Welding galvanized steel presents unique challenges. The zinc coating vaporizes at welding temperatures, creating health hazards, weld defects, and quality concerns. Understanding proper procedures for welding galvanized steel safely and effectively is essential for fabricators and welders.

The Challenge of Welding Galvanized Steel

The zinc coating (45-300 μm) vaporizes above 907°C, creating zinc oxide fumes (hazardous to breathe), porosity in the weld metal, increased spatter, and risk of metal fume fever.

Health and Safety Requirements

Metal Fume Fever

Inhalation of zinc oxide fumes causes flu-like symptoms: chills, fever (onset 4-10 hours after exposure), nausea, headache, muscle aches. While self-limiting (24-48 hours), repeated exposure can cause long-term health effects.

Required Safety Equipment

1. Respiratory protection: PAPR or P100-rated particulate filters minimum
2. Local exhaust ventilation: Fume extraction within 300mm of welding arc
3. General ventilation: Minimum 2,000 CFM per welder indoors
4. Protective clothing: Fire-resistant jacket, gloves, apron

OSHA PEL for zinc oxide fume: 5 mg/m³ (8-hour TWA).

Pre-Weld Preparation

Zinc Removal Options

Method 1: Grinding — Remove zinc 25-50mm beyond each side of the weld joint. Precise but generates zinc-containing dust.

Method 2: Chemical stripping — Apply zinc-stripping compound. No dust but chemical waste disposal required.

Method 3: Welding through zinc — Acceptable with specific procedures, enhanced fume extraction. More spatter and potential porosity.

Welding Process Selection

GMAW (MIG Welding)

Most common process. Shielding gas: 75% Ar / 25% CO₂. Wire: ER70S-6 (deoxidizers manage zinc contamination). Technique: slight weave to allow zinc vapor escape.

FCAW (Flux-Cored Arc Welding)

Flux composition helps manage zinc contamination. Use stringer beads rather than weave. E71T-1 (gas-shielded) or E71T-11 (self-shielded).

SMAW (Stick Welding)

E7018 (low hydrogen) for structural welds. Remove zinc from joint area for best results.

Preventing Porosity

1. Remove zinc from the weld zone (most effective)
2. Use a root gap of 1.5-3mm to allow zinc vapor escape
3. Use deoxidizing filler wire (ER70S-6)
4. Maintain correct travel speed
5. Use correct stick-out (10-15mm for GMAW)

Post-Weld Treatment

After welding, the zinc coating is destroyed in the HAZ (10-25mm each side). This area must be restored:

1. Zinc-rich paint: Minimum 90% zinc in dry film. Two coats. Most practical solution.
2. Zinc spray (thermal spray): Professional process, best match to original coating.
3. Cold galvanizing compound: 95%+ zinc content. For small areas.
4. Re-hot-dip galvanizing: Entire assembly re-galvanized. Most durable but requires fitting in galvanizing kettle.

Structural Welding Considerations

• AWS D1.1: Requires zinc removal from weld area for adequate fusion
• WPS qualification: Must be qualified on galvanized material if production welding is on galvanized
• Inspection: RT and UT can detect zinc-induced porosity

Summary

Welding galvanized steel requires careful attention to safety (fume management), preparation (zinc removal), process selection, and post-weld treatment (recoating). By following proper procedures, welders can produce high-quality joints while protecting health and maintaining corrosion resistance.

CoreMetal Steel supplies galvanized steel in sheet, coil, pipe, and structural forms — all hot-dip galvanized to ISO 1461 or ASTM A123 standards.