Repair & Prevention of Cracking in an Existing Tippler

Photograph of tippler during installation

Cracks in the Cage Structure

A number of cracks were identified in the cage structure of an existing rotary tippler, during routine site inspection, after approximately 10 years in operation. These cracks were immediately addressed using temporary repair procedures by the port operator.

While the temporary repair prevented immediate disruptions to the port operation, a long-term structural solution to the tippler cage structure was required in order to prevent similar cracks from reappearing. A conceptual structural modification was developed with the aid of Finite Element Analysis (FEA). A three-dimensional FEA model of the tippler cage structure was created and analysed to determine the extent of the highly stressed regions. This allowed the structural modification to be designed effectively and efficiently, as well as minimising the tonnage of the structural remediation work.

Comparative analysis with the existing (unmodified) tippler structure was carried out to verify the effectiveness of the structural modification. The final design solution was proposed to the port operator and the Original Equipment Manufacturer (OEM) for their acceptance and approval. The proposed structural modification has since been approved by the OEM and successfully implemented on site.

LEC’s Finite Element Analysis (FEA) Capabilities

Why use FEA ?

Structures in the resource and heavy industrial sectors are often geometrically complex and cannot be readily simplified to a traditional beam/frame structural analysis approach. Advanced Finite Element Analysis (FEA) techniques facilitate a more accurate representation of plated structures and thick casting / forging components using 2-D and 3-D elements, respectively.

What FEA software does LEC use ?

LEC use MSC.FEA finite element software, which is a combination of MSC.Patran (finite element modeling pre- and post-processing software) and MSC.Nastran (finite element analysis solver). Nastran is a finite element analysis program that was originally developed for NASA, in the late 1960’s, in the United States. LEC personnel have been using MSC.Nastran software since 1992.

What FEA is not

FEA is not a silver bullet for complex structural problems. The old adage of “garbage in garbage out” is very applicable to FEA computer analyses. Proper selection of solution parameters, element types, mesh density, load & boundary constraints are essential in order to produce a reliable finite element analysis model. One also cannot underestimate the importance of the interpretation of the finite element analysis results. This interpretation skill will allow the analyst to make sound engineering decisions based on the analysis results. That is why all LEC’s advanced structural analyses using finite element modeling, analysis and design checks are carried out in-house by highly experienced and dedicated LEC specialist engineers and technologists.

Typical FEA workflow

LEC retain MSC.FEA licenses for the following advanced structural analysis:

Solution Type	Typical Application on LEC’s Projects
Linear static analysis / linear buckling analysis	Independent design review and development of design solution for a variety of structures in the resource and heavy industrial sectors.
Natural frequency / modal analyses	Dynamic sensitive structures (e.g., stacks/chimneys), preliminary analysis for structures subjected to vibrating loads (e.g., crushers).
Transient dynamic analysis (frequency/time domain)	Detailed dynamic analysis for structures subjected to vibrating loads
Geometric and material non-linear analysis	Structural forensic investigation.

LEC’s typical finite element analysis workflow is shown in the diagram below:

Click here to explore some of the projects completed by LEC personnel using finite element analysis.

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.