Repair welding of nuclear power valve castings

Because of the particularity of the working condition of nuclear power valves, the internal quality requirements of castings are very strict, and RT is generally required Flaw detection to ensure its internal quality, but there are always some defects in the casting, some of which are allowed to exist, and some are not allowed to exist. For the defects that are not allowed to exist, if their quantity and size meet the “Specification for weld repair of castings”, they can be repaired by weld repair. As far as casting itself is concerned, casting defects within a certain range can be eliminated by means of patching. For nuclear power valve castings, the control of repair welding is more strict. The specific control requirements for repair welding are as follows:

1.Truthfully record defects

For casting defects, defect records shall be made. For important parts (general body, cover and door), each casting requiring repair shall be provided with a sketch map, indicating defect type, location and size of pit left after excavation. Write down the specific operation parameters during welding and repair. In the future, users can track these parts.

2.Implement the welding repair application system

In case of over standard defects of nuclear power valve castings, the casting unit must apply for the repair before welding, and the specific implementation plan shall be formulated with the approval of the design and process departments, and the repair can only be carried out after the approval of the chief engineer. The major event of casting repair welding has been checked layer by layer.

3.Serious welding repair operation specification

In the repair welding process of castings, the welders with nuclear power welding repair qualification must carry out welding. In the process of welding repair, it must be carried out in strict accordance with the process requirements and operation specifications. The welding rod shall be dried and kept warm during the use process to maintain a certain interlayer temperature.

4.Heat treatment after welding

After the repair welding of castings, there is a change from liquid state to solid state in the repair welding area. The edge area of the repair welding undergoes the heating and cooling process to produce stress. At the same time, the local structure of the repair welding also changes. Therefore, after the repair welding of castings, heat treatment must be carried out to make the structure and performance of castings consistent, and the stress can be eliminated. However, the number of heat treatment of castings can not be too many, so we use raw RT and repair welding, generally the number of heat treatment of castings is not more than 2.

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