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Porosity In Welding – Types & How To Fix Welding Porosity?

If you are a professional welder, you can agree to the fact that welding is not a simple process and it takes years of practice and dedication to master the craft. Even if you have started welding recently, you can pretty much start developing reliable joints on your workpiece. However, there are a few problems that will commonly occur with the projects that are quite annoying, to say the least.

One such problem is porosity in welding. This is basically an imperfection that results in cavities on the weld, making the joint weaker, or completely disengaged in some cases. As you can imagine, it can get pretty annoying to see the welding process fail, especially after a long and continuous weld.

Today, we are going to take a porosity in welding and try to understand the problem, its types, the reasons behind the problem, and how you can avoid porosity while you are welding. So, this guide can definitely be helpful for those who are just starting to get into welding jobs and facing problems like porosity on a frequent basis. You can also prevent a lot of other similar problems by following the same tips.

Understanding Welding Porosity

Before we can understand the types of reasons behind the occurrence of porosity, we need to discuss what it actually is. There are a lot of welding defects that inexperienced or even professional welders face regularly. But, porosity is something that has a major effect on the end results. If the problem is severe, a lot of welders would need to repeat the process in order to ensure a reliable joint.

Welding porosity is a basic welding defect that is the result of additional gasses trapped below the welding surface. Since these glasses are trapped before the solidification of the weld, it creates a number of pores or pockets of air after the gasses are released. These pores can appear on the surface of the weld so that the welder can easily identify the problem and take the necessary measures. But sometimes, the pores are within the weld bead which makes the defect almost unidentifiable in a lot of cases.

What Are The Different Types Of Porosity

Now that you understand what porosity actually means, you can determine whether it is the same problem that you are facing with your welds or not. But since this is basically an abnormality caused by the presence of unwanted gasses, it appears on different levels and has varying defects on the weld beads. Based on that, there are 4 basic types of welding porosity that are commonly observed in the welding process. With this classification in mind, you can easily identify the type of welding porosity in your case and take necessary measures accordingly.

1. Surface Porosity

This is the most common type of welding porosity which is widely observed in a lot of cases. Due to the release of excessive gasses trapped inside the weld beads, surface porosity is formed. From the top angle, you can easily identify the pores present on the welding beads. While the problem is not that severe in this case, it still makes the bead weaker and causes stress concentration around the pores. And not to mention, it can appear quite bad on workpieces that are supposed to appear aesthetically pleasing. Surface porosity could be evenly spread across the bead, or appear at random places.

2. Subsurface Porosity

Unlike the previous type, subsurface porosity is quite difficult to identify since you cannot see it from outside. As the name suggests, subsurface porosity is below the surface of the weld. In this case, the excessive gasses on the inside of the weld bead did not escape. Thus, there would be internal pores of gasses inside the weld beads, or bubbles forming on the top of the bead.

It is caused by the quick solidification of the weld beads that trap the gasses permanently inside the bead. To observe subsurface porosity, you will need an X-ray machine. Or, you could just grind the top surface of the weld bead to check the presence of subsurface porosity.

3. Wormholing

This is a special type of welding porosity that is mostly observed in flux core welding. It is revealed when the slag is removed from the welding bead after the welding is done. In terms of appearance, the porosity looks like there are worms present on the inside of the bead. Thus, the name wormholing. The pores formed in wormholing are elongated and can be observed from the top angle directly since they appear on the surface.

4. Cratering

Compared to other types of welding porosity, cratering is quite different in terms of appearance as well as occurrence. This is basically a small crater or a hollow opening created around the end section of the welding bead. Unlike other porosity defects, cratering is caused by the shrinking of metal during the solidification process. This also results in the weakening of the weld and the chances of failure are quite high in the case of cratering. So, it is important to look out for cratering apart from other types of welding porosity.

Reasons Behind The Welding Defect

Now that you can easily identify the type of porosity appearing in your welding jobs, let us try to understand the reasons behind the occurrence of this problem. There are a lot of reasons that could cause welding porosity and compromise the integrity and reliability of the welding bead. But, some of the common reasons that are proven to be the culprit in a lot of cases are explained below. While some of these factors are purely external, some are caused by improper setup or technique.

1. Contamination At The Surface

Contamination of the surface is one of the basic reasons behind welding porosity, and is also pretty common since the workpieces that you get are not always pure and properly cleaned. It usually occurs when the raw material is not stored properly and comes in contact with environmental factors like rain or moisture, causing it to develop impurities on the surface. Even after cutting or polishing the surface, some of these impurities may not be removed fully, causing porosity.

It is quite difficult to identify porosity caused by contamination since it occurs randomly. The effects will be severe around the parts where the concentration of impurity is high. And as for the severity of the problem, it can range from small gaps all the way up to larger and more problematic holes.

2. Shielding Gas Coverage

Improper shielding gas coverage can also cause welding porosity. It is caused by very little gas coverage or no gas coverage at all. But, it should be pretty obvious that it only occurs with welding procedures that utilize a shielding gas such as MIG or TIG welding. The main function of the shielding gas is to avoid contact with the weld bead in front of the surrounding environment. And when it comes to welding, even the surrounding air and gasses could be considered a contaminant.

