The maximum principal stress of the 20in 600Lb all welded body pneumatic ball valve is 15MPa based on 1.5 times of the rated working pressure, and the maximum axial strain is 728 according to the finite element calculation με (i.e. 0.000728 ε）， If the minimum acceptable CTOD=0.005in (0.1225mm) given in Appendix A of API 1104 is considered, the maximum defect size limit is 0.3in, equivalent to 7.6mm. The measured CTOD=0.008in (0.196mm), and the corresponding allowable defect size is 0.45in (11.4mm), according to the requirements of JB4730-94 Class 1 pressure vessel, the allowable defect size is less than 0.15in (3.765mm), so the actual joint still has a relatively high safety margin. NDT for all welded valve body welds shall be carried out according to the requirements of Class 1 pressure vessel in JB4730-1994, and the weld defect size shall be less than 0.15in (3.675mm). Therefore, when the welded joint of the fully welded valve body meets the CTOD fracture toughness value of more than 0.005 in (0.1225 mm), and the NDT of welds meets the requirements of JB4730-94 for Class 1 pressure vessels, it can be recognized that the post weld heat treatment free process is safe and reliable.

5. Operation and use
1) Before operation, confirm that pipelines and valves have been flushed.
2) The operation of the valve drives the valve rod to rotate according to the input signal of the actuator: when the valve rotates 1/4 circle (90 °) in the positive direction, the valve is closed. When the valve rotates 1/4 turn (90 °) in the opposite direction, the valve opens
3) When the direction indicating arrow of the actuator is parallel to the pipeline, the valve is open; When the arrow is perpendicular to the pipeline, the valve is closed
6. Maintenance has a long service life and maintenance free period, which will depend on the following factors: normal working conditions, maintaining a harmonious temperature/pressure ratio, and reasonable corrosion data.