The production of high quality silicon steel strip requires high annealing temperatures, and at
present the burners used are operating close to their upper temperature limit. This shortens their life-time
considerably. The main failure of the burners is caused by a sharp breakage of the inner nozzle tube.
This in turn diverts the flame and causes flame impingent on the outer tube casing.
A failure investigation was performed in order to decide the exact cause and suggest measures in
order to allow a life-time improvement and/or increase the temperature. Three burners at different stages
of degradation were used for the investigation.
The alloy used for the inner nozzle and the outer tube casing was EN: G-NiCr28W (a Cr2O3 former).
SEM/EDX analysis showed that Cr disappears from the steel in an alarming rate, most probably by
water vapor enhanced evaporation. The protective Cr2O3 decomposes with catastrophic oxidation and
spallation as a result. The thinning of the tube wall and the appearance of holes eventually causes the
break.
This type of failure might be avoided by choosing an alloy that forms Al2O3 instead of Cr2O3.
One such candidate would be Alloy 60 HT R that forms Al2O3 and has good mechanical strength up to
1250°C.
Keywords: High temperature corrosion, Gas-burners, Flue gas, Water vapor, Cr-evaporation, Al2O3