Three common welding defects and their causes shared by welding rotator manufacturer.

Welding is a key work in the construction of large scale installation project. Due to the different level of technical workers, welding process is good and bad, easy to exist a lot of defects; The types and causes of defects are sorted out in order to reduce or prevent the occurrence of welding defects and improve the quality of the completion of the project.

1. The size of welding seam is not up to the requirements, mainly manifested as thick welding wave, uneven shape, too low or too high weld reinforcement height, different width of welding wave, unilateral or excessive subsidence of fillet weld, etc. The reasons are as follows: 1. 2. Excessive or small welding current, improper selection of welding specifications; 3. Uneven speed and improper Angle of electrode (or welding handle).

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2. The crack, mainly for the shape of the crack tip sharp, stress concentration is serious, to withstand alternating and impact load, static tension, is the most dangerous defects in the weld. According to the causes, it can be divided into cold crack, hot crack and reheat crack. (cold crack) refers to the crack produced below 200℃, which is closely related to hydrogen. The main reasons for its generation are: 1. 2. Improper selection of welding materials; 3. Welding joint is rigid and unreasonable; 4. The weld and its vicinity produce brittle and hard structure; 5. Improper selection of welding specifications. (thermal crack) refers to the crack generated above 300℃ (mainly solidified crack), which is mainly caused by the following factors: 1. It is easy to appear when welding pure austenitic steel, some high nickel alloy steel and nonferrous metal. 2. The weld contains more sulfur and other harmful impurities. 3. Improper selection of welding conditions and joint forms. The stress annealing crack is eliminated. It refers to the intercrystalline cracks generated in the heat-affected zone in the high-strength welding area due to post-welding heat treatment or use at high temperature. The main reasons are: 1. Improper heat treatment conditions for stress relief annealing. 2. Influence of alloy composition. Elements such as chromium, molybdenum, vanadium and boron tend to increase the reheat crack. 3. Improper selection of welding materials and welding specifications. 4. Unreasonable structural design causes large stress concentration.

3. Stoma; In the welding process, due to the gas in time to escape in time and the formation of holes in the weld metal or surface, the reasons are: 1. 2. The welding process is not stable, the arc voltage is high, the arc is too long, the welding speed is too fast and the current is too small; 3. Oil and rust on the surface of filler metal and base metal are not cleaned; 4. The arc starting point is not melted by receding method; 5. The preheating temperature is too low; 6. Not stagger the position of arc ignition and arc quenching; 7. The welding area is poorly protected and the weld pool area is too large; 8. Air holes are easy to appear in ac power supply, and the reverse connected air holes have the least tendency.

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