9 Most Common Defects In Welding and How You Can Avoid

Welding is an intricate task. It involves so many variables that mistakes are inevitable most of the time. Even for seasoned welders, minor defects are difficult to avoid. A thorough understanding of the nature, properties, and causes of defects is needed to avoid them.

Cracking is the most common welding defect. Porosity, lack of penetration, presence of undercut, excessive reinforcement, etc., are also pretty familiar. Interestingly, lack of skill is not the sole reason behind these defects. Metallurgical properties and relevant factors also play a huge role in all of them.

Welding defects and welding discontinuities can be confusing. All defects are discontinuities, but all discontinuities are not defects. Knowing the difference is crucial when discussing welding defects. In this article, I will discuss relevant topics regarding welding defects, along with the most common defects in welding. So, let’s go!

9 Welding Defects That Every Welder Should Know

Knowing about common welding defects is barely enough to prevent them. But if you know them, you can at least identify what’s wrong with your weld and take the necessary measures. Here are the nine most common welding defects:


Cracks in welds are the most common defect. They are also considered quite dangerous and can compromise the strength of the weld. Cracks occur mostly due to temperature shifts and the properties of the metal. There are two major types of weld cracks; hot cracks and cold cracks. There are also crack types like lamellar tearing, crater cracks, etc.

Hot cracks occur when the hot weld pool turns solid from liquid form. This crack occurs at a temperature of more than 10,000 degrees Celsius. Cold cracks occur after the weld completely cools down. It can take place days after the weld is completed. Cold cracks are common in steel welding.

Cracks occur for many reasons. Contamination of the welding field is the main reason and most common reason. Not preheating the metal pieces before welding can also cause cracking. Solidification shrinkage, poor joint design, the composition of the steel, etc., also contribute to cracking.

A contamination-free welding zone can prevent cracks 90% of the time. So, clean the welding site properly and use the correct shielding gas. Joint design is a factor that many welders often overlook. Thus, having a thorough understanding of this subject is essential. Proper welding speed, right amperage, preheating, etc., also aids in preventing cracking.


Porosity is exactly what the name suggests. Due to trapped gasses, pores form inside the welding field. Porosity is also called wormhole weld. It can occur on the surface of the weld or inside. Gas bubbles that come into contact with the weld usually bubble out of the molten weld pool. Those who can’t form the porosity.

Porosities can weaken the joint and deteriorate the overall quality of the weld. Any contaminant, such as rust, dust, oil, grease, paint, etc., can result in porosity. However, mishaps in shielding gas usage are the main reason behind porosity. If you select an improper gas, or if the mixing is not appropriate, the shielding gas won’t repel atmospheric gasses from the welding field.

If the gas flow is too much, in that case, the shielding gas can’t work up to the mark. Surface contamination, moisture, using a long arc, etc., are the associated factors. Properly cleaning the weld surface, using the right electrodes, and being meticulous with the shielding gas are the best ways to avoid porosity in your weld.


An undercut is when there is a lack of weld material at the edges of the weld bead. When viewed from a cross-section, undercuts appear as notches. It can occur either at the top or bottom of the weld. The base metal surface does not meet at the same plane due to the presence of an undercut.

The weld loses thickness because of the undercut. It can result in compromised strength of the weld joint. There are three types of undercuts: continuous undercut, inter-run undercut, and intermediate undercut.

The welder’s lack of skill is the reason for the undercut most of the time. If the welder holds the electrode at the wrong angle, it delivers excessive heat to the edges of the weld bead. It results in notches at the edge. Also, too high current, too fast welding, using a large electrode, improper filler metal, etc., are the reasons for undercuts.

To avoid undercut formation, there is no better alternative than developing skills in welding. You have to know what type of electrode you should use, the right angle, proper current and amperage, and maintain the right speed.


Make sure you check our article 9 Great Tips to Prevent Overlap in Welding

Overlap is the opposite of an undercut. When the weld pool overflows and the weld face extends to the surface of the base metal without a proper joint, this is known as overlap. It is also called overfill. Overlap does not fuse with the base metal. The causes of overlap are more or less similar to the causes of the undercut.

