Underground » Maintenance
The Stage One report is attached to the Stage Two Report available here. 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. The information compiled in this document 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/requirements.
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:
a) Hydraulic hose assembly duty - there is a need to understand loading severity under various operating conditions. It was proposed that representative samples (i.e. 4 - 6 weeks) of in-service pressure history data are established for two longwall system designs; namely, Joy and Bucyrus/Caterpillar longwall systems. This information would be utilised to:
- establish effective fatigue life of hoses for selected longwall hose assemblies based on representative pressure history data; and
- identify possible design improvements to LW hydraulic circuits/components to reduce any extreme loading conditions identified.
b) Life cycle management strategies - develop fit-for-purpose specifications and selection criteria for hose assemblies. The key objectives are:
- determine the extent of deterioration, in-service life and safety factors for a sample of aged hoses;
- verify the compliance of selected new and used/aged hoses with the applied safety and fatigue (design life) requirements, based on in-service pressure profiles data; and
- determine the adequacy of current hose assembly burst and endurance tests prequalification criteria, which are considered as some of the most important parameters used in hose performance specification.
Whilst 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. 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/guidelines (i.e. MDG41) for evaluating the performance of hose assemblies used in longwall hydraulic systems.
The longwall system hydraulic pressure monitoring programs carried out at Mandalong mine and Newlands Northern Underground (NUG) mine revealed significant anomalies in system pressure measurements for different longwall equipment. The key finding was the presence of significant pressure spikes in some hydraulic circuits of NUG longwall system. Many of these pressure spikes 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. 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.