Spot It Before You Scrap It: Common Welding Defects Explained

Whether you are on the shop floor, in the classroom, or overseeing production, weld integrity is the backbone of safe and reliable manufacturing. Welding defects don’t just affect appearance; they undermine safety, weaken performance, and shorten the lifespan of a finished part. In high-stakes industries, weld quality isn’t just important; it’s non-negotiable.

Understanding the root causes of common defects, along with how to prevent and correct them, is essential for producing reliable, high-integrity welds. Prevention starts long before the arc is struck: with proper technique, the right equipment, and thorough preparation.

With that foundation in mind, let’s take a closer look at the most common welding defects—and how they compromise your weld.

Porosity

Porosity occurs when pockets are trapped in the solidified weld metal. The porosity is typically caused by contamination of oil, moisture, or dirt; the amount or leakage of shielding gas; and incorrect welding speed. These bubbles can lead to weld failure, corrosion, and compromised overall quality.

Fix: (Cup size, torch angle, adjust CFH for better coverage)

• Adjust shielding gas
• Thoroughly clean base metal
• Modify welding speed as needed

Cracks

Cracks are linear separations along or near the weld, occurring in the base metal, weld metal, or both. They are often the result of stress, improper heat control, or lack of critical steps like preheating of the base metal. Cracks are generally classified as hot or cold:

Hot cracks develop during the solidification and crystallization of the weld. They can appear as:

• Solidification cracks are often caused by impurities, high carbon content, or disrupted heat flow.
• Liquation cracks occur when low-melting constituents overheat and partially melt.

Cold cracks can be more unpredictable, appearing hours or even days after the weld has solidified. They typically run parallel to the fusion boundary and may grow due to residual tensile stresses.

Fix:

• Control heat input
• Properly preheat thick metals
• Select the right filler.

Undercut

Undercut is a groove along the weld toe that reduces the base metal’s thickness and weakens the joint. Where the weld melts the base metal, but there is insufficient filler metal to fill the resulting groove. There is a substantial threat to the structural integrity of the joint. This also creates a place for contaminants to build up, which could accelerate corrosion rates.

Fix: (Increase weld wire size while reducing speed; torch angle may need to be adjusted.)

• Reduce welding current
• Adjust travel speed
• Correct electrode angle
• Adjust torch angle
  
  

Incomplete Fusion

Incomplete fusion occurs when base metal and weld metal are not properly joined, and the weld fails to penetrate through the base metal or previous weld passes. Unlike a simple surface blemish, this type of defect represents a physical lack of bonding. This defect can lead to weak and unreliable joints that are likely to crack, leak, or fail under stress and pressure.

Fix: (Use a smaller diameter weld wire in your root pass.)

• Increase heat input
• Improve torch angle
• Thoroughly clean surfaces
  
  

Overlap

Overlap occurs when weld metal flows over base metal without bonding. The weld pool flows excessively, extending beyond the toe. Surplus filler matter spreads beyond the weldment, failing to create a solid joint. Like a swimming pool overflowing when the water exceeds capacity and it is no longer contained.

Fix:

• Increase welding current
• Adjust technique
• Proper electrode selection
  
  

Spatter

Spatter consists of small droplets of molten metal outside the weld pool that stick to the surrounding base metal, creating a rough, uneven finish. This can detract from aesthetics and functional qualities of the welded material. Beyond the surface, spatter can indicate underlying inefficiencies or imbalances in the welding process. This demands additional cleaning, grinding, or polishing, introducing time-intensive steps that hinder welding productivity.

In industries where appearance and precision matter, such as automotive and aerospace manufacturing, spatter removal isn’t optional. Left unaddressed, these deposits can interfere with mechanical movement, compromise seals, or even introduce weaknesses that affect structural integrity.

Fix:

• Adjust voltage/amperage
• Clean tip

Preventing weld defects comes down to discipline, attention to detail, and knowledge of the material. When welders understand the causes of common defects and are equipped to address them correctly, weld integrity is preserved and quality remains consistent.

Want a quick reference you can keep on hand? Download our PDF covering common welding defects, their causes, and proven fixes.

Have a welding challenge you are dealing with on the shop floor? Share it in the comments—we would love to hear from you.