[Latest 2022] What Is Welding Porosity? Root Causes, Prevention & Fixes

Every welder has encountered welding porosity.

Nothing irritates a welder more than watching sparks and little explosions mid-bead, knowing what will happen when the hood is lifted.

We will explore what it is, what causes it, and what we can do about it in this article.

What Is Welding Porosity?

Welding porosity is a welding defect caused by trapped gases in the molten weld puddle during solidification, resulting in pockets or pores on the surface or within the bead. Porosity can arise on the surface of a weld or within the weld bead.

Various Types Of Porosity

There are four distinct types of weld porosity.

The Porosity of the Surface

Surface porosity, often known as surface-breaking pores, is one of the most visible types. It is the porosity that resembles swiss cheese to the naked sight.

Welding Porosity

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

The Porosity of the Subsurface

Additionally, subsurface or scattered porosity can be concealed beneath the bead’s surface. This type of porosity is more difficult to identify.

An X-ray or a grinder are effective tools for detecting this type of porosity. Additionally, this porosity can be seen as a little bubble that swells as the bread cools.


Wormhole porosity is evident only after the slag is removed from a bead using a flux-based technique.

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


Cratering is an example of a particular type of porosity. Cratering is a little indentation at the end of a bead typically found.

Cratering is a solidification phenomenon caused by gravity and the contraction of molten metal. Regardless of the type of porosity, it can cause a weld to fail inspection, fail, or, in the worst-case scenario, inflict injury to someone, depending on the integrity of the weldment.

Why Is Porosity Created?

A variety of factors can cause porosity. Among these are the following:

  • Contamination that has been deposited on the base metal
  • Atmosphere infiltrating the weld pool as a result of insufficient shielding gas or flux
  • Issues with the machine’s mechanical operation
  • Incorrect welding procedure


The material to be welded may be contaminated with various contaminants, including paint, oil, moisture, mill scale, and even the oil left on your grimy gloves when handling the item. These impurities rapidly ignite into fumes that become trapped within the weld pool, preventing the formation of a solid weld structure.

Gas Shielding Issues

The shielding gas or flux keeps the molten puddle from reacting with the surrounding atmosphere. When this shielding gas is applied incorrectly, or the flux becomes polluted with moisture, porosity occurs.

Without sufficient shielding gas, the weld will be oxidised at best. Typically, the liquid metal reacts with the surrounding atmosphere, trapping gases such as oxygen and nitrogen within the weld pool and resulting in porosity.

Additionally, excessive shielding gas flow pressure can be a concern when the gas flow rate is excessive; turbulence forms within the shielding envelope. It will draw the surrounding environment into the insulated area, resulting in porosity.

Mechanical Issues

Difficulties with the welding equipment can also result in bead issues. The most frequently encountered problems are as follows:

  • Outside air will infiltrate into the shielding gas delivery system through cracked MIG liners, worn O-rings, or unsecured fittings.
  • MIG nozzles clogged with spatter might cause shielding gas to be disrupted.
  • Shielding gas bottles themselves may be polluted with contaminants, contributing to porosity in the weld bead.


Another approach to creating porosity in a bead is poor technique. For instance: 

  • A TIG torch or MIG stinger held at a severe angle may result in gas not entirely covering the puddle in the shielding gas.
  • Moving too quickly for the available protection can also reveal the puddle.

Preventing Porosity

What can we do to prevent porosity now that we understand the causes?

By performing some of the following procedures, you can decrease the likelihood of developing porosity.

Preparation of Materials

Preparation of the weld metal is critical for a high-quality bead.

Certain techniques are capable of welding through mill scale, paint, primers, or other metal coatings. Even primers that are engineered to be welded through are available.

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

  • Additionally, paint and other coatings should be ground, sanded, or media blasted away to expose the naked, clean base material.
  • Aluminium can be wire brushed to remove the oxide coating using a specialised stainless steel wire brush. Nota bene: The wire brush must be dedicated to aluminium to prevent ferrous metal from being transferred to the aluminium, potentially increasing contaminants.

Cleaning of Materials

Once all coatings have been removed from the material, you can start cleaning. Acetone is the most often used cleaner. Acetone is a fantastic solvent for oils and other pollutants.

Additionally, isopropyl alcohol and lacquer thinner works well. Additionally, chemical solutions are tailored to certain materials, such as Aluma-Clean for aluminium.

Simply avoid using chlorinated brake cleaners. The brake clean might leave a layer that emits harmful smells when burned. Apply the cleaning solution with a non-linting cloth. Another tip for cleaning metal is to wipe in a single direction, preventing pollutants from being splattered around the joint.

Machine Maintenance

Machine maintenance is also critical, not just for a porous weld but also for the bead’s overall quality.

The following is a list of routine maintenance tasks that you should perform:

  • Cleaning and changing MIG liners regularly.
  • Cleaning contact tips and nozzles of excessive splatter.
  • Check the tightness and cleanliness of the mating surfaces on the fittings on welders and regulators.
  • Lenses, diffusers, collet bodies, and O-rings used with TIG gas must be kept clean and debris-free.

Additionally, your welding rod and wire need to be cleaned.

Take a rod from a new tube and rub it across it with an acetone-soaked towel; you’ll be shocked at what comes from the factory!

Storing Stick Electrodes Properly

Moisture can taint stick rods.

You need to store the rods in a dry, sealed environment. If rods absorb moisture from the surrounding environment, they can be dried. Rod ovens are speciality ovens used to dry metal rods.

Concerns About the Environment

Additionally, the environment might contribute to porosity.

A small quantity of air movement is all that is required to disrupt the shielding gas. Open doors, fans, and even welding machine cooling fans might cause enough disruption to produce pores in the bead.

Therefore, to assist in reducing porosity, evaluate your surrounding environment and decrease air movement where possible.

How Do You Correct For Porosity?

Even after taking all precautions, there is a potential that porosity will manifest.

To repair a weld porosity properly, you need to remove the porous area of the weld. Welding over the affected bead will produce the same outcome.

Often, the best tool for this activity is a thin grinding wheel. The porosity is eliminated with the least amount of base metal reduction possible. After removing the damaged section, you must clean it thoroughly to ensure no impurities have been reintroduced.

Begin slightly ahead of the remaining bead and work your way back up to the existing weld.

Keep an eye on the toes of the weld to ensure they match the width of the original bead and complete it.


What are the primary factors that contribute to porosity?

Porosity is typically caused by contamination on the base metal, atmosphere entering the weld pool due to insufficient shielding gas or flux, mechanical faults such as broken MIG liners, worn O-rings, or loose fittings, or poor welding technique.

Is it possible to weld over porosity?

No, as the defect will continue to exist. To eliminate the flaw, you must first remove the porous area of the weld down to the base material and then clean it before rewelding that section.


Porosity can cause issues for both novice and professional welders. We will all face this issue along our metal melting adventure. However, it is also repairable and, in many situations, entirely avoidable. Preparation and maintenance are critical in preventing porosity throughout the welding process.

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