Open Cut » Maintenance & Equipment
Failure of a dragline boom support strands can have catastrophic consequences for the equipment leading to damage and downtime. Currently, in-situ inspection of the boom support strands is undertaken using radiographic techniques. These techniques are particularly valuable in displaying the distribution of fractures within a rope or strand. However, as cross-sections increase, the standoff distance between the radiographic source and the component also increases, reducing the image sharpness and resolution. For the large diameter cables 80-110mm which can contain up to 320wires, correlations between radiographic indications and actual fracture counts, determined through destructive examination, shows variations as high as 300%. This variation can be critical as this analysis is informing decisions regarding the suitability of a strand for continued operation. These decisions are often based on OEM guidelines of cable removal after 10% of fractured wires have been detected.
An additional constraint associated with radiographic inspection is the requirement that all personnel must be excluded from the vicinity during exposure of the radiographic source, meaning that other maintenance work is delayed.
Alternative test methods using Magnetic Flux Leakage (MFL) may be more appropriate, but require relative movement between the strand and detector. A current limitation of MFL instruments however is that they do not allow the inspection of the most critical part of the strand, adjacent to the terminations.
This phase of the project, in collaboration with ResTech, developed a proof of concept prototype MFL instrument capable of more accurately determining the number of broken wires, and verified its accuracy against actual wire fracture counts. The new instrument would provide increased accuracy of wire fracture count while eliminating the need for exclusion zones currently required with radiographic testing.
The instrument prototype has been constructed and Calibration and testing has begun using a test cable constructed with internal fractures and initial results appear to be positive with various internal breaks displaying indicative signatures. While there are many parameters yet to be optimised to further improve feature extraction and fault detection, the preliminary results are encouraging.