Welding Porosity Causes & Types With Prevention

Welding Porosity Causes & Types With Prevention - My Welding Yard

What is Porosity in Welding?

Porosity is a common defect in welds which is due to the trap of gas bubbles in the welded zone. Sometimes due to the in-efficient technique of welding gas pores are created, which in the weakness of the welded part, both strength-wise and appearance-wise.

When the welded metal is molten, it can be contaminated by gases like hydrogen or oxygen, resulting in pores in the weld, and this whole phenomenon is known as Weld Porosity. Luckily porosity is a defect that has a prevention rate of up to 90% and can be prevented using some common precautionary measures and understanding its cause.

Many beginners don’t have knowledge about porosity, and this costs them time and money. My Welding Yard’s detailed article will give you deep insight into porosity, its common causes, types, and how you can prevent them. After reading this article, you will know everything about porosity and will be able to give porous-free shining welds.

Common Causes of Porosity in Welds

Inappropriate Gas Cylinder 

If the gas cylinder is out of order, it will not provide enough shielding gas for the welds. Environmental gases like oxygen and nitrogen can enter the welded zone resulting in contamination creating air pores. Also, the turbulence of gas can create porosity in the welded area. Turbulence is the high flow of gas that can take air in it, resulting in air pores. Before welding you need to check the gas hose properly, any holes in the hose from which air can enter can cause porosity in the welds.

Presence of Moisture

 Welds are susceptible to environmental conditions. Moisture and dew drops can cause the weld’s temperature to fall quickly giving is not enough time to settle, thus producing air pores. Also, the tools used in weldings like filler rods, welding flux, electrode wires, and base metals can get easily contaminated by moisture. Thus, it would be best if you cleaned all the tools with a cloth in order to clear haze or contaminates on them. Using a proper shielding gas is also a wise step and saves the welds from porosity.

Inefficient Welding Procedure

You should configure your welds properly according to the situation of the workpiece. Exposure to chemicals like zinc for weld cleaning can also cause porosity. Galvanizing is frequently chosen for purposes of weld cleaning, which also releases a gas that creates adverse effects on the quality of the weld. In order to avoid porosity, you should configure your welds properly and choose a proper technique of cleaning after welds.

The Contaminated Surface of the metal

The paint or grease available on the workpiece can also result in damaging the weld’s quality. The oils or moistures present on the weld’s surface can form contaminating gases or chemicals because of the high temperature of the welding gun. Thus, it is best to remove paint from the surface of the welding material and cleanse it well before welding.

Different Types of Porosity & Their Prevention

Due to the variety in the condition of welding and the difference in parameters, porosity can take variable forms. Each form has a different cause and can be prevented using specified techniques. Basically, porosity has three states which are as follow:

Surface Breaking Porosity

This type of porosity appears in the form of evenly distributed holes throughout the welding surface. This type of porosity usually occurs when welding a material coating over it, particularly zinc coating. When the welding gas combines with these layers of chemicals over the surface of the metal, it generates different chemicals. It will also produce fumes, which are dangerous for the health of the welder.

Air contamination in the shielding gas can also result in the distributed porosity. Environmental gases like nitrogen, oxygen, and hydrogen can get mixed into the welding pool and cause bubbles to appear on the surface. T-joints are vulnerable to this kind of porosity because of the fillet welding by the worker on both sides.

It is noteworthy that not all the primers applied over the surface generate pores. There are specific primers that don’t need to be removed before welding the material. Welding skills also matter when you are talking about surface porosity. In-efficient welding techniques like setting the gas flow rate too high or any leaks in the gas cylinder can also cause distributed porosity to appear.


You must properly check the gas source and eliminate any turbulence or leaks if there are any. Filler metal should be mixed with a sufficient level of de-oxidant is preferable to use. You should use the technique for welding the material properly without reducing the gas flow or increasing it too much.

Furthermore, the environmental conditions also matter; you should dry out all the equipment before use and clean any moisture if appearing on the workpiece. If a coating is appearing on the welding material, you should check its thickness is below the maximum applicable thickness and the type of primer is also recommendable to work with.

Wormhole Pores

Due to excess gas, elongated pores can appear on the surface known as wormhole pores. The leading cause of wormholes is the excess of gas trapping in the material’s surface. This type of defect usually appears in the crevices of the material or in T-joints. Most of the factors are typical between elongated pores and surface pores. Or we can say a wormhole pore is an advanced form of the ordinary pore.


A welder should use the gas appropriately in the welding process in order to prevent elongated pores from appearing. You should remove the surface contamination, and clear any coating or grease appearing on the material. The geometry of the joint is also essential when you are talking about wormholes. You should prevent the usage of gas in the corners of the workpiece. 

