Operational Failure of Vertical Roller Attached to a Grinding Mill: Root Cause Analysis

In the present incident, one of the rollers of
the grinding mill in the cement plant failed during operation, exhibiting longitudinal cracking over the inner surface. Deposition welding was carried out just before the incident to match the worn-out profile of the roller. Investigation revealed that the subsurface of the cracked region contained discontinuities like blow holes (B1.0 mm) and fine cracks (0.2–2.0 mm length). Chemical analysis of the alloy showed low nickel (0.5 wt.%) and high tungsten
(*1.0 wt.%) concentration. The deviation in composition
reduced the ductility of the component. The microstructure of the alloy consisted of complex carbides (50–200 lm)
embedded in a martensite–austenite matrix. Under cyclic
loading, the fatigue crack was initiated from the subsurface
containing discontinuities and bulky carbides. Low
toughness (*2 J) and high residual tensile stress
(*170 Mpa) of the material facilitated crack propagation
in the thickness direction. The final failure of the component occurred due to overload.