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Maintenance Definitions


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Asset Management

"The organization of an asset’s life cycle to achieve the lowest life cycle cost with the maximum availability, performance efficiency, and highest quality (maximum OEE). In other words, asset management is the systematic process of planning and control of a physical asset throughout its life.  This may include the specification, design, and construction of the asset, its operation, maintenance and modification, and its disposal.  Asset management provides a strong focus on technical aspects of a facts-based, proactive management attitude with a mission, vision, and objectives derived from that of the company. "

(U.K. Institute of Asset Management)

Asset Criticality Analysis

Criticality analysis is a method for identifying product or process criticality for the purpose of prioritizing activities like design and maintenance. It is a process of decomposing product or process into hierarchical components, followed by study of their failure modes and effects, and (where appropriate) their causes. Criticality is the  combined measure of the failure mode probability and the severity of its effects.





Loss % Of Production


no injury

No damage

Zero effect

No impact

0 < 1


Slight injury

Slight damage

Slight effect

Slight impact

0 < 1


Minor injury

Minor damage

Minor effect

Limited impact

1 < 10


Major injury

Local damage

Localised effect

Considerable impact

> 10


Single fatality

Major damage

Major effect

National impact

> 10


Multiple fatalities

Extensive damage

Massive effect

International impact

> 10



Asset Knowledge Science (AKS)

"An SKF process of documenting asset knowledge relevant to monitoring and diagnosing asset anomalies. The process encompasses generic literature, OEM and SKF information, and asset unique details. The goal is to provide a structure to justify which measurements are needed to detect and diagnose failures in an early stadium. The AKS is used to tune an SKF decision-support system called @ptitudeTM"


CMMS Computerized Maintenance Management System

Computer systems that schedule, track and monitor maintenance activities and provide cost, component item, tooling, personnel and other reporting data and history. CMMS systems can often be interfaced with production scheduling and cost systems, and may be used to follow preventive maintenance policies.

CSI Customer Satisfaction Index

Measures the satisfaction of a service from its customers, often assessed by a survey _tcm4-80600.pdf

CSImaint Customer Satisfaction Index of Maintenance Service

Measures the satisfaction of the maintenance service from the customer, i.e. operation and other stakeholders



"An item of equipment has suffered a failure when it is no longer capable of fulfilling one or more of its intended functions. Note that an item does not need to be completely unable to function to have suffered a failure. For example, a pump that is still operating, but is not capable of pumping the required flow rate, has failed. In Reliability Centered Maintenance terminology, a failure is often called a Functional Failure"

Maintenance Terminology - Some Key Terms The Reliability Revolution By Sandy Dunn, Webmaster, Plant Maintenance Resource Center

Failure Mode (Cause)

  • "..a failure mode can refer to a physical event / mechanism that gave rise to a failure (e.g., moisture corrosion, fatigue, wear).

  • Or from a functional point of view, a valve can have several failure modes such as, "fails to operate on demand, valve leakage," etc.

  • In a formal Reliability-centered Maintenance (RCM) program, deeper failure modes are considered as failure causes.

  • Failure modes may also be defined according to the effect by which a failure is observed. A high level model system may include the following general failure modes:

  • CRT: General Critical Failure resulting in 100% production loss.

  • DEG: Degraded Equipment Performance, resulting in partial production loss while waiting for repair and 100% production loss during repair.

  • INC: Incipient failure. Equipment failure did not result in immediate production loss.? The failure was found during other repair / scheduled maintenance activities.? 100% production loss during repair.

  • UNK: No impact details are recorded in database.? 100% loss of equipment item on repair.

