There are following technical methods of welding repair:
(1) Remediation of welding work environment requirements
The ambient temperature for repairing welding shall not be lower than 10 °C, and the natural ventilation is good; when using gas shielded welding, the wind speed is not more than 2 m/s, and the wind speed of other welding methods is not more than 8 m/s. The welding repair environment should have good visual conditions and can be illuminated with auxiliary light sources if necessary. In the field welding repair site, a simple work shed should be built to avoid open-air operation and avoid welding work in rainy or wet conditions.
(2) Mark the repair
At the repairing construction site, the name and number of the repaired workpiece shall be checked according to the rework procedure specification, and the welding defect cleaning, groove preparation, welding equipment, welding materials (model, drying), preheating temperature, welding process parameters, etc. shall be checked. When repairing welding using a variety of welding methods, it is necessary to clarify the application area of each welding method and welding material, and determine the corresponding welding order and weld thickness according to the different requirements and characteristics of the underlying layer, the filling layer, the cover layer and the sealing layer.
Repair welding that requires preheating should be carried out as continuously as possible. According to the actual situation of the weldment, the tempered or oxy-propane flame is used to preheat or partially reheat the weldment, check the preheating temperature, and frequently check the weld bead temperature during the repair process. When the preheating temperature is high or the heat dissipating area is large, the non-welding zone of the weldment may be covered with the heat insulating material. If the weldment temperature is lower than the specified preheating temperature lower limit, the repair welding operation should be stopped and reheated.
(4) Tooling and process measures
For the welding structure with large degree of restraint, easy to generate welding residual stress or repair welding requirements to control deformation, the following measures can be taken: using symmetrical welding or rotating the workpiece; controlling the welding heat input, using appropriate welding current, welding speed, and moving strip Way, multi-layer multi-pass welding; control welding sequence, reduce heat input of base metal; hammering (removing stress) on repairing weld bead in time, maintaining a certain hammering density; adopting process of segmental reflow or jump welding Measures.
(5) slow cooling and post heat treatment
For materials with high sensitivity to cold cracks and weld repairs with high degree of restraint, after welding, it should be slowly cooled (covered with thermal insulation material) or immediately post-heat treated, that is, after the repair is completed, the welded parts are heated to 250-350 immediately. °C, and kept for 2 ~ 3h, then slowly cooled to room temperature, used to reduce the hydrogen content of the weld and the metal near the seam. It should be noted that post-heat treatment is not a substitute for post-weld heat treatment, which is two concepts.