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Plant-wide reliability

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Logistics operations

This is what we call Plant-wide reliability. For many years, analysts have tried to identify critical areas in their process plants. In an environment of thousands of pieces of equipment with different process conditions and a great deal of interdependency amongst the different units, it becomes quite hard to get an overall picture. That’s not even the key problem – the key problem on carrying out a reliability analysis on a plant wide basis is capturing the interaction between units. For instance, a storage tank may sustain production whilst a failure occurs on an upstream unit, hiding the unreliability of the upstream unit. Availability, a traditional KPI, is not enough to describe these interdependencies, different production rates, and operational flexibility presented by process plants. Availability is a bi-modal answer – a system is either available or not, working or not. A process plant could run with half of its capacity. Taking all that into account, criticality analysis at unit level is not dependent just on the reliability of a system but also throughput and system configuration! In order to get a better understanding of the performance of different units which should be combination of equipment criticality and operational constraints, a new parameter must be used – unit utilisation. Unit utilisation is a measure of the achieved average actual unit throughput over life. It is calculated by determining the achieved unit throughput rate averaged over life and dividing it by the unit capacity. It approximates to the On-Stream Factor which is the fraction of the time that a process unit is operating. Utilisation losses are caused by:

  • Capacity not required during normal throughput – ‘unused capacity’
  • Unit unavailability (internal/external)
  • Feed constraints
  • Downstream constraints

Note that actual utilisation can never be higher than the unit availability!

Unit analysis may not truly quantify the impact of bad performing systems at a Supply Chain level:

Network of units

Storage (and Linepacking operations for gas) may mitigate for unreliability:Storage tank and linepacking

Alternative sources may mitigate for unreliability:

Boost another product source

Plant-wide reliability captures the full supply chain performance and empowers analysts to truly identify areas of improvement and optimise the system

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