Welding defect can be defined as any deviation in size and shape of the given metal structure in regards to 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 so as 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
External 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
These 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 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:
Causes of Cracks
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
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 runs parallel to the metal weld.
Causes of Undercuts
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 actually collapse with time.
Causes of Porosity
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
Internal Welding Defects Explained
i. 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
ii. Incomplete Penetration
Incomplete penetration results when the depth of the weld is not sufficient. 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
vi. 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 also 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
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.