Welding Defects Explained

Welding defects can be disastrous.    

If your weld isn’t successful, the finished product can undergo failure and risk 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 Technology 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 hands-on lab training. After graduation, they can use their knowledge to pursue a career in the industry.¹

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

Key Summary Points

• Welding defects can lead to product failure and dangerous operation, making it crucial to identify and repair them.
• Universal Technical Institute's 36-week Welding Technology program teaches students how to prevent welding defects and pursue a career in the industry.
• Common welding defects include cracks, slag inclusions, porosity, undercut, spatter and overlap.
• Repairing welding defects often involves grinding or chipping away the affected area and rewelding with proper techniques.
• Prevention of welding defects includes proper pre-heating, removing slag particles, ensuring proper alignment and cleanliness and using the correct welding angle, filler material and shielding gas.

Harms of Welding Defects

Welding mistakes can be hazardous during both manufacturing and servicing. 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 reduce product durability over time
• Health and safety hazards since cracks can allow hazardous materials to escape from pipes/machinery and cause structures and materials to fail

Read: What is Welding Burnback?

Causes of Welding Defects

Defects can occur because of a variety of reasons and can impact the quality and integrity of a welded structure. Identifying their root causes is essential for figuring out effective solutions and ensuring future welds are successful. Below are some common causes of welding defects:

• Porosity: Gas pockets become trapped in the weld pool, often due to contaminated materials or insufficient shielding gas.
• Cracking: Stresses within the weld metal and heat-affected zone can lead to cracks, typically caused by rapid cooling or improper welding techniques.
• Incomplete fusion: When the weld metal fails to properly fuse with the base materials, it’s usually due to inadequate heat input or incorrect welding angles.
• Undercutting: Material is melted away from the weld edges, leaving grooves along the weld seam. Can be caused by excessive welding speed or high welding current.
• Overlapping: When the weld metal overflows onto the base metal without proper fusion, it’s often due to a too-slow welding speed or excessive welding current.
• Slag inclusions: Non-metallic solid materials get entrapped in the weld metal, often caused by improper slag removal between welding passes or inadequate cleaning of the base metal.

6 Examples of Bad Welds

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

For the most part, preventing problems with welding is a matter of executing proper welding techniques. Aspiring welders can enroll in UTI’s 36-week Welding Technology program, which teaches the techniques used in four major welding processes – GMAW, GTAW, SMAW and FCAW and 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.

Repairing

For the most part, welded components that have cracked must be replaced and rewelded immediately. While some types of weld 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.

Prevention

Proper pre-heating of the weld area allows the metal to expand slowly and evenly, reducing      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 weld defects form when slag particles become trapped inside a weld.

Repairing

Weld defects can be repaired by grinding or chipping away the surrounding material. Then, the material is rewelded using low heat.

However, this method should be used with caution since 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.

Prevention

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 often caused by trapped gas or a lack of filler material during welding, resulting in the incomplete fusion of metal pieces.

Repairing

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.

Prevention

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.

Repairing

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.

Prevention

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.

Repairing

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.

Prevention

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.

Repairing

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.

Prevention

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.

Industry-Aligned Welding Training

UTI's 36-week Welding Technology program offers students the technology and instructional support they need to learn these skills in SMAW, GTAW, FCAW and GMAW welding.

Graduates from our welding program earn a diploma or certificate to show employers that they’ve received training that prepares them for the role to which they are applying! Completing our program can assist aspiring welders in honing these skills, which is required to successfully complete important welding tasks!

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

Welding Defects FAQs

1. What are the most common visual welding defects?

The most common visual welding defects include cracks, slag inclusions, porosity, undercut, spatter and overlap. These weld defects can compromise the integrity and strength of a weld if not properly addressed and promptly repaired.

2. How can undercut welding defects be prevented?

Undercut welding defects can be prevented by using less heat and maintaining proper arc length and angle control. Ensuring the electrode is positioned correctly close to the weld puddle can also help achieve the desired weld appearance and strength without causing undercut.

3. What is the most severe welding defect?

Cracking is considered the most severe welding defect because it significantly weakens the structure and can lead to failure. Cracks must be addressed immediately, often through complete rewelding, as they cannot remain within acceptable parameters for final products.

4. How do you fix welding defects?

Fixing welding defects depends on the type of defect, but common methods include grinding, rewelding and using proper filler materials. Techniques to repair defects often focus on removing affected areas and ensuring clean, smooth surfaces to prevent recurrence.

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!    

Want to find out more about how you can train to become a welder at Universal Technical Institute? Request more information online or call us at 1-800-834-7308 to contact an Admissions Representative and get your questions answered. When you're ready to start learning, apply to our welding school!