Root Cause Failure Analysis of Non-Drive End (NDE) Bearing Failure in updraft-drying (UDD) Fan

Title: Root Cause Failure Analysis of Non-Drive End (NDE) Bearing Failure in updraft-drying (UDD) Fan.

Abstract:
A premature failure of the non-drive end (NDE) journal bearing in an updraft-drying (UDD) fan at the pellet plant was investigated using a structured format of Root Cause Failure Analysis (RCFA). The fan, designed for a service life of 120 months, however it failed within one month of installation, causing an unplanned shutdown. During field observations, it revealed a sharp rise in bearing temperature (65°C to 110°C) leading to fan trip. Post-failure inspection showed complete babbitt wipeout, severe wear on one half of the bearing, and pitting marks on the shaft journal. Analysis indicated that improper alignment and levelling during replacement of shaft and impeller, like inadequate lip and radial clearances, and absence of high precision checks (using theodolite) were primary contributors. Secondary factors included use of an old spare shaft with surface pitting and malfunctioning of the fresh air damper, which aggravated thermal stress.

Corrective actions involved realignment using metallic shims, clearance adjustments, and fresh air damper repair. Preventive recommendations include developing a detailed installation checklist, adding temperature and pressure sensors with interlocks, and exploring shaft repair via laser cladding. This case underscores the criticality of precision in installation practices and proactive condition monitoring to prevent early bearing failures of fans in high-temperature applications.

Keywords: Journal bearing failure, UDD fan, alignment error, clearance deviation, thermal stress.