About Incomplete Welds

Incomplete penetration refers to the defect that the base metal is not melted and the weld metal fails to enter the root of the joint. According to the welding method, it can be divided into intermediate incomplete penetration and root incomplete penetration.

The root incomplete penetration is due to the fact that the liquid weld metal mostly exists in the single-sided welding of V-shaped or U-shaped groove and does not enter the blunt edge of the root. The middle incomplete penetration mostly exists in the double-sided welding of double-u-shaped or double-V-shaped groove because the liquid metal does not enter the middle.

Incomplete penetration defect of weld

Incomplete penetration of the weld will reduce its effective area and seriously reduce the strength and other mechanical properties of the weldment. Incomplete penetration will also seriously reduce the fatigue strength of the weld and cause stress concentration. When the weldment is under load stress, incomplete penetration may develop into cracks, which may eventually lead to weld cracking.

Incomplete penetration is more harmful than porosity, slag inclusion, tungsten inclusion and other defects, which belongs to more harmful defects.

Causes of incomplete penetration

1) The blunt edge is too large, the groove angle is small, the diameterof the selected electrode is too large, the assembly gap is small orthe edge is staggered, so that the deposited metal can not reach theroot.

2) The welding current is too small, the welding speed is too fast, thearc penetration is reduced, and the molten pool becomes shallow.

3) Due to improper operation, the arc cannot play a role here due to theheat loss caused by the magnetic bias blowing of the arc, or thedeposited metal cannot be transported to the predetermined position,or due to the short arc burning time of the arc or the failure toform a certain size of weld hole at the root of the groove, resultingin incomplete breakdown welding formed by one side welding and twosides.

preventive measure

1) Select appropriate groove angle, blunt edge size and assemblyclearance to prevent misalignment.

2) Select appropriate welding current, transportation angle andelectrode diameter. If the uneven thickness of electrode coatingcauses local arc, it shall be replaced in time.

3) aster the correct welding operation method and send the manual arcwelding belt and argon arc welding wire stably and accurately.Skillfully decompose the weld hole with appropriate size, and sendthe deposited metal to the root of the groove.