Client: E. J. O’DONOVAN & Associates
1. Project Background
CMP Engineers was engaged to perform a finite element analysis (FEA) of a dead-shaft conveyor pulley and end disc that failed in operation after approximately 18 months of service. The failure occurred at the welded connection between the pulley shell and end disc. The scope included modelling the pulley and comparing resulting stresses with design criteria specified in BS7608 ‘Fatigue Design and Assessment of Steel Structures’ for welded connections. The analysis was prompted by the need to understand the root cause of the premature failure and to inform future design and maintenance strategies.
2. Challenge
The main challenge was to determine why the pulley shell to end disc welded connection failed after a relatively short service life, despite being designed for much longer operation. The investigation needed to consider cyclic loading, weld quality, material properties, and thermal effects. Constraints included limited historical data on operational loads and the necessity to provide actionable recommendations for both repair and future design improvements.
3.Solution
CMP Engineers undertook a comprehensive FEA, analysing the pulley under normal running belt tensions of 50, 100, and 200 kN. The geometry was modelled from supplied CAD drawings, and loading was applied as a constant pressure over the 180° wrap angle. The analysis included:
- Material Assessment: The pulley and end plate were made from AS3678/Grade 350 steel, with yield strength of 350 MPa and ultimate tensile strength of 450 MPa.
- Fatigue Analysis: Stresses at the welds were compared to BS7608 criteria. The shell to end disc weld was classified as category F, and the end disc to bearing housing weld as category F2. The FEA showed that, for a belt tension of 50 kN, the stress range (16.3 MPa) was below the endurance limit for infinite life (19.1 MPa for F category welds).welded joint.
- Visual Weld Examination: Post-failure inspection revealed poor weld quality, including over-roll at the weld toe, lack of fusion, and internal cavities. These defects increased stress concentrations, reducing fatigue life to approximately 18 months—consistent with the observed failure.
- Thermal Analysis: Thermal stresses were found to have a negligible effect on fatigue life for the
welded joint. - Recommendations: The analysis concluded that failure was likely due to poor weld quality and/or material defects, rather than design inadequacy. Recommendations included improving weld quality and inspection procedures for future pulleys.
4. Outcomes
CMP Engineers is a Brisbane based mechanical engineering design and consulting firm working across mining, industrial, civil and marine projects.
Tangible Results:
- Provided a clear root cause analysis for the premature failure of the conveyor pulley.
- Demonstrated that, as designed, the pulley should not have failed under normal operating loads, highlighting the critical impact of weld quality.
- Delivered actionable recommendations for improving weld procedures and inspection regimes.
Intangible Results:
- Enhanced client confidence in CMP Engineers’ technical expertise and analytical capabilities.
Informed future design and maintenance strategies for conveyor pulleys.
Key Learnings:
- High-quality welding and thorough inspection are essential for the longevity of welded structures subject to cyclic loading.
FEA is a powerful tool for diagnosing failures and validating design criteria.
Client Feedback:
- The client received a detailed report and recommendations, supporting their maintenance and procurement decisions.