2. The residual stress analysis of the weld is as mentioned above. The residual stress of welding is caused by the uneven temperature field on the weldment during welding. The temperature of the weld and its surrounding area rises sharply, and the uneven expansion caused by the uneven temperature field results in the residual stress of welding. However, the welded joint of the full welded valve body is a typical thick wall multi-layer weld. The welding heat affected zone has experienced repeated heating and cooling, resulting in coarse grain structure in this area, which constitutes a weak toughness zone of the welded joint.

As polytetrafluoroethylene (PTFE) has strong corrosion resistance, stable performance, resistance to aging, low friction coefficient, easy forming, and stable size, it can also be filled and added with appropriate materials to improve its comprehensive performance, and obtain butterfly valve sealing materials with better strength and lower friction coefficient, overcoming some limitations of synthetic rubber, As a result, polymer materials represented by polytetrafluoroethylene and their filling modification materials have been widely used in butterfly valves, which further improves the performance of butterfly valves. Butterfly valves with wider temperature and pressure ranges, longer sealing performance and service life have emerged.