Fatigue failures of welded conveyor drums

Abstract

This paper analyses the fatigue failure of a number of welded steel drums which were key components in a large new conveyor system for handling minerals. Each drum consisted of a cylindrical shell carried on a solid circular shaft. The shaft projected beyond both ends of the shell, and was supported in self-aligning bearings. The shell was attached to the shaft by fixing a pair of annular plates between the shaft and the ends of the shell. The outer circumference of each plate was welded to the shell, and the inner circumference was welded to a boss which was keyed to the shaft. The drums rotated in service at 0.5–1 s −1. Failures occurred after 1–4 weeks of commissioning trials, corresponding to 0.6–4.6 million revolutions of the drums. Fatigue cracks initiated at the toes of the welds between the plates and the bosses, and propagated through the plates until the shell became detached from the shaft. An elastic analysis showed that high cyclic bending stresses were produced at the plate-boss welds when the drums were loaded by the tension in the conveyor belt. The stress ranges in the failed drums were comparable to the fatigue strengths of welds in structural steel, as given in BS 5400: Part 10: 1980. As a consequence a total of ≃140 drums were condemned throughout the whole of the plant, with major cost implications.