How things fail

"Reliability has two broad ranges of meanings:

  1. Qualitatively-operating without failure for long periods of time just as the advertisements for sale suggest, and
  2. Quantitatively-where life is predictable long and measurable in test to assure satisfactory field conditions are achieved to meet customer requirements.

Reliability is concerned with failure-free operation for periods of time, whereas quality is concerned with avoiding non-conformances at a specified time prior to shipment thus reliability measures a dynamic situation but quality measures a static situation. As in physics, statics is easier to understand and calculate than dynamics which involves higher levels of math and greater mental capabilities for comprehension."

- H. Paul Barringer

We study failed items for the same reason we do autopsies on humans: we want the data and we want it categorized correctly for making important decisions.

Failures require:

  1. A time origin which must be unambiguously defined;
  2. A scale for measuring the passage of time/starts/stops/etc., which motivates failure;
  3. The meaning of failure must be entirely clear for recording the event.

Failures during an asset's life can be attributed to the following causes:

Design Failures: This class of failures take place due to inherent design flaws in the asset or system. In a well-designed system, this class of failures should make a very small contribution to the total number of failures. Research by Winston Ledet (outlined in Don't Just Fix It, Improve It! A Journey to the Precision Domain) showed that approximately 20% of corrective work orders could be traced to poor design, build and installation issues.

Failure patterns Failure patterns (Courtesy of

Infant Mortality: This class of failures cause new (and repaired) assets to fail. In "Reliability-Centered Maintenance" by Nowlan and Heap, up to 72% of failures are in the "worse new" or "worse repaired" (infant mortality) category.

Infant mortality random failure pattern Infant mortality random failure pattern (Courtesy of

Random Failures: Random failures can occur during the entire life of an asset. These failures are also referenced in "Reliability-Centered Maintenance" by Nowlan and Heap. Up to 77-92% of failures are random in pattern.

Wear Out: Once an asset has reached the end of its useful life, degradation of component characteristics will cause assets to fail. Ledet research stated that "wear out" as a cause for a corrective work order is 12% or less. Nowlan and Heap and related research shows 8-23% of failures are wear out related.

The following graphs shows the contribution of the different failure modes towards the overall failure rate.

Contribution of different failure modes towards component failure

Where does preventive maintenance fit with these patterns?

Where does what some call "predictive" maintenance, but we call asset condition management, fit in?

Where does prescriptive maintenance fit with these patterns?

What else should we understand about failure?

Find Terrence O'Hanlon on LinkedIn.

Terrence O'Hanlon

Terrence O’Hanlon, CMRP, and CEO of® and Publisher for Uptime® Magazine, is an asset management leader, specializing in reliability and operational excellence. He is a popular keynote presenter and is the coauthor of the book, 10 Rights of Asset Management: Achieve Reliability, Asset Performance and Operational Excellence.

Upcoming Events

August 9 - August 11 2022

MaximoWorld 2022

View all Events
80% of newsletter subscribers report finding something used to improve their jobs on a regular basis.
Subscribers get exclusive content. Just released...MRO Best Practices Special Report - a $399 value!
The Three Laws of Preventive Maintenance

The Three Laws of Preventive Maintenance

Each preventive maintenance task in an Uptime Elements developed Reliability Strategy is generated for an identifiable and explicit reason

Digital Built America: Smarter, More Sustainable and Resilient

Digital Built America: Smarter, More Sustainable and Resilient

Building back better means transitioning the current infrastructure to smarter, more sustainable forms of development to safeguard the country’s future.

DIPF Curve and RCM Failure Patterns

Predictive Maintenance Deja Vu All Over Again

Compared to total asset failures, what percentage of asset failures can be "reliably predicted" with predictive maintenance?