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SESK: Stuff Everyone Should Know · sesk.info/weld-porosity-contamination

Which base metal condition can lead to porosity in a weld?

Oil, grease, mill scale, rust or moisture on the metal.

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  1. Oil, grease, mill scale, rust or moisture ✔
  2. Clean, dry, freshly ground metal
  3. Metal that is slightly magnetic

Why: Contaminants on the surface burn off in the arc and release gas that gets trapped in the weld. Cleaning to bright, dry metal before welding prevents it.

Huh, didn't know that: Hobart says to store welding wire somewhere clean and dry, near the welding area temperature, to avoid condensation.

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References

Answer: Oil, grease, mill scale, rust or moisture. Contaminants on the surface burn off in the arc and release gas that gets trapped in the weld. Cleaning to bright, dry metal before welding prevents it.

  1. Hobart Brothers, MIG Troubleshooting for Metal-Cored and Solid Wire www.hobartbrothers.com/resources/technical-articles/mig-troubleshooting-for-metal-cored-and-solid-wire
    Base metal contamination with oil, grease, mill scale, rust and/or moisture can also lead to welding porosity.
    Checked 2026-10-10.

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