1. Overview
The lower ring is made of martensitic stainless steel (ZG00Cr13Ni4Mo) and is primarily used in hydropower stations for structural protection and support. Due to the high-performance requirements, it demands specialized casting and heat treatment processes. The casting has a relatively thin wall, with an average thickness of approximately 106 mm. This makes the casting process challenging, as it is difficult to fill the mold completely and can lead to shrinkage cavities in the central area, which significantly affects the mechanical strength of the component. Moreover, repairing such castings is also problematic, as welding can result in a hardened microstructure, increasing the risk of post-weld cracking. Our company successfully produced the lower ring using a custom casting method. However, after machining and ultrasonic testing, some defects were still found to be above acceptable limits. To address this, we implemented a specialized repair welding process that effectively resolved the issues. The three-dimensional illustration and physical image of the lower ring are shown in Figure 1 and Figure 2 respectively.
Figure 1: 3D Illustration of the Lower Ring
Figure 2: Physical Image of the Lower Ring
2. Repair Welding Process and Operation Steps
The casting was produced without any machining allowance, making it more sensitive to temperature changes during repair welding. If the welding temperature is too high, it can cause deformation or even cracking. To overcome these challenges, our welding team developed a detailed and controlled repair welding process: 1. Local preheating temperature is maintained between 70–110°C. 2. The interpass temperature is strictly controlled at 80–160°C. 3. Electrodes are dried at 350°C for 1.5 hours and then stored in a thermos bucket to prevent moisture absorption. 4. Special attention is given to ensuring proper fusion between the weld and the base metal. It's crucial to avoid slag inclusion, especially at the root and joint areas. 5. A single-layer multi-pass welding technique is used. Swinging is strictly prohibited. Each layer should not exceed 6 mm in thickness to minimize welding stress. 6. Welding parameters include a 4 mm diameter electrode, with a current range of 150–170 A and short arc operation. 7. After welding, hammering is performed to relieve residual stresses. 8. The interpass temperature must be carefully controlled at 80–160°C. Continuous and rapid welding is strictly avoided to prevent excessive stress and deformation. 9. During the repair process, special care is taken to ensure good fusion along the groove edges, preventing defects like incomplete penetration and slag inclusion. 10. If poor fusion or cracking is detected during welding, the process is immediately stopped, and the area is cleaned using a grinding wheel or head before re-welding. After welding, the component is wrapped in asbestos felt to cool gradually. Photos of the repair welding process are shown in Figure 3 and Figure 4.
Figure 3: Welder Using Wind Target for Stress Relief
Figure 4: Repair Welding Temperature Approximately 76°C
For more detailed information, please refer to the attachment.
Hard Seal Sphere Seat Assembly
Hard Seal Sphere Seat Assembly,Hard Sealed Seat,Hard Sealed Fixed Sphere,Hard Sealed Regulating Sphere
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