Explanation of common defects in ERW welded pipes:
Undercut
Undercut is a groove that appears along the centerline of the weld in the transition area between the edge of the weld and the pipe body. Undercut occurs when welding speed, current, voltage and other conditions are not properly matched.
lap welding
The upper and lower edges of the steel plate are misaligned and butted, resulting in uneven welds, which become pipe seam misalignment or pipe seam lap welding.
Weld
During the welding process, the molten metal flows to the unmelted base metal outside the weld, forming a metal nodule.
Overheated
During the welding process, the temperature of the molten metal is too high and flows out from the groove, causing weld defects.
Welding offset
The weld bead deviates from the welding center line, causing the weld seam to deviate.
Stomata
During welding, the bubbles in the molten pool fail to escape during solidification and remain in the weld to form cavities. Stomata can be divided into dense stomata, worm-like stomata and needle-like stomata.
Slag
The slag remaining in the weld after welding is called slag inclusion. Slag inclusion is a kind of solid inclusion defect, which is the molten slag remaining in the weld. According to its forming situation, it can be divided into linear, isolated and other forms. Slag inclusion will reduce the plasticity and toughness of the weld; its sharp corners often cause stress concentration, especially in welds with a large tendency to air quenching, cracks often form at the apex of the sharp corners. Often, when castings are under stress, cracks will first appear and develop along the slag inclusions in the weld, resulting in a decrease in strength and cracking of the weld.
Not penetrated
The phenomenon that the root of the joint is not fully penetrated during welding also refers to the phenomenon that the weld depth does not meet the design requirements.
Hot cracks
In submerged arc welding (SAW), hot cracks can occur in the weld, especially at the arc starting and arc extinguishing craters due to the large temperature difference. Hot cracks are most likely to occur when the weld stress is high or when the Si content in the weld metal is high.
Welding gray spots
Welding defects unique to the
high-frequency resistance welding (HFW) welding method. It is characterized by a gray area without metallic luster that appears on the macro port of the weld of the tensile specimen or impact specimen. It is generally believed that gray spots have no significant impact on the strength level of the weld, but have a greater impact on the toughness and plasticity of the weld.
Trench corrosion
Groove corrosion is a special corrosion phenomenon in
ERW steel pipe welds. The selective localized corrosion phenomenon in the welding zone of resistance welded pipes serving in media such as seawater and industrial water is called groove corrosion. It usually starts from the surface in the form of continuous or discontinuous grooves. It can cause the welded pipe to last for years to several years. Corrosion and perforation during the year.
Pressure pit
Roll pits or hard objects between the roller surface and the tube blank cause low concave indentations on the surface of the tube.
