Welding is a crucial fabrication technique that enables the fusion of parts using heat and pressure. When done properly, welded joints produce a strong bond that can hold metal parts together for years. However, certain welding defects can compromise the integrity of welded parts. Defects occur due to poor technique or use of substandard material during welding. Common welding defects include porosity, blowholes, cracks and lack of fusion, among others. Sources of such defects must be identified and prevented to ensure strong welds. This article explores common welding defects and how to prevent them.

Porosity

Porosity is one of the most common types of weld defects. Porosity can occur externally on the face of a weld or internally in a metal. The latter is difficult to detect, and x-rays must be used to test for such porosity. Trapped gases create weak welds that can collapse over time. There are several reasons why porosity occurs during welding; for example, due to poor gas shielding, nitrogen, oxygen and hydrogen are absorbed into a molten weld pool. Such gases are then released on solidification and trapped in the metal being welded. Contamination such as rust, oil and paint can also lead to porosity. Use of the wrong type of shield gas also contributes to porosity. Besides, poor welding techniques, including improper placement of torch and excessive stick-out, can cause porosity. However, the defect can be prevented by identifying and removing the source of gas. For instance, hydrogen can be controlled by degreasing and cleaning workpiece surfaces thoroughly. Also, consider drying the flux and electrode before welding to remove hydrogen. For surface coatings, it is advisable to clean joint edges before welding. Prevention of air entrainment calls for the sealing of air leaks to eliminate draughts. Moreover, ensure that there is no weld pool turbulence. Other preventive measures include the reduction of gas flow and the use of fillers with enough deoxidants.

Weld Cracks 

Weld cracks are common yet unacceptable defects by any standards. Common types of cracks include crater cracks, cold cracks and hot cracks. Common causes of cracks during welding include poor joint design, high speed of welding at a low current, contamination of base metal, lack of preheating and residual stress. You can prevent cracking by preheating a metal before welding it to remove impurities. Also, ensure proper joint design and effective cooling of a weld to avoid residual stress.

Lack of Fusion 

Improper torch handling, high travel speed and low heat can lead to a lack of fusion during welding. Welders are advised to direct an arc at the leading weld edge of a puddle to prevent improper fusion. Besides, a reduction of puddle size by reducing wire-feed speed or travel rate can remedy this problem. Moreover, an electrode should always be kept at the edge of a puddle.