What Causes Porosity in MIG Welding & How To Fix It

Porosity is a welding defect that causes gas trapped into the weld puddle while welding. During the generation of weld beads, if gas or other contaminants get trapped inside the weld puddle, small gas pockets or voids become visible on the weld. It minimizes the quality of the welds.

Causes Of Porosity in MIG Welding

Porosity in MIG (Metal Inert Gas) welding is a common defect that compromises the integrity of your welds. Understanding the causes of porosity is vital to maintaining high-quality welds.

Below are reasons for porosity in MIG welding:

reasons of porosity in mig welding
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  • Gas Contamination: If shielding gas is contaminated by air or moisture and get stuck inside the weld puddle, it can lead to porosity. Ensure that your gas flow is adequate and free from contaminants to prevent the issue.
  • Dirty Base Metal: Grease, dirt, or rust on the base metal can create voids or porosity on the weld metal while mig welding. Cleaning the metal surface thoroughly before welding is essential. If you weld the dirty metal with a mig welder, porosity is a must. You may use stick welding technique (SMAW) on dirty metal to prevent porosity issue.
  • Moisture: Wet materials can introduce hydrogen into the weld pool, causing porosity. It’s imperative to keep everything dry, including electrodes and work materials.
  • Improper Techniques: Welding techniques, such as incorrect angle or speed, can affect gas coverage and lead to porosity. Employ correct welding techniques consistently.
  • Faulty Equipment: Leaks or obstructions in the welding gun or liner can disrupt gas flow. Which in turn causes porous weld. Regularly inspect and maintain your equipment to ensure it is functioning correctly.

To reduce porosity in your MIG welding projects, it is critical to control these variables with precision and care. Your attention to detail and proper setup can significantly decrease the occurrence of porosity, ensuring stronger and more reliable welds.

Watch the video for better understanding the causes of porosity.

How to Fix Porosity Issue After MIG Welding

A metal plate with visible porosity, a welding machine, and a technician inspecting the weld
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When you encounter porosity in MIG welding, it’s essential to address and fix it promptly to ensure the integrity of the weld. Here are the steps to rectify the issue:

  1. Identify the Extent: Carefully examine the weld and determine the extent of the porosity. If the cavities are shallow, they can be repaired without complete removal.
  2. Grind Out the Defects: Use a thin grinding wheel or a file to remove the porous sections from the weld. You must grind down heavily ensuring all compromised material is eliminated.
  3. Prepare for Re-welding: Clean the area thoroughly after grinding. Remove all contaminants that could potentially cause further porosity.
  4. Adjust MIG Welder Settings: Verify that your MIG welder settings are appropriate for the material and thickness. Ensure the gas flow is correct and the wire speed is suitable. For example, to weld thicker metal set the feed speed ranging from 240 to 290 ipm. Keep travel speed between14 and 19 ipm. Stick out the wire from the nozzle at 5/8 inch or shorter.
  5. Perform a Test Weld: Before redoing the weld, conduct a test run on a scrap piece to ensure the settings are optimized to prevent additional porosity.
  6. Re-weld the Area: Once satisfied with the test weld, carefully reweld the ground-out sections. Weld in short, controlled bursts to minimize heat input.
  7. Inspect the Repair: After re-welding, inspect the repair and ensure that there are no signs of porosity in the new weld. Using non-destructive testing methods such as visual inspection or dye penetrant are enough for verifying the repair quality.

Remember, prevention is always better than repair. To keep porosity at bay in future welds, maintain clean base and filler materials, ensure proper gas coverage, and store consumables in a dry environment as advised by the consumable producer’s recommendations.

Preventing Porosity Before MIG Welding

A welder adjusts gas flow and electrode angle to prevent porosity in the metal during MIG welding
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Proper preparation and technique are crucial to prevent porosity in MIG welding. Here are some steps you can take:

  • Surface Preparation: Clean the welding surface rigorously to remove any contaminants such as oil, rust, or paint. Use a metal brush or grinder for best results.
  • Choose Correct Filler Material: Ensure that you are using the right kind of filler metal to match the base metals. This compatibility can reduce the chances of weld metal porosity.
  • Proper Shielding Gas Coverage: Employ a precise gas flow rate, typically between 20 to 25 cubic feet per hour (cfh), to maintain good shielding gas coverage and exclude air from the weld pool.
  • Welding Equipment Check: Before starting, check your welding equipment, especially the MIG gun and gas nozzles. Check for any obstructions or damage that could affect the gas flow.
  • Machine Settings Control: Adjust the machine settings based on the welding procedures provided in international weld codes. Considering the factors such as voltage, amperage, and wire feed speed before welding.
  • Steady Welding Speed: Maintain a consistent travel speed, measured in inches per minute or feet per hour, to avoid cold lapping and ensure uniform heat distribution.
  • Welding Parameters Optimization: Tailor the welding parameters according to the weld joint’s thickness to establish an optimal fusion of the filler material and base metal.
  • Welding Techniques Mastery: Adopt welding techniques that avoid excessive manipulation of the welding gun to maintain a stable arc and minimize disturbance to the shielding gas.

Adherence to these methods is essential in producing a strong, defect-free weld when MIG welding.

Frequently Asked Questions (FAQ)

Understanding the causes of porosity in MIG welding is crucial for achieving strong, defect-free welds. In this section, we address some common concerns related to factors that can lead to porosity.

1. How can improper shielding gas coverage lead to porosity in MIG welding?

Improper shielding gas coverage can introduce contaminants into the weld pool, allowing various gases to get trapped within the molten metal. That results in the formation of porosity upon solidification.
It is vital to maintain the correct flow rate and composition of the shielding gas to prevent this.

2. What role does welding technique play in the prevention of porosity during MIG welding?

Your welding technique is a critical factor in preventing porosity. Techniques such as maintaining a consistent travel speed and angle ensure effective gas shield and properly distributed heat. It reduces the likelihood of gas entrapment.

3. In what ways can contamination of the base metal contribute to porosity in MIG welding?

Contaminants on the surface of the base metal, such as oil, dirt, or rust, can cause gases to be released into the weld pool during welding. That leads to the creation of porosity.
Ensuring the base metal is clean before welding is necessary to reduce the risk of porosity.

4. How does the choice of filler metal affect the occurrence of porosity in MIG welding?

The composition of your filler metal can influence the development of porosity. Some filler materials may contain impurities that can outgas during welding.
Selecting a high-quality filler metal appropriate for the base material and welding application can help minimize porosity.

5. Can incorrect welding parameters such as voltage and amperage cause porosity in MIG welds?

Incorrect welding parameters, like voltage and amperage, can lead to an unstable arc and improper penetration, which in turn can trap gases in the weld and form porosity.
It’s essential to set and adjust the MIG welding parameters according to the material thickness and type.

Last words

Porosity compromises the integrity of metal joints. So it is important to consider the problem seriously. There are many reasons for porosity as I have covered. The good news is that you can fix that.

However it is not wise to break the weld and re-weld to eliminate the porous joint as it can cause further weaker joint than before. So prevention is better in all ways.

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