Welding defects and remedies

Defects in welds are caused by either the wrong choice, or violation of manufacturing technology of welded construction, as well as the use of low-quality welding materials and low-skilled welder.
Defects are divided into external and internal. Moreover, external defects can be detected by visual inspection with the naked eye or with a magnifying glass with a tenfold increase, while for the establishment of internal defects require the use of special methods: metallographic examination, chemical analysis, mechanical testing, X-raying or gamma-rays, magnetic and ultrasonic methods controls. To detect defects weld must first clear the slag, scale and metal splashes.
The external defects include: violation of the size and shape of the joint, the undercut area fusing, burnout, inundation, lack of fusion, surface oxidation, nezavarennye craters, surface pores, longitudinal and transverse cracks.
The internal defects include: internal pores, lack of fusion, non-metallic inclusions and cracks.
Violation of sizes and shapes shown in the seam too strong and abrupt transition from the base metal to weld, and in nepolnomernosti height and width of the joint. In manual welding of these defects arise as a result of sloppy preparation welded edges, wrong choice of welding current, low build quality welding and low-skilled welder. Defects of weld shape may arise as a result of fluctuations in voltage at work. With automated welding breach size and shape of joints may be due to non-compliance of the welding process (welding speed, the feed rate of the electrodes, welding current) and improper cutting seam.
Undercut area looks like a fusion of the narrow grooves in the base metal along the edge of the weld. This defect occurs when reinforced burner, welding elongated arc, the wrong position of the electrode or torch and welding rod and welding high current.
Burnout is a through-hole in the weld. The main reasons for its occurrence are as follows: small thickness of welded metal, oversized flame, a large welding current, a slight dulling of welded edges and uneven gap between them in the distance.
Influx - leakage of weld metal of the cold surface of the base metal or previously performed without roller fusing with it. The defect occurs when low-quality electrodes and welding speed mismatch and welding current cut of the joint, as well as low-skilled welder.
Lack of penetration appears as a local lack of fusion welded edges ground and weld metal, and can be the result of poor preparation welded edges (no gap, a great dulling, slight bevel angle), displacement of the electrode to one of the edges, quickly move the electrode along the seam.
Surface oxidation - oxidation of the weld metal and adjacent base metal mainly because of a strong oxidizing environment, very high power torch flame, a large arc length too strong welding current, slow moving electrode or torch along the seam.
Surface and internal pores are the result of contact with a metal seam various gases produced during welding (nitrogen, hydrogen, carbon dioxide, etc.). Nitrogen gets into the seam of the air with enough careful protection of the molten metal in the weld zone. Of the components of the coating of the electrodes, water and oil produce hydrogen. Carbon monoxide occurs in welding steel during the combustion of the contained carbon. The fact that the high content of carbon in the electrode and the work began, and the deficit in the weld pool and deoxidizing welding speed carbon monoxide has no time to wear off and remains in the metal. Thus, porosity - up sloppy preparation welded edges (rust, grease, pollution), the lack of de-oxidants, the use of wet flux-coated electrodes with a raw and high welding speeds.
External and internal cracks (cracks) occur mainly as a result of the stresses occurring in the metal due to its uneven heating, cooling and shrinkage. Alloy and high-carbon steel during cooling after welding quenched and the result of this may be cracks. The high content of steel impurities (sulfur and phosphorus) can also cause cracking. Note that the external and internal cracks are the most dangerous and unacceptable defects stitches.
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