Backing Gas Calculator
Calculate purge volume and gas requirements for root weld protection.
Oxygen Level Requirements
| Material | Max O2 (ppm) | Notes |
|---|---|---|
| Titanium | <50 | Critical - use oxygen analyzer |
| Duplex SS | <100 | Prevents nitrogen loss |
| Austenitic SS | <250 | Prevents oxidation/sugaring |
| Nickel Alloys | <100 | Sensitive to oxidation |
| Cr-Mo Steel | <500 | PWHT may clean up minor oxide |
Backing Gas Best Practices
Purging Principles
- Volume Changes: 5-7 volume changes typically reduces O2 to acceptable levels
- Laminar Flow: Introduce gas gently to avoid turbulence and air mixing
- Vent Position: Vent at highest point, inlet at lowest for heavier-than-air gas
- Seal Quality: Use water-soluble dams or inflatable bladders
Monitoring Tips
- Oxygen Analyzer: Essential for critical materials, verify before starting root
- Maintain Purge: Continue trailing gas during and after welding until cool
- Reduce Flow: Lower flow during welding to prevent turbulence at root
- Check Leaks: Verify dam seals and connections before purge