If the shielding gas is covering the weld bead effectively, it can prevent other gasses from getting trapped inside the surface. Failing that, you will start to notice numerous pinholes around the welded surface. Fortunately, this problem can be resolved by grinding the top surface a little bit. If the pinholes are deep, it means that there is almost no gas coverage available.

3. Moisture On The Weld Surface

Moisture is also a common cause of porosity in welding. However, a lot of moisture present on the surface of the workpiece is instantly vaporized due to the heat. But, if the moisture quantity is too much, the metal starts melting before all the moisture could be removed. This results in the moisture gas getting trapped inside the molten metal, or the welding bead. Just like improper gas coverage, porosity caused by moisture creates numerous large holes in the welding bead.

The trapped moisture can also cause problems with the welding and result in hydrogen cracking over time. It also indicates problems with the flux electrodes such as moisture or impurities on the surface of the electrode. Such electrodes can introduce hydrogen into the weld which gets trapped inside the bead. It can effectively weaken the welding bead and damage the process.

4. Incorrect Welding Technique

Lastly, an improper welding technique could also introduce welding porosity. It results in a lot of different types of porosity since there are a lot of ways a welding process can be done wrong. For example, if the angle of the welding torch is too steep, it could result in improper gas shielding. Or, if you are moving the welding torch too fast, it could also result in welding porosity due to non-uniform heating. In the case of TIG welding, if you remove the shielding gas too quickly, it results in cratering at the end of the welding bead.

Is It Possible To Avoid Welding Porosity?

Well, yes. Now that you completely understand what porosity is and why it occurs in the welding process, you can easily follow some tips mentioned here to avoid porosity in your jobs. It is crucial to create strong and reliable welds since most welded jobs are supposed to be under a lot of stress. So, you need to take all preventive measures to avoid defects like porosity that can compromise the quality of the weld.

1. Material Preparation

One of the first practices that you should get a habit of is preparing the weld metal properly before you start the process. While there are a lot of welding procedures that can weld through a variety of surface finishes or layers like primers, paints, and other types of coatings, you need to ensure that the method you are using is capable of doing the same or not for your workpiece. For an assured welding result, the best way is to perform the welding on clean metal.

The process of material preparation is pretty easy and it does not involve anything more than grinding or polishing the top surface of the workpiece for a few minutes. For example, if you are working with hot-rolled steels, you need to ensure that the mill scales are properly removed. As for a painted or coated surface, you can have the surface polished to reveal the clean metallic surface beneath the coating.

2. Material Cleaning

Apart from preparation, it is also important to clean the workpiece before you start working on it. Once you clear up the coating or polish the surface, you will have to introduce a cleaning solution to get rid of the residue particles to obtain a clean surface. One of the most effective compounds for that is Acetone. It can effectively dissolve oils and a variety of other contaminants to offer a properly clean surface.

If that’s not available, you can also use isopropyl alcohol as an alternative. There are a lot of chemical solutions that are specifically designed for a certain type of material such as Aluminum. While you are selecting a cleaning solution, just make sure that you avoid the ones that can leave a film or layer behind. Such cleaners can generate toxic fumes at the time of welding that can be harmful to the welder.

3. Machine Maintenance

Apart from the workpiece, you also need to pay attention to the machine and see if there are any problems with the welder itself. Taking good care of your welder will not only prevent defects like welding porosity but also improve the overall quality and reliability of the process. Here are some basic tips to keep the welder in perfect shape.

  • Make sure you regularly clean the MIG liners
  • If there is an excessive concentration of spatter on the nozzle, you need to clean it right away.
  • Check all the fittings and connecting parts and ensure there is no loose contact.
  • Keep the welding rod as well as the welding wire clean and free from contaminants.

4. Environmental Problems

As you may already know, there are a lot of external factors that can also introduce welding porosity. While there is little you can do to avoid surrounding problems, you can effectively simply change the surroundings to prevent the ill effects altogether. For example, if there is a strong wind where you are working, you can choose to move the setup to a relatively closed area. For external jobs, it would be helpful to create an obstacle to diffuse the wind before it comes in contact with the weld.

How To Fix Welding Porosity?

Even after taking all the precautions stated above and performing a perfect welding motion, it is still possible to observe porosity which simply cannot be avoided. When such an effect is observed, the only thing left to do is try and apply some quick fixes to resolve the problem. The best way to fix porosity in welding is to remove the porous section completely by grinding and re-welding the affected area.

The best tool for such a job is a small and thin grinding wheel. Such a tool will allow you to remove the porous surface of the welding bead while keeping the rest of the bead as well as the base metal unaffected. Once you clean the porous surface, make sure you clean the base metal before attempting to weld again to reduce the chances of porosity.


We hope that you have thoroughly understood the severity of the porosity welding defect and its severity while going through our guide. Here, you can learn about different reasons that could potentially cause the welding defect and a variety of solutions that you can apply to prevent that. Since this problem is equally frustrating for both, experienced as well as novice welders, it will certainly help you if you understand the main causes behind the problem and practice the tips to avoid generating welding porosity on your jobs.

Source: Porosity In Welding

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