Multi-Pass Welding Strategies: Heat Control and Sequence Planning

Multi-Pass Sequence Planning

1. Root Pass Design. Use short-circuit transfer with CORGON® 10 for penetration control. Target 2-4mm deep penetration with consistent keyhole for full joint thickness.
2. Fill Pass Strategy. Switch to spray transfer with CORGON® 18 for productivity. Plan pass sequence to minimize distortion - alternate sides or use backstep technique.
3. Interpass Temperature Control. Monitor with infrared thermometer. Maintain 150-250°C for carbon steel, 100-150°C for stainless steel to control grain structure.
4. Cap Pass Finishing. Reduce current 15-20% and slow travel speed for smooth profile. Consider CORGON® S5 for reduced spatter on visible surfaces.
5. Pass Cleaning Protocol. Wire brush and grind each pass before next application. Remove all slag, spatter, and oxidation for proper fusion.

Critical Multi-Pass Welding Mistakes

• Don't exceed maximum interpass temperature - overheating causes grain growth and reduced toughness. Use temperature crayons for monitoring.
• Don't skip cleaning between passes - trapped slag or oxidation causes lack of fusion defects that may not be visible on surface.
• Don't use same parameters for all passes - root needs penetration, fill needs deposition rate, cap needs appearance. Optimize each pass function.
• Don't ignore backing gas on root passes - atmospheric contamination on back side creates porosity and reduces corrosion resistance.
• Don't rush cooling between passes - rapid cooling can cause cracking. Allow natural cooling or use controlled preheat.
• Don't neglect pass sequence planning - random pass placement increases distortion and residual stress. Follow qualified procedures.

Pass-Specific Optimization Strategies

Root pass (first pass): Short-circuit transfer mandatory for control. Use FORMIER® backing gas when possible. 80-120A current, 16-19V, travel speed 100-150mm/min for keyhole control.

Hot pass (second pass): Slightly higher current to burn out any root pass defects. Short-circuit or spray transfer. Focus on sidewall fusion and root pass tie-in.

Fill passes (bulk deposition): Spray transfer for efficiency. CORGON® 18 or CORGON® 25 depending on penetration needs. 200-300A, 6-8 m/min wire feed, travel 400-500mm/min.

Cap pass (cosmetic finish): Lower current for smooth profile. May use short-circuit for better control. Consider weaving technique for wider cap coverage.

Thick plate (>25mm): Plan 4-8 passes minimum. Use temperbead technique where each pass refines the grain structure of previous pass heat-affected zone.