Maintenance Types

Mo'tasem Abushanap [email protected]

Maintenance Types

RCM and its strategies

Definitions & Applications

Reliability Centered Maintenance (RCM):

Reliability centered maintenance (RCM): integrates preventive maintenance (PM) with predictive

testing and inspection (PT&I) and repair(known as reactive maintenance), with also proactive

maintenance to increase the probability for a machine to function in the designed way , so it can

reaches its designed life cycle with the minimum maintenance costs, and minimum downtime,

RCM integrates these strategies and principles to gather so they are optimally integrated, so all

strategies advantages can be achieved, so resulting by maximizing reliability of systems and

components while minimizing maintenance cost and downtime.

RCM Analysis:

The main questions to be asked while analyzing are:

1- What does system/component/device do?

2- What are component/system functions?

3- What functional failures can be occur?

4- What are the likely consequences (seriousness) of these failures?

5- What can be done to reduce the probability of these failures (solutions or improvements,

or replacements)?

RCM

Reactive Preventive PT&I Proactive

- small items

- non critical

- inconsequential

- unlikely to fail

- redundant

- subject to wear out

- consumable

- known to failure

pattern

- random failure

- not subjective to

wear out

- PM induced

failures

- root cause failure

analysis

- age exploration

- failure moods and

effect analysis

- commissioning


RCM objectives (Nowlan & Heap):

1- Insure realization of the inherent safety and reliability levels of the system/components.

2- Restore the system/components to these inherent levels when deterioration occurs.

3- To obtain the information and data necessary for design the improvement and

adjustments of these items where their inherent reliability start to be inadequate.

4- To achieve these goals at minimum total cost, including maintenance cost, support costs,

and economic consequences of operational failure.

Types of Reliability Centered Maintenance (RCM):

Rigorous RCM Approach (classical RCM).

Intuitive RCM Approach (Streamlined/ Abbreviated).

RCM Strategies

1- Reactive (repair) maintenance, run to fail maintenance (RTF).

2- Preventive maintenance (PM), time based maintenance.

3- Predictive testing and inspection (PT&I), condition based maintenance.

4- Proactive maintenance.

Reactive Maintenance (Run to Fail):

reactive maintenance (repair) : referred to break down, repair, fix-when-fail, or run-to-fail (RTF)

maintenance , trouble calls (TCs) are typical type of reactive maintenance , when applying this

technique, maintenance, components repair, or replacement happens only when failure takes

place in the component's functional tree, this technique assumes failure is equally likely to happen

in any system, component or device, and failure is age related, this leads to identify a specific

group of repair parts, as being more necessary or desirable that others.

Prioritizing Reactive maintenance in a system

Priority Criteria based on consequences of components/systems

number description

1 Emergency Safety of life or property threatened.

Immediate serious impact on mission

2 Urgent Continuous facility operation Threatened. Impending serious impact on mission.

3 Priority Degrades quality of mission support. Significant and adverse

effect on project.

4 Routine Redundancy available. Impact on mission insignificant

5 Discretionary Impact on mission negligible. Resources available.

6 Deferred Impact on mission negligible. Resources unavailable.

Preventive Maintenance (PM):

Preventive Maintenance (PM): is time based maintenance where maintenance occurs according to

a predetermined scheduled plan, it consists of regular scheduled activities such as adjustments,


replacements, inspections, calibration, lubrications, repair of systems and components, the

schedules done on a predetermined time intervals, ( operating hours , cycles and time), in an

attempt to reduce system failure.

Depending on the time intervals, preventive maintenance (PM) can result in a significant increase

in inspections and routine maintenance, preventive maintenance (PM) also reduces the frequency

and effectiveness of unplanned machine breaks and downtime, for the components and system

with defined age related wear patterns.

Preventive maintenance assumes that overhauls of machinery by disassembly and replacement of

worn parts, restores the machine to a likely new condition with zero harmful effect, this renewal

task based on the perception that new components and systems are less likely to fail than old ones

of the same design.

Time intervals or interval sets are usually determined by 'Mean Time Between Failure' (MTBF).

Predictive Maintenance (Predictive Testing and Inspection (PT &I)):

Predictive Maintenance (Predictive Testing and Inspection (PT &I)): it is a condition based

maintenance, by monitoring the condition of systems and components, uses nondestructive tests

techniques, visual inspection, performance records and data to assess the machinery condition,

Predictive Maintenance (Predictive Testing and Inspection (PT &I)) replaces periodic time

maintenance that are scheduled only when warranty by components condition, continuing

analysis of components condition monitoring data allows planning and scheduling of

maintenance activities in advance of serious and functional failures.

Methods and ways to determine the condition of components/systems & identify the precursors of

failure:

1- Trend analysis.

2- Pattern recognition.

3- Data comparison.

4- Test against limits & ranges.

5- Correlation of multiple technologies.

6- Statistical process analysis.

Proactive Maintenance (root cause maintenance):

Proactive Maintenance (root cause maintenance): Improves maintenance through better design

installation, maintenance activities, work men ship and scheduling.

Characteristics of proactive maintenance:

1- Using feedback and communications to ensure that changes in design or procedures are

rapidly made available to designers and managers.

2- Employing a life cycle view of maintenance and supporting functions.

3- Ensuring that nothing affecting maintenance and it is occurs in isolation.

4- Employing continuous process of improvement.


5- Optimizing and tailoring maintenance techniques and technologies to each application.

6- Integrating functions that support maintenance into program planning.

7- Using root cause failure and predictive analysis to maximize maintenance effectiveness.

8- Adopting an ultimate goal of fixing components permanently.

9- Periodic evaluation of technical content and performance intervals of maintenance tasks

(PM & PT&I).

Essential techniques to extend the component life or reach its designed life:

1- Specifications of new/rebuilt components.

2- Commissioning.

3- Precision rebuild and installation.

4- Failed components analysis.

5- Root cause failure analysis.

6- Reliability engineering.

7- Rebuilt certification/verification.

8- Age Exploration (AE) and the relationship with replacement of obsolete items (ROI).

9- Recurrence control.

Applications of maintenance strategies:

Strategy Applications

Reactive 1- Industry.

2- Factories. 3- Everywhere where unplanned failure

takes place.

Preventive 1- US Navy.

2- Cars and automobile. 3- Lubricated systems.

4- Calibrated systems.

5- Everywhere when failure pattern is known.

Predictive 1- US navy.

2- NASA technologies.

3- Electrical Surveys. 4- Mechanical Surveys.

5- HVAC systems.

6- Building Surveys.

Proactive 1- Controlling Lubricant fluids.

2- Controlling Hydraulic fluids.

3- Controlling Coolants.

4- Controlling Air. 5- Controlling Fuel.

6- HVAC systems.

Reliability Centered Maintenance 1- Aviation Industry. 2- Spacecraft Industry.

3- Nuclear Industry.

4- Department of Defense in US.

Documents

Maintenance Types