By Allan Black, Joy Global and Janse Van Rensburg, Anglo American-South Africa
Coal operating companies are faced with reduced capital expenditure while still needing to improve productivity and extend the life of core assets. Working directly with end user mine specialists an Extended Life Testing Program has been introduced to greatly increase the operable life of existing powered roof support installations. The introduction of this predictive tool that can determine when individual components will reach the end of their serviceable life.
This Extended Life Testing can realize an additional 15,000 to 30,000 cycles out of a roof support that was originally specified for only 30,000 cycles depending on the operational loading and duty cycle. This can sometimes push capital expenditure five to seven years into the future. To gain detailed knowledge of the duty and current structural competence, a representative roof support is taken out of service, stripped and fully evaluate. The support is then tested up to target number of life cycles and a test protocol is developed using load cases that are tailored to replicate the typical, actual service experienced by the roof support to date.
A detailed report is issued indicating when components either have or will likely reach the end of their serviceable life. A detailed Life-cycle Management plan is proposed allowing the planning of future maintenance budgets with a high level of accuracy and confidence in the life of the supports or support components going forward.
A powered roof support supplied in 2009 and initially tested up to 30,000 cycles was examined with a requirement to extend the support’s life to 45,000 cycles. The support had seen 13,000 underground cycles in some pretty tough conditions. It was dismantled and visually inspected, with all cracks and damage identified and assigned unique crack identification marks. The components were then shot blasted and visually inspected with the addition of magnetic particle NDT testing to establish the location of any additional weld cracks. Hinge pins and bores were also examined, measured and recorded.
Based on the results of these inspections, a unique test program was agreed upon that best replicated the load cases the support had seen in actual service.
The test was suspended after 19,000 cycles (a total of 32,000 cycles including those seen underground) due to the catastrophic failure of the lower links. Other structures of the roof support showed signs of fatigue but still maintained their prime function. The lower links were replaced, and the test resumed. Deterioration was monitored throughout the extended testing but didn’t impact the structural performance and the support achieved the target 45,000 cycles. A comprehensive plan was devised advising on when to carry out proactive replacement of the lower links, as well as any other work required to take the supports to the required 45,000 cycles.
Extended life testing, taking a support past its original life cycles, including comprehensive plans based on test results predicting when components are likely to reach the end of their serviceable life allows maintenance budgets to be developed to a high level of accuracy giving end users and mine owners confidence going forward.