Failure Rate

Failure rate refers to the overall speed of failures, or the number of failures that occur in a given time frame, usually expressed in years. The total number of failures within an item population is divided by the total time expended by that population during a particular measurement interval under stated conditions. Failure rate is the ratio of the number of failures that occur in an interval to the size of the original population, divided by the length of the time interval. Other formats include the number of failures per year, and in some cases, it is common to express failure rate as the number of failures per hour, or the number of failures of an item per unit time. This can be applied to:

  • Observed failure rate: as computed from a sample

  • Assessed failure rate: as inferred from sample information

  • Extrapolated failure rate: projected to other stress levels



"a structured process, ..intended to proactively identify equipment modifications and/or safety devices required in order to avoid any significant safety or environmental incident as a result of equipment failure. Similar, in some respects to Reliability Centered Maintenance, but not as rigorous as Reliability Centered Maintenance in identifying underlying causes of failure, and does not consider, in any depth, the possibility of avoiding such incidents through applying appropriate Proactive Maintenance tasks." KeyTerms.htm


Infant Mortality

The relatively high conditional probability of failure during the period immediately after an item returns to service. KeyTerms.htm

Inherent Reliability

A measure of the reliability of an item, in its present operating context, assuming adherence to ideal equipment maintenance strategies. /KeyTerms.htm


Key Performance Indicators

A select number of key measures that enable performance against targets to be monitored.  


Lean Maintenance

Lean Maintenance is the application of lean principles in maintenance environments to increase value within the organization by elimination of waste through TPM.

Reliability Goes Nonfat With Lean Maintenance , Maintenance Technology

Six Sigma Keys to Lean Maintenance , Howard C. Cooper, Amemco, Maintenance    Technology

Measuring the effectiveness of Lean thinking activities within Maintenance PPT

Process Cost Reduction Through Proactive Operations and Maintenance , State-of-the-Art Report Food Manufacturing Coalition for Innovation and Technology Transfer

Lean Maintenance Reliability Tech Group

LCC Life Cycle Cost

The total cost of one piece of equipment during its operating life

LCP Life Cycle Profit

The total profit of one piece of equipment during its operating life


Maintenance Best Practices

The maintenance practices that enable a company to achieve a competitive advantage over its competitors in the maintenance process


The ease and speed with which any maintenance activity can be carried out on an item of equipment. May be measured by Mean Time to Repair. Is a function of equipment design, and maintenance task design (including use of appropriate tools, jigs, work platforms etc.).  


OEE Overall Equipment Effectiveness  (See More Details)

OEE is a comprehensive metric that indicates the relative productivity of a piece of equipment, a work cell, or an entire production line compared to its theoretical performance.

OEE (Overall Equipment Effectiveness)= Availability x Performance  x Quality Rate

OPE Overall Equipment Efficiency

Based on these three components of efficiency – Equipment, People and Space

= OEE (Overall Equipment Effectiveness) x LOE (Labor Operating Efficiency) x Capacity Usage %

Operating Efficiency (Labor Operating Efficiency) LOE

= Empowered % x Annual Labor Retention x Non Absenteeism %


Proactive Maintenance

"Proactive operations and maintenance (POM) is the detection and diagnosis of off-normal equipment
operation and the identification of the root-cause stressor(s) responsible for the condition. Two things should
be noted from this definition: 1) operations has now been engaged and integrated into the maintenance
equation and 2) finding the root-cause stressors (parameters outside the design envelope) responsible for the
off-design condition is now the prime directive."

Process Cost Reduction Through Proactive Operations and Maintenance , State-of-the-Art Report Food Manufacturing Coalition for Innovation and Technology Transfer

Patterns Of Failure

Failures manifest in one of four primary patterns.  They are described below together with their approximate percentage contribution to the whole shown.

  • Wear out - constant hazard rate with a distinct wear out region

  • Bathtub - infant mortality, constant hazard rate, and distinct wear out

  • Constant – constant hazard rate with little or no changes over the life

  • Infant mortality - infant mortality followed by a constant hazard rate

P-F Interval

A term used in reliability-centered maintenance.  The time from when a potential failure (P) is first detected on an asset or component using a selected predictive maintenance task, until the asset or component has failed (F).  Reliability-centered maintenance principles state that the frequency with which a predictive maintenance task should be performed is determined by the P-F Interval.



Quick Start Reliability (QSR)

For facilities organized in a classically reactive structure or hierarchy, often with absent or sub-optimized
maintenance/reliability engineering capabilities, SKF offers the Quick Start Reliability program. A basic first step in the evolution of maturity of an operation to the more advanced maturity phases of the complete AEO process, Quick Start Reliability is:

  • Targeted to those clients that are in the lower maturity phase (firefighting) in the maturity pyramid.

