Porosity is a common problem in welding. It can happen when so much gas comes from the weld pool that the metal freezes and leaves a hole in it. What is Porosity in Welding? What causes it, and how can you avoid porosity during your next welding project?
What is porosity in welding?
Porosity in welding happens when a gas or impure substance is absorbed into the weld. This is called a cavity, and it can happen when someone makes the weld in the wrong place, but also when stray things like dirt and waterfall onto it.
Porosity occurs when the molten weld pool absorbs oxygen, nitrogen, and hydrogen. These gases are released and become trapped in the weld metal when it cools and solidifies.
The nitrogen and oxygen that are in the weld pool usually come from having bad gas. If you have 1% air entrainment, this will make your weld pool have pores. When it is more than 1.5%, there will be holes on the surface of your welds. Leaks in the gas line, too high a gas flow rate, draughts, and turbulence can cause porosity problems with your welds.
Hydrogen is found in many different places. Sometimes, the hydrogen comes from water that isn't dried off of metal or wire. Sometimes, grease or oil can make hydrogen too. That's why it's important to dry off the metal and wire before you start working on it.
When you weld, it can create a lot of smoke. The risk is greater when you make T-shaped joints in the welding and certain types of joints (like when you weld on both sides and there's a fillet). If the primer is low, we should not have to remove it. But if the primer is too high, we might see problems like porosity, especially when using other welding processes other than MMA (SMA).
What Are The Types Of Porosity In Welding?
The following are the different types of porosity in welding.
- Distributed porosity & surface-breaking pores
- Crater pipes
01. Distributed porosity & surface-breaking pores
Pores are small holes in your metal. Some pores break the surface of the metal. Usually, these pores are found throughout the weld bead and show a lot of porosity in the metal.
Porosity is a problem when gas particles get into the weld pool while it is still molten. The gas particles can't stay there forever. When the pool solidifies, they come out and make a hole in the metal. This might happen because you didn't use enough to protect from gas particles getting into the weld pool.
Air can get trapped in the shielding gas and cause porosity, even if it is just a small amount. It will break the surface. This often happens when there is 1.5% air mixed with the shielding gas.
Sometimes pores happen because of gas leaks, high rates of gas flow, and draughts. Sometimes the weld pool is bumpy, and that can cause pores.
Distributed porosity and surface-breaking pores in welding are common problems that can lead to expensive repairs.
Preventing these problems is simple with the right tools, but most welders don't know about them or how they work.
There are many preventative measures, such as welding with argon gas shielding and using low hydrogen electrodes.
There is also the option to use deoxidizers (such as calcium boride) and de-rusting agents that will help too. A welder can't go wrong when following these tips:
- Find the leak. Seal it up.
- Make sure that the weld pool doesn't have turbulence in it.
- Use filler with enough deoxidants in it.
- Lower the flow of gas if it is too high.
- Avoid draughts.
- You need to dry the electrode and flux.
- Clean the workpiece surface.
- Make sure that you clean your joint edges before welding.
- It's important to make sure that the weldable primer is below the maximum thickness.
When you weld, herringbone-looking things might show up on the radiograph. These herringbone-looking things are called Wormholes.
Wormholes are holes in welds. They happen when metal is being welded. It happens when there are a lot of gas bubbles that get trapped in the metal as it hardens. This is usually because of something on the surface, like paint or dirt, or too much paint on the metal first.
The most likely place to get trapped in an aperture. For example, when there is a T-shaped piece that has been welded on both sides.
When welding joints in metal plates, make sure that the coating thickness on the edge of the vertical member is not over 20µm through over-spraying.
To prevent wormholes, you must take specific actions. This will ensure that you can create a quality weld.
- To avoid wormholes, you want to make sure that you clean the area before welding.
- You also need to ensure there is no grease on the workpiece, any rust, or leftover NDT chemicals.
- Make sure the surfaces are clean. Remove any surface coatings.
- Check the primer thickness is below the maximum allowed amount.
03. Crater pipe
A crater pipe forms when the weld pool is finally solidified. This happens because of shrinkage on solidification. If there are places where the liquid becomes more solid, crater pipes will form.
Extinguishing the welding arc will make the weld pool solid. If you use TIG welding, stopping the wire before extinguishing the arc can make its crater. And cratering can mean your pipe isn't perfect.
You're tired of having crater pipes on your welds. It's time to find out what crater pipes are, why they form, and how you can avoid them.
Crater pipe is a common problem that plagues many welding projects. They occur when the weld pool solidifies too quickly or unevenly, leaving little holes in the finished product. But cratering doesn't have to be an issue for your next project if you follow these tips.
- When welding, you can use a "run-off" tag to make the arc stop burning outside of the welded joint.
