Understanding Reliability Engineering

May 24, 2022

What is RCM - Reliability Centered Maintenance?

•A principled methodology to define a new or update a legacy maintenance regime, and then modify it as learning and data is subsequently gathered.

•There are variants of the RCM process, MSG3 in aerospace, The Nuclear Industry variant, NATO and various militaries have a version, and general industry can use the Allodon version (RCM II)  first published by the Late John Moubray. International standards SAE JA1011 and JA1012 define what must be present to be an RCM process. 

What is RCA – Root Cause Analysis?

•This is a process for investigating the cause and, effect chains associated with failures, to find (root) causes.  Root causes may be prevented or avoided by the organization that has suffered the failures.  The intent is to prevent similar failures from occurring in the future.  

Several processes were used to Conduct RCA, including fishbone Isigawa diagrams, asking ‘5 why’s, and Apollo RCA. 

What is a failure mode?  The state that we observe when a component has failed.

•Words used to describe failure modes include “Leak”, ”cracked”, “deformed” etc.

•Words such as ‘corrosion’, and ‘erosion’ are failure mechanisms that lead to the failure modes.


What is an FMEA?  A failure modes and effects analysis.

•We determine the functions of a component, how they may functionally fail, how often and what the effects and impact of failure are, and how detectable the failure is.

•The analysis of likelihood, impact, and detectability are scored to produce a Risk Profile Number (or criticality of the component’s failure modes).  This study forms the basis for the RCM process.

What is Weibull? – Statistical Distribution

•Proven to be applicable for life or failure studies.  The study may be conducted by capturing a part’s ages at the time of failure or planned change.   The data is then fitted to the Weibull distribution and checked for the goodness of fit to obtain the Weibull parameters, “shape”,  “scale” and possibly “location”.

•The Weibull parameters can be used to determine patterns of failure (premature, random, or wear-out) that may then determine the most effective maintenance interventions or maintenance tasks that would be applicable.

What is a CMMS?

•A Computerised Maintenance Management System (CMMS), enabling the maintenance workflow for physical assets.

•The primary functions of a CMMS are: To contain a register of assets breaking down to their maintainable items; a schedule of planned and corrective tasks, and the steps and resources required to complete work, including time and cost estimates.

•The logic for sequencing tasks, a plan for when scheduled and corrective work may be carried out, and a repository of any post-work test data.  

•A CMMS is most often supplied as a software application, examples being extensions to Enterprise Resource Planning (ERP) systems, such as planned maintenance modules and Enterprise Asset Management (EAM) systems.

What is master data and why is it important?

•Master data is used to capture details of maintenance strategy/tactics within a CMMS. In SAP typical master data items include Task Lists (labor and parts requirements for a planned task) and Maintenance Items (planned maintenance intervals).

•Many people underestimate the power of effective master data. Asset management capability is directly linked to the quality of master data.

What are maintenance “strategies” or “tactics”?

•Both terms mean the same thing in the asset management space (it just depends on your organisational terminology preference).

•The term refers to the approach to managing an asset to achieve desired function and performance. Strategies/tactics are often formed based on the outputs of FMEA, manufacturer recommendations, legislative requirements, and evolutionary inputs such as defect elimination and feedback from the front line.

•These terms mean different things, but they are commonly used interchangeably in the asset management space.

What is “material waste” in the context of maintenance strategies?

•Often in production-focused environments, when an asset requires corrective maintenance, a part is replaced. That same part can then be replaced soon after with a preventative strategy resulting in a wasted life.

•There are obvious financial and environmental impacts however most importantly increased safety risk.

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