  • Designed to establish a maintenance process where none exists or is sub-standard.

  • Focused on the first 90 days of the overall change management plan for maintenance.

  • Geared to quickly put a performance management culture or process in place.

  • An 8-step process that identifies a plant’s best “early wins” and implements a program to achieve them.

  • Built around performing the right work at the right time in the right way—on equipment that is business critical.

  • The best course of action when a plant has neither the time nor the funding to conduct a comprehensive maintenance strategy review.


RCM Reliability Cantered Maintenance

"An on-going process which determines the mix of reactive, preventive, and proactive maintenance practices to provide the required reliability at the minimum cost. It can use diagnostic tools and measurements to assess when a component is near failure and should be replaced. The basic thrust is to eliminate more costly unscheduled maintenance and minimize preventive maintenance."

"Methodology used to define a maintenance program while having reliability as an input to the decision making process. Originally developed by the aviation industry and known as MSG-3 (Maintenance Steering Group), Reliability Centered Maintenance or RCM has since been adopted by many different industries."

"RCM focuses on Function, not Equipment, and its ultimate benefits are to drive down corrective maintenance costs and to reduce costs associated with outages and downtime. In a system there are the following three types of possible failure:

  1. Functional failures that would be observed or evident to the crew operating the system

  2. Potential failures which would be uncovered by the maintenance crews

  3. Hidden failure of redundant systems that would only be observed under test conditions.

In order to avert these types of failure there are the following four Scheduled Maintenance Tasks in RCM:

  1. On Condition Inspection of items to find and correct any Potential Failures.

  2. Rework at, or before, some specified age limit.

  3. Discard at, or before, some specified life limit.

  4. Failure-Finding Inspections of hidden function items to correct Functional Failures.

The procedure can be undertaken by using a yes/no decision diagram called the RCMII Decision Diagram that guides the analyst through the dominant failure modes towards one or more appropriate scheduled maintenance tasks

RCM Tools

  •  Poka yoke

It is the principle to make products, process, or services failsafe by incorporating mistake-proof techniques into the design.

  • Failure Mode, Effect and Criticality Analysis (FMECA)

It is the detailed study of a system to determine which features are critical to various modes of failure.

  • Just-in-time

Failures occur and firms must be prepared to respond quickly. Just-in-time has built-in failure recovery, as does a good supplier/subcontractor network.

  • Crisis management

It is a function in place by major corporations and governments to respond to failure that may be on a large scale.


Reliability is the confidence one has in a product, process, service, work team, or individual to operate under prescribed and expected conditions.

A product assembled in a series arrangement of components R1, R2,…, Rn  has a system reliability, RS, given by

RS =  R1 * R2 * R3 * R4 …Rn.

  • If a failure would be problematic, backup systems operate in the eventual failure of the principal system.
    Here, components
    R1, R2,…, Rn are connected in a parallel giving a system reliability

RS 1 = (1- R1)(1- R2)(1- R3)(1- R4)…(1- Rn).

  • The failure rate measures the reliability of products. It can be determined by one of the following ratios:

                                                      Number of products which failed

            Failure Rate (%) =  ____________________________________

                                               Total number of products tested

                                           Number of products which failed

                     Failure Rate (N) =  _______________________________________

                                 Number of unit hours of operating time

  • The mean time between failures (MTBF) is the reciprocal of the failure rate (N):


           MTBF       =  _____________

           Failure Rate (N)

                                           Operation Time for units

                     MTBF     =   __ __________________________

                                        Number of Products which failed

  • The failure rate profile can be expressed by a bathtub curve showing high failure rates at the beginning and the end, and normal failure between these extremes.

Risk Based Inspection RBI

Risk-based inspection refers to the application of risk analysis principles to manage inspection programs for plant equipment. RBI has been used in the nuclear power generation industry for some time and is also employed in refineries and petrochemical plant. The ultimate goal of RBI is to develop a cost-effective inspection and maintenance program that provides assurance of acceptable mechanical integrity and reliability.

