So what is porosity and what triggers it? In a nutshell, porosity occurs when gases like nitrogen, oxygen, or hydrogen get trapped as the molten weld pool cools down. These gases either form a pore at the surface or a void beneath the ground.
This may happen for several reasons, which we shall discuss in this post. We’ll also go over the procedure on How to Fix Welding Porosity.
Contents
Consequences of Negligence
You’ve pulled down your hood. You’re welding a great, smooth groove weld. Everything appears to be in line. You are focused!
The weld puddle then begins to sputter slightly. You think, “It’s just excess mill scale burning off the plate’s edge.” Nothing major, right? You keep welding. To evaluate your efforts, you then raise your hood. You scrape off the debris to reveal the shine of a perfectly placed weld. Your heart, however, aches. You have porosity.
Porosity: What is it?
When undesirable gases are entrapped within the molten weld pool during solidification, it leads to welding porosity, which creates pits or pores on the exterior or within the bead. Porosity can appear on a weld’s edges or inside the welded joint.
There are various forms of porosity, and each has its own problems. Among them are:
Distributed Porosity
The presence of pores everywhere around the weld.
Surface-Breaking Pores or Subsurface Porosity
The pores that damage the texture. A grinder or an X-ray is a helpful instrument for detecting this kind of porosity. Another sign of this porosity is a little bubble that grows larger as the bead cools.
Wormholes
The elongated pores that appear on radiographs as a herringbone chevron pattern. Wormhole porosity cannot be seen until the slag has been separated from a bead that has undergone flux.
Crater Pipes
A hole at the end of a weld run formed due to contraction during solidification.
Whatever form of porosity you encounter, it can cause a weld to break, fail, and, in the worst-case scenario, cause harm to someone depending on the quality of the machinery.
The Mechanism of Porosity Formation
The porosity is affected by a variety of external factors, including heat and air moisture, filler or filler wire, hydrogen and air from the welding processes, and more. Water reacts with liquid metal during the MIG welding to form hydrogen atoms. The temperature may drop as the welding process progresses, causing the number of hydrogen atoms to decrease. The solubility of the hydrogen atoms in the molten pool can impact porosity development.
Bubbles are created when hydrogen is dissolved. The flow of the liquid metal influences the movement of the hydrogen atoms. It reduces temperature and cooling affects hydrogen solubility and promotes porosity. This is due to the reason that hydrogen can no more bypass the molten pool of liquid.
Detection and Correction
Type 2, Surface-breaking flaws can be identified using a penetration or ferromagnetic particle inspection approach.
Ultrasonic inspection or radiography is used to find underground faults. Typically, radiography is more efficient at accurately identifying porosity flaws. However, it can be challenging to find tiny pores, especially in dense areas.
If the porosity is widely spread, the entire weld should be stripped away as countermeasures rather than the regular localized scraping or grinding. The joint should be re-prepared and re-welded under the appropriate welding technology.
What Is the Cause of Welding Porosity?
Porosity can emerge in all welding procedures and postures, and its underlying cause might change depending on the circumstances. The following list includes some of the most likely welding porosity causes as well as unique situations that can only occur during particular welding techniques.
Issues with Shielding Gas
Shielding gas or flux prevents the molten puddle from directly interacting with the surroundings. Porosity will occur when the flux is infiltrated with moisture, or this shielding gas is injected incorrectly.
A weld that is poorly shielded will, at best, be oxidized. The liquid metal will most often react with the air, confining gases like oxygen and nitrogen and leading to porosity in the weld pool.
Another issue could be an excessive shielding gas flow pressure. The shielding envelope will become chaotic if the gas flow rate is too high. This will create porosity by sucking the surrounding airflow into the area that is supposed to be insulated.
Fast or Unsteady Welding
The reel tension can become problematic if you weld at an improper speed and move too softly (or even too slowly). When the extra wire falls, it may end up in your weld puddle, contaminating it before it has a chance to freeze.
Ensure your wire feeding mechanism works appropriately and maintain a smooth, even tone while you weld. Rushing can cause wire feed supply problems, incorrect shielding gas coverage, and porosity.
Unsanitary Conditions
Your welding equipment requires regular maintenance. Before beginning a new welding venture, make sure everything is tidy and dry. Weld puddles can readily become porous when grease, rust, granules, and dirt from your welding gun are around.
Remember to clean the item or materials you are welding as well. You should search for and eliminate things like:
• Water and oil
• deterioration and rust
• Cleanup Coatings (like zinc plating)
• Plastic laminate
Investing in a good grinder and sandpaper is a sensible move to eliminate coatings, dyes, laminates, corrosion, and oxidation more quickly.
