Why Weathering Steel Welding Needs Control
Welding weathering steel requires more care than ordinary mild steel: the weld metal and heat-affected zone must maintain corrosion behavior similar to the base plate, and the joint must be free of defects that could initiate corrosion. The requirements below follow established welding practice for weathering structural steels.
1. Environmental Requirements
The welding site should be in still air at a temperature above 5 °C.
When the ambient or workpiece temperature is below 5 °C, welding is not allowed without partial preheating of the weld area.
2. Welding Machines and Electrode Selection
Both DC and AC arc welding machines can be used.
For welding and repairing weathering-steel structures, use weathering steel electrodes (for example J502-type low-alloy weathering electrodes).
For joints between ordinary steel and weathering steel, ordinary carbon steel electrodes (such as J442, J506, J507 types) can be used.
Use DC reverse polarity when welding with alkaline (basic) electrodes (J507 can only be used with a DC machine).
3. Preparation Before Welding
Electrode drying: alkaline electrodes (J506, J507) are dried at 350–400 °C for 1–2 h; acidic electrodes (J502, J442) at 150–200 °C. Dried electrodes are kept in an insulation holder and removed as needed; unused electrodes must be re-dried the next day, with a maximum of 3 re-drying cycles.
Preheating: preheat the weld area uniformly to about 150 °C before welding (local preheating is acceptable).
Surface preparation: remove rust, oil and contamination from the weld area before welding.
4. Precautions During Welding
Do not strike the arc on non-welded surfaces - arc strikes damage the protective surface.
Use short-arc operation with narrow weld beads; keep the weld area clean of rust, oil and water.
5. Post-Weld Quality Inspection
The weld surface should be smooth, and the transition between the weld and the base metal even.
The weld must be free of cracks, slag inclusions, incomplete penetration, incomplete fusion and arc craters; undercut depth should not exceed 0.5 mm.
6. Post-Weld Heat Treatment
After welding, cover the weld area with asbestos cloth (or an equivalent insulating material) and allow slow cooling to room temperature, which relieves stress and prevents cracking in the heat-affected zone.
Frequently Asked Questions
Q: Which electrodes should be used for weathering steel?
A: Weathering-grade low-alloy electrodes (for example J502-type in the Chinese system, or E7018-W-type international equivalents) so the weld forms a matching patina; confirm consumables against the qualified WPS.
Q: Is preheating required when welding weathering steel?
A: Preheating to about 150 °C is recommended for the weld area, especially at low ambient temperatures or for thick sections.
Q: Why must electrodes be dried before use?
A: Moisture in the coating causes hydrogen-induced cracking; drying at the recommended temperature removes moisture before welding.
Q: What defects are unacceptable after welding?
A: Cracks, slag inclusions, incomplete penetration or fusion, arc craters and undercut deeper than 0.5 mm.
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