A risk based approach to inspection planning is used to

  • Ensure risk is reduced to as low as reasonably practicable

  • Optimize the inspection schedule

  • Focus inspection effort onto the most critical areas

  • Identify and use the most appropriate methods of inspection



SCADA (Supervisory Control And Data Acquisition) system refers to the combination of telemetry and data acquisition. It consists of collecting information, transferring it back to a central site, carrying out necessary analysis and control, and then displaying this data on a number of operator screens. The SCADA system is used to monitor and control a plant or equipment. Control may be automatic or can be initiated by operator commands.

"Innovative Technologies for Transportation and Utility Industries"

SCADA system incorporates both hardware and software and provides central monitoring and control of plant and facilities. SCADA typically consist of a “Master Terminal Unit" (MTU) and one or more “Remote Terminal Units" (RTU).

Single Minute Exchange of Dies (SMED)*

Setup reduction or SMED is the technique for reducing the downtime associated with a process as it changes from making one product to another. (Note: SMED measures the overall changeover time from the time that the last good product was made, to the moment the first good unit of the new product is made).


It involves reorganizing the work, so all ‘external work is done while the machine is running (such as preparing tools and paperwork etc), and reducing the work required when the machine is stopped (using quick release clamps etc). The goal of many setup reduction programmes is to achieve tool (or die) changeovers in less than 10 minutes, thereby making the JIT goal of a batch size of one attainable.



TEEP Total Effective Equipment Performance

TEEP is a measures of the effective utilization of equipment assuming continuous 24 hour/day, 365 day/year operation.

Total Productive Maintenance (see more details)

"A company-wide equipment management program, with its origins in Japan, emphasizing production operator involvement in equipment maintenance, and continuous improvement approaches." KeyTerms.htm#U

An Introduction to Total Productive Maintenance TPM, Plant Maintenance Resource Center  Asset Management: Phase II Total Productive Maintenance, PPT,


The application of managerial, financial, engineering, and other skills to extend the operational life of, and increase the efficiency of equipment and machinery.

"A combination of management, financial, engineering, and other practices applied to physical assets in pursuit of economic life-cycle costs (LCC).  Its practice is concerned with specification and design for reliability and maintainability of plant machinery, equipment, buildings, and structures with their installation, commissioning, maintenance, modification, and replacement, and with feedback of information on design, performance, and costs" (from the definition endorsed by the British Standards Institute).

Total Asset Management

"an integrated approach (yet to be developed!) to Asset Management which incorporates elements such as Reliability Centered Maintenance, Total Productive Maintenance, Design for Maintainability, Design for Reliability, Value Engineering, Life Cycle Costing, Probabilistic Risk Assessment and others, to arrive at the optimum Cost-Benefit-Risk asset solution to meet any given production requirements"

Maintenance Terminology - Some Key Terms The Reliability Revolution By Sandy Dunn, Webmaster, Plant Maintenance Resource Center


A stop, or full or substantial interruption of plant production.  Generally turnaround is considered to be a period longer than 24 hours.

Types of Maintenance

Breakdown Maintenance

"It is used when the equipment failure does not significantly affect the operation or production or generate any significant loss other than repair cost."

Preventive Maintenance

"Maintenance (including inspection, cleaning, and repair) of equipment on a regular basis that is sufficient to prevent unplanned failure."

"It is a daily maintenance (cleaning, inspection, oiling and re-tightening), designed to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration."

Effective PM activities enable a company to achieve a ratio of 80 percent proactive maintenance to 20 percent (or less) reactive maintenance.

It is further divided into:

Periodic Maintenance

"Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems."

Predictive Maintenance (Condition Based Maintenance)

"Maintenance based on actual condition, obtained from non-invasive test, operating and condition monitoring."

"This is a method in which the service life of important part is predicted based on inspection or diagnosis, in order to use the parts to the limit of their service life." It manages trend values, by measuring and analyzing data about deterioration and employs a surveillance system, designed to monitor conditions through an on-line system.

"An equipment maintenance strategy based on measuring the condition of equipment in order to assess whether it will fail during some future period, and then taking appropriate action to avoid the consequences of that failure. The condition of equipment could be monitored using Condition Monitoring, Statistical Process Control techniques, by monitoring equipment performance, or through the use of the Human Senses. ... KeyTerms.htm

Corrective Maintenance

It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability