Subsequently, in 2000, the British Bureau of Standards published BS7910-1999 Guidelines for Acceptance and Assessment Methods of Defects in Metal Structures, which uses the failure assessment diagram (FAD) based on the principle of fracture mechanics to assess defects in metal structures. According to the test method of BS7448 Part II, the American Petroleum Institute added Appendix A to the standard of API 1104 Pipeline Welding and Related Facilities, and proposed the acceptance standard of pipeline welding joint CTOD value. Det Norske Veritas DNV-OS-401 also puts forward an evaluation and acceptance standard for CTOD value in the acceptance evaluation of engineering projects, so as to carry out engineering evaluation for post weld heat free treatment of large structural parts. CTOD value is actually related to such factors as welding base material, welding wire, flux, welding process, welding method, weld structure size and thickness, and is a comprehensive parameter and performance index of material resistance to cracks.

Advantages of pneumatic butterfly valve?
There are many advantages in the application process, and the following are nine of them:
1. The pitch of pneumatic butterfly valve is sensitive;
2. The pneumatic butterfly valve has good flexibility, no blockage and stiffness;
3. The pneumatic butterfly valve has light weight and good caliber divergence;
4. The pneumatic butterfly valve has good flexibility, repeated bending and flexibility;
5. Pneumatic butterfly valve has good corrosion resistance and high temperature resistance;
6. The pneumatic butterfly valve has good anti rat bite and wear resistance to avoid abrasion of internal wires; 7. The pneumatic butterfly valve has strong bending resistance, tensile strength and lateral pressure resistance;
8. The pneumatic butterfly valve is soft, smooth and easy to position the threading device;
9. PVC pneumatic butterfly valve has good waterproof performance