Prevention is better than cure

Reliability-centered maintenance (RCM) reduces the risk of equipment failure to a more-than-satisfactory level.

By Richard Rosales

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Most people, especially those from a family with a history of a particular illness, schedule regular checkups throughout the year. Knowing which weaknesses reside in a person’s system allows taking measures to prevent a serious and possibly long-lasting human downtime. Even if something goes wrong, a well-documented patient history might mean the difference between life and death.

In many industries, managers work hard to reduce equipment downtime. What better way of doing this than by subjecting plant equipment, just like people, to regular checkups. Some equipment might be prone to more problems than others and will require greater attention. To determine what must be done to ensure that a physical asset continues to do what its users want it to do in its present operating environment, managers use reliability-centered maintenance (RCM), which helps to define a complete maintenance regimen and is a process that can form a vital part of a company’s preventive maintenance program.

RCM is a term that’s widely used in industry. However, it isn’t always well understood. It requires plant personnel to monitor, assess, predict, and generally understand how physical assets work. This identifies certain failure modes, thereby enabling appropriate maintenance tasks to be established. RCM is described as “a systematic approach to defining a routine maintenance program composed of cost-effective tasks that preserve important functions.”

RCM history

The RCM process has its roots in commercial aviation, and the acronym was coined in a 1978 report titled “Reliability Centered Maintenance,” which was authored by F. Stanley Nowlan and Howard Heap — two employees of United Airlines — and sponsored by the U.S. Department of Defense (DOD). This report embodied the latest technologies commercial aviation developed and used over a period of time dating back to the early 1960s.

The RCM process can be a vital part of a preventive maintenance program.

– Richard Rosales

The commercial airline industry worked closely with the Federal Aviation Administration (FAA) to establish a well-structured RCM process, which was necessary to meet the FAA requirements of ensuring more reliable commercial aircraft and better safety performance. Until then, the performance records of the commercial airline industry were poor. However, their involvement in developing the process demonstrated a clear understanding of the consequences of not using a sound approach, such as RCM. These consequences included unreliable equipment with the possibility of a catastrophic failure while in the air, resulting in multiple fatalities.

The results of their efforts are evidenced by the fact that commercial airline travel is now much safer than driving on a public road. The commercial airline industry continues to use the RCM process to ensure the continued safe and reliable aircraft performance.

Verifying a true RCM process

Since the late 1980s and early 1990s, many companies have been using the RCM process for their own assets. In answer to this demand, a number of RCM derivatives, each claiming to be as good as or better than the original, have materialized. Unfortunately, some have modified the process to such an extent that it no longer provides the same benefits as the original.

As a result and in an effort to qualify a process as an RCM process, the Society of Automotive Engineers (SAE) developed and published a standard that would prove a process was truly an RCM process. This document, SAE standard JA 1011, was published in 1999 and is now used by many companies. It requires a candidate RCM process to satisfactorily answer seven questions in sequential order. In addition, it must provide the basis for answering these questions satisfactorily.

The main players

The classical RCM process begins with a review of the individuals involved in the analysis. To conduct an RCM analysis effectively, the participants must know about the system or equipment under review. In other words, participants such as operators and those who maintain the system must work with the system on a daily or frequent basis. In addition, front-line supervision in both the operating and maintenance are also involved. Others, such as OEM representatives and subject matter experts, are brought into the analysis as needed. The subject matter experts might not have in-depth knowledge of the system but are typically experts in areas such as engineering, safety and quality management. A key player is the RCM facilitator who orchestrates the group during the analysis.

The RCM process

The cornerstone of the RCM process is understanding that there are six failure patterns to be considered when defining maintenance strategies. The commercial airline’s extensive analysis of failures determined that 20% of equipment failures are a result of time-based failure patterns (as seen in the three graphs to the left in Figure 1), while the remaining 80% aren’t time-dependent (right three graphs). Even though the majority of maintenance work was performed after a set number of run hours — where typically 85% of components were taken through overhauls — the failure question wasn’t solved because the majority of failures weren’t time-dependent. As a result, infant mortality was introduced as components were overhauled, leading to the realization that condition-based maintenance was the best solution to asset failures.

(Figure 1) Failure patterns: The commercial airline industry determined that only 20% of equipment failures are a result of time-based failure patterns.
(Figure 1) Failure patterns: The commercial airline industry determined that only 20% of equipment failures are a result of time-based failure patterns.

The RCM process begins with an understanding of how a system is being used, the system’s operating context . This is followed by the seven questions:

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