In mining and heavy industries, maximising asset utilisation requires more than just tracking downtime – it demands a deeper understanding of failure patterns.
Traditional Pareto charts, while useful, often overlook key reliability insights. Enter the Jack-Knife diagram (JKD), a tool developed by Professor Peter Knights over 25 years ago to prioritise maintenance efforts more effectively.
How the JKD works
Unlike Pareto charts which rank failures by cumulative downtime, the JKD plots downtime events using two axes: mean time to repair (MTTR) and the number of events (N).
The resulting logarithmic scatter plot categorises failures into four quadrants:
- Acute and chronic failures: frequent, high-downtime issues requiring urgent attention
- Acute failures: rare but high-impact events
- Chronic failures: frequent, low-downtime events that disrupt operations
- Ideal zone: low-frequency, low-impact failures (the goal for all assets)
By shifting failures from high-priority quadrants to the ideal zone, reliability engineers can target sustainable performance improvements.
Why JKD outperforms Pareto analysis
A Pareto chart suggests that 80 per cent of downtime stems from 20 per cent of failures. However, this approach may misrepresent chronic problems.
For example, a single 500-hour failure may dominate a Pareto chart but 10 failures of 50 hours each (causing repeated operational disruptions) might be undervalued.
The JKD highlights these chronic reliability risks that otherwise go unnoticed, ensuring maintenance teams tackle the right problems first.
Implementing JKD
- Gather failure data: document downtime events, failure types, and repair durations
- Plot the JKD: use log-log scales to visualise patterns in failure frequency versus downtime impact
- Identify priority areas: focus on acute and chronic failures that disrupt reliability
- perform root cause analysis (RCA): address underlying issues through redesign, operational changes, or improved maintenance tactics
- Track improvements: monitor how failure patterns shift over time, ensuring interventions are effective
A detailed example and template of how to do this in Excel can be found here:
A continuous improvement tool
JKDs are not static; they evolve with new data. Companies can adjust chronic and acute failure limits over time or fix them to track long-term reliability gains.
For industries relying on heavy equipment – mining, oil and gas, manufacturing – JKDs offer a more actionable approach to reliability engineering. By uncovering hidden inefficiencies, this method drives more strategic maintenance decisions, reducing costs and improving equipment availability.
Want to optimise your fleet’s reliability? Contact Pardus Consulting for expert analysis and tailored maintenance solutions.
