Think Overall Inspection Effectiveness

By Drew D. Troyer, CRE, CMRP, Contributing Editor

Properly selected and executed inspections are a foundational element of any plant maintenance-and-reliability strategy and plan. While I’ll address specific inspections in future columns, here, the focus is on a way to track their value.

For purposes of this discussion, the term “inspection” refers to any machine observation. Performed on dynamic or static equipment, they can be visual/sensory or gauge- or instrument-enabled. Regardless of form, the objective is to determine whether interventions are required to ensure equipment, process, and/or plant reliability and, in some cases, safety and environmental goals.

OIE (overall inspection effectiveness) is a leading metric for evaluating the critical inspect-to-work process.

OIE (overall inspection effectiveness) is a metric that I created to easily assess the efficacy of any type of inspection. It’s simply the sum of three elements expressed as percentages (see diagram).

Percentage of scheduled inspections that are completed on time: This is relatively straightforward. As an example, if 100 inspections were scheduled for completion during a given week and 80 of them were actually completed, the score would be 80%.

Percentage of found problems that are corrected prior to a functional failure: The purpose of inspections is to find problems and/or irregularities that can be fixed or adjusted on the spot or that lead to the creation of a work request, which can be executed prior to functional failure. Like the previous metric, this is a simple binary percentage. If 100 problems were found and 80 of them were fixed or adjusted on the spot or successfully completed by way of a work request, the performance would be 80%.

Percentage of inspection-directed work with no rework within 30 days: Again, this is a simple binary percentage. If 100 inspection-directed repair jobs were completed and 80% had remained clear for at least 30 days, the score would be 80%, i.e., only 20% of the jobs required rework.

Let’s now calculate OIE based on those hypothetical examples. To recap, 80% of the scheduled inspections were completed on time; 80% of the problems revealed by inspections were corrected prior to functional failure; and 80% of machines receiving inspection-directed repairs made it 30 days without a new failure. Given those percentages, the OIE calculation would be 0.8 x 0.8 x 0.8 = 0.512 or 51.2%.

At this point, I hope you’re thinking two things:

• OIE looks a lot like the OEE (overall equipment effectiveness) metric.

• OIE’s second and third elements are influenced by maintenance-work planning, scheduling, and execution, not just inspections.

As for the similarity to OEE, you are absolutely correct. That was by design. Unfortunately, although OEE is simple and intuitive, it’s a lagging metric.

In contrast, OIE is a leading metric. Accordingly, if OIE increases, you can expect OEE to increase. I’ve devised several OEE-styled leading metrics (OIE is just one of them).

As for the relationship between inspection, work-planning, work-scheduling, and work-execution processes, that also was by design, i.e., allowing users to monitor the entire inspect-to-work process. For further information on creating and executing effective inspect-to-work processes, see my detailed article on the topic in an upcoming Efficient Plant e-newsletter. EP

Based in Tulsa, OK, industry veteran Drew Troyer is principal with Sigma Reliability Solutions. Email Drew.Troyer@sigma-reliability.com.