10 Common Welding Defects and How to Avoid Them

Written By: Liam Bryant

There are many types of welding defects. They include lack of fusion, slag inclusion, lack of penetration, cracks, warpage, and burn-through.

You’ll inevitably cross paths with at least one of these defects during your welding career. However, understanding why each of them happens will help reduce the likelihood of them plaguing your welded joints.

This is why I’ve compiled this guide to gather all the information you need in one place.

Read on to find out more about what each of these defects looks like and what their most common causes are.

What Are Welding Defects?

Before we dive into the different types of defects that may affect your welds’ quality, let’s first have a brief overview of what welding defects are.

Welding defects refer to any inconsistencies or discontinuities in the structure of a welded joint. Such imperfections can be related to the joint’s shape or the distribution of materials within it.

Many factors could lead to defects in your welds. The most common ones include the incorrect choice of materials, lack of skill from the welder, and using an unsuitable welding current or speed for the job at hand.

Here are some of the most common welding defects that you’re likely to encounter:

1. Lack of Penetration

One of the more common welding defects you may see is a lack of penetration. This refers to the welding groove being too narrow. This doesn’t allow the material being welded to fill up the joint completely.

This is problematic because it has a negative effect on the strength of the joint. As such, this makes it more susceptible to breakage.

This defect is usually caused by incorrect joint preparation and a faulty mixture of shielding gas. 

10 Common Welding Defects and How to Avoid Them

2. Lack of Fusion

Similarly to incomplete penetration, a lack of fusion in a welded joint involves gaps in it. This happens as a result of the flame not heating up the materials enough to fully melt. This makes them solidify before they’ve completely filled up the joint.

Common causes for a lack of fusion include using a welding current that’s too low. Reasons also include welding with the torch not being at the optimum angle, as well as using a weld pool that’s too big.

3. Undercut

When an undercut defect occurs, it leads to your welded joint having an inconsistent thickness. This will manifest itself as a slight depression at the edge of the welded area

Not only is this an issue aesthetically, but it also has functional implications. That’s because it causes the welded joint to be weaker and more likely to fail when exposed to stress or pressure.

In order to avoid having undercuts when you’re welding, you should make sure to move the torch at the correct speed. You should also use an appropriate welding current too.

10 Common Welding Defects and How to Avoid Them

4. Spatter

Another common welding defect is spatter. This is when residual droplets of molten metal splash onto the surface of the material you’re welding. When these droplets solidify, they remain etched onto the surface, making it look less than ideal.

Although spatter doesn’t affect the strength of your welded joint in any way, it’s still an issue because you’re going to need to remove it. This takes additional time and effort.

In order to avoid this, you should ensure that you’re using the correct arc length, welding current, and polarity.

10 Common Welding Defects and How to Avoid Them

5. Slag Inclusions

Slag (a non-metallic byproduct of welding) can become an issue when it isn’t handled the right way.

This is because the presence of slag on the surface of your welded joint, or inside it, can compromise the joint’s structural integrity and weaken it.

Slag inclusion may occur due to an incorrect welding angle or welding speed. It might happen if you don’t clean the edge of your weld consistently as you’re working on it either. 

Furthermore, if you’re using a welding current that’s not heating the materials up enough, this may also cause slag inclusion.

welding slag

6. Cracks

This welding defect is just as bad as it sounds. After all, you never want your welded joint to have fractures in it.

This isn’t just because cracks look unappealing, but it’s also because they create high-pressure areas in your weld. That causes it to be prone to breaking when exposed to the slightest degree of stress.

Cracks often occur as a result of the materials you’re welding cooling too fast. In order to avoid this, you should preheat these materials to make them cool down slower. Additionally, you should ensure that you’re using the correct mix of sulfur and carbon

7. Porosity

Having too much porosity in a welded joint is also considered a defect. Porosity refers to the amount of gas that’s trapped inside the joint. If there are too many gas bubbles within the welded area, this can severely reduce the strength of the joint.

You may be wondering where this gas is coming from in the first place. The answer is that when you heat metals, it’s completely normal for gasses, such as carbon dioxide and hydrogen to be produced.

The key is to allow these gasses to escape before the materials you’re welding solidify and trap the gasses inside.

porosity in welding

8. Overlap

Overlap is the polar opposite of an undercut. It refers to excess material seeping over the welded joint, resulting in an elevation at its edge. Just like undercuts, overlaps don’t bode well for the structural integrity of your weld.

The main reasons why an overlap may occur include choosing the incorrect welding technique and materials for the task at hand. Overlaps may also happen because you haven’t properly prepared the materials to be welded.

welding overlap

9. Warpage

Warpage is another issue that you may come across during your welding career. It involves the distortion of the dimensions and configuration of the metals you’re welding. 

This typically happens when you have a lapse in judgment when choosing the heat settings to use for a particular weld. This results in excessive expansion or contraction of the materials, and in turn, causes them to warp.

10. Burn Through

The final welding defect on our list is burn through. This is when you burn right through the metal you’re welding. Needless to say, this is one of the more problematic defects you can encounter.

The primary reason why burn-through may happen is that you’ve used a significantly higher level of heat than you should have. As a result, the heat from the torch melts a hole through the metal, destroying it instead of creating a stable structure.


Throughout your journey as a welder, you’ll definitely have to deal with welding defects no matter how skilled you are.

These defects are structural and aesthetic imperfections that affect the quality of your welded joint. Their main causes are choosing the wrong welding technique or using welding heats and speeds that aren’t suitable.

Some of the more common welding defects you may come across include lack of fusion, slag inclusion, lack of penetration, cracks, warpage, and burn-through.