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Six Types of Welding Defects

Apr 3, 2023 ·

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Welding defects can be disastrous, potentially leading to product failure and dangerous operation.

That’s why identifying and repairing these defects is critical. With enough industry knowledge and experience, welders can prevent them from occurring in the first place.

Universal Technical Institute's 36-week welding program includes welding courses that help students obtain these skills! UTI’s welding students can learn how to complete successful welds free of defects through online and hands-on lab training. After graduation, they can use their knowledge to pursue careers in the industry.1

Our guide can also help you avoid common welding defects, so stay tuned to learn more! We'll give you an overview of some common welding flaws and how to avoid them.

Harms of Welding Defects

Welding defects can be hazardous during both the manufacturing and servicing processes. Here are a few reasons why:

  • Reduced structural strength, resulting in the failure of the welded component, machinery or structure
  • Increased repair or replacement costs to correct defective parts    
  • Increased maintenance costs since faulty welds continue to reduce product durability over time
  • Health and safety hazards if cracks allow hazardous materials to escape from pipes and machinery and cause structures and materials to fail

Read: What is Welding Burnback?

Six Examples of Bad Welds

Welding requires very specific technical and safety procedures, which means that poor welding practices can lead to a variety of weld defects.

For the most part, preventing these defects is a matter of consistently performing sound welding techniques. UTI’s 36-week Welding Technology program teaches the techniques used in four major welding processes – GMAW, GTAW, SMAW and FCAW – and then provides lab training to put these skills into action!    

1. Cracks

Cracking or fissures within the metal are signs of weld distortion and are frequently caused by incompatible welding processes and improper filler metal use. This is especially true for steel, which has a high carbon content and cools quickly after welding. Since it’s so susceptible to high stress concentrations, the metal can cool and distort after welding, usually when done too quickly and unevenly.


For the most part, welded components that have cracked must be replaced and rewelded immediately. While some types of defects can remain on the final product within acceptable parameters, cracking is not one of them, making it one of the more serious welding defects.


Proper pre-heating of the weld area allows the metal to expand slowly and evenly, which reduces the possibility of weld shrinkage. Welds should also be made with the proper filler metal, in the correct positions, and with techniques that allow for better-controlled cooling.

2. Slag Inclusions

Slag inclusions are groups of small, elongated slag particles. They're lumpy and usually found near the weld's surface.

Viewing them requires a magnifying lens since they’re almost imperceptible to the naked eye. These defects form when slag particles become trapped inside a weld.


This weld defect can be repaired by grinding or chipping away the material surrounding it before rewelding using low heat. However, this method should be used with caution because it introduces extra heat into the area, which can weaken the surrounding metal. Any slag that remains on the surface should also be removed before rewelding begins.


Slag particles must be removed from the weld zone prior to welding. There are several ways to accomplish this, the most common being to chip away at thicker slag layers with an air-cooled hammer or a mechanical grinder. Thinner slag deposits can be broken off with a wire brush.

Read: Polarity in Welding: The Beginner’s Guide

3. Porosity

Welding porosity is characterized by tiny cavities throughout the welded joint and typically appears as gaps on top or beneath the surface. These flaws are frequently caused by trapped gas or a lack of filler material during welding, resulting in the incomplete fusion of metal pieces.


Fixing welding porosity depends on the type of porosity being dealt with. Grinding out as much of the affected area as possible while avoiding damage to the surrounding areas is sufficient for most types of porosity and should prevent further contamination of the welded material.


Before welding, ensure that all components and joints are properly aligned, beveled and cleaned of grease, oil, moisture and rust. Use the correct shielding gas in the right quantities to avoid introducing excess oxygen into the weld area.

4. Undercut

Undercut can be identified by a groove along the edge of the weld bead that occasionally extends into the base metal. This can happen when too much heat is applied to the weld joint, causing it to melt excessively.


Undercutting can be welded over, which may include the addition of filler material and then grinding it down to create a smooth surface. However, welders must weld carefully near undercut areas because overheating can cause additional undercut and contaminate surfaces with slag particles.


Using less heat can keep the weld joint from melting excessively. Proper arc length and angle control also helps ensure that the operating electrode is close enough to the weld puddle and can achieve the desired weld appearance and strength.

Read:What is Fabrication in Welding?

5. Spatter

Welding spatter appears on welding seams as small, raised dark globules or lines of molten metal and can also be round with jagged edges. Spatter occurs when molten metal droplets are expelled from the weld, leaving unwanted deposits on the workpiece's surrounding surfaces.


To remove large pieces of spatter, use a grinding wheel or wire brush. For complete removal of finer spatter, you might need a file or scraper instead. Nonmetallic abrasives, like emery cloth or glass beads, can be used with these tools to refine the repair.


It's critical to use the correct welding angle, amount of filler material and amount and type of shielding gas. It’s also important to choose the correct electrode for the material being welded to help create a smoother arc. This calls for an electrode with a good arc length and stability, as well as one that is not overly aggressive to avoid spatter.

6. Overlap

Excessive heat application can cause materials to improperly fuse together, creating overlapping grained ridges, edges or excess weld beads – all of which are examples of overlap.


To repair overlap, welders can grind away excess material until the surface is smooth again. Before rewelding, technicians should use a high-quality filler rod that matches the base metal. They should also check that all surfaces are clean and free of contaminants to ensure a seamless weld.


Overlap can be prevented by maintaining a consistent travel speed and angle with each pass. Adequate joint preparation can also help to avoid excessive gaps between pieces, especially with proper joint alignment.

The best way to deal with welding defects is through prevention, which you can learn by developing essential industry skills used in different types of welding! Technical training can also help you achieve credibility on paper and practice typical welder's duties prior to pursuing a career!

UTI's 36-week Welding Technology program offers students the instructional support and technology they need to learn these skills. Graduates from our welding program can also earn a diploma or certificate to show employers that they’ve received training that prepares them for the role to which they are applying!

Read: Welding Joint Types: Butt, Lap, Tee, Edge Joints & More

Learn to Avoid Welding Defects With Skills Learned at UTI!

Welding defects can cause major product failure if not identified and dealt with appropriately. To avoid these costly issues, welding professionals should identify and address them as soon as possible!

Welding training at UTI can help aspiring welders gain skills and knowledge to pursue a career in welding. Curriculum developed with Lincoln Electric instructs aspiring welders on four main arc welding types: SMAW, GTAW, FCAW and GMAW. Completing our program can assist aspiring welders in honing these skills, which is required to successfully complete important welding tasks!

Want to find out more about how you can train as a welder? Request more information to get your questions answered. When you're ready to start learning, apply to our welding school!

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1) UTI is an educational institution and cannot guarantee employment or salary.

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Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


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