Everyone must have seen the body of a fully welded ball […]
Everyone must have seen the body of a fully welded ball valve. We all know that the welded joints are generally designed for narrow gap thick wall submerged arc welding, and the fully welded valve bodies are mostly super thick cylindrical welded joints. Everyone must be wondering why this is so?
1: Heat treatment technology treatment
The thick-wall multi-layer welding process is a process of repeated heating and cooling of metal materials, resulting in inhomogeneity and deterioration of the welded joint structure, high residual stress, and even welding defects. Welding is the last process after the product is assembled. There are non-metallic sealing material rubber and PTFE plastic in the valve cavity, so post-weld heat treatment is not allowed.
2: Treatment at the joint
In the design of the valve body welded joint, for alignment and positioning, there is an annular assembly gap at the root of the weld. Under the action of internal pressure and external load, this gap will produce a stress concentration that is several times the normal working stress. Make it difficult for engineers to deal with.
The stress concentration in the root gap of the valve body welded joint, residual stress, and the deterioration of the structure have become the weak link in the valve body structure, which has attracted the attention of the valve community at home and abroad, but there has not been any relevant report to solve this problem, and it has become this product. A hidden danger in the integrity of the structural boundary.