Weld defects are imperfections or flaws that can occur in welded joints, which can affect the strength, integrity, and performance of the welded structure. Weld defects can be caused by a variety of factors, including poor design, inadequate preparation, incorrect welding techniques, and inadequate inspection and testing. Some of the common types of weld defects include:

• Incomplete fusion: This is a defect where the weld metal does not fully penetrate or fuse with the base metal, and a gap or void is left between the weld and the base metal. Incomplete fusion can be caused by insufficient heat or penetration during welding, or by the presence of contaminants or oxides on the base metal.

• Incomplete penetration: This is a defect where the weld metal does not fully penetrate the thickness of the base metal, and a lack of fusion is present at the back of the weld. Incomplete penetration can be caused by inadequate welding current or voltage, or by incorrect welding parameters or techniques.

• Porosity: This is a defect where small voids or bubbles are present in the weld metal, which can weaken the weld and reduce its strength and ductility. Porosity can be caused by the presence of air, moisture, or gas in the weld metal, or by inadequate preheat or interpass temperature.

• Slag inclusion: This is a defect where slag, which is a non-metallic material that forms during welding, is trapped in the weld metal or the weld joint. Slag inclusion can be caused by inadequate cleaning or chipping of the weld, or by incorrect welding techniques or procedures.

• Lack of sidewall fusion: This is a defect where the weld metal does not fully fuse with the base metal along the sides of the weld, and a lack of fusion is present in the weld joint. Lack of sidewall fusion can be caused by inadequate heat input, or by incorrect welding techniques or procedures.

• Undercut: This is a defect where the weld metal is not properly supported by the base metal, and a groove or depression is formed along the edge of the weld. Undercut can be caused by excessive heat input, or by incorrect welding techniques or procedures.

• Overlap: This is a defect where the weld metal extends beyond the edge of the base metal, and an excess of weld metal is present in the weld joint. Overlap can be caused by inadequate joint preparation or fit-up, or by incorrect welding techniques or procedures.