08/20/2019 by allgastechnologies 0 Comments
What are Welding Defects – Types, Causes and Remedies?
Welding defect can be defined as any deviation in size and shape of the given metal structure regarding technical and design requirements. The deviation can be caused by process limitation in terms of wrong welding process/technique or due to certain human behavior.
Welding defects can occur at any stage of the welding process and they can affect both the inside and outside of the metal structure. Although it is almost impossible to create a defect-free weld, it is important for you to reduce their occurrence to prevent loss of material and maintain the intended quality.
It is important to note that some of the defects are permitted if they do not compromise set standards and quality, but some like cracks cannot be accepted. Having said that, this guideline will help you to detect these common welding defects, their causes and remedies.
Types of Welding Defects
Defects in welding joints are classified into 2 broad categories .i.e. those that occur internally and those that occur externally.
- External Welding Defects – are also known as surface of visual defects because they manifest themselves on the surface itself. They include surface cracks, overlaps, undercuts, porosity, and spatter. We will discuss each one of them in the next section.
- Internal Welding Defects are defects that occur at some depth in the material. They are visually invisible since they are not present on the surface, but they carry equal weight as the external ones. These defects include incomplete fusion, slag inclusion, and incomplete penetration.
External Welding Defects Explained
Cracks – Cracks are the most common defects and they can occur anywhere on the surface of the weld material. Some cracks can also be present inside the weld material especially on areas that are affected by direct heat (HAZ). Cracks presents themselves in two major types:
- Hot Cracks– These cracks occur during the welding or during crystallization where temperature can be as high as 10000-degrees Celsius.
- Cold Cracks– Cold cracks occur after completion of the welding process or during the solidification process. They are normally visible after several hours or even several days after welding.
Causes of Cracks
- Wrong joint design.
- Contamination of the base metal coupled by poor ductility.
- Use of hydrogen gas as a shield gas while welding ferrous metals.
- High content of carbon and sulfur in the base metal.
- High welding current.
- Rapid cooling of the weld joint.
- Inadequate preheating.
- Residual stress can also lead to cracks.
- Avoid rapid cooling of the weld area.
- Preheat the metal to the required level.
- Consider a low-hydrogen electrode.
- Use the correct joint design.
- Use proper amperage settings.
Overlaps – Overlap results when the weld pool overflows on the surface of the weld metal. The molten metal does not fuse with the base metal leading to an overlap which may extend to form an angle not exceeding 90 degrees.
Causes of Overlaps
- Large deposition at a go.
- Using the electrode at the wrong angle.
- Using too high current.
- Longer arc.
- Employ the right welding technique to avoid wrong arc length.
- Position the electrode at the appropriate angle.
- Use correct deposition during each run.
- Use low welding current.
Undercuts – Undercuts presents themselves as narrow gutters on the base metal next to the weld metal near the edge. This occurs when the base metal melts away from the weld area reducing the thickness of the base metal and the result is a weakened workpiece. These undercuts run parallel to the metal weld.
Causes of Undercuts
- Too fast weld speed.
- High arc voltage.
- Too large electrode.
- Use of wrong filler metal.
- Decrease the travel speed, but at the same time not too slow.
- Use the right electrode size and it should be positioned at the correct angle; between 30 to 45 degrees
- Reduce the length of the arc and lower the voltage.
- Use proper current and pay close attention to thinner areas and edges.
Porosity – Porosity is a condition that manifests itself inform of gases or air bubbles that are trapped in the weld metal. It is mainly as a result of contamination of the weld metal, which is weakened, and it can collapse with time.
Causes of Porosity
- It can occur when the electrode is not well coated.
- Presence or oil or rust on the weld surface can cause porosity.
- Use of incorrect shielding gas or improper shielding.
- Too high gas flow.
- Presence of moisture on the weld zone.
- Improper surface treatment.
- Clean the materials and the weld surface before you begin welding.
- Slow the welding process to allow the gases to escape.
- Make sure that the surface is free from oil or rust and any other contaminant.
- Make sure that the gas flow meter is configured with the correct flow settings.
Spatter – Spatter occurs when metal particles from the weld is stuck on the area adjacent to the weld area. This defect is common in gas metal arc welding and it is sometimes very hard to remove the particles.
Causes of Spatter
- Running on very high amperage can cause spatter.
- Use of incorrect polarity.
- Irregular wire feeding.
- Contamination of the weld surface
- This defect can also result from improper gas shielding.
- Positioning the electrode at a very steep angle.
- Eliminate any feeding issues.
- Use the right polarity as per weld requirements.
- Adjust the amperage settings.
- Clean up the surface before you do any welding.
- Use proper gas shielding.
- Increase the plate angle according to the condition of the welding.
Internal Welding Defects Explained
Incomplete Fusion – Lack of fusion or incomplete fusion occurs when the weld metal and the base metal are not accurately welded due to improper melting resulting into unfilled gap. Improper fusion can also occur between layers within the weld itself. Although this is an internal problem, it can be manifested on the outer surface too if the outer sidewall is not properly fused with the parent metal.
Causes of Incomplete fusion
- Incomplete fusion can result from low heat input.
- Using wrong electrode diameter when compared to the thickness of the material.
- Too fast travel speed can lead to incomplete fusion.
- Sometimes the weld pool may be too large, running ahead of arc and this can lead to incomplete fusion.
- Improper placement of bead.
- Try to increase the travel speed to minimize the chances of incomplete fusion.
- Position all beads properly to avoid sharp edges from meeting each other.
- Try to reduce the deposition rate.
- Make sure the molten weld does not flood the arc.
Incomplete Penetration – Incomplete penetration results when the depth of the weld is not enough. As such, the metal grove is not filled fully meaning that the weld does not extend through the entire joint.
Causes of an Incomplete Penetration
- Improper joint alignment
- Moving the bead too fast which means little deposition of the weld metal
- Too much space between welded metal can cause incomplete penetration.
- Using too low amperage which may not be enough to melt the metal completely.
- Ensure enough deposition of the weld metal.
- Employ correct joint geometry and ensure proper alignment.
- Use proper welding amperage
- Reduce the speed of travel.
Slag Inclusion – Slag inclusions are compounds such as oxides that are mainly trapped in the weld or on the surface of the weld zone. These compounds are byproducts of welding processes such as stick welding and arc welding. In addition, insufficient cleaning can leave some slag behind which reduces the strength of the weld and it can act as a starting point of serious cracking. Serious slag inclusion may require you to do a re-weld.
Causes of Slag Inclusion
- Too little current density which may not be enough to provide enough heat to melt the weld metal.
- Failure to do proper cleaning, especially after a welding pass.
- Too fast cooling of the weld pool may be a potential for slag inclusions.
- Welding at an inappropriate angle and wrong rate of travel.
- Increase the current density to appropriate levels.
- Increase the welding speed so that weld and slag don’t mix.
- Clean all surfaces including all edges and previous welds.
- Ensure that the weld pool cools down moderately, not to fast but not too slow either.
As a parting shot, we can all agree that it is important for you to identify and remove any defect that may be present in your workpiece. We believe that this article has comprehensively addressed those defects and we hope that it will help you during any manufacturing process to prevent loss of material and to keep you safe.
This blog post is brought to you by the folks at Toolshaunt.com.