The key finding of the report – which is stage two of research on performance-based specifications for longwall hose assemblies – is the detection of the presence of significant pressure spikes in some hydraulic circuits of the NUG longwall system.

Many of these were characterised by high-frequency pressure oscillations and high-pressure rise rates.

“Currently the industry approach is that all pressure cycles above the selected range threshold value should be equally considered in hose fatigue damage calculations,” according ACARP.

“This assumption has been questioned by project industry monitors as previous work conducted with rock burst valves suggested that hydraulic hoses did not appear to have fully reacted to transient pressure spikes when exposed to impact shock loads.

“It was agreed in consultation with the project industry monitors to expand current project objectives in order to investigate the dynamic response characteristics of the longwall hydraulic hoses when subjected to pressure spikes with variable amplitude and pressure rise rates.”

A separate laboratory experimental program was conducted to investigate this aspect of hydraulic hose response.

The longwall pressurised fluid power systems are a potential major hazard that may result in fatal injuries if they are not properly controlled and maintained.

The objective of this project was to assist the mine personnel in formulating management systems for the mitigation and control of the risks associated with longwall hose assemblies.

This research should also assist longwall systems designers, manufactures and regulatory bodies in assessing the safety aspects of fluid power systems including design and development of fit for purpose equipment and safety standards and requirements.

The investigation undertaken during this project included the following main steps: establishment of Mandalong and Newlands mine longwall system pressure monitoring programs methodology; design and installation of hydraulic pressure monitoring equipment at the two mines; analysis of data collected from pressure monitoring programs and summary of key observations; analysis of results derived from aged hoses burst and impulse testing programs; assessment of remaining safety factor and fatigue life for selected hose assemblies based on measured pressure profiles; and review of the adequacy of hose burst and impulse cycle tests (endurance tests) recommended by current Australian Standards for evaluating the performance of hose assemblies used in longwall hydraulic systems.

The development of hose assembly risk management strategies was covered in detail in the Stage One report, “Reducing the Risk of Hydraulic Hose Assembly Failures on Longwall Systems”

The aim of this Stage Two project was to address the following important issues/gaps of knowledge identified in the previous project. These gaps include hydraulic hose assembly duty.

There is a need to understand loading severity under various operating conditions. It was proposed that representative samples – of 4-6 weeks – of in-service pressure history data be established for two longwall system designs, namely, Joy and Caterpillar longwall systems, according to ACARP.

This information would be utilised to establish effective fatigue life of hoses for selected longwall hose assemblies. It would also identify possible design improvements to longwall hydraulic circuits/components to reduce any extreme loading conditions identified.

“While this report has been primarily written to address some of the needs associated with hydraulic systems, its findings may be applicable to other underground and surface mining applications,” ACARP said.