 3 times of the working stress at the root of the weld; The welding residual stress of thick wall weld has reached the tensile strength of valve body material, endangering the structural safety of valve body. Therefore, post weld heat treatment can refine the grain size of weld and heat affected zone, reduce the welding residual stress value and improve the fracture toughness of welding structure according to the requirements of the bidder. However, due to the particularity of the structure of the all welded body pneumatic ball valve, the all welded body cannot be subject to post weld heat treatment.

Consider pressure test conditions
When designing and calculating the bellows compensator, the designer usually only considers the stress calculation under the design condition, and rarely considers the stress calculation of the experimental pressure. Under normal conditions, the experimental pressure does not exceed the rules of the design specification, and the selected bellows parameters can meet the requirements of the design conditions. However, when the design temperature of the contraction joint is higher than the experimental temperature, The test pressure shall be corrected according to the bellows data. Due to the existence of the temperature correction coefficient, the test pressure of the contraction joint working at high temperature may be much higher than the design pressure, or even multiple of the design pressure. According to the design rules, Design the temperature correction coefficient for the test pressure of the pressure pipe system or equipment pipe system with contraction joint according to the temperature correction coefficient of the pressure pipe system or equipment data Driver