How to prevent lack of penetration and lack of fusion when welding

The direct harm of incomplete penetration to the welded structure is toreduce the bearing cross-sectional area and mechanical properties ofthe welded joint. Stress concentration caused by incomplete penetration is far more harmful than strength reduction. The welded structure subjected to impact load, alternating load, low temperature work or stress corrosion will lead to brittle fracture. Incomplete fusion will reduce the effective thickness of the welded structure,and it is easy to cause stress concentration at the edge of the incomplete fusion workpiece during use. The stress concentration willspread outward to form cracks, which will lead to the cracking of the whole weld.

1. Incomplete penetration of the root of a welded joint is called incomplete penetration. Incomplete penetration defects may occurduring single-sided welding and double-sided welding.

Causes of incomplete penetration defects: improper selection of welding parameters, such as too small welding current, improper electrode angle, too fast running speed, too small butt gap, arc deviation,improper groove angle, etc. Operation error, such as centerdis location during double-sided submerged arc welding without groove;Poor groove processing, such as one side is too thick, one side istoo thin, or the blunt edge is too thick, the welding current is too small, etc.

Preventive measures for incomplete penetration defects: high current welding is the basic method to prevent incomplete penetration defects. For fillet welds, AC can be used instead of DC to prevent magnetic bias blowing. In addition, the groove shall be designed reasonably and kept clean. Short arc welding can also prevent the occurrence of incomplete penetration defects.

2. Incomplete fusion between weld metal and base metal or between weldmetal and weld metal is called incomplete fusion. Incomplete fusionoften occurs in groove sidewall, Multi-layer Weld interlayer and weldroot. Sometimes, if the bond is tight but not welded, microcracks usually appear at the end of the unfused zone.

Causes of incomplete fusion defects: there is oil stain or rust on the welding surface and it is not cleaned up; Welding current is too small; Insufficient swing of welding gun; Unreasonable groove and dead angle; The welder increases the current without authorization to speed up the welding speed, etc.

Measures to prevent incomplete fusion: carry out correct welding operation,adopt high welding current and keep the groove clean.