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How to overcome porosity in welding

Updated: Feb 22

Porosity, what is it?

Welding porosity is a welding defect that creates pockets on the surface of a weld or within the bead. This is due to unwanted gases being trapped within the molten weld puddle. There are a few different types of porosity:

  • Surface Porosity. - The most obvious porosity, the pockets are sat right on top of the bead and you will be able to spot them easily,

  • Subsurface Porosity. – Can be hidden under the surface and is usually harder to detect. You can find this with a grinder, or it can also form a small bead as the bead cools.

  • Wormholing. – This is only found when the slag is removed, they are elongated pockets that look like a worm hence the name.

  • Cratering. – This is a small divot usually found at the end of the bead.

Why does porosity happen and how can we sort it out?

Porosity can happen for many reasons but we can help you get to the best solution in lcuindg ing finding quality equipment. Now let's break it down to help you get the best weld for your applications:

  • Contamination of material. – Contaminations on materials such as oil and moisture will evaporate when welding, turning into a gas that may be trapped in the weld. Not allowing for a solid weld structure.

  • Shielding gas problems. – The shielding gas protects the weld pool from reacting with the atmosphere. If improperly applied this is when porosity will occur or if the flux is contaminated with moisture.

  • Mechanical problems. – Ensuring you have quality equipment is massively important. Mechanical problems have been a leading cause of leaving you with porosity in your welds. This is why having your welding machine serviced is important. (Get more information on the service and repair of your welder.) Even something as small as loose fittings can give you porosity issues.

  • Improper technique – Unfortunately it might be your welding giving you porosity.

  • Dirty Electrodes - Tungsten electrodes should be clean and free of any contaminants, as impurities can enter the weld.

  • Gas Flow Rate: Incorrect gas flow settings, either too high or too low can affect the quality of shielding gas coverage and lead to porosity.

  • Tungsten Electrode type: When considering weld porosity, the selection of a tungsten electrode can have an indirect impact. It is essential to prepare the tungsten correctly, which involves grinding and keeping the electrode tip clean, to ensure a quality weld. If the electrode is contaminated or inadequately prepared, it may introduce impurities into the weld, increasing the risk of porosity.

What we’d suggest

To avoid porosity on your welding applications we’d suggest ensuring you keep this in mind:

  • Preparation & Cleaning – This is such an important step to get the quality results you need. Including removing primer, paints, and contaminants on the surface of the metal. Using a cleaning solution to ensure all contaminants are removed and the fabrics used don’t leave any lint behind.

  • Welding Machine Maintenance – If your welder isn’t in good condition, YOU WILL get porosity. Having regular servicing on your welding equipment can ensure that everything is working. This involves cleaning and repairing if needed. We can help with that!

  • The correct storage of Electrodes. – Ensuring your electrodes are stored in a dry-sealed case so they don’t attract moisture. Moisture can affect your weld. An electrode oven can be a solution to dry your electrodes. Contact us for more information on available storage options and ovens.

  • Working on your technique. - If you're still experiencing porosity after trying all the above solutions. Try to alter of your technique, here are a few things to try.

    1. An extreme angle can result in gas not completely enveloping the puddle in the shielding gas, so try adjusting your angle.

    2. Try slowing down, if you’re moving too fast the amount of shielding available could also expose the puddle.

    3. Removing the shielding gas too early WILL cause a crater at the end of your bead! Increasing the post-gas setting on your MIG machine.

  • Gas Cup / Gas Lens - Using a gas lens gives a directed, laminar flow of gas, providing better coverage and also allowing the use of a longer electrode stick out for accessing narrow gaps. Use the correct-sized gas lens to ensure complete coverage of the weld pool.

  • Back Purge: In situations where the backside of the weld cannot be accessed, consider back purging to displace atmospheric gases. Back purging involves introducing inert gas on the backside of the joint to maintain a shielded environment.


TIG Welding Stock Image

In conclusion

You can follow these steps to try to avoid porosity in your welds:

  1. Keep it clean!

  2. Check your gas flow.

  3. Ensure your equipment is up to scratch.

  4. Work on your technique.


Now you can take all these precautions and porosity can still arise so how do you fix it?


You will need to repair it by removing the area of the weld down to the base material. Using a grinding wheel, re-clean to ensure no more contaminants. Then start welding ahead of the remaining bead and back up to the existing weld. If you try to weld straight over the porosity, you will end with the same result. As well as the structure of the weld will not be correct.


Starting out in welding porosity and other welding defects isn’t an easy fix but something that takes time and practice to overcome! Happy welding!


Let us help you get started in welding, we work with the best brand and provide quality welding equipment with your needs, and budget in mind, shop now. With the quality equipment and knowledge to help you get the results you want. Contact us for more help.


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