RCM

1. Firoozeh Nateghi2. Arash Sepehri3. Hossein Fotoohi Maleki4. Jamshid Soorani5. Ehsan Pourabedin6. Ali Reza Mani

Reliability Centered Maintenance (RCM)

RCM is a process to help people determine the best policies for managing the functions of physical assets—and for managing the consequences of their failures.

Society of Automotive Engineers (SAE) has developed a standard, to provide criteria that can be used to evaluate a maintenance-program-development process and determine whether it is RCM process or not.

Adapted from SAE website

Reliability Centered Maintenance by: John Moubray

1965: Studies show scheduled overhaul of complex equipment has little or no effect on in-service reliability

1970: RCM had its beginning in the commercial airline sector in 1970's. At that time, the commercial airline industry was experiencing high number of crashes in the take-offs which majority of them was related to equipment failures

After applying the RCM method, it proved to be highly successful; in commercial airlines it reduced crashes from 60 per million take-offs to only 2 per million and more important than that reduced the equipment related crashes from 40 per million to only 0.3 per million take-offs.

RCM History

Source: The value of RCM in business today

Source: www.plant-maintenance.com

RCM considers all asset management options:

• On-condition tasks or condition monitoring• Scheduled restoration tasks• Scheduled discard tasks• One-time changes

Hardware design Operating procedures Personnel training Other aspects of the asset outside the strict world of

maintenance

• Default actions

RCM

• “RCM is the optimum mix of reactive, time or interval based, condition based and proactive maintenance practices”

Adapted from WBDG site : www.wbdg.org

Fig. 1. Components of an RCM Program.


Failure Patterns

Source: www.plant-maintenance.com

Stan Nowlan and Howard HeapStudies

They recognized that maintenance was a

contributing factor to many of the failures

but in some other cases maintenance was

able to improve the situation. They looked

for patterns and found them. There were

actually six patterns of Conditional

Probability of Failure.


Failure Patterns

– Pattern A; High incidence of failure at the beginning followed by a constant or increasing conditional probability of failure then a wear-out (Bathtub curve)

– Pattern B; Classic wear-out, shows constant or increasing conditional probability of failure then a wear-out.

– Pattern C; Gradual aging wear out age is not identifiable

– Pattern D; Best new, low conditional probability of failure

– Pattern E; Totally random, constant conditional probability of failure at all ages

– Pattern F; High rate of failure probability at the beginning but decreasing and getting constant after coming into service

RCM Questions1. Functions: what are the functions and associated desired standards of

performance of the asset in its present operating context?

2. Functional failures: in what ways can it fail to fulfill its functions?

3. Failure modes: what causes each functional failure?

4. Failure effects: what happens when each failure occurs?

5. Failure consequences: in what ways does each failure matter?

6. Proactive tasks and task intervals: what should be done to predict or prevent each failure?

7. Default actions: what should be done if a suitable proactive task cannot be found?

Q1.FUNCTIONS Criteria

• The operating concept of the asset shall be defined. The same hardware does not always have the same failure management policy in all installations

• All the functions of the asset shall be identified.• All function statements shall contain a verb an

object and a performance• Performance standards shall be in the same

level as owner’s desired performance


Q2.Functional Failure Criteria

• All the failed states associated with each function shall be identified. If functions are well defined listing functional failures is relatively easy.


Q3.Failure Modes Criteria

• All failure modes reasonably likely to cause each functional failure shall be identified.

• The method used to decide what constitutes a “reasonably likely” failure mode shall be acceptable to the owner or user of the asset.

• Failure modes shall be identified at a level of causation that makes it possible to identify an appropriate failure management policy.

• Lists of failure modes shall include o failure modes that have happened beforeo failure modes that are currently being prevented by existing

maintenance programso failure modes that have not yet happened but that are thought to be

reasonably likely (credible) in the operating context. • Lists of failure modes should include any event or process that is

likely to cause a functional failure, including deterioration, human error whether caused by operators or maintainers, and design defects.

