Failure Analysis of Radiant Tube Burners in Continuous Annealing Line (CAL) of an Integrated Steel Plant
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of Radiant Tube Burners in Continuous Annealing Line (CAL) of an Integrated Steel Plant P. Saravanan • Gadadhar Sahoo S. Srikanth • K. Ravi
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Submitted: 19 August 2010 / in revised form: 16 November 2010 / Published online: 5 January 2011 ASM International 2011
Abstract Failure analysis of radiant tube burners (ACI HK 40 with composition *25 wt.% Cr, *20 wt.% Ni) removed from a continuous annealing line (CAL) of a cold rolling mill (CRM) of an integrated steel plant was performed using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and microhardness measurements. Studies revealed that the failures were mainly attributed to combined influences of creep and carburization-assisted localized oxidative attack. A suitable heat-resisting cast austenitic stainless steel was identified as a candidate alloy to replace the previously used ACI HK 40 alloy. Keywords Cast austenitic stainless steel Radiant tube CAL CRM
Introduction Centrifugally cast tubular HK/HP series austenitic steels are widely used in elevated temperature and corrosive environments, e.g., petrochemical industries [1, 3]. This study is, however, focused on the failure analysis of radiant tube burners in continuous annealing line (CAL) of cold rolling mill (CRM) of an integrated steel plant. Continuous annealing lines (CALs) are equipped with radiant tube
P. Saravanan (&) G. Sahoo S. Srikanth K. Ravi Chemical Analysis and Corrosion Engineering Group, R&D Centre for Iron and Steel, Steel Authority of India Ltd, Ranchi 834002, India e-mail: [email protected]
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burners fabricated from centrifugally cast ACI HK 40 grade heat-resisting austenitic stainless steel containing *25 wt.% Cr and *20 wt.% Ni. During operation of CAL, the cold-rolled (CR) steel strips are made to pass between two rows of radiant tube heaters that are located above and below the pathway of steel strips. The moving strip is heated by radiation from the outside radiant tube while the radiation is emanating from the inside flame tube. The schematic of radiant tube burner is provided in Fig. 1. The radiant tubes are mounted at both the ends (walls) of the furnace. The tubes are supported by the refractory support at the far-off end of the furnace. These burners are operated at high temperature (*750–800 C) using a fixed stoichiometric ratio of air and mixed fuel gases from a coke oven and blast furnace. The mixed combustion gas passes through the tube and are exhausted at the other end of the tube. The average service life of radiant tubes at CRM is about 9 months, while the minimum service life is as low as 1 month at some critical locations. The premature failures occur in the form of perforations, punctures, sectional thinning, and gross deformation of the burner assemblies. In general, around 40–60 burners are replaced per year. As a result, a considerable economic loss occurs every year both due to frequent shutdowns of the CAL for burner replacements and associat
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