1. Shielded Metal Arc Welding (SMAW, Stick Welding)
Advantages: Flexible for on-site/outdoor/complex joints (overhead/vertical), no gas dependency (resists cold wind), uses low-hydrogen electrodes to avoid cold cracking.
Scenarios: Field repair of small structural parts (guardrails, communication towers) in frigid regions.
Key Rules: Use E5015-G/E5016-G electrodes (dry at 350–400°C), preheat 100–150°C (150–200°C for ≥25mm plates), maintain short arc.
2. Gas Metal Arc Welding (GMAW, MIG Welding)
Advantages: High efficiency (continuous wire feeding), controllable heat input, argon-rich gas (80% Ar+20% CO₂) ensures clean welds with Cu/Cr retention.
Scenarios: Batch production of thin-medium parts (signage frames, purlins) or workshop prefabrication.
Key Rules: Use ER50-G/ER50Ni1 wire, heat wire feeder (if <0°C), control heat input 20–35kJ/cm, use windscreen outdoors.
3. Submerged Arc Welding (SAW)
Advantages: High deposition rate for thick plates (≥20mm), flux isolates arc (low hydrogen/impurities), slow cooling reduces HAZ brittleness.
Scenarios: Thick structural members (bridge beams, pipeline supports) in cold areas.
Key Rules: Match SJ101G/SJ102 flux with H08Mn2NiMoA wire (preheat flux 250–300°C), maintain interpass 150–200°C.
4. Gas Tungsten Arc Welding (GTAW, TIG Welding)
Advantages: Precise heat control (minimal HAZ), ultra-low hydrogen, ideal for thin plates (3–10mm) or critical root passes.
Scenarios: Thin-walled parts (lighting fixtures) or pressure-bearing component roots (water tank nozzles).
Key Rules: Use 99.99% Ar (backing gas for roots), preheat 80–150°C, use water-cooled torch.
Avoid: Oxy-acetylene welding (excess heat) and self-shielded FCAW (high hydrogen/unstable arc).