The event that causes functional failure is failure mode


Q4.Failure Effects Criteria• Failure effects shall describe what would happen if no specific task

is done to anticipate, prevent, or detect the failure. • Failure effects include all the information needed to support the

evaluation of the consequences of the failure, such as:a) What evidence (if any) that the failure has occurred (in the case of

hidden functions, what would happen if a multiple failure occurred)b) What it does (if anything) to kill or injure someone, or to have an

adverse effect on the environmentc) What it does (if anything) to have an adverse effect on production or

operationsd) What physical damage (if any) is caused by the failuree) What (if anything) must be done to restore the function of the system

after the failure.


Q5.Failure Consequences Criteria

• The assessment of failure consequences shall be carried out as if no specific task is currently being done to anticipate, prevent, or detect the failure.

• The consequences of every failure mode shall be formally categorized as follows:

o The consequence categorization process shall separate hidden failure modes from evident failure modes.

o The consequence categorization process shall clearly distinguish events (failure modes and multiple failures) that have safety and/or environmental consequences from those that only have economic consequences (operational and non-operational consequences).


Q6.Proactive Tasks Criteria

It is complicated and its criteria are presented in two groups;

• Failure Management Policies

• Scheduled tasks and intervalso Proactive taskso Default actions


Failure Management Policies• The selection of failure management policies shall be carried out as

if no specific task is currently being done to anticipate, prevent, or detect the failure.

• The failure management selection process shall take account of the fact that the conditional probability of some failure modes will increase with age (or exposure to stress), that the conditional probability of others will not change with age, and the conditional probability of yet others will decrease with age.

• All scheduled tasks shall be technically feasible and worth doing (applicable and effective), and the means by which this requirement will be satisfied are set out under scheduled tasks in the failure management section.

• If two or more proposed failure management policies are technically feasible and worth doing (applicable and effective), the policy that is most cost-effective shall be selected.


Scheduled Tasks and Intervals

• All scheduled tasks; performed at fixed, predetermined intervals, including continuous monitoring (zero interval).

• Specific kind of scheduled taskso On-conditiono Scheduled discardo Scheduled restorationo Failure finding


Identifying tasks• In the case of an evident failure mode that has safety or environmental

consequences, the task shall reduce the probability of the failure mode to a level that is tolerable to the owner or user of the asset.

• In the case of a hidden failure mode where the associated multiple failure has safety or environmental consequences, the task shall reduce the probability of the hidden failure mode to an extent which reduces the probability of the associated multiple failure to a level that is tolerable to the owner or user of the asset.

• In the case of an evident failure mode that does not have safety or environmental consequences, the direct and indirect costs of doing the task shall be less than the direct and indirect costs of the failure mode when measured over comparable periods of time.

• In the case of a hidden failure mode where the associated multiple failure does not have safety or environmental consequences, the direct and indirect costs of doing the task shall be less than the direct and indirect costs of the multiple failure plus the cost of repairing the hidden failure mode when measured over comparable periods of time.


On-condition tasks(condition-based, condition monitoring)

• There shall exist a clearly defined potential failure. • There shall exist an identifiable P-F interval (or failure

development period). • The task interval shall be less than the shortest likely P-F

interval. • It shall be physically possible to do the task at intervals

less than the P-F interval. • The shortest time between the discovery of a potential

failure and the occurrence of the functional failure (the P-F interval minus the task interval) shall be long enough for predetermined action to be taken to avoid, eliminate, or minimize the consequences of the failure mode.


Scheduled discard task

• There shall be a clearly defined (preferably a demonstrable) age at which there is an increase in the conditional probability of the failure mode under consideration.

• A sufficiently large proportion of the occurrences of this failure mode shall occur after this age to reduce the probability of premature failure to a level that is tolerable to the owner or user of the asset.

RCM selects scheduled discard only when there is clear evidence that the asset experiences wearout


Scheduled Restoration tasks

• There shall be a clearly defined (preferably a demonstrable) age at which there is an increase in the conditional probability of the failure mode under consideration.

• The task shall restore the resistance to failure (condition) of the component to a level that is acceptable to the owner or user of the asset.

• A sufficiently large proportion of the occurrences of this failure mode shall occur after this age to reduce the probability of premature failure to a level that is tolerable to the owner or user of the asset.

