How to Fix MIG Porosity in Carbon Steel Welds

Q: Can I weld over galvanized coating without porosity issues?

No, galvanized coating must be removed. Zinc vaporization creates gas bubbles trapped in the weld metal. Remove coating 25mm each side of the weld and ensure proper ventilation.

Q: How do I know if contaminated wire is causing porosity?

Check wire surface for rust, oil, or moisture. Wire stored improperly or exposed to humidity absorbs contaminants. Use fresh wire from sealed packaging and store in dry conditions.

Q: Should I use different gas mixtures for different steel thicknesses?

Yes. Thin steel ( 15mm) needs higher CO₂ like CORGON® 25 for adequate penetration. CORGON® 18 is the versatile middle choice.

MIG porosity in carbon steel is typically caused by contaminated base metal, incorrect gas flow rates, or atmospheric contamination during welding [S1]. The solution involves thorough cleaning, proper gas selection (Ar/CO₂ mix like CORGON® 18), and ensuring adequate 12-15 L/min shielding gas coverage [S2]. However, pure CO₂ while cheaper increases porosity risk compared to optimized Ar/CO₂ blends [S3].

Last verified: February 2026 | Sources: [S1] AWS D1.1:2020, [S2] ISO 14175:2008, [S3] Welding Journal Vol. 102 2023

Step-by-Step Solution

Clean the base metal thoroughly. Remove all rust, mill scale, oil, grease, and paint from the weld area and 25mm on either side.
Check gas flow rate. Set flow to 12-15 L/min for most applications. Too high causes turbulence, too low allows air entrainment.
Verify gas mixture. Use appropriate Ar/CO2 ratio for material thickness - 18% CO2 for general purpose, 25% CO2 for thick sections.
Inspect gas delivery system. Check for leaks at connections, damaged hoses, or contaminated gas supply.
Adjust welding parameters. Reduce travel speed if moving too fast, increase voltage for better penetration.
Check wire condition. Ensure wire is clean, dry, and properly stored - contaminated wire creates porosity.

Common Mistakes to Avoid

Don't use pure CO2 for critical applications. While cheaper, pure CO2 creates more spatter and oxidation than Ar/CO2 mixes.
Don't ignore wind protection. Even slight drafts can disrupt gas coverage and cause porosity.
Don't reuse contaminated wire. Wire exposed to moisture or contamination should be discarded or properly reconditioned.
Don't increase gas flow excessively. Flow rates above 20 L/min typically create turbulence rather than better coverage.
Don't weld over primer or coatings. These must be completely removed to prevent gas entrapment.

Material-Specific Considerations

For thin steel (<3mm): Use lower CO2 content (10-15%) to reduce heat input and spatter.

For thick steel (>10mm): Higher CO2 content (20-25%) provides better penetration and faster travel speeds.

For galvanized steel: Increase ventilation and reduce heat input to minimize zinc vaporization.

Recommended

CORGON® 18

Industry Standard

Why CORGON 18 works for carbon steel MIG: The 18% CO2 content provides excellent arc stability, good penetration, and minimal spatter while maintaining superior mechanical properties in the weld metal.

How to use for best results: Set gas flow to 12-15 L/min, ensure pre-flow time of 0.5 seconds, and maintain consistent torch angle. The optimized Ar/CO2 ratio reduces porosity risk compared to pure CO2.

Complete Product Review CORGON vs CO2 Comparison Gas Selection Guide

Frequently Asked Questions

Why does pure CO₂ cause more porosity than Ar/CO₂ mixes?

Pure CO₂ creates more violent arc characteristics and oxidation potential. The argon in CORGON® 18 (82% Ar + 18% CO₂) stabilizes the arc and reduces atmospheric contamination while maintaining good penetration [S3].

What's the optimal gas flow rate to prevent porosity?

12-15 L/min is optimal for most carbon steel MIG applications. Higher flow rates (>20 L/min) create turbulence that draws in air, while lower rates (<10 L/min) provide insufficient coverage [S2].

Can I weld over galvanized coating without porosity issues?

No, galvanized coating must be removed. Zinc vaporization creates gas bubbles trapped in the weld metal. Remove coating 25mm each side of the weld and ensure proper ventilation [S1].

How do I know if contaminated wire is causing porosity?

Check wire surface for rust, oil, or moisture. Wire stored improperly or exposed to humidity absorbs contaminants. Use fresh wire from sealed packaging and store in dry conditions [S1].

Should I use different gas mixtures for different steel thicknesses?

Yes. Thin steel (<3mm) benefits from lower CO₂ content like CORGON® 10, while thick steel (>15mm) needs higher CO₂ like CORGON® 25 for adequate penetration. CORGON® 18 is the versatile middle choice [S2].

🔧 Critical Quality Issue