Common Welding Defects: Types, Causes and Prevention

2026-07-28

welding defects are problems. They affect the quality, strength and safety of welded joints. We can sort welding defects into two main types based on their positions. They are surface defects and internal defects.

1. Surface Welding Defects

Surface defects appear on the weld surface. People can find them through direct visual checks. The common surface defects are as follows:

Incorrect weld size: The height, width or extra reinforcement of the weld fails to meet required standards. This happens when welding parameters, groove design or welding speed are not suitable.
Undercut: A groove forms at the weld edge between weld metal and base metal. It reduces the effective thickness of base metal. It also causes stress concentration.
Weld overlap: Extra molten metal flows onto the base metal surface. This metal cannot form good fusion with the base material. It will lower weld strength.
Burn-through: Molten metal passes through the back of the joint. It usually comes from too high welding current, slow welding speed or an overly large root gap.
Surface weld cracks: Cracks belong to the most dangerous welding defects. They greatly threaten the safety of structures.

2. Internal Welding Defects

Internal defects hide inside the weld. People need non-destructive testing methods to detect them. Typical choices include ultrasonic testing and X-ray inspection.

Common internal defects include:

Incomplete penetration: Weld metal cannot fully reach the inside of the joint. This weakens the welded connection.
Lack of fusion: Weld metal cannot fully combine with base metal or earlier weld layers. Common reasons are insufficient heat input, unclean surfaces or improper welding operations.
Internal porosity: Gas bubbles get trapped inside the weld when the metal solidifies. Porosity weakens mechanical properties. It also harms the tightness of welds.
Slag inclusion: Slag remains stuck inside the weld. It often occurs without thorough cleaning between welding passes or improper welding parameters.

Main Causes of Welding Defects

Many different factors lead to welding defects. The key factors are listed below:

Unsuitable welding current, voltage or travel speed
Wrong welding angle and operating methods
Dirty base metal or welding wire
Poor joint preparation and assembly work
Insufficient cleaning between weld layers
Unstable shielding gas protection

How to Reduce Welding Defects

To improve welding quality, it is important to select suitable welding parameters, maintain clean welding surfaces, use proper welding techniques, and choose reliable welding equipment.

As a welding machine manufacturer, we focus on developing reliable equipment with stable arc performance and accurate parameter control. Our welding machines are designed to help users achieve better weld consistency, reduce welding defects, and improve working efficiency.

With years of experience in welding equipment manufacturing, we continue to provide practical welding solutions for different industrial applications.