Crater Pipes

Crater Pipes are not actual porosity, but these are defects that generally appear on a surface affected by porosity. This happens primarily due to the shrinkage of the welding surface and the volume changes, that are accompanied by a welding process. Crater Pipes usually appear due to the rapid solidification of a welded part. TIG welding is most vulnerable to crater pipes and contaminated welding wire usage.


Amateur welding technique is the leading cause of crater pipes appear. You should be careful about the flow of gas throughout the welding process. When welding, you should not abruptly reduce the welding current and use a  filler metal to compensate for shrinkage.

Porosity in Different Welding Processes

Porosity in TIG welding

TIG welding consists of only four components, an electrode, the rod, the shielding gas, and the metal to be welded. Common causes of porosity are due to contamination and moisture. Sometimes a user can use too much shielding gas that can affect the quality of the weld.

Zinc coating or galvanized metal used in passivating the weld can also be a cause of porosity in TIG welding. As welders usually use TIG welding on thin metals; sometimes setting them too high can also be a cause of porous welds. The low-quality filler material used can also cause the pores to appear on the welding surface. We have a guide about TIG welders that will help you in choosing the right one.

Porosity in MIG Welding

The leading cause of pores in MIG welding is the shielding gas that can get trapped in the weld. Inadequate gas can also be a significant cause of the defect. The dirty base material can also result in porosity in the MIG welding procedure. Usage of extreme gun angle or extended the wire too far from the nozzle can cause bubbles in your welding stream. Excessive spatter in MIG welding can also be defective so always use the best mig welder for your work.

Porosity in STICK Welding

In stick welding, inadequate environmental conditions usually account for the un-aesthetic welds. However, painted or rusted metal can also affect the physical appearance of the welding metal a significant bit. Travel angle is also critical, and you should use proper welding techniques in order to prevent perforable surfaces.

Porosity in Aluminum Welding

Trapped gas is the one leading cause of insufficient aluminum welding. Aluminum welding is also very sensitive. It uses AC output which requires the users to set all the parameters like frequency and amplitude to great precision. Aluminum freezes comparatively fast. If all the gas from the weld pool doesn’t get a chance to leave the surface that causes the metals to get affected by porosity.

Porosity in Stainless Steel Welding

Stainless steel is very sensitive to impurities. It would be best to make sure that you use all the equipment made up of stainless steel. Secondly, the filler metal selected should also be one that is suitable for welding stainless steel. One frequent cause of the porosity in stainless steel welding is the position of the gas hose against the solenoid. You should make sure that gas is not escaping from the weld pool in any way and the technique of welding is very p in stainless steel.

Porosity in Submerged Arc Welding (SAW)

Damped flux is a common cause of porosity in the SAW method. Another factor is the preheating temperature. Too much preheating can cause the surface to change its shape or color. The flux used in SAW should also be in accordance with the base material, or otherwise, you will see the pores on the surface. In order to prevent the porosity, you should select the welding parameters precisely and keep your surroundings moisture-free.

FAQs (Frequently Asked Questions)

How do you fix porosity in welding?

Porosity is due to the contamination of the weld by atmospheric gases basically nitrogen, oxygen, or other gases. The main cause of porosity in most cases is the leak or the turbulence of gas.  In order to fix porosity, you need to trace the cause of it and eradicate its cause. Check your gas flow and avoid any drafty conditions. Moisture or paint on the surface of the workpiece also needs to be eliminated in order to save yourself from the weld.

Can you weld over porosity?

Welding over the weld is a very common occurrence and many times you will need to accomplish it. However, in the multi-pass welding process, if your previous weld has a defect then your next weld will be defective. You will need to clear the surface against porosity before welding it. You will need to clean the surface using any chemical means before welding it.

How much porosity is acceptable in a weld?

According to the American Welding Society, the amount of porosity acceptable in welding is 9.5mm in diameter. The porosity should not exceed up to 3.4 inches in a 12-inch length of the weld. However, you should take all the necessary, measures to reduce the size of porosity as much as possible.

What is Cluster Porosity?

Cluster porosity happens when flux coated electrodes are contaminated by moisture. This moisture on the surface of the welding metal turns into the gas when the temperature rises and becomes trapped in the weld pool when you start welding the surface. Cluster porosity is like regular porosity in the radiograph but it is indicated by closely congested portions.


In this article, we have discussed the most common defect which appears in the welds, the porosity. We have discussed all the common cause of it and why does it appear in the different welding process. We have also mentioned some methods of its prevention in order to safe your welds against it. In other words, this article is a complete guide to help you know everything about porosity and how can you enjoy your welding experience free from porosity.

Hello Everyone, I am James from Kentucky and been into this welding fiasco for 13 years in that time I have worked as a private welder and did most of the auto restoration work. In this recent, COVID-19 outbreak I decided to start a welding blog and share welding tips along with product reviews.

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