Because of the inhomogeneity, deterioration and defects of the welded metal materials, there are three basic assumptions in materials science; The continuity hypothesis, uniformity hypothesis and isotropy hypothesis are not satisfied, which requires the application of fracture mechanics theory. The task of fracture mechanics is to use linear elastic fracture mechanics and elastic-plastic fracture mechanics to solve the crack problem of components based on the fact that there are macro microcracks in the components. Namely, the crack size, working stress and the ability of materials to resist cracks (that is, the crack tip opening displacement CTOD fracture toughness value) in the component are quantitatively linked, and the safety and life test analysis and evaluation are carried out for the components containing microcracks and joints with poor quality tissue.

3. Adjustment of valves. After the valve is assembled, install the positioner and adjust the air source pipe. The calibration points shall not be less than 5 points, 0%, 25%, 50%, 75% and 100%. Slowly input the signals of each point into the locator in turn, and observe whether the travel pointer corresponds to the scale scale. Otherwise, it should be repeatedly adjusted until it reaches the standard.