Sometimes, porosity is elongated and may appear to have a tail. This is the result of gas attempting to escape while the metal is still in a liquid state and is called wormhole porosity. All porosity is a void in the material and it will have a higher radiographic density than the surrounding area. Cause: Improper weld termination techniques Repair: If no cracks exist, simply fill in the crater. Generally welding from beyond the crater back into the crater. Longitudinal Crack Definition: A crack running in the direction of the weld axis. May be found in the weld or base metal. Sometimes, if there is turbulence in the weld pool, it may cause pores. Wormholes are a fancy word for elongated pores that show up on the radiograph with a herringbone appearance. Because wormholes are elongated pores, they indicate that there is a large amount of gas that was trapped in the weld metal during the solidification process.
What is Porosity in Welding
Porosity is defined as cavities (weld metal contamination) that is produced when gas is trapped inside a weld metal. Gases or Shielding gases released when the torch is applied to treated metal, the gases are absorbed into the molten metal and then released as the molten metal solidifies. In some cases, the shielding gas does not completely get to the weld pool, it’s the atmospheric air that affects the weld bead.
Types of Porosity in Welding
Porosity is classified according to the shape, size, and location of occurrence. Gas cavities in some instances may assume elongated shape (wormholes), some occur in the spherical shape. On the other hand, some cavities occur only on the weld surface, and some occur throughout weld metal. Generally, these gas cavities may either appear singly ( called void) or may be uniformly distributed throughout the weld, and sometimes may appear in a clustered form.
Causes of Porosity in Welding
As stated earlier, cavities are produced when gas contamination is trapped during the solidification process of welding. Knowing the causes and the possible preventive measures for this welding defect (porosity) is an essential part of welding. Below are some of the possible causes of porosity.
1. Moist Electrode
To avoid porosity, it’s recommended the welder should use baked electrodes in stick welding to avoid the involvement of moisture in the weld metal.
On one end, steam may be driven out from the heat of the welding which may create small pores in the weld metal. Porosity could also occur during welding when low hydrogen electrodes or stainless steel electrodes are not properly kept in a dry condition.
What Causes Worm Holes In Mig Welding
Though some moisture content is required in low hydrogen electrodes in order to achieve better performance, however, if the moisture content exceeds some certain level, the weld metal may be prone to porosity.
This welding flaw can be prevented by preheating the parent material in order to remove any moisture.
The electrodes should also be stored in dry weather conditions. Also, the electrodes should not be oven-baked in any case before use. This is because a little amount of moisture is required to achieve a clean weld.
2. Inconsistent shielding gas
Porosity problems could also arise as a result of inconsistent gas shielding. This called for the need of a welder to properly check gas hose attachment and to remove hose contamination if at all any. Firm connection stops any loss of gas shield and hence, no air entrapment. Additionally, draughts and airflow in the shop may cause restrictions in gas flow.
3. Contaminated surface
What Causes Wormholes In Welds
Contaminations of different kinds on the surface of the metal to be welded could cause porosity. Any dirt; paint, rust, grease or oil on the surface of the weld material may contribute to gas cavities formation when exposed to high welding temperature.
4. Too High gas flow
When the rate of gas flow is high, it may cause turbulence as a result of which air may be drawn into the weld metals creating porosity. An optimize gas flow delivers high-quality welds with little or no air loss. Apart from serving as a protective measure, it also helps cut the cost of production
5. Very High Arc Length
Excessively high voltage causes too high Arc length, which in turn may lead to porosity. If the operator holds the gun far away from the joint (keeping the arc length longer), the magnitude of heat is reduce, and this may cause the entrapment of atmospheric air. To avoid this problem, it’s recommended that the average arc length should be maintained.
6. Inadequate Electrode Deoxidant
During solidification procedure, excess oxygen (O2) comes out from the weld metal as a result of the reduced solubility; the oxygen may combine to form carbon monoxide (CO) that may cause porosity. In order to avoid that, some deoxidants are usually added in electrodes, parent metals, and even filler metals to remove the oxygen content (deoxidation). Hence, the lack of adequate deoxidants causes poor deoxidation, which may cause porosity. To prevent this, always use electrodes with adequate deoxidants.
7. Openwork Surface
Welding in an open surface brings about atmosphere air contamination into the weld metal. Introduction of air from the backside through the root opening can cause air entrapment in the weld puddle. To prevent this, the weld joint should always be protected from such kinds of crevices.
8. Improper Surface Treatments
Release of gases during painting (surface treatments) may affect the weld characteristics. Treatments such as galvanizing or Zinc coating produce gas and some other unwanted particles. To prevent this, research on the possible chemical reactions prior to making any treatment.
9. Laminated surface
Just like incorrect surface treatments, the laminated surface may as well create disturbances in welding (cavities). When welding laminated workpiece, the weld joint should carefully be prepared to ensure that a quality weld is produced.
10. Inappropriate flux
Welding flux can absorb moisture; this means the flux must be treated with great care (must be supplied in dry condition) to avoid porosity. Also, the use of low activity flux can cause surface porosity; high activity flux delivers high-quality welds with no air cavities.
How to Prevent Porosity in Welding
By this time we all know what porosity in welding is, and it’s possible causes. Porosity is basically a weak, air-filled weld that could be caused by so many factors during the welding process. We have discussed some of those factors above. Now Let’s look at some tips for preventing porosity in welding.
1. Surface preparation
Proper cleaning of the surface of the material to be welded is very important to ensuring clean and porosity-free weld. When the surface of the material is not properly cleaned before welding, the after-effects of fabrication may lead to surface contamination or air cavities.
This will, in turn, leads to shabby welds with poor mechanical properties. To eliminate this problem, concentrated cleaning liquids such as EZ Wipes can be used to remove fluid lubricants, inks, oil, and grease or other adhesives.
2. Proper working conditions
The environmental condition of the workplace plays a very big role in determining the weld quality. For instance, welding shops can get very hot while welding, trying to open the door windows for proper ventilation may lead to contaminations. Therefore, it’s essential to monitor strong airflows or currents in the workplace in order to achieve quality welds.
3. Moderate Gas flow
It’s very important to monitor the flow of the gas shield. This is because the more powerful the flow of the gas is, the more the air is disturbed. Too high gas flow provides room for contaminants to mix with the weld puddle; this will, in turn, cause impure weld. Though the rate of gas flow may vary depending on the metal to be welded, it is essential to ensure the correct rate of flow for each application. This will help improve the quality and efficiency of the weld.
4. Check Your Equipment
Always inspect your equipment to make sure it’s 100% fit before you start working. This will help deliver Porosity free welds. For instance, checking all connections prior to striking the arc will help ensure accurate flow of gas shield. Also, Overtime hoses may unexpectedly begin to leak, the wiring may become frayed or exposed, or the tip of the weld gun may become clogged. Checking and fixing all these problems will greatly help prevent the problem of porosity and other welding defects.
Remark
Preventing porosity in welding is a must; it helps improve welding quality, durability, and purity. Welding strength, durability, and purity are very important in making sure your weld meets the codes and standards of American Welding Society (AWS). Make sure you keep these tips in mind when you embark on your next welding project.