With BS7448 Part 2, Fracture Toughness Test Part 2: Determination Method of KIC Value, Critical CTOD Value and Critical J Value for Welding of Metallic Materials, proposed by British Welding Research Institute in 1997, BS7448 Part 1 has been supplemented for the characteristics of non-uniformity of performance and residual stress in various areas of welded joints, This is the internationally recognized test standard for determining the CTOD fracture toughness of welded joints. For example, API 1104 Appendix A, DNV-OS-401 and BS7910 are all used to assess the integrity of welded structures according to the test specification of fracture toughness CTOD value of BS7448 Part 2.

Selection of butterfly valve
The butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc shaped butterfly plate rotates around the axis with a rotation angle of 0 ° - 90 °. When it rotates to 90 °, the valve is fully open. The butterfly valve is simple in structure, small in size and light in weight, and only consists of a few parts. The valve can be quickly opened and closed only by rotating 90 °, which is simple to operate. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the resistance of the medium flowing through the valve body, so the pressure drop generated by the valve is very small, so it has good flow control characteristics. Butterfly valve has two sealing types: elastic seal and metal seal. For elastic sealing valve, the sealing ring can be embedded on the valve body or attached to the periphery of the butterfly plate. Metal sealed valves generally have longer service life than elastic sealed valves, but it is difficult to achieve complete sealing. The metal seal can adapt to higher working temperature, while the elastic seal has the defect of temperature limitation. If the butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of the valve. The structure principle of butterfly valve is particularly suitable for making large diameter valves. Butterfly valves are not only widely used in petroleum, gas, chemical, water treatment and other general industries, but also used in the cooling water system of thermal power stations. The commonly used butterfly valves are wafer type butterfly valve and flange type butterfly valve. Wafer type butterfly valve uses stud bolts to connect the valve between two pipe flanges. Flange type butterfly valve has flanges on the valve, and bolts are used to connect the flanges on both ends of the valve to the pipe flanges.