1. Defect characteristics
Unfused refers to the phenomenon that the weld metal is not completely melted and bonded with the base metal or between the layers of the weld metal. Failure to penetrate refers to the phenomenon that the root of the welded joint is not completely penetrated.
Both non-fusion and non-penetration will reduce the effective cross-sectional area of the weld, reducing the strength and tightness.
2. Causes
The cause of non-fusion: the welding current is too small or the welding speed is too fast, resulting in insufficient heat, and the base metal and filler metal cannot be fully melted. The groove angle is too small, the gap is too narrow or the blunt edge is too large, so that the arc cannot penetrate deep into the root of the groove during welding, resulting in the base metal and the weld metal not fused. There are impurities such as oil stain and rust on the surface of the weldment, which affects the melting and fusion of the metal. Improper operation, such as incorrect electrode angle, improper way of transporting the bar, etc., makes the arc deviate from the edge of the groove or fails to adequately cover the groove.
Causes of non-penetration: Similar to some reasons for non-fusion, such as too small welding current, too fast welding speed, inappropriate groove size, etc. When welding, the arc is too long, and the arc heat is dispersed, resulting in poor melting of the root metal. The assembly gap of the weldment is uneven, and it is easy to have no weld penetration in the part with a large gap.
3. Processing
Unfused treatment: For non-fused surfaces, a grinding wheel can be used to polish off the unfused parts and then re-weld. When re-welding, the welding process parameters should be adjusted to ensure sufficient heat input to fully melt the base metal and filler metal. For internal non-fusion, it is generally necessary to use non-destructive testing methods to determine the location and extent of non-fusion, and then use carbon arc gouging or machining methods to remove the non-fusion parts, and then carry out repair welding. When repairing welding, pay attention to cleaning the groove, control the welding angle and the way of transporting the bar.
Impervious treatment: If the depth of unwelded penetration is shallow, the unpenetrated part can be removed by grinding with a grinding wheel, and then repair welding. For large depths, it is usually necessary to use carbon arc gouging or machining to remove all the parts of the weld penetration until good metal is exposed, and then repair welding. When repairing welding, the welding current, voltage and welding speed should be strictly controlled to ensure that the root can be fully penetrated.
4. Repair welding material
Generally, welding materials that are the same or similar to the base material of the valve should be selected. For example, for common carbon steel valves, E4303 (J422) welding rods can be selected; For stainless steel valves, the corresponding stainless steel welding rods can be selected according to the specific materials, such as A102 welding rods for 304 stainless steel valves, A022 welding rods for 316L stainless steel valves, etc.
Tianjin Tanggu Water-Seal Valve Co.,ltd mainly produce butterfly valve, gate valve, Y-strainer, balancing valve, check valve, etc.
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Company Name: Tianjin Tanggu Water-Seal Valve Co., Ltd.
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Address:No.105, No.6 road, Industrial park, Xiaozhan Town, Jinnan District
City: Tianjin
Country: China
Website: https://www.tws-valve.com/
