What Causes Holes In MIG Welding?

There could be several reasons why you are finding small (or larger) holes appearing in your MIG welding. The cause can be determined by first assessing what sort of holes they are. For example, pinholes may be caused by something different compared to wormholes.

Any sort of hole in a fresh weld is an unwelcome sight. Holes in a weld are typically referred to as ‘porosity’ or ‘porous welds’. Now, when it comes to porosity, there are many ways that you can handle it, but this may well depend on the extent of the porosity and the types of holes it has created (pinholes or wormholes). Let’s explore the exact causes of holes in more detail, and assess whether it is ever ok to weld over holes and how (if at all) you may be able to fix them.

What causes pinholes in TIG welds?

The cause of pinholes in TIG welds can vary, and it is important to identify the correct cause to properly rectify it. The first cause could be down to the shielding gas. You may find that you get pinholes in your weld if your gas is not shielding the bead adequately. Check this to see if this is the root of the issue first.

There are many issues involving gas that could cause pinholes. This is because the gas shielding is designed to protect the weld from oxidising in the air due to the heat produced. If this gas shield is disturbed in any way then you can expect pinholes to form.

Things that can cause the shield to be disturbed include the gas being off, holding the torch at an incorrect angle, too much gas, problems with the gas delivery (reduced flow), gas being contaminated with moisture, and even airflow from wind and drafts if you are working outside or in a drafty room.

Another issue to check for is in regards to the amperage. If your amperage is set too high then you may find that you get pinholes in your weld. Ensure the amperage is set to the correct amp for your needs.

Too high an amperage can mean too high a current, and this can produce excess heat. Any extra heat can cause faults such as pinholes in the weld bead. You can find the proper settings in the manual that came with your welder which will tell you what amperage is needed for what metal.

Another issue that may cause pinholes in your fresh TIG weld is moving too quickly with the electrode. This can cause mini gaps and pinhole like holes to appear in the bead. Ensure you keep a steady pace and take your time.

You may also find that pinholes can form if your arc is too long. This happens when the electrode is held too far away from the weld puddle, causing the bead to heat. Excess heat, as you know, can cause issues such as gaps and pinholes. Keep the electrode closer so the arc is right.
These are just some of the issues that can cause pinholes in TIG weld. The list is not exhaustive and you should refer to your specific manual to try and identify the cause.

What causes wormholes in MIG welding?

Wormholes in MIG welding can be caused by several different issues. Much like the appearance of pinholes in TIG welds, it is important to identify the cause of them to adequately solve the problem. However, suffice to say that the most common cause of wormholes in MIG welding is thanks to gas.

Wormholes tend to form a pattern akin to herringbone and indicate that there has been a large amount of gas when forming the bead. This then gets trapped and solidifies in the weld metal. These wormholes, also known as piping, are elongated holes with spherical porosity.

The best way to deal with porosity such as wormholes is through prevention. Around 90% of these holes can be prevented. Identifying the causes can turn a disaster welding job into something that will be acceptable under welding codes.

Can you weld over porosity?

No, it is not recommended that you weld over porosity. If aid porosity exceeds the allowable limits, then anything that you weld on top of it will also have the same levels of porosity. Porosity travels and never leaves the original weld pass that was made. With this in mind, the best way to deal with porosity is to remove it. This can be done via grinding or air carbon arc gouging.

How do you fix porous welds?

The best way to fix porous welds is to remove the original weld. Some people may try and weld over it. This may seem like it is working but in reality, it will never get rid of or fill the original weld holes underneath. With this in mind, you run the risk of creating porosity in any new weld too, as weld holes travel. Remove any porosity with air carbon arc gouging, or grind it away and start afresh.

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