What is RCM?

 

Reliability Centred Maintenance (RCM)

What is RCM

Reliability cantered maintenance (RCM) is a concept of maintenance planning to ensure that systems continue to do what their user requires in their present operating context. Successful implementation of RCM will lead to increase in cost effectiveness, reliability, machine uptime, and a greater understanding of the level of risk that the organization is managing.

There are four principles that are critical for a reliability centred maintenance program:

1.      The primary objective is to preserve system function

2.      Identify failure modes that can affect the system function

3.      Prioritize the failure modes

4.      Select applicable and effective tasks to control the failure modes.

7 questions that need to be asked for RCM

It is defined by the technical standard SAE JA1011, Evaluation Criteria for RCM Processes, which sets out the minimum criteria that any process should meet before it can be called RCM.

The seven questions that need to be asked for each asset are:

1.      What are the functions and desired performance standards of each asset?

2.      How can each asset fail to fulfil its functions?

3.      What are the failure modes for each functional failure?

4.      What causes each of the failure modes?

5.      What are the consequences of each failure?

6.      What can and/or should be done to predict or prevent each failure?

7.      What should be done if a suitable proactive task cannot be determined?

Advantages	Disadvantages
Implementing RCM increases equipment availability, and reduces maintenance and resource costs.	RCM does not readily consider the total cost of owning and maintaining an asset. Additional costs of ownership, like those considered in evidence-based maintenance, are not taken into account, and are therefore not factored into the maintenance considerations.

The RCM process: 7 steps to implement reliability centered maintenance

There are several different methods for implementing reliability centered maintenance that are recommended, summarized in the following 7 steps.

Step 1:

Selection of equipment for RCM analysis

The first step is to select the piece of equipment for reliability centered maintenance analysis. The equipment selected should be critical in terms of its effect on operations, its previous costs of repair, and previous costs of preventive maintenance.

Step 2:

Define the boundaries and function of the systems that contain the selected equipment

The equipment belongs to a system that performs a crucial function. The system can be large or small, but the function of the system, and its inputs and outputs, should be known. For example, the function of a conveyor belt system is to transport goods. Its inputs are the goods and mechanical energy powering the belt, while its outputs are the goods at the other end. In this case, the electric motor supplying the mechanical energy would be considered as part of a different system.

Step 3:

Define the ways in which the system can fail (failure modes)

In step 3 the objective is to list all of the ways that the function of the system can fail. For example, the conveyor belt may fail by being unable to transport the goods from one end to the other, or perhaps it does not transport the goods quickly enough.

Step 4:

Identify the root causes of the failure modes

With the help of operators, experienced technicians, RCM experts and equipment experts, the root causes of each of the failure modes can be identified. Root causes for failure of the conveyor could include a lack of lubrication on the rollers, a failure of a bearing, or a loosened belt.

Step 5:

Assess the effects of failure

In this step, the effects of each failure mode are considered. Equipment failures may affect safety, operations, and other equipment. The criticality of each of these failure modes can also be considered.

There are various recommended techniques that are used to give this step a systematic approach. These include:

1.      Failure modes and effects analysis (FMEA)

2.      Failure, mode, effect and criticality analysis

3.      Hazard and operability studies (HAZOPS)

4.      Fault tree analysis (FTA)

5.      Risk-based inspection (RBI)

The most important failure modes will be determined at the conclusion of this systematic analysis. Ask yourself questions such as “Does this failure mode have safety implications?”, and “Does this failure mode result in a full or partial outage of operations?”. Your answer is the most important failure modes that should be prioritized for further analysis. Importantly, the failure modes that are retained include only those that have a real probability of occurring under realistic operating conditions.

Step 6:

Select a maintenance tactic for each failure mode

At this step, the most appropriate maintenance tactic for each failure mode is determined. The maintenance tactic that is selected must be technically and economically feasible.

Condition-based maintenance is selected when it is technically and economically feasible to detect the onset of the failure mode.

Time or usage-based preventive maintenance is selected when it is technically and economically feasible to reduce the risk of failure using this method.

For failure modes that do not have satisfactory condition-based maintenance or preventive maintenance options, then a redesign of the system to eliminate or modify the failure mode should be considered.

Failure modes that were not identified as being critical in Step 6 may, at this stage, be identified as good candidates for a run-to-failure maintenance schedule.

Step 7:

Implement and then regularly review the maintenance tactic selected

Importantly, the RCM methodology will only be useful if its maintenance recommendations are put into practice. When that has been done, it is important that the recommendations are constantly reviewed and renewed as additional information is found.

Conclusion

Reliability centred maintenance identifies the functions of the company that are most critical and then seeks to optimize their maintenance strategies to minimize system failures and ultimately increase equipment reliability and availability. The most critical assets are those that are likely to fail often or have large consequences of failure. With this maintenance strategy, possible failure modes and their consequences are identified; all while the function of the equipment is considered. Cost-effective maintenance techniques that minimize the possibility of failure can then be determined. The most effective techniques are then adopted to improve the reliability of the facility as a whole.

 

FAILURE ANALYSIS

Types of failure analysis:

1.      FMEA/FMECA =>Failure mode and effect analysis/Failure mod effect and criticality analysis.It is a step by step approach for identifying all possible failures in a design, a manufacturing or assembly process of a product or services.

2.      Fault tree analysis

3.      Cause and effect analysis (fish bone analysis)

4.      Sequence and event analysis

5.      The 5 whys

6.      Root cause analysis

 

MTBF: Mean time between failure.

The average time elapsed between a failure and the next time it occurs.

MTBF = Total Up Time/No of Breakdown

MTTR: Meantime to repair

Time takes to run a repair after the occurrence of the failure.

MTTR = Total Down time/No of Break down

Availability % = ( MTBF/(MTBF + MTTR)) x 100

Failure Rate (n) = 1/MTBF

Reliability = e^(-nt)t = total time

Types of condition based maintenance

1.      Vibration analysis

2.      Infrared (IR)– High temperature

3.      Ultrasonic – Deep surface defects

4.      Acrostic–Detects gas, liquid, vacuum leak

5.      Oil analysis – Number and size of particles in sample to determine asset wear.

6.      Electrical

7.      Operational performance–Measure pressure, temperature and flow.

CBM Tool

1.      Thermometer

2.      Machine condition advisor – It measures vibration of machine.

3.      Grease test kit

4.      Oil check monitor –To check water content, fuel contamination, metallic content, oxidation etc. In oil.

5.      Stroboscope – Used in rotating objects, gear wheel, fan blade

6.      Electronic stethoscope – To hear bearing and machine noise.

7.      Sound pressure meter

8.      Infrared thermometer

9.      Ultrasonic leak detector

10.  Laser/contact tachometer

11.  Belt alignment tool

 

Vibration analysis:

In this method 5 characters are checked to analysis the machine condition.

1.      Frequency ( 1 Hz = 60 cycle/min or 30 Hz = 1800 rpm)

2.      Displacement (mils or micron)

3.      Velocity (mm/sec)

4.      Acceleration (mm/sec²)

5.      Phase angle