Fatigue Cracking of Rail Wagons

Consistent fatigue cracks were observed in a number of coal wagons, which had resulted in loss of revenue for the rail operator. Structural modification of the wagon body structure was required to prevent the crack from re-appearing. The main challenge on this project was to develop an effective solution while minimising the increase in wagon tare mass. Any increase in the ore wagon weight would reduce their payload and the associated revenue.

As part of the design process, a finite element model of the wagon was created. The model incorporated sufficient details to reasonably predict the location and magnitude of stress concentrations and hence locations where fatigue cracking may initiate. Fatigue analysis was carried out in accordance with the recommendations given by the Association of American Railroads (AAR), Fatigue Design of New Freight Cars. The results from this analysis were in close agreement with the locations of the existing cracks.

Based on this assessment, a local structural strengthening solution was developed to effectively reduce the fatigue stress. The geometry of the local strengthening was optimised to minimise the weight and for ease of installation. The proposed structural modifications (<1% of the wagon tare mass) have since been successfully implemented and have extended the service life of the wagons by at least 15 years.

Service Life Extension for a Bucketwheel Reclaimer

A bucketwheel reclaimer had been decommissioned after 25 years due to extensive structural defects, including cracking in the luffing pivot rocker region.

For these defects to be repaired, the traditional approach would be to fully dismantle the reclaimer in the reverse order to which it had been constructed, however this would require an extensive laydown area, high capacity cranage and months of construction work with the associated high risk. Another alternative would be the complete replacement with a new reclaimer, which would require a significant cost and timeframe for the procurement and commissioning of the new machine.

Instead, an in-situ structural remediation solution was undertaken which enabled the client to resume operations in 12 months, sooner than a traditional refurbishment and at a cost saving of several million Australian dollars.

The major remediation works included:

• Repair of structural cracking in the rocker arm assembly.

• Hydraulic luffing cylinders were removed, refurbished and re-installed.

• Slew bearing replacement.

• Bucketwheel replacement, including shaft and drive assembly.

• Replacement of heavily corroded structural members on bucketwheel boom.

The superstructure of the reclaimer was lifted in-situ with the boom and counterweight still assembled, which allowed the change out of the slew bearing and the repair of the rocker assembly.

This implementation required purpose-built temporary luffing cylinders, temporary support frames, and the installation of safety features such as strain gauges to monitor the loads and stability throughout the construction process.