1. Pre-Welding Preparation
Surface Cleaning
Remove mill scale, rust, oil, and moisture from weld areas
Use grinding or abrasive cleaning (avoid chlorinated solvents)
Joint Design
Use standard joint types (butt, fillet, lap)
Maintain proper root gap (typically 1-3mm for butt joints)
Preheating
Not usually required for thin plates (<25mm) at ambient temperature >5°C
For thicker sections or low temperatures:
Preheat to 100-150°C (measure with temp sticks)
2. Recommended Welding Processes
| Process | Suitable For | Notes |
|---|---|---|
| SMAW (Shielded Metal Arc) | Field welding, repairs | Use low-hydrogen electrodes |
| GMAW (MIG/MAG) | Production welding | Best for automation |
| FCAW (Flux-Cored) | Outdoor welding | Good penetration, wind-resistant |
| SAW (Submerged Arc) | Thick plates, long seams | High deposition rates |
3. Filler Metal Selection
Matching composition: Use weathering steel electrodes/wires
AWS/SMAW: E7018-W (e.g., LB-52U)
AWS/GMAW: ER70S-6 with weathering flux
JIS: D5016, D5018 for SMAW
Key requirements:
Low hydrogen (<5ml/100g)
Moisture control (re-dry if exposed)
4. Welding Parameters (Typical)
| Process | Current | Voltage | Speed | Gas (if applicable) |
|---|---|---|---|---|
| SMAW | 110-140A (3.2mm) | 22-26V | - | - |
| GMAW | 180-220A | 24-28V | 30-50cm/min | 75% Ar + 25% CO₂ |
| FCAW | 200-280A | 24-32V | 40-60cm/min | Self-shielded or CO₂ |
5. Post-Weld Considerations
Slag Removal: Clean thoroughly between passes
Interpass Temperature: Keep below 250°C
Post-Weld Heat Treatment (PWHT):
Not required for most applications
For thick sections (>50mm), consider stress relief at 580-620°C
Corrosion Protection:
Allow natural patina formation (no painting needed)
If painting is required, use weathering-resistant primers
6. Common Defects & Prevention
| Issue | Cause | Solution |
|---|---|---|
| Porosity | Moisture, contamination | Clean surfaces, dry electrodes |
| Cracking | High restraint, hydrogen | Preheat, low-H electrodes |
| Poor patina | Wrong filler | Use matching weathering consumables |
7. Standards & Certification
JIS G 3125: Base material specification
AWS D1.1/D1.5: Welding procedure qualification
ISO 15614: Procedure test requirements
