Teach you how to identify and prevent incomplete penetration and incomplete fusion during steel pipe welding

The direct harm of incomplete penetration during steel pipe welding to the welded structure is to reduce the load-bearing cross-sectional area and reduce the mechanical properties of the welded joint. The stress concentration caused by incomplete penetration is far more harmful than the reduction in strength. Welded structures that bear alternating loads, impact loads, stress corrosion, or work at low temperatures often suffer from brittle fractures.

Incomplete fusion not only reduces the effective thickness of the welded structure, but also easily generates stress concentration at the unfused edge during the use of the workpiece, and expands outward to form cracks, thereby causing the entire weld to crack.

(1) Incomplete penetration during steel pipe welding is the phenomenon in which the root of the welded joint is not fully fused. Incomplete penetration defects may occur during both single-sided welding and double-sided welding.

1) Causes of incomplete penetration defects during steel pipe welding: Improper selection of welding parameters, such as too low welding current, too fast running speed, improper electrode angle, arc blow, too small butt gap, and improper groove angle, etc. Incomplete penetration has little to do with welding metallurgical factors; operating errors, such as center deviation during double-sided submerged arc welding without groove; poor groove processing, such as too thick blunt edge, or one side is thick and the other side is thin, plus the welding current is too small.

2) Preventive measures for incomplete penetration defects during steel pipe welding: Using a larger current for welding is the basic method to prevent incomplete penetration defects during steel pipe welding. For fillet welds, using AC instead of DC can prevent magnetic blow. In addition, reasonable groove design and keeping the groove clean, using short arc welding and other measures can also effectively prevent the occurrence of incomplete penetration defects during steel pipe welding.

(2) Incomplete fusion The part that is not completely melted and combined between the weld metal and the parent material or between the weld metal and the weld metal is called incomplete fusion. Lack of fusion often occurs on the side wall of the groove, between layers of multi-layer welding, and at the root of the weld. Sometimes the gap of lack of fusion is very large and difficult to distinguish from slag;

Sometimes, although the joint is tight, it is not welded, and micro-cracks often occur at the end of the unfused area.

1) Causes of lack of fusion defects: The welding surface is not cleaned, with oil or rust; the groove shape is unreasonable, with dead corners; the welding current is too small; the welding gun does not swing fully: the welder arbitrarily increases the current to speed up the welding speed, etc.

2) Preventive measures for lack of fusion defects: use a larger welding current, perform welding operations correctly and keep the groove clean.