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  • Risk-based Maintenance Management and Reliability Centred Maintenance


    Introduction

    Strategic maintenance management is essential to maintain the integrity of physical assets and ensure business survival and success. An effective way to support strategic maintenance management is through a risk-based approach.

    Risk-based maintenance originated in the 1980s and 1990s and has received a recent boost in interest from companies putting in place robust performance standards to avoid catastrophic equipment failures.

    An additional driver is that many companies are adopting asset management standards ISO 55000:2014, 55001:2014 and 55002:2014. These standards require companies to develop a set of structured documents which cover the maintenance of assets including data, information, costs and people throughout their lifecycle. They must also use risk as a basis for decision making and continuously improve their processes.

    Risk-based maintenance management vs reliability centred maintenance (RCM)

    Another way that risk can be used to regulate maintenance is using reliability centred maintenance (RCM). RCM can be used to choose which method is best-suited to a particular asset, while risk-based maintenance management is used to select which assets a maintenance program should target.

    What is risk-based maintenance management?

    Maintaining assets, rather than simply waiting for them to break down, delivers significant cost savings, as the cost of repairing an equipment breakdown is three to five times the cost of the same repair done in a planned manner, prior to failure. But maintenance budgets are limited, and engineers and managers need tools to help them allocate resources for the best results.

    Risk-based maintenance management prioritises the maintenance of assets that carry the most risk if they were to fail. This approach allows engineers and maintenance managers to determine the most economical use of limited maintenance resources to minimise the total risk of failure across a facility.

    The main phases are:

    • criticality assessment
    • development of risk-based maintenance program and strategies
    • risk-based maintenance planning
    • risk-based allocation of spares and repairs

    The risk-based maintenance system is set up during the project phase of establishing a facility, then continued into the operation phase.
    A diagram of the risk-based management process is shown below.
    506268542_riskbasedmaintenanceflow.jpg.3a09a62852947f99384513cc892449b1.jpg
    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    Criticality assessment

    The goal of maintenance is to deliver a proper balance of maintenance activities to identify and prevent impending failures. By understanding which assets are the most important through a criticality assessment, engineers and maintenance managers can determine how to most effectively schedule maintenance activities of the right equipment at the right time to reduce risk over the whole facility.

    Criticality of equipment is based on the consequence of failure (CoF). Higher consequences lead to higher criticalities. Consequences can include impacts on safety, environment, reputation and production. One approach to evaluating the criticality of failure consequences is summarised below.

    criticality.jpg.c23185533912bff877d4c4cf0e0a23e6.jpg

    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    The criticality evaluation score can then be used to allocated a criticality ranking to equipment as shown below.

    836826022_criticalityranking.jpg.8220852b3687a499c7f06b7f5a2eb3eb.jpg
    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    Criticality assessment should not be confused with assessing the risk of equipment failure, which is the product of the probability of equipment failure and the consequence of that failure.

    Risk-based maintenance program and planning

    After completing a criticality assessment, facilities can set up a risk-based maintenance program based on the criticality ranking of assets. An example is shown below.

    program.jpg.fd3d7b30b463a09786f89ac52fc3f93e.jpg
    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    Principles for the maintenance program are:

    • assets with a greater risk and consequence of failure are maintained and monitored more frequently to achieve tolerable risk criteria
    • assets with a lower risk have a less stringent maintenance program

    This means that the total risk of failure is minimised over the facility. It is important to keep the maintenance program flexible, and develop it through a dynamic process of collecting information on operating conditions and revisiting the frequency of inspection and testing.

    The next stage is maintenance planning for both preventative and corrective maintenance. This includes allocating maintenance resources , sourcing parts and properly training staff. Emergency management circumvents the planning process, but all other maintenance should be planned.
    In order to prioritise work orders for risk-based maintenance planning, a work order priority matrix (as shown below) can be used.

    1816773772_planningmatrix.jpg.7821f5ae023b8bf0bb07b0855a5937c0.jpg
    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    Other methods, such as a ranking index for maintenance expenditures (RIME) can also be used. However RIME is complicated, and based on criticality rather than risk.

    If implemented correctly, risk-based maintenance planning should lead to a shift from corrective or reactive maintenance to condition-based maintenance, which is economical and provides evidence to back up maintenance budgets.

    Risk-based spares and repairs

    Finally, risk-based categorisation of spares and repairs can be put in place. Critical spares should be kept on site. An example of a risk-based spares matrix is shown below.

    spares.jpg.73e7ce3e20564335e4afbf1a2b4132d3.jpg
    Diagram courtesy of David Finch, Maintenance Integrity Solutions

    For effective risk-based spares stocking, engineers and maintenance managers should understand that a critical machine part is not necessarily a critical spare part. The time needed to obtain parts is also a consideration, as parts that can be obtained quickly can be ordered as required. Another factor to take into account is connection between the failure mode and the maintenance response, as some parts fail unexpectedly and catastrophically, while other failures can be predicted through condition monitoring or other maintenance activities.

    Benefits and limitations of risk-based maintenance

    The benefits of risk-based maintenance are summarised below:
    provides a systematic approach to determine the most appropriate asset maintenance plans

    • reduces the risk of asset failures to an acceptably low level
    • supports decision-making about how best to allocate limited maintenance budgets
    • provides opportunities to identify and eliminate low-value maintenance tasks

    A limitation is that a highly sophisticated team is needed to quantify the risks of different maintenance tasks.

    Sources:

    The content on this page was primarily drawn from the following sources:

    Edited by Nadine Cranenburgh


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