3. Refer to DNV-OS-C401 (Det Norske Veritas) standard for safety assessment, and it is qualified if the CTOD value is greater than 0.15mm. Actual measurement of development process joint; C is greater than 0.15mm, indicating that the joint can be used without heat aging treatment. Fig. 3 The relationship between the allowable defect size and the maximum allowable strain of different CTOD values is shown in Appendix A of API 1104 Welding of Pipes and Related Facilities, which gives the relationship between the allowable defect size and the allowable strain when the TCTOD values are 0.005 in (0.1225 mm) and 0.01 in (0.245 mm) respectively, as shown in Fig. 3. It can be seen from the figure that the larger the CTOD value is, the better the fracture toughness of the weld is, and the allowable defect size can be increased. According to the curve between the maximum allowable axial strain and the allowable defect size when the minimum CTOD value of the welded joint of the all welded valve body is equal to 0.197mm (0.0078in).

Precautions for stainless steel pneumatic butterfly valve device
Stainless steel pneumatic butterfly valve, including conduit and bellows outside the conduit, are all stainless steel pipes. Both ends of the hose are connected with flanges. The flanges at both ends are connected by positioning bolts and set outside the bellows. The positioning bolts are connected with the flanges through nuts. It is mainly used for the exhaust pipeline of internal combustion engine in the marine system, as the compensation installation of pipeline thermal expansion and cold contraction, and can vibrate with the pipeline thermal expansion stress and pulse impulse in the system.
The contraction joint is a flexible structure set on the vessel shell or pipeline to compensate the additional stress caused by temperature difference and mechanical vibration. Precautions for stainless steel pneumatic butterfly valve shrink joint device:
1. When the stainless steel pneumatic butterfly valve contraction joint device is installed, its model, specification and pipeline configuration shall be checked, which must meet the design requirements.
2. The corrugated contraction joint in the sleeve shall pay attention to the movement direction of sleeve pipe and medium in the direction, and the rotation plane of hinge rotation plane stress and displacement of hinge type corrugated contraction joint.
3. Corrugated contraction joints of "cold spring" are required, and deformed auxiliary components shall be equipped with pipes before disassembly.
4. It is prohibited to adjust the device error of the pipeline by using the deformation method of bellows shrink joint, so as not to affect the bellows shrink joint with normal function, reduce the service life, improve the pipeline and equipment, and support the load of members.
5. During the installation of stainless steel pneumatic butterfly valve, the corrugated shell splashed by welding slag and other mechanical damages are not allowed.
6. For the pipeline behind the device, remove the device of the corrugated contraction joint and transport the yellow auxiliary positioning members and fasteners as soon as possible, and install the restrictions to the designated position according to the design requirements, so that the pipeline system has sufficient compensation ability under the environmental conditions.
7. All activities of the stainless steel pneumatic butterfly valve may be caused by the external members being stuck or limiting their range of activities. It should be ensured that the activities are normal.
8. For water pressure test, one end of the corrugated shrink pipe shall be fixed on the pipe support and reinforced, and the line shall not move or rotate. The gas corrugated contraction joint and its connecting pipeline should pay attention to the need for additional temporary support during water filling. The ion content of 96 chlorine in water cleaning solution for hydraulic test shall not exceed 25 ppm