What are the common quality defects in steel welding?
- Inclusions
- Lack Of Fusion
- Porosity
- Undercut
- Underfill
- Cracks
- Spatter
- Excess Reinforcement
- Overlap
Welding is a common fabrication method in the metal fabrication industry. It is used to make nearly every metal product, even large structural steel pieces. And though welding experts make it look easy, it comes with a steep learning curve.
Welding defects are very common and can be caused by several things such as using the wrong welding process or using an incorrect welding pattern. Such defects are permissible, but others can cause metal products to lose structural integrity. Fortunately, these quality defects in steel welding can be avoided with the right knowledge and equipment. Read on to learn how!
What Is A Weld Defect And How Is It Different From A Weld Discontinuity?
Any metal fabrication process acknowledges that imperfections are inevitable. Hence, the term “tolerances”. This term defines what is acceptable for metal products before it is considered a defect.
When it comes to imperfections for steel welds, there are two types: discontinuities and defects. A discontinuity is an imperfection in the physical structure of a material, which changes its properties. A discontinuity can be classified as internal, external, volumetric, and planar. However, discontinuities have the potential to become defects. Once a discontinuity exceeds the tolerances that are typically followed for code or industry standard, then it is considered a weld defect.
Here are the most common quality defects when it comes to steel welding:
Inclusions
An inclusion happens when a solid foreign object is caught in the weld. These objects could be metal particles, slag, or chemical reaction products like oxide, dust, and debris. Inclusions could affect the toughness and weldability of a metal piece. In particular, slag inclusions could greatly decrease the structural integrity of the weld.
Lack Of Fusion
This is an incomplete weld which happens when the welder could not accurately weld the material and the metal piece pre-solidifies. This creates a gap between the weld material and the piece, as it could not be filled with the molten weld material.A lack of fusion may also happen on multi-run welds, creating gaps in the adjacent layers of weld metal. This may happen due to improper handling of the welding operator or incorrect joint design and fit-up as well. This is a serious quality defect.
Porosity
Porosity refers to cavities, such as blowholes and wormholes, that are found in the welded material. This defect is caused by the entrapment of gas or small bubbles in the welded zone.
Porosity commonly occurs when the welder uses insufficient or excessive shielding gas while welding. But, it may also be caused by the contamination of the weld joint by debris and dirt. This issue can be localized in one part of the weld or distributed uniformly throughout the weld metal.
Undercut
While welding a metal piece, the base of the metal can melt away from the weld zone. When this happens, a groove is formed in the shape of the notch, which creates a defect called an undercut.
Undercuts are most commonly formed at the toe of the weld and are more likely to happen when doing multi-run welds. These defects can be caused by using a welding current or travel speed that is too high or through an incorrect operator technique. This can be a serious defect for structural metal pieces because undercuts reduce the fatigue strength of the joint.
Underfill
Underfills refers to defects that can occur either continuously or intermittently on the surface of a weld. Here, there is an insufficient deposition of the molten weld material, causing an external and easily identifiable defect on the surface of the metal piece. Simply put, an underfill is an undersized weld. Using too high welding travel speeds or too high heat inputs can cause the weld to underfill the joint. This is considered a minor welding defect and can be easily repaired by filling the joint in the rest of the way until the surface is leveled.
Cracks
Cracks are the most serious and unwanted weld defect. This is because they can easily lead to the failure of the welded structure if not remedied. Most cracks are present at the surface or otherwise found inside the weld material. Depending on the type of crack, this defect can be caused by many factors.
For example, crater cracks are most commonly caused by too high welding currents and incorrect termination of the welding arc. Another example is centerline cracks, which are caused by incorrect consumable selection or excessive joint restraint.
Any type of crack that shows up during and after welds should be thoroughly inspected. In most cases, you may need to redo the weld or start on a new piece altogether when there are cracks.
Spatter
This defect happens when molten particles from the weld bead are splattered around the weld zone. This is considered a minor defect and in most cases doesn’t affect the structural integrity of the piece. Instead, it gives the steel an unappealing appearance.
Spatter is typically caused by instabilities in the metal transfer, such as using high welding currents, long arcs, incorrect polarity, or shielding gas.
Excess Reinforcement
Excess reinforcement happens when too much welding material is deposited onto the metal piece. This can be caused by excessive current, too slow travel speeds, and incorrect joint fit-up. A too-thick weld doesn’t necessarily mean it’s tougher. In most cases, too much weld material is a surefire way to ruin your steel product. When this defect occurs, the weld will likely need to be ground out completely and redone.
Overlap
Overlap happens when the weld material placed at the joint flows over onto the surrounding metal piece and cools down. This creates an overlapping section that is not completely fused to the base metal piece. This can be caused by the wrong welding torch angle or too slow travel speeds. A defect is also considered an overlap if the welded material rolls beyond the weld toe and forms an angle less than 90 degrees.
Key Takeaway
There are many different quality defects in steel welding that you have to keep an eye out for. While some may be easily fixed, others may severely impact the integrity of your structural steel pieces.
The easiest way to make sure that your welding is of an acceptable standard is to work with a highly experienced metal manufacturer, like Regan Industrial Sales, Inc.! All of our structural steel pieces are made using the finest materials and workmanship — and if you see any of the defects described above, we can quickly rectify the issue. Contact us today to learn more!
