Almost every weld will contain a slight imperfection. The key is to determine whether the flaw is acceptable or not. Failure to recognize the welding defect can put your asset and equipment at risk. The earlier you catch the defects, the easier it will be to fix them and avoid damage to your property.
In general, most welding defects are prominent on the surface and can be observed with the naked eye. It is also possible to recognize improper labor technique, wrong setup of equipment, and adverse environmental effects such as low temperature and moisture during the welding process.
However, extensive knowledge and keen observation are necessary to detect the various visual welding defects and prove the reliability of the work.
What Are the Types of Visual Welding Defects?
Here, let's explore the types of visual defects in welding, how they occur, and how to mitigate them.
As the name implies, the spatter defect in welding appears as small globules of metal scattered across the surface of the weld. They are expelled during the weld process and get stuck to the surface. They can even splatter across the worksurface and nearby areas. It’s important to keep your workbench safe and clean.
What Causes Spatter?
- Using excessively high welding current.
- Using a weld pool that is too hot or cold.
- Welding on a contaminated metal surface.
- Using a large arc or a wet electrode during the process.
- Interruption in the arc flow.
Prevention of Spatter:
- Welding on a dust-free and dry surface.
- Using clean welding tools.
- Optimizing the proper arc length and welding current.
- Using AC power to avoid electrical interruption.
- Using a steel milling disc to minimize the appearance of spatter on welds.
The welding crack is one of the most undesirable defects in the product. It can occur at the surface, inside the weld material, or in the heat-affected zone. The presence of such abnormality can cause complete failure of the welded structure. They are classified as:
- Hot cracks: They occur during the welding process with temperatures exceeding 10,000C.
- Cold cracks: The deformation takes place after the weld is created and the metal is cooled down at room temperature.
- Crater cracks: The weld crater usually becomes apparent at the end of the welding process, before the operator completes the task.
What Causes Cracks?
- Using improper design concept
- Using hydrogen as a shielding gas when welding ferrous materials like steel, iron, copper, and lead.
- Not preheating the metal before starting the welding process.
- Presence of residual stress.
- Presence of excessive sulfur and carbon in the metal.
- Poor flexibility of the metal.
- Improper filling of the crater.
Prevention of Weld Cracks?
- Preheating the weld and reducing the cooling speed joining before starting the process.
- Use weld joints to reduce the gap between the two pieces.
- Use suitable materials as shielding gas.
- Using optimal speed and current during the weld process.
- Cleaning the surface properly before welding.
- Allowing metal to cool off properly after the weld.
- Using the correct mixture of sulfur and carbon in the metal.
The undercut is the formation of grooves in the weld toe. They run parallel to the weld metal and can weaken the complete structure by trapping water and dirt between the joints. It is also very visible and can ruin the aesthetics.
However, in many cases, an undercut below 1/32” is harmless. Anything above this range should be observed critically.
What Causes Undercuts?
- Using an improper angle of the electrode.
- Using a very large electrode.
- Using contaminated shielding gas.
- Welding at a very high current.
- Welding at a very high speed.
- Holding a long arc length.
Prevention of Weld Undercut:
- Reduce the arc length or lower the arc voltage.
- Choosing the correct electrode size.
- Using a shielding gas which is compatible with the metal.
- Holding electrodes at the right angle. Ideally, the holding angle should be between 30 - 45 degrees.
- Ensure that you are working on a stable surface.
- Welding on a clean surface.
Porosity is defined as the presence of excessive cavities such as gas or air bubbles in the weld metal. The cracks are highly visible. They are also very destructive, especially in the metal inert gas (MIG), and can weaken the welded structure.
The main types of porosity in the weld include:
- Surface porosity: They are spread out on the top of the bead and appear like swiss cheese.
- Subsurface porosity: Hidden beneath the surface of the bead. It may require an x-ray for accurate detection.
- Wormholing: They are elongated and appear like worms have burrowed in the weld.
- Cratering: Found at the end of beads in the form of dents.
What Causes Porosity?
- Dirty or contaminated metal surface.
- Using an inappropriate coating on the electrode.
- Using improper shielding gas.
- Using very high gas flow.
- Presence of moisture in the welding electrode.
Prevention of Porosity:
- Cleaning the weld surface and material before initiating the weld process.
- Minimize surrounding air movement to avoid disruption to the shielding gas.
- Using dry and high-quality electrodes.
- Configuring the optimal gas flow.
The overlap occurs when the filler material at the weld toe covers the base metal without bonding. This usually happens due to an excessive flow of weld metal.
Overlap weld can result in a lack of fusion between the pieces. It can also cause concentrated stress on the structure.
What Causes Overlaps?
- Applying improper welding techniques.
- Using improper size electrodes in welding.
- Applying high welding current.
- Welding at the wrong position.
Prevention of Overlap:
- Improving welding techniques.
- Using optimal size electrodes.
- Applying correct deposition of welding current.
Distortion is another common visual welding defect that can modify the shape of the welded structure. It is usually found on thinner welding plates where there is a lack of surface to spread the welding heat.
Besides appearing unattractive, the distortion can reduce the reliability of the welded structure.
What Causes Distortion?
- Using the slow speed of arc travel.
- Putting extensive and unnecessary time into the welding process.
- Using a large number of passes.
- Not measuring the instruments to achieve diameter accuracy.
Prevention of Weld Distortion:
- Avoiding stainless metal to weld.
- Using a weldable metal type to avoid a significant number of passes.
- Maintaining the speed of arc travel.
- Using a measuring instrument to ensure accuracy.
How to Avoid Visual Defects in Welding?
The best way to avoid visual welding defects is to thoroughly examine before, during, and after the welding process. Here are some steps to follow:
- Inspecting all material before starting the weld.
- Utilizing clean material and surface.
- Ensure all welding codes and standards are deployed.
- Check the finishing of the weld.
- Use the optimal size of electrodes.
- Use a welding toolbox to properly store and carry the equipment.
- Inspect each weld pass.
There is no denying the importance of detecting visual welding defects. They not only help avoid the deterioration of structure but also ensure the value of the project. Therefore, we have listed the main types of defects possible in welding to help you minimize their occurrence or reduce their impact.
Giving proper attention to the details, including the technique and material, can help prevent many weld-related defects. Identify them using the above guide and act before your welded structure becomes a hazard.