RCM selects scheduled discard only when there is clear evidence that the asset experiences wearout


Q7.Default Actions

• This question pertains to unscheduled failure management policies: the decision to let an asset run to failure, and the decision to change something about the asset’s operating context (such as its design or the way it is operated).

• Failure finding tasks• Run to failure• Changing the operating context


Failure Finding Tasks

• Failure-finding tasks are scheduled tasks like the proactive tasks. However, failure-finding tasks are not proactive. They do not predict or prevent failures. They detect failures that already have happened, in order to reduce the chances of a multiple failure—the failure of a protected function while a protective device is already in a failed state


Run to Failure

• In cases where the failure is hidden and there is no appropriate scheduled task, the associated multiple failure shall not have safety or environmental consequences.

• In cases where the failure is evident and there is no appropriate scheduled task, the associated failure mode shall not have safety or environmental consequences. In other words, the process must not allow its users to select “run to failure” if the failure mode, or (in the case of a hidden failure) the associated multiple failure, has safety or environmental consequences.


RCM analysis Selection of Maintenance Actions • Tool: Decision Tree analysis & Mistake Proofing• Options

– do nothing: run to failure– prevent: scheduled or non-scheduled tasks– predict: checking the condition of equipment and

detecting failure – redesign

• Equipment• Detection• Process• Procedures

Source: Reliability-Centered Maintenance and Real-Time DiagnosticsDennis Wilson, Jeff Johnson & John Lowell

RCM Implementation—Eight Steps

1. Define the scope and objectives of the project

2. Establish review groups

3. Train the review group

4. Estimate the amount of time to review the selected equipment

5. Plan meetings

6. Plan senior management audits

7. Implement the selected tasks

8. Document the tasks and procedures

RCM Principles• RCM is Function Oriented. • RCM is System Focused • RCM is Reliability-Centered• RCM Acknowledges Design Limitations• RCM is Driven by Safety, Security, and Economics• RCM Defines Failure as "Any Unsatisfactory Condition• RCM Uses a Logic Tree to Screen Maintenance Tasks. • RCM Tasks Must Be Applicable• RCM Tasks Must Be Effective• RCM Acknowledges Three Types of Maintenance Tasks :

o Time directed (PM)o Condition directed (CM)o Failure finding (Proactive Maintenance)

• RCM is a Living System



Types of RCMThere are different ways to conduct and implement

an RCM program;• Classical/Rigorous

Classical or rigorous RCM provides the most knowledge and data concerning system functions, failure modes, and maintenance actions addressing functional failures of any of the RCM approaches

• Intuitive/Streamlined/AbbreviatedThe intuitive approach identifies and implements the obvious, usually condition-based, tasks with minimal analysis. In addition, it culls or eliminates low value maintenance tasks based on historical data and Maintenance and Operations (M&O) personnel input.


Decision Making on Techniques

The decision of what technique to be used is based on;• Consequences of failure• Probability of failure• Historical data available• Risk tolerance• Resource availability


Advantages of RCM1. Increasing the input; for example by more customers' satisfaction

about the products or services.2. Reducing the maintenance costs, for instance by reducing the

maintenance amount.3. Reduction of production losses by improved operation performance4. Improving the quality of products and services.5. Reducing the warranty costs, for example because of better quality

of products.6. Improving the safety.7. Increasing the reliability of products.8. Education; improved overall level of skill and technical knowledge

9. Rationalization; unnecessary preventive work is eliminated10. Greater motivation of individuals

Difficulties in Implementation of RCM

• 1. Potential cost savings means reduction in labor use that could mean loss of jobs. This leads to increased resistance to implementing the RCM program. (HR Problem)

• 2. Getting some analysts to participate in the program, causes some problems due to the time commitment it requires. In fact, the analysis time competes with their job responsibilities.

• 3. Implementation of RCM program takes a lot of time, especially in large and complex industries (even some years).

• 4. RCM is not cheap; it imposes many accomplishing costs to system, for example training costs and costs of employing some new experts for replacement with those who entered in the program and have not enough time to fulfill their responsibilities as before.

• 5. Dealing with hidden failures causes challenges for many analysts (and then others) not familiar with the concept.


Date post:	20-Jan-2015
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