Reliability Centered Maintenance

Written by Nicholas Kamuda
Bookmark and Share

Over the last 20 years or so, business and physical asset management has seen a general shift towards Reliability Centered Maintenance practices. Prior to the 1970s, most asset management was arguably comprised of methods for addressing failures and prolonging equipment life through fixed-interval strategies. In the decades since, those strategies have been revised, reversed, or updated to function with complex modern physical assets.

A Brief History of Reliability Centered Maintenance

The first industry to recognize that traditional maintenance practices were no longer compatible with the rapid advancement of modern assets was the commercial aviation industry. In the early 1960s, representatives from different sectors of the aviation industry--the FAA, the aircraft manufacturers, and the major commercial airlines-- put their heads together to develop new maintenance strategies that were informed by the complexities of modern aircraft. Called the Maintenance Steering Group Task Force, they sought to direct maintenance towards the aspects of asset management that required attention. The resulting studies formed the basis of modern Reliability Centered Maintenance and RCD practices.

The United States Department of Defense, interested in the findings of the civil aviation industry, commissioned a report in 1976 which was released in 1978. The report was titled "Reliability Centered Maintenance," and helped promote the concept that maintenance should be aimed at maintaining the functionality of assets, not necessarily the asset itself. The growing complexity and inter-dependency of modern assets means that a failure mode of a modern asset affects many different aspects of a business, from production cost to customer service, product quality, safety and environmental integrity. By targeting the functionality of assets, businesses can maintain service and production, both of which are essential to the security of a modern business.

The Maintenance Steering Group Task Force also discovered that the failure pattern upon which traditional (fixed interval) maintenance is based was not applicable for most components on aircraft. The traditional view, that components operate reliably for a certain period and then wear out, was found to apply to
only 2% of items. The well-known bathtub curve, in which a high incidence of failure (known as infant mortality) followed by a constant conditional probability of failure followed by a wear-out was found to apply to only 4% of items.

The remaining components followed a further 4 models of conditional probability of failure, with the majority of them falling into a pattern that showed almost no correlation between operational age and failure rate. This data almost proves fixed-interval strategies to be incompatible with modern assets. Moreover, many of the results of other recent studies support the idea that fixed-interval strategies may have negative consequences. Overhauls, once thought to extend operational life by pushing back the "wear-out zone," are often found to actually introduce another "infant mortality" period into an otherwise stable asset or system.

Producing a Reliability Centered Maintenance Plan

Reliability Centered Maintenance and RCM 2, identify the maintenance requirements of each physical asset in its operating context. A multi-disciplined team answer a series of specific questions to identify the appropriate failure management policies. The first stage in the process is to identify what functions the asset is expected to perform including equipment performance in its present operating context. These functions are then subject to the remaining RCM questions.

Next, every reasonably likely failure mode that would cause a loss of each function must be identified to an appropriate level of detail along with the effects that each failure mode would have on other assets or aspects of the business. The resulting analyses can be organized in a database covering many assets.

The RCM decision making stage identifies an appropriate failure management policy to deal with the consequences of each failure mode (safety, environment, cost, unavailability, mission failure etc). Failure management policies include condition based maintenance, scheduled restoration, scheduled discard, failure finding, one-time changes (such as physical redesigns, training recommendations and procedural changes) and no scheduled maintenance.

Bookmark and Share