The use of the terms Reliability (R) and Maintainability (M) are now in vogue. Does improvement in Reliability and Maintainability (R&M) relate to Maintenance Optimisation or Asset Optimisation? In this paper we would examine whether such a relationship exists. We would also explore whether the DOM (Design Out Maintenance) strategy can be effectively employed in improving Reliability and Maintainability (R&M) of an industrial facility or engineered systems in order to achieve the twin objectives of profitability and sustainability.
First let us state the definitions of Reliability and Maintainability. Then let us expand on what is actually meant by Maintenance or Asset Optimisation.
Reliability — “The probability that an item will perform a required function, under a stated condition for a stated period of time.”
Reliability is therefore the extension of quality into the time domain and may be paraphrased as the ‘probability of a non-failure in a given period of time.
Maintainability — “The probability of repair in a given time.
Expanding on that, Maintainability means the probability that a failed item will be restored to operational effectiveness within a given period of time when a repair action is performed in accordance to prescribed procedures.
Maintenance Optimisation or Asset Optimisation:
The idea of an optimised maintenance program suggests that an adequate mix of maintenance strategies and actions needs to be formulated and fine tuned in order to improve uptime and extend the total life cycle of the physical asset and assure safe working conditions while bearing in mind limiting maintenance budgets and environmental legislations. This does not seem to be straightforward and may require a holistic view. Therefore, a maintenance concept for each installation or factory it is necessary to plan, control and improve the various maintenance strategies, actions and policies as applied to that installation within the given constraints of time, manpower, skills, kowledge, budgets and legislations.
A maintenance concept or strategy may in the long term even become a guiding philosophy for a facility to performing maintenance/engineering. In some case, advanced maintenance strategies are almost considered policies on their own. What is certain is that maintenance strategies determine the business philosophy concerning maintenance and engineering and they are needed to manage the complexity of maintenance per se. In practice, it is clear that more and more companies are spending time and effort determining the right maintenance concept and strategies applicable in their context.
The usual mix of maintenance strategies that are used for Maintenance/Asset Optimisation are RTF(Run to Failure), TBM (Time Based Maintenance), UBM (User Based Maintenance; also known as Opportunity Maintenance), CBM (Condition Based Maintenance), E-Maintenance and DOM (Design Out Maintenance).
At present, RTF, TBM, UBM, CBM and E-Maintenance accept the inherent reliability of the physical asset, which they intend to maintain as a given fact. The governing concept is that once a machine is designed, manufactured and installed the upper limits of reliability and maintainability are fixed and can not be improved upon during the operational stage. This is true to a great extent. However, such implicit acceptance effectively limits the upper limits of productivity, performance and profitability of a manufacturing facility. Hence, maintenance, as usually practiced, will fail to sync with the constant market pressure of improving productivity, performance, profitability and sustainability. Failure to do so can often force a company out of business or settle for lower profits till new or additional equipment are purchased to meet desired business goals. Clearly, this is a costly proposition even for cash rich companies.
The alternative lies in innovating or making greater use of DOM (Design Out Maintenance) strategy on a given set of physical assets considering the operating context of a facility. DOM — instead of considering a system as given, looks at the possible changes (usually small innovations) or possible measures needed to avoid or minimise maintenance in the first place. Adopting a DOM policy implies that maintenance is proactively involved at different stages of an equipment life cycle to solve problems of failures or solve problems that prevents an organisation to achieve its business goals. This may be either done at the procurement stage or after the installation stage, when a machine is in operation. Therefore, it is prudent to apply the DOM strategy both at the procurement stage and at the operating stage to get the best benefits.
Ideally DOM strategy intends to completely avoid or minimise maintenance throughout the operating life of equipment. Though it may appear on the surface to be unrealistic it is completely possible to do so. One approach will be to consider a diverse set of maintenance requirements at the early stages of equipment design during the procurement process based on available knowledge of potential failure patterns and problems studied against business requirements. The other approach will be to consider the behaviour of the equipment during the operating stage and eliminate, avoid or minimise possibilities of failures through simple modifications/innovations on existing equipment.
As a consequence, equipment modifications along with process modifications and modification of maintenance processes are geared either at increasing reliability by raising the MTBF (Mean Time Between Failures) or improving maintainability by lowering MTTR (Mean Time To Repair). This may be done in various ways. In some situations, both MTBF and MTTR are to be addressed simultaneously. Per se DOM aims to improve the following:
1. Equipment Availability by extending the MFOL (Mean Free Operating Life),
2. Production Capacity by minimising unplanned downtime,
3. Safety (by eliminating the consequences of failures and reducing failure rates),
4. Extend the total life cycle of an equipment (by using an equipment for the maximum possible years)
5. Life Cycle Costs (LCC) by minimising maintenance costs
6. Sustainability through optimised use of resources to run the system at the best operating condition.
In all the above cases it is imperative to lower or effectively contain the failure rate, potential hazards of an equipment and minimise loss or excess use of resources.
Modifications (usually small innovations), which lie at the heart of DOM may include the following (not an exclusive list):
- change of dimensions and material flows
- change of material
- change of condition of surfaces, structures and interfaces
- change of ergonomics
- change of maintenance process, planning and procedures
- change of designs, controls and knowledge
- change of items and parts, lubricants and redundancy
- change through effective scaling
- change in use of resources
- change in set ups, speeds, and operational processes
- change of environment, reactions and interactions
- change of thermal and energy flows
However, adoption of DOM strategy does not exclude application of other available strategies in the whole process of improvement. Judicious application of all available strategies is often necessary to achieve the business goals of a manufacturing facility for which a completely new process has been developed, which critically focuses on improving Reliability and Maintainability of a facility. Finally, it depends on the how the DOM projects are formulated, implemented and managed across a manufacturing facility. Here agility and constancy of purpose are two critical management factors that would determine the quality of the results — profitability and sustainability, which effectively translates to lowering the Total Cost of Ownership of facility, which is the essence of Asset or Maintenance Optimisation.