According to the valve body material, welding current, welding speed and other welding process parameters, the thermal elastoplastic finite element method can be used to calculate the distribution of welding residual stress of all welded valve body. According to the calculation, the maximum welding residual stress of the valve body reaches 407MPa, far exceeding the yield strength of A105 material. Figure 1a Comparison of Calculation and Measurement Values of Axial Residual Stress of Valve Body (Simulation Distribution Results and Test Results of Welding Residual Stress in Different Directions) Figure 1b Comparison of Calculation and Measurement Values of Circumferential Residual Stress of Valve Body (Simulation Distribution Results and Test Results of Welding Residual Stress in Different Directions) Figure 1c Residual stress distribution curve in the thickness direction of valve body (simulation distribution results and test results of welding residual stress along different directions) Figure 1a and Figure 1b show the measured and calculated results of welding residual axial stress and welding residual circumferential stress respectively. It can be seen from the figure that the maximum axial stress and circumferential stress are on the outer surface of the weld center of the thick wall cylinder of the valve body, the residual stress is tensile stress, and the inner surface is compressive stress. Figure 1c shows the distribution of welding residual stress along the weld thickness direction. It can also be seen from Figure 1 that the maximum welding residual axial and circumferential calculated stress can reach the tensile strength of A105 material.

Applicable scope of non-metallic contraction joint:
1. Flue system of power plant
2. Low pressure air flow pipeline system of chemical plant
3. Pipeline system of cement plant
4. Flue system of thermal power plant
Maintenance and replacement performance: non-metallic contraction joints do not need maintenance during the normal service life cycle, and replacement of non-metallic contraction joints is much easier than that of metal contraction joints. This is especially obvious for large-sized contraction joints.
Service life: The service life of the contraction joint is closely related to the environmental conditions. In coal-fired power plants, generally speaking, the service life is more than 5 years. Under the condition of operating temperature lower than 300 ℃, it is not uncommon to use it for 8-9 years. The condition of oil fired power plants is relatively complex. If light oil and diesel oil are burned, the service life of the shrink joint can be 3-4 years. If heavy oil or crude oil is burned, due to frequent cleaning, the damage to the shrink joint is relatively serious, which usually takes only 1-2 years.
Application pressure: non-metallic contraction joints can be divided into composite contraction joints and rubber contraction joints. The working pressure of the composite shrink joint generally does not exceed 0.5 atmospheric pressure (50Kpa), and the pressure of the rubber shrink joint can reach more than 10 atmospheric pressure, or even higher.
Application medium: non-metallic contraction joint is generally only applicable to gas.