Porosity in Welding | Types & How to Fix Welding Porosity


If you are a professional welder, you will agree that welding is a difficult technique that requires years of skill and dedication to master. Even if you are new to welding, you can already begin constructing reliable joints on your workpiece. However, there are a few issues that will frequently arise with the projects that are, to say the least, vexing.

Porosity in welding is one such issue. This is essentially a defect that causes cavities on the weld, making the joint weaker or, in extreme circumstances, totally disengaged. As you might imagine, seeing the welding process fail, especially after a long and continuous weld, can be rather irritating.

Today, we’ll look at porosity in welding and try to grasp the problem, its different varieties, the causes of the problem, and how you may avoid porosity during welding.

So, this tutorial will undoubtedly be useful for people who are just beginning out in welding tasks and are frequently confronted with issues such as porosity. By following the same advice, you can avoid a variety of other problems.

What is Welding Porosity?

Welding porosity is a welding flaw caused by undesirable gases retained in the molten weld puddle during solidification, resulting in pockets or pores on the surface or within the bead. Porosity can develop on the weld’s surface or within the weld bead.

Different types of porosity

There are four types of weld porosity that can appear in various ways.

Surface Porosity

Surface porosity, often known as surface-breaking pores, is one of the most visible types. This is the porosity that seems to the naked eye to be swiss cheese.

The pores are either directly on top of the bead, uniformly distributed, or distributed randomly throughout the bead.

Subsurface Porosity

Subsurface or dispersed porosity can also be found beneath the bead’s surface. This type of porosity is more difficult to identify.

This type of porosity can be discovered using an X-ray or a grinder. This porosity can also be seen as a tiny bubble that swells when the bead cools.


Wormhole porosity is only evident when slag is removed from a bead produced using a flux-based method.

Wormholes are elongated pores that appear to be the result of a worm burrowing its way along the top of the bead or down into the bead.


Cratering is an example of porosity. A crater is a tiny depression found at the end of a bead.

Cratering is a phenomenon caused by gravity and molten metal shrinkage during solidification.

Depending on the integrity of the weldment, any form of porosity can cause a weld to fail, fail, and, in the worst-case scenario, injure someone.

Reasons Behind The Welding Defect

Now that you can easily identify the sort of porosity that appears in your welding projects, let us try to understand why this problem occurs. There are numerous causes of welding porosity that might jeopardize the integrity and dependability of the welding bead.

However, some of the most common factors that have been confirmed to be the perpetrator in many cases are discussed below. While some of these issues are entirely external, others are the result of poor setup or practice.

Contamination At The Surface

One of the most prevalent causes of welding porosity is surface contamination, which is caused by the fact that workpieces are not always pure and well-cleaned.

It commonly happens when raw material is not properly stored and comes into touch with external variables such as rain or moisture, causing contaminants to form on the surface. Even after cutting or polishing the surface, some of these contaminants may remain, resulting in porosity.

Because contamination causes porosity at random, it is difficult to identify. The impacts will be severe in areas where the impurity concentration is high. In terms of severity, the problem might range from minor gaps to larger and more significant holes.

Shielding Gas Coverage

Welding porosity can also be caused by insufficient shielding gas coverage. It is caused by insufficient or non-existent gas coverage. However, it should go without saying that it only occurs with welding processes that use a shielding gas, such as MIG or TIG welding. The shielding gas’s primary duty is to keep the weld bead from coming into touch with the surrounding environment. When it comes to welding, even the ambient air and gases might be considered contaminated.

If the shielding gas effectively covers the weld bead, it can prevent other gases from becoming trapped inside the surface. If this fails, you may observe several pinholes around the welded surface. Fortunately, this issue can be remedied by lightly sanding the top surface. If the pinholes are deep, it indicates that there is nearly no gas covering.

Moisture On The Weld Surface

Moisture is another common source of welding porosity. However, the heat rapidly vaporizes a large amount of moisture present on the workpiece’s surface. However, if the moisture content is too high, the metal begins to melt before all of the moisture has been removed. As a result, moisture gas becomes trapped inside the molten metal or the welding bead. Moisture porosity, like insufficient gas coverage, causes numerous big holes in the welding bead.

The trapped moisture can also cause welding issues and result in hydrogen cracking over time. It also shows issues with the flux electrodes, such as moisture or contaminants on the electrode’s surface. These electrodes can introduce hydrogen into the weld, causing it to become stuck inside the bead. It has the potential to weaken the welding bead and disrupt the operation.

