TL;DR
Oxygen ingress into the galvanizing furnace oxidizes the strip surface and causes coating adhesion failures. Find and seal the oxygen ingress point and restore the protective HNX gas ratio before resuming production.
What you might see
- oxygen sensor reading above the maximum inside the furnace
- strip surface oxidation visible after the furnace
- hydrogen concentration dropping below the minimum
- furnace seal air ingress alarm active
Likely causes
Furnace seal failure at the entry or exit snout allowing air ingress
Protective gas (HNX) supply pressure drop below the minimum furnace pressure
Strip entry curtain or seal worn allowing air entrainment at strip speed
Furnace shell weld cracked allowing air to seep through the insulation
Required tools
- Oxygen analyzer for furnace atmosphere
- Soap solution or gas leak detector for shell seam check
- Protective gas flow meter
- LOTO kit for furnace section maintenance
Safety first
- Hydrogen in the furnace atmosphere is flammable and explosive. No ignition sources near the furnace entry, exit, or seals.
- The furnace interior and strip are at temperatures above 800 degC. Full thermal PPE for any furnace area work.
Procedure
- 1
Stop the strip line at reduced speed and do not run strip through the zinc pot until the furnace atmosphere is restored.
Warning: The galvanizing furnace atmosphere contains hydrogen. No open flames or ignition sources near the furnace seals or entry throat. - 2
Check the protective gas supply pressure and verify flow to each furnace zone.[1]
- 3
Inspect the furnace entry and exit seals for damage or excessive wear.[1]
- 4
Check the furnace pressure differential to atmosphere. Pressure below atmosphere confirms a seal or shell leak.
- 5
Use a soap solution along furnace seams and welds to locate any shell leak while the furnace is still slightly pressurized.
- 6
After sealing the ingress point, purge the furnace with clean HNX gas until the oxygen sensor confirms the oxygen level is below the maximum.
- 7
Run a length of dummy strip through the furnace and check the surface condition before resuming production strip.
Sources
Tenova Tenova LOI Continuous Galvanizing Line (CGL) general technical documentation, Tenova
General continuous galvanizing line furnace atmosphere control and seal maintenance procedures (general)
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