- Before moving to the next electrode or weld run, grind out the run you just finished.
- You want to keep the size of the weld pool small, so you can use slope down or crater fill functions to control that.
- When welding, you need to add filler. If not, the weld pool will shrink, and that is bad.
What causes porosity?
- Use of too high gas flow.
- Contaminated surface.
- Improper gas shield.
- Incorrect surface treatment.
- Inadequate electrode deoxidant.
- Using a longer arc.
- The presence of moisture.
- Presence of rust, paint, grease, or oil.
01. Excessive gas flow
When you're welding, there can be a lot of gas. It's important to ensure that the gas hose from the gas cylinder to the power source/welding torch / Gun does not have any holes or loose fittings. This is because if it does, air will get in and cause porosity in your weld pool.
Flow meters are tools that help you make sure gas is safe to use on the weld. They must be checked before welding starts. Measure the pressure of gas and make sure it is high enough, but not too high.
02. Contaminated Weld Metal Surface and Electrode
If the metal or electrode is dirty, it will create gas. Oil, grease, and water can contribute to this problem. This is because of how hot the weld pool is getting while solidifying. If you have contaminated material heated for too long, you might have a porosity problem with your welds.
To get the metal to weld together, it needs to be cleaned. You need to make sure that the metal is free from things like oil or grease. The material you are welding should also be clean, which means oil-free without any other contaminants like dust or paint.
03. Improper gas shield
Gas shielding is one of the most important reasons for porosity. If gas shielding is not done correctly, air can easily get into the weld metal, forming rust. Too much airflow and draughts in the area can also cause porosity.
It is important to make sure that the gas pipeline or hose is connected properly before you start welding. To avoid too much airflow, you need to protect the welding with a shield. The shielding needs to be strong and thick enough to block the airflow. Otherwise, it can interfere with the quality of your welding.
04. Incorrect surface treatment
Sometimes, surface treatments like painting can cause the release of gases. This can make the metal porous. You can't paint if it will make the metal too wet or too dry. You need to predict what kind of reaction will happen before you paint.
To avoid problems, you need to predict the chemical reactions of the material first. Use E6010 welding rod.
05. Inadequate electrode deoxidant
When a material is being melted and cooled for a welding process, the oxygen that comes out of the metal can react with other gases in the air and form carbon monoxide. This can cause porosity or holes where things should go.
To remove the extra oxygen from metal, there are some chemicals that you can add. These chemicals are called "deoxidants." If these deoxidants aren't enough or are not working well enough, then the extra oxygen in the metal will form a gas called "carbon monoxide," which will cause a problem. The gas will make porosity in metal.
Before welding, first, de-oxidize the metal. This will ensure that the metal does not react to oxygen, and then it will be safe for welding.
06. Using a longer arc
Sometimes if the arc length is too high, it will not be strong enough. This is because the air in our atmosphere gets trapped inside this weld pool. The air causes turbulence, and it weakens the weld. This is one reason you can reduce arc length down to almost half and still get a strong weld.
The arc distance should be correct. Use the right welding technique.
07. The presence of moisture
It can be difficult to weld metal with moist electrodes, but if the moisture levels get too high, it will hole the welding.
So try using low-hydrogen electrodes, which need some moisture. The water helps. But if there is too much water, then it can cause holes during the process.
You should use a dry electrode that has no water because that could cause holes during the welding.
Use dry electrodes and materials. If the material is not dry, it may start corroding.
08. Openwork surface
Whenever the metal is exposed to air, it can be absorbed through the root opening. Then, as a result, porosity is formed. This happens because there might be too much hydrogen or oxygen in the welding atmosphere.
You need to use a metal that is not in the air or get into the weld. You can change your electrode to avoid oxidation.
09. In-appropriate flux
Generally, welding fluxes, base metal, filler rods, electrodes wires, or powders can easily soak up water. If they do this, it may be the cause of weld defects. When low activity flux is applied, the weld metal will be porous.
You have to make sure that the metal you are welding with is dry. The metal should not have any moisture in it, or there will be bad welds. If your metal does not have enough flux, the weld will be bad and might even have holes. So use high activity flux instead.
Fluxes are a chemical formulation of a compound that helps purify the surface of the materials to be welded, remove slag and contamination before welding. It influences pore formation, penetration, and wetting & provides a protective atmosphere for the arc, so that good high-quality metal is deposited at the weld area.
10. Improper welding procedure
Porosity may occur if you do not make a good decision before welding. If you don't set the parameters right and do not weld properly, it might happen easily.
Welding is hard. You must take care of the weld's WPS. The machine must be calibrated for voltage and current readings before welding. The electrodes must be within the specifications. Although various techniques can be used, you will need to know the key elements of TIG welding, which is a preferred method for welding magnesium parts.
How do you prevent porosity in welding?
Porosity is caused by the introduction of air into molten metal, which then cools and solidifies with pockets of gas trapped inside. This causes welds to be weak, brittle, or even crack under pressure.
Porosity in welding leads to costly repairs and downtime. Here are some tips for preventing porosity in welding.
- Check the flow rate for your gas.
- Make sure the gas flow rate isn't excessive.
- Look for any signs of a gas leak.
- Maintain a proper distance between the tip of your tool and the work surface.
- Keep out of drafty situations.
- To weld, clean the surface first.
- Keep an eye on your travel angle.
01. Check the flow rate for your gas
To shield gas, ensure you have enough air for your process. You usually need 30-50cfh in any wire process. There is more variance in GTAW because there are different types of cups. But in general, any wire process will usually require about 15-25cfh.
02. Make sure the gas flow rate isn't excessive
High flow rates for wire processes can cause porosity. The reason is that when the flow rate is high, it causes turbulent air in the shielding gas. This makes it easier for air to enter the weld and make a bubble. You should not increase your flow rate past 60 if you do not want this to happen.
03. Look for any signs of a gas leak
Make sure all connections are tight and not damaged. Check for leaks in the back of the wire feeder and make sure it is pushed in as far as it can go. Also, make sure that o-rings on the power pin (the end of the gun) are not broken or worn.
04. Maintain a proper distance between the tip of your tool and the work surface
This is usually 3/8" to ½" for GMAW transfer and 5/8" to 1" for GMAW spray. Too much CTTWD will decrease gas coverage.
Using a torch that is too large for the material will lead to longer transfer times, which can cause insufficient penetration. Using too small of a tip could increase travel speed, but it will also decrease deposition rates and change arc character due to increased voltage drop across the electrode.
05. Keep out of drafty situations
Drafts happen when a door or fan is open. If the wind blows, it can move around the shielding gas and make holes in your weld. I think this is because of Clause 7.11 in AWS D1.1:D1.1M:2020 Structural Welding Code - Steel, where it says that if there is wind over 5 miles per hour [8kph], you cannot weld with GMAW, GTAW, EGW, and FCAW-G processes because of porosity in your weld. So make sure that you don't have any doors or fans open when you're welding, and if they're closed, then put something else in front of them to block the wind from blowing on your welder's area.
06. To weld, clean the surface first
Contaminants such as dirt, grease, oil, and paint can make the metal weak. This is because it is easy for these things to go through the metal. There are many ways to fix this problem. One way is to grind off the zinc coating before welding. If you can't do this, use a process that won't be as hard on the metal as SMAW (stick) or FCAW-SS (self-shielded flux-cored). Another way would be to use an S-3 wire with a shielding gas mix with high CO2 content (C25 gas) for GMAW processes.
07. Keep an eye on your travel angle
In welding, you need to watch your angle. You should keep it between 10-20 degrees from perpendicular. If your angle is too high or low, there will be problems such as porosity and spatter.
If you are welding on aluminum, porosity can be worse than if you weld on things like carbon steel or stainless steel. Steel is okay with having a lot of water, rust, paint, and oils because the wires have deoxidizers that help to reduce or eliminate the porosity. Aluminum does not have these wires, so if there is any moisture, it will make it harder to weld.
A welder must accurately determine the porosity of a weld to make an educated decision about whether or not it is safe. Porosity can be determined by using different types of testing such as magnetic particle inspection; liquid penetrates inspection and x-ray radiography. We hope you found this post helpful.
Why is porosity bad in welding?
Porosity can make a weld unstable. This is because gas might be inside the weld, which will cause the weld to be less strong. It also might take up a lot of time and money to fix it, which would not be good.
How to repair porosity in welding?
If you have porosity in your welding, then it can't be fixed. You have to remove the bad weld and make a new one. But you can fix porosity before it happens by cleaning well, ensuring there is enough gas flowing through the machine, and checking workplace conditions are good for welding.
How much porosity is acceptable in a weld?
Some porosity is okay in welds. It should not be more than 9.5mm or 3/8 of an inch, or 19 mm or 3.4 inches, whichever is smaller. There are rules for how much porosity can be in a weld, and they're from the American Welding Society.
Can you weld over porosity?
You can weld over porosity. Porosity is a problem that you can fix if your porosity does not exceed allowable limits. If it exceeds those limits, then you will need to remove it. This means that the weld needs to be air gouged and ground off. This is important because any weld with porosity cannot be trusted and will not have very good structural integrity if there are any forces on it at all.