Improper welding technique is the principal reason. If the electrode is too large, it can also cause overlapping of the weld pool. Long arcs, improper electrode angulation, excessive current, large deposition, etc., also cause overlap.

Like undercut, the best way to avoid overlap is to have exceptional skill and knowledge in welding. Have a crystal-clear idea of the electrode angle and maintain it throughout the procedure. Using a small electrode, minimal current during welding, and proper technique is the way to prevent overlap.


Underfill is like the worst version of the undercut. Undercut occurs when the weld bead’s surface sits below the base metal level. The weld bead is thinner than the base metal when viewed from the cross-section. Underfill is very detrimental and can drastically affect the joint quality.

Fast welding speed is the main reason behind the underfill. If you move too fast along the weld bead, an adequate amount of filler metal won’t get enough time to be deposited into the joint. It will result in less-than-ideal thickness of the bead and underfill.

Like most welding defects, expertise is the remedy here. Don’t move the electrode too fast along the weld bead. Use the correct instruments and settings. Make sure the electrode or filler wire is the right size.

Lack of Fusion

In welding, the filler metal fills the joint and fuses with the face of the entire joint. When the filler metal can’t fuse with the base metal, it is called a “lack of fusion.” It is also known as “cold lapping” or “cold shut.” Lack of fusion can occur both inside the welding and on the surface. It is divided into three categories: lack of sidewall fusion, inter-run fusion, and root fusion.

Lack of sidewall fusion occurs when the filler metal can’t fuse with the sidewalls of the weld joint. A lack of root fusion occurs when the filler metal fails to fuse with the weld root. And, a lack of inter-run fusion is when there is a lack of fusion between adjacent weld passes.

Common reasons for lack of fusion are low heat, the inadequate diameter of the electrode, excessive speed, faulty bead placement, large root face, small root gap, etc. To ensure proper fusion, maintain a steady travel speed, but not too much. Properly prepare the edges and maintain adequate root gaps.

Improper Penetration

Incomplete or improper penetration can seem confusing with a lack of fusion. Lack of fusion can occur at any part of the weld. It means that the filler metal has penetrated all the way through but was unable to fuse with the base metal.

Improper penetration means when the filler metal cannot fill the joint to the bottom. The filler metal doesn’t fully extend through the thickness of the joint. When viewed from a cross-section, the absence of filler metal at the bottom of the weld is visible. This type of weld defect severely weakens the weld joint.

If the gap between the two weld pieces is too much, the filler metal can’t penetrate to an adequate thickness. Also, just like a lack of fusion, moving the bead too fast doesn’t give the filler metal enough time to penetrate to full death. Large electrodes, misalignment, etc., are also the factors behind the lack of penetration.

Complete knowledge of joint design and preparation can prevent most cases of improper penetration. Besides this, you should practice properly aligning and using the right-sized electrode to avoid this situation.

Excess Reinforcement/Penetration

The terms “excess reinforcement” and “excess penetration” are used interchangeably, but that’s incorrect. But for the sake of your understanding, I will discuss both of them in the same section of this article.

Excess penetration means when the weld bead exceeds the root and comes out of the bottom of the weld joint. Excess reinforcement means excess filler metal on top of the weld bead. In the cross-sectional view, it looks like a mountain. That’s why it’s also called “mountain range reinforcement.”

The main way to prevent excess reinforcement is to maintain a proper speed. If you are welding too slowly, the excess filler will be placed on the bead. Also, with the correct amperage and voltage, the right amount of heat can prevent excess reinforcement. Proper alignment plays an important role in preventing this kind of weld defect.

Burn Through

Excessive heat can melt the faces of the joints. It occurs when the heat exceeds the melting point of the base metal on a large scale. It is also called “melt-through.” When it occurs, the strength and integrity of the joint are severely compromised.

Burn through usually occurs when the base metal is too thin, usually less than 1/4 of an inch. But it can also happen if the welding settings are too high. If your welding speed is too slow, it means that metal is getting excessive heat at a given time. It can also cause burn through.

The solution is simple. Use the correct settings and ensure that your travel speed is not too slow. The excessive gap between the base metals causes burn-through, so try to minimize the gap. Be extra cautious when welding thin metal pieces.

