Welding repair of casting block valve

Because of its low manufacturing cost and good comprehensive performance, steel castings are often used in the plug valve of thermal power plant. Because of its long-term operation under the harsh conditions of high temperature, high pressure and vibration, and large thick wall castings usually have some internal defects that cannot be eliminated during manufacturing, internal stress release and expansion and contraction stress caused by temperature change The stress results in the local porosity and cracking of the casting itself.

It can save a lot of manpower, material resources and maintenance time to repair the valve with cracks by using proper welding process. However, if the repair process is improper, the weld will crack or fall off, resulting in more serious safety accidents and losses. Combined with the actual situation of the equipment, two different repair processes of heterogeneous cold welding and hot welding were adopted for the valve bodies made of two kinds of materials, which eliminated the major hidden dangers of the equipment. The differences of repair welding processes of different materials were discussed.

(1) using nickel based welding materials to repair castings by heterogeneous cold welding process has the characteristics of simple process, low cost and easy implementation, which is not high requirement for working environment. It is suitable for plug valve repair welding process made of low alloy steel.

(2) for the plug valve made of high alloy steel with high cold crack sensitivity, the hot welding process requires preheating and post weld heat treatment, which increases the complexity of the welding process, but the overall heating of the valve body is uniform, the welding residual stress is small, and the structure of the valve body is uniform after welding. In view of the large-scale plug valve made of different materials, the repair welding process can obtain good results.