A simplified approach for asset criticality ranking can provide
important insights.
@ KUMAR R. IYER, INDORAMA INDIA
INTRODUCTION
Plants rely on a wide variety of assets. Some are mission-critical, i.e., required for production, safety, or
environmental compliance, while others handle non-crucial functions.
This difference in criticality affords an opportunity to prioritize maintenance strategy and optimize
maintenance costs.
Thus, many manufacturers perform asset criticality ranking (ACR) or equipment criticality ranking (ECR)
and often mark the criticality class in the equipment master of the enterprise resource planning (ERP) system.
However, most organizations carry out this exercise as a sort of mechanical drill and don’t give it proper
importance, time, and effort. No wonder such companies fail to leverage the exercise to formulate
maintenance strategies based on equipment criticality.
ACR involves ranking assets based on a well-structured procedure. An asset gets marks for various
parameters, with the consolidated score leading to its classification into a criticality category.
Usually, for simplicity, the ranking consists only of A, B and C categories.
There’s no right way of doing ACR. The ISO standards on asset management (ISO 55000, 55001 and
55002) don’t prescribe any methodology.
So, manufacturers employ disparate methods and approaches to suit their needs, with varying levels of
effectiveness.
The classical ACR method is like failure-modes-and-effects analysis (FMEA) and risk-based inspection
(RBI).
Each asset gets a risk priority number (RPN) that’ computed based on the history (frequency) or probability
of failures and their consequence or impact. Then, the actions required to minimize the risks are listed.
(Completion of the prescribed actions may lead to a revised RPN number the following year.)
This methodology not only makes the ACR process very complicated and time consuming but also very
subjective — which can lead to erroneous classifications. For instance, a rubber-lined storage tank for weak
phosphoric acid that ruptured in the past may get categorized as a critical asset because of that failure
while a production-critical high-speed compressor with no failures during the last 10–15 years of operation
may get classified as semi-critical.
The objectives of FMEA and RBI differ from those of ACR; tying them together dilutes FMEA and RBI and
complicates the ACR process.
