Why do cracks occur when patch welding is done on sand holes in the volute of a pump, and how can this be resolved?

Cracks can occur in the casing of mechanical pumps during the repair welding of sand holes, and this may be due to the following reasons: 1. **Thermal stress**: During welding, high temperatures and rapid cooling rates cause thermal stress in the material of the casing in the weld area. Defects or irregularities in the material surrounding the sand hole can lead to cracks as the thermal stress is released. 2. **Mismatched welding materials**: The type of electrode used (E308-16) must be compatible with the material of the volute (S30408, i.e., 304 stainless steel). Although stainless steel electrodes are used, if their chemical composition differs significantly from that of the base material, this mismatch may lead to cracks. 3. **Improper welding process parameters**: Welding parameters such as current, voltage, welding speed, preheating temperature, and post-weld slow cooling methods, if not strictly controlled, can lead to overheating of the welded area or an inappropriate cooling rate, thereby increasing the risk of cracks. 4. **Insufficient pre-welding preparation**: If the surface of the volute is not cleaned properly before welding, or if there is oil, rust, casting defects, etc., around the sand holes, this can lead to poor welding quality and thus cracks. 5. **Welding technique operation issues**: Manual arc welding requires a high level of skill from the operator; improper welding techniques (such as incorrect welding posture and angles, as well as uneven welding speed) can lead to defects and cracks in the weld. Solution: 1. **Pre-welding preparation**: Thoroughly clean the sandhole area and the surrounding material before welding to ensure there is no oil, rust, or other impurities. Furthermore, if possible, the sand holes should be appropriately shaped to create a geometry suitable for welding. 2. **Preheating**: For S30408 material, very high preheating is generally not required, but appropriate preheating can even out the temperature of the base material and reduce thermal stress in the welding area, thereby minimizing the formation of cracks. 3. **Optimize welding parameters**: Adjust appropriate parameters such as welding current, voltage, and speed to ensure a smooth welding process with an appropriate penetration depth. 4. **Slow cooling measures**: Appropriate post-weld heat treatment, such as slow cooling or tempering, is carried out after welding to reduce residual stresses in the welded area and minimize the risk of cracks. 5. **Use appropriate welding materials**: Select welding materials whose chemical composition and thermal expansion coefficient are closer to those of the base material, in order to reduce cracks caused by material mismatch. 6. **Improve welding skills**: Enhance the welding techniques of operators to ensure proper welding practices and prevent welding cracks caused by technical issues. 7. **Post-weld inspection and treatment**: Non-destructive testing, such as radiographic testing or ultrasonic testing, is carried out after welding to ensure the quality of the welds. If cracks appear, they should be welded and repaired promptly. Through the above methods, the formation of cracks during welding can be reduced or avoided. It should be noted that, depending on the specific materials and manufacturing processes, detailed process adjustments and optimizations may be necessary in light of the actual conditions on site. .

If there are no issues with the welding process, the quality of the base material, or the filler material, it is most likely stress concentration.

See if, with low pressure, trying adhesive filling would work. Fusion welding is very difficult.

The pressure isn’t too high; you can give it a try. Filling the glue from the inside should work. If using fusion welding, it is best to try it first on other materials of similar kind. When using stainless steel or cast iron welding materials, the workpiece needs to be preheated before welding, and tapping and vibration should be applied while welding. I’ve seen it, but it’s quite difficult. For reference.

Stress concentration occurs, and this is also related to the lack of heat treatment after welding~~

The casting is porous; cracks are caused by welding thermal stress. Preheat to 150°C and cool slowly. The key is to perform soldering and tap the joints promptly to relieve stress.

Indeed, loose castings are the main reason. Also, before welding it is necessary to ensure that any defects have been removed thoroughly using PT testing; furthermore, the heat input during welding should be kept as low as possible, and the welding rod should not be moved back and forth (the weld width shown in the image is too large – generally, the weld width for stainless steel should not exceed 3 times the diameter of the welding rod).