Air Drafts
Since welding is a hot profession, it may seem comfortable to cool off with a chilly breeze in the window, but doing so could damage your weld. Strong winds and air currents might sweep your shielding gas away and let atmospheric gas into the weld puddle, destroying your work and effort.
The angle of the Welding Gun and Nozzle Spacing
During MIG welding, you must always be watchful and ensure your gun is held at the highest 15-degree angle, often perpendicular to the weld joint. The gas flow will expand out too far if you place the weld gun at an extensive-angle and could even draw air in from behind you.
The real problems arise when the nozzle is not held near enough to the piece to be welded. It may result in a number of issues, including:
• Reduction in the volume of shielding gas surrounding the weld puddle
• A faulty weld.
• Permit the weld puddle to come into direct interaction with atmospheric gas.
Welding poorly involves holding the gun at a too broad angle and keeping the nozzle too far away.
However, since this issue merely requires practice, everything will be fine.
Prevention Mechanisms
A piece of welded metal has weld porosity if microscopic holes and gaps are in it. Before they impact your project, you need to fix the welding porosity causes because it can lead to various issues with your welds. Prevention can be challenging, given the wide range of potential causes for porosity. The vast majority of problems, however, can be resolved by taking one or a combination of the following preventive measures:
Examine Your Gas Supply
Keep an eye on the gas shield flow. Air is disturbed more when gas is flowing at a higher pressure. This may result in impurities interacting with the weld puddle, resulting in an improper weld. Even though flow rates can differ, choosing the right flow rate for each procedure is crucial. This can boost productivity and guarantee a good weld. Consult your gas supplier for guidance if you are unsure about the ideal flow rate.
Get Rid of Contaminations
The area to be welded has to be cleaned. The risk to porosity is further increased by contaminants, including humidity, grease, oil, cutting fluids, corrosion, pigment, and other forms of hydrocarbons. Surface-coated materials, such as galvanized steel will be problematic.
In many cases, the metal is the source of the surface contamination rather than dirt or oil. In this case, the zinc layer should be ground off. Grind the metal until the mill scale is completely gone. Make sure not to grind deep into the base metal, though.
Test Your Tools
Hoses could begin to leak over time, or wire may be exposed or damaged. Check all links before hitting an arc to ensure that you receive a proper flow from your gas shield. Examine the weld gun’s tip to verify it is neat and tidy; sometimes, the tip may get congested, resulting in impurities in the weld. Check the hub or drive rollers’ strength. Performance issues with wire feeding can result from poor tension.
Working Environment
Welding shops can become extremely warm; therefore, you should wait before opening the front door for circulation. The weld puddle or gas shield could be affected by strong air currents or flows in your workplace, so keep an eye out for these. Monitor your voltage and arc length. The greater the distance between the gun and the weld location, the more likely it is that air and gas may work their way into the weld puddle, potentially causing bubbles to form and eventually leading to a poor weld.
Go Slowly and Steadily
The wire feed from the reel should leave the machine smoothly when MIG welding. Ensure that your wire feeding system has a simple brake that can be adjusted and set the proper tension so the wire won’t stall. Be careful to weld slowly and steadily. Any hurry can frequently result in weld porosity as wire feed issues can slow output.
Frequently Asked Questions
1. Is it possible to weld over porosity?
Welding over porosity is often a wrong choice. If it is deep, it needs to be crushed out and re-welded. Nevertheless, there are circumstances where a weld may not be critical and only have a few pinholes. Often these structural welding rules allow for a predetermined length and number of pinholes. To be sure you can’t just trigger a few tiny pores, it’s always wise to check with the CWI (Certified Welding Inspector).
2. What Does Welding’s Undercut Mean?
Contrary to porosity, undercut is usually a consequence of poor welding technique. An undercut is a joint that has rough edges or cracks around the borders or below the joint because the filler material fails to cover the joint space properly. Weld inspectors view it as a flaw even though it is relatively easy to fix.
3. What Percentage of Porosity Is Tolerable in A Weld?
This question cannot be answered generally because it depends on your country’s welding construction code. The American Welding Society, therefore, requires the following: Visible porosity should have dimensions of no more than 3.4 inches (19 mm) per 12-inch length of the weld.
If unsure, double-check your welding construction code and re-weld the joint.
Conclusion
Understanding the welding porosity causes can help you prevent most of it. You’ve already achieved victory in half if your machine is set up correctly, you have adequate gas coverage, and your material is free of contaminants. Keep in mind that it is much more effective—and less frustrating—to hold back welding to ensure the weld is going well than grind out 16 inches of bad weld, particularly if it is in a tight area. You can set benchmarks by knowing how a good weld feels. When something “simply doesn’t feel right,” you can use this to your advantage.