Incorrect Welding Technique

Finally, incorrect welding methods may result in welding porosity. Because there are numerous ways for a welding process to go wrong, it results in a wide range of porosity. For example, if the welding torch angle is excessively steep, it may result in inadequate gas shielding. Alternatively, moving the welding flame too quickly may result in welding porosity owing to non-uniform heating.

When TIG welding, removing the shielding gas too soon leads to cratering at the end of the welding bead.

How to Prevent Porosity

What can we do to prevent porosity now that we know what causes it?

You can lessen the likelihood of porosity by doing some of the following steps.

Material Preparation

Weld metal preparation is critical to producing a high-quality bead.

Some welding methods can weld through mill scale, paint, primers, or other metal coatings. There are even primers that can be welded through.

However, for a pure bead, clean metal is always preferable, especially when TIG welding. To accomplish this, ensure that:

  • The Mill scale should be eliminated from hot-rolled steels.
  • Paint and other coatings should be ground, sanded, or media blasted off to expose bare clean underlying material.
  • To remove the oxide layer, wire brush aluminum with a stainless steel wire brush.
  • To avoid introducing ferrous metal to the aluminum and perhaps adding contaminants, the wire brush must be dedicated to aluminum.

Material Cleaning

After all, coatings have been removed from the material, a cleaning solution should be employed.

Acetone is the most commonly used cleaner. Acetone is very effective at dissolving oils and other pollutants.

Isopropyl alcohol and lacquer thinner are also effective. There are also chemical solutions tailored to certain materials, such as Alma-Clean for aluminum.

Just avoid using chlorinated brake cleaners. When the brake cleaner is burned, it might leave a coating that emits harmful gases.

To apply the cleaning solution, use a non-linting cloth. Another useful tip for cleaning metal is to only wipe in one direction; this avoids impurities from smearing around the joint.

Machine Maintenance

Machine maintenance is also necessary, not only for a non-porous weld but also for overall bead quality.

You should perform the following simple maintenance tasks:

  • Cleaning and replacing MIG liners on a regular basis.
  • Getting rid of surplus splatter from contact tips and nozzles.
  • Check the welder and regulator fittings for tightness and cleanliness of mating surfaces.
  • TIG gas lenses, diffusers, collet bodies, and O-rings must all be kept clean and debris-free.
  • You should also clean your welding rod and wire.

Tip: Take a rod from a new tube and wipe an acetone-soaked cloth across it, and you’ll be surprised by what comes from the factory!

Properly Storing Stick Electrodes

Moisture might taint the stick rods themselves.

Rods should be stored in dry, sealed storage. If the rods do absorb moisture from the air, they can be dried.
Rod ovens are specialty ovens used to eliminate moisture from rods.

Environmental Problems

Porosity can also be influenced by the environment.

It only takes a tiny movement of the air to disrupt the shielding gas. Open doors, fans, and even cooling fans from welding machines can provide enough disruption to cause pores in the bead.

Consider your surroundings and restrict surrounding air movement where possible to assist reduce porosity.

How To Fix Welding Porosity?

Even after taking all of the procedures listed above and conducting a flawless welding action, porosity is still possible and cannot be avoided. When such an effect is detected, the only option is to try to apply some short modifications to resolve the situation. The best technique to repair porosity in welding is to totally remove the porous region by grinding and rewelding the affected area.

A small and thin grinding wheel is the perfect instrument for the job. With such a tool, you may remove the porous surface of the welding bead while leaving the rest of the bead and the base metal untouched. To limit the likelihood of porosity, after cleaning the porous surface, clean the base metal before attempting to weld again.


What are the main causes of porosity?

Contamination on the base metal, atmosphere sneaking into the weld pool owing to incorrect shielding gas or flux, and mechanical concerns such as cracked MIG liners, worn O-rings, or loose fittings, or poor welding technique are common reasons for porosity.

Can you weld over porosity?

No, because the flaw will still exist. You must first completely remove the flaw by removing the porous area of the weld down to the base material and then cleaning it before rewelding that section.

How do you repair porosity?

The only way to repair a weld porosity correctly is to remove the porous area of the weld all the way down to the base material. Welding over the problematic bead will result in the same effect.


We hope that after reading our tutorial, you have a clear understanding of the severity of the porosity welding problem and its severity. Here, you can learn about the various causes of welding defects as well as the various methods that may be used to prevent them.

Because this problem is equally frustrating for both expert and rookie welders, understanding the major reasons for the problem and using the techniques to avoid generating welding porosity on your assignments will undoubtedly help you.

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