Return to Service of a Derailed Grab Unloader

Due to an unforeseen event, a clamshell bucket grab unloader moved away from its parked position and derailed, causing visible damage to the pier leg and bridge structure.

The derailment resulted in an offset between the shear leg and the pier leg that caused the bridge structure to skew 10 degrees from its neutral position. This excessive skew angle resulted in contact between the pier leg and the bridge structure which caused visible structural deformation and local plate buckling. The structural damage due to this incident was investigated using three-dimensional finite element analysis (FEA) to simulate the contact condition and to compare the FEA model’s results with the detailed site survey measurements. This facilitated the calculation of the locked-in structural forces in the grab unloader at its derailed position. The buckling modes predicted by the FEA results correlated with the buckling modes visible on the derailed grab unloader.

Structural damage on the grab unloader, caused by the derailment incident.

These FEA results formed the basis for the re-railing methodology, in consultation with the heavy-lifting contractor, which involved pulling the shear leg structure to align with the pier leg structure and then lifting & rotating the pier leg structure to return the long travel wheels back onto the rail. Temporary supports were installed to ensure the safety and stability of the grab unloader during the re-railing process.

Structural plate buckling caused by the derailment incident.

Once the machine was returned to its normal operating position on the rails, several repairs were necessary to remediate the structural damage caused during the derailment. The design of these structural repairs was undertaken using detailed finite element modelling and analysis (FEA) to ensure that the proposed structural repairs met or exceeded the design requirements of the original structure.

The grab unloaded was successfully returned to operation after the completion of the structural repairs and recommissioning of the mechanical, electrical and control systems.

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.

Why do I need an independent design review?

Every machine is unique

When procuring a new Mobile Bulk Materials Handling Machine (BMHM), such as a bucketwheel reclaimer, stacker reclaimer, stacker, bridge/portal-type reclaimer or ship loader, the machines configuration will depend on many factors:

• Required throughput;

• Stockpile layout and footprints;

• Yard conveyor arrangements;

• Bund or wharf rail gauge;

• Properties of the material to be handled.

It would therefore be very unlikely to find an “off-the-shelf design” that would suit all the required design parameters for a particular mine or port site.

Higher rates of structural failure

A new BMHM is a major capital expenditure asset with an expected design service life of 25+ years, however, they experience a higher rate of structural failure when compared to other heavy industrial structures.

Historical evidence shows that catastrophic structural failures can occur at any time during a machine’s service life, including during the commissioning stage.

Safety and cost benefits

Engaging an independent or third-party design reviewer during the early stages of procurement can provide many benefits:

• Implement “Safety in Design” early in the design phase;

• Satisfies legislative requirements (duty of care / due diligence);

• Anomalies in the machine configuration and potential constructability issues can be identified and notified to the supplier (OEM) early in the design phase;

• Design code compliance issues can be identified in the design phase and promptly rectified;

• Costly production delays due to design issues and associated on-site remedial work can be minimised;

• Identifying design issues early in the design phase minimises cost overrun and schedule delay;

• Structural modifications can be incorporated during fabrication without undue cost or schedule penalty;

• Minimise the risk of commercial and/or legal disputes which potentially lead to expensive litigation.

Prevention is better than Remediation

LEC personnel have undertaken independent detailed design reviews, structural condition assessments and failure investigations for more than 50 bulk materials handling machines since 1993. Often this involved detailed Finite Element Analysis (FEA) using 2D and 3D elements.

Based on our experience, the detailed design review often identifies structural design issues related to:

• Safety in Design;

• Omissions and ambiguities in the Technical Specification documents;

• Materials and constructability issues;

• Serviceability issues;

• Member strength issues;

• Member and local plate buckling issues;

• Fatigue service life compliance.

These design issues can generally be resolved with the Original Equipment Manufacturer (OEM) during the design phase, thus eliminating potential schedule drift and cost overruns.

An independent detailed design review can be carried out in accordance with the following standards, generally nominated in the client’s technical specification for the new Bulk Materials Handling Machine:

• Australian Standard AS 4324.1

• FEM Section II (2 131 / 2 132)

• ISO 5049-1

Click here to contact LEC and discuss your requirements for an evaluation of a machine’s technical specification and an independent design review.

Weighing of a Stacker Reclaimer

A rail-mounted bucket wheel stacker reclaimer had recently been refurbished following a partial structural failure, but before it could be returned to service it was necessary to weigh the machine to confirm its as-built condition matched the design intent for balance, stability, slew bearing loads and wheel loads.

LEC prepared a weighing method statement and undertook on-site supervision of the weighing, which was undertaken by jacking the eight-wheel bogie structures.

LEC then processed the site measurements to calculate the total weight and weight distribution (centre of mass) of the stacker reclaimer, and compared these to the design values to determine whether re-ballasting might be necessary to ensure the slew bearing service life would not be compromised due to an out-of-balance condition.