Other Welding Defects

Aside from the defects I mentioned above, tons of different defects can be present in a weld. Some of these are quite common, while some are rarely seen. But as a welder, you should know their names. So here are some more welding defects:

  • Warpage
  • Slag inclusion
  • Torn Surface
  • Root Concavity
  • Stray Arc
  • Spatter
  • Incorrect profile
  • Grinding Mark
  • Distortion
  • Under-flushing
  • Irregular Width
  • hot tear
  • Mechanical damage
  • Convex and concave weld
  • Chipping Mark

Are Welding Defects And Welding Discontinuities The Same Thing?

You might often hear the terms “welding defects” and “welding discontinuities.” The welding defect is pretty self-explanatory. It means defects in the welding. It can be inside the welding or on the surface. But what is welding discontinuity?

Welding defects and welding discontinuities bear almost the same meaning. Discontinuities are negligible defects. Minor defects that do not compromise the joint strength and quality of the overall structure are called discontinuities. Discontinuities are an inseparable part of welding.

No matter how expert you are or how meticulously you weld, the welding won’t be 100% perfect. There will always be discontinuities. As long as those discontinuities are not detrimental to weld quality, they can be ignored and do not need any correction.

But when any discontinuity is too big to ignore, it automatically falls into the category of defects. Welding defects cannot be ignored and need correction. Everything I discussed above is present in every weld on a smaller scale. But when their presence is detrimental to the weld quality, they are referred to as welding defects.

How Can You Avoid Welding Defects?

Every welding defect happens for some reason. If you know what is causing a defect, you can easily avoid the causative factors and thus prevent the defect from happening again. If you look closely, you will see most defects occur because of excess speed, improper welding rod selection, improper joint preparation, excessive heat, etc.

All of these stem from one reason: a lack of knowledge and expertise. So, take your time and first learn the basics of welding slowly. Then try to understand the advanced concepts. What you are doing and what you should do. It should prevent most welding defects from occurring.

Some basic steps apply to all types of welds. You can largely avoid welding defects if you know and implement these tricks. Here are those:

Use Low Hydrogen Fillers

Hydrogen-induced cracking is a common defect in steel welding. Before purchasing, make sure you get electrodes with low levels of diffusible hydrogen. Hydrogen-induced cracking or cold cracking when the weld cools down. Thick metal pieces are more prone to such cracking, so always use filler rods with the least hydrogen.

Match The Filler Metal

The filler metal should match the properties of the base metal. Both physical and mechanical properties should match, or at least should be close. It will ensure the optimum strength and improved properties of the weld joint. When welding dissimilar metals, match the filler with the lower-end metal.

Store The Filler Rods Properly

Filler rods melt and make the weld joint. So, the condition of the filler rods plays a huge role in the weld quality. If you store them in an unfavorable condition, they will acquire oil, dust, moisture, etc., and subsequently, degrade the quality of the rods.

If you weld with such contaminated rods, the weld quality will be less than average. So, store them as per the manufacturer’s guidelines. Keep them in their original packaging. Don’t open another packet before finishing the prior one. Always use welding gloves so that filler rods don’t catch moisture from your hands.

Gain Knowledge On Joint Design

Joint design is widely disregarded by many welders. But many don’t know that how you prepare the joints can single-handedly determine the weld quality. The joint depends on the type of the base metal, the filler metal, the thickness, the welding type, etc.

You cannot just ignore something that’s associated with so many variables. If you have read the above section where I discussed the common defects, you will see that faulty joint design is associated with most of them. If you know the ins and outs of joint preparation, hopefully you can steer clear of most welding defects.


There is no alternative to practicing. Only consistent exercise can make you a better welder than you were yesterday. Learn all the nitty-gritty of welding from an experienced trainer. Don’t be shy about asking questions. Learn from your mistakes. Don’t give up and keep practicing every day to overcome the defects.


Welding defects are a vast topic. There are countless different defects resulting from hundreds of different factors. Discussing all of them to this limited extent is anything but possible. But if you know the most common defects and related factors, you will be able to get through them most of the time.

That’s what I focused on in this article, and I believe this write-up could give the least insight into the most common defects in welding.

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