Metal Fabrication Resources by Blackstone Advanced Technologies

4 Common Weld Defects & How to Prevent Them in Your Design

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Has your manufacturer ever handed you a finished product that’s an eyesore or, even worse, poorly put together? It may be due to pesky weld defects.


Twists and turns are common when it comes to welding metal. Check these common welding afterthoughts for signs your vendor is not prepared to help your project reach its potential.


4 Weld Defects

1. Porosity

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Let us translate: Porosity = gas bubbles. Porosity occurs when shielding gas becomes trapped within the weld and releases through the weld after it hardens. The release of the gas leaves tiny holes in the weld. Porosity is especially destructive in metal inert gas (MIG) or stick welds.


  • Cracks both visible and internal
  • Weakened weld joints

What can you do?:

  • If using multiple metal types, make sure you’re specifying similar ones.
  • Have a certified welding inspector use X-rays and ultrasound to check for holes.

2. Overlap

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Overlap is an excess of weld metal beyond the weld root. This is a type of weld discontinuity, not necessarily a weld defect. Weld overlap frequently occurs with fillet or butt welds (common weld types in metal fabrication). This may be due to insufficient heat application.


  • Little to no fusion of the pieces
  • Concentrated stress under load

What can you do?:


Use a metal type and grade more agreeable with high-heat conditions

  • Find a more skilled, experienced welder

3. Distortion

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Distortion can result when the parent metal being welded on warps due to excessive heat created by the welding process. This usually occurs on thinner gauge sheet metals as they lack the surface area to dissipate the heat. It also can occur when creating longer welds, due to there being an extended length of time when the metal is exposed to heat.


  • Warped metal isn’t structurally sound

What can you do?:

  • Avoid stainless steel, since it’s especially prone to shifting position during a weld
  • Use a more weldable metal type and grade so less passes are necessary
  • Stop specifying so many welds!

4. Lack of Fusion

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This occurs when the parent metal and the weld metal do not completely adhere to each other. Lack of penetration occurs when a weld does not begin at the root of the weld groove. These usually occur due to poor welding technique -- perhaps an incorrect angle, excessive speed, or insufficient arc length.


  • Connection won’t be solid or long-lasting

What can you do?:

  • Find a more skilled, experienced welder
  • Use a thinner piece of metal

Leave No Room for Error

The ideal way to prevent weld defects is to involve your manufacturer in the early going. Making sure you’re giving your vendor the right design specifications will reduce the potential for welding errors.


You’ve been warned: Don’t make the welding portion of your manufacturing process an afterthought!

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