Preventive Maintenance Management Techniques
Preventive Maintenance Management Techniques
Manufacturing system consisting of facilities and equipments are important resource for an organization. These are constantly being used for adding value to the products produced by the organization. Hence, the facilities and equipments are to be kept healthy and in good operating condition for avoiding excessive downtime and also interruption in production. The design life of the majority of the facilities and equipments needs periodic maintenance.
Manufacturing system has been rapidly developing during last several decades. Within this advancement, maintenance has become an important supporting factor. Maintenance aims to develop reliable production processes so that they can perform as expected. Out of several maintenance strategies, preventive maintenance is one of the strategy which prevents incipient failures.
Nowadays, the efficiencies and effectiveness of the whole manufacturing operation are dependent on the sustainable performance of the facilities and equipments, which can lead to valuable improvements in terms of quality, cost, and time. In order to produce better product quality at a minimal cost, the availability and reliability of equipments (the production line) plays a central role in sustaining a competitive edge by the organization over its competing organizations.
Manufacturing system in engineering terms is the assemblage of equipments which consists of mechanical and / or electrical devices which transmits energy to assist in the performance of human tasks. It normally refers to the production lines (facilities) by which equipment, tools, as well as materials, people, and information, are utilized to produce value-added physical products. Hence, systems are considered to be an inevitable part of production, which need constant attention and maintenance to achieve the desired operating conditions.
Unfortunately, a system is always subject to deterioration in the course of continuous operations. The function of a system changes over time and the importance of maintenance to the system increases because of technical developments, the changing statutory regulations, and variances in operational environments. Moreover, the complexity of a system is a crucial component of the critical requirements of safety and costs throughout its life cycle. Hence, maintaining a system is extremely important as it needs a proper and effective maintenance policy in the organization to ensure that there is a capability exists in the system to perform its required functions. The basic objective of the maintenance policy is to reduce unplanned system break-downs and to increase the available operational time.
Manufacturing system is one of the spearheads in the production chain where multi-dimensional management practices take place. It aims to improve better efficiency, effective, and economics to help the organization survive in a highly competitive environment. Maintenance contributes to the organization in extending effective operational system life, increasing reliability, and system availability.
Maintenance is combination of administrative and technique to maintain or restore the optimal conditions of the facilities and equipments so that they can perform the needed function. Maintenance which aims to support the continuity of production process, has impacts on the functioning of the equipments. Maintenance positively improves the equipment reliability and ensures the sustainability of the production process. Maintenance gives a positive impact in improving the reliability of the equipment to ensure the sustainability of the production process. On the other hand, maintenance activities result in additional costs. These costs relate to maintenance policy (breakdown, or preventive maintenance), maintenance personnel, and spare parts inventory etc. Further, time is needed for maintenance which consume a considerable portion of the overall production time.
In general, maintenance is defined as the combination of all technical and administrative actions, including supervision, which ensure that a manufacturing system is in its required functioning state. Maintaining a manufacturing system is normally related to maintenance actions such as repairing, replacing, overhauling, inspecting, servicing, adjusting, testing, measuring, and detecting faults in order to avoid any failure which leads to interruptions in production operations. Performance measurement for maintenance of the manufacturing systems can be based on several factors. Effective maintenance can reduce the consequences of failure and extend the life of a manufacturing system. Implementation of maintenance refers to maintenance policies, which can be defined as the plans of action used to provide direction and guidelines to carry out further maintenance actions needed by a manufacturing system.
Past and present maintenance practices in both the private and public sector plants imply that maintenance is the actions associated with equipment repair after it has broken. The dictionary defines maintenance as ‘the work of keeping something in proper condition; upkeep’. This implies that maintenance is the actions taken to prevent the equipment from failing or the repairing of the normal equipment degradation experienced with the operation to keep it in proper working order.
Unfortunately, several organizations do not expend the necessary resources to maintain equipment in proper working order. Rather, they wait for equipment failure to occur and then take whatever actions are necessary to repair or replace the equipment. However, nothing lasts forever and all equipment has associated with it some predefined life expectancy or operational life.
Failures in equipment take place because of fatigue, corrosion, wear, overload, contamination, and misalignment. The mean time between failure (MTBF) is the failure frequency of the equipment. It measures the average time which the equipment is operating between breakdowns or stoppages. It is measured in hours, and helps the organization to understand the availability of the equipment and whether there exists a problem with the reliability of the equipment. The MTBF is a measure of the reliability of an equipment. The higher is the value of MTBF, the more reliable is the equipment.
MTBF calculates the average period between two breakdowns. In other words, it determines the reliability of the equipment. It determines how long an equipment works until it gets broken down. It helps in making data-driven decisions on maintenance scheduling, safety, inventory management, and equipment design without relying on subjective observations. The MTBF formula divides an equipment’s total number of operational hours in a period by the number of failures which have occurred on the equipment during that period. MTBF is frequently measured in hours. The MTBF calculation takes into account all types of failure as defined above, but it does not include scheduled maintenance, like inspections, re-calibrations, or preventive parts replacements. MTBF = number of operation hours/number of failures. The probability (P) that the equipment is going to work for some time ‘t’ without failure is given by equation P(t) = (e)-t/MTBF. In preventive maintenance management, equipment inspections, lubrication, repairs or rebuilds are scheduled based on the MTBF statistic.
The need for maintenance is predicated on actual or impending failure. Ideally, maintenance is performed to keep the equipment running efficiently for at least during the design life of the equipment. As such, the practical operation of the equipment is time-based function. If a person is to graph the failure rate of an equipment against time, it is likely that the graph has a shape of a bath tub (Fig 1). The bath tub curve indicates that a new equipment has a high probability of failure during the first few hours or weeks of operation, normally caused by manufacturing or installation problems. Following this initial period, the probability of failure is relatively low for an extended period of time. Following this normal life period of the equipment, the probability of failure increases sharply with elapsed time or hours of operation.
Fig 1 Equipment failure rate overtime
In the figure, the Y-axis represents the failure rate and the X-axis the time. From its shape, the bath tub curve can be divided into three distinct areas namely infant mortality, useful life period, and wear-out period. The initial infant mortality period of bath tub curve is characterized by high failure rate followed by a period of decreasing failure. Several of the failures associated with this region are linked to poor design, poor installation, or misapplication. The infant mortality period is followed by a nearly constant failure rate period known as useful life. There are several reasons for failure of the equipments in this region. Frequently it is acknowledged that poor operation and maintenance play an important role. Good maintenance practices can extend the useful life period. The wear-out period is characterized by a rapid increasing failure rate with time. In majority of the cases, this period encompasses the normal distribution of design life failures. The design life of the equipment needs periodic maintenance.
Over the last several decades, different practices to how maintenance can be performed to ensure equipment reaches or exceeds its design life have been developed. In addition to waiting for a piece of equipment to fail (breakdown or reactive maintenance), other popular practices are preventive maintenance, and predictive maintenance. Another maintenance practice which is also followed in some production plants is the reliability centered maintenance. Out of the three popular practices, preventive maintenance is a very reliable practice and several organizations make use of this practice to keep their facilities and equipments healthy. Breakdown maintenance is basically the ‘run it till it breaks’ maintenance mode. No actions or efforts are made to maintain the equipment as the designer originally intended to ensure that the design life is reached. Preventive maintenance is important for reduction of equipment downtime, and for reduction of environmental and workplace hazards. Fig 2 shows the three popular maintenance practices.
Fig 2 Types of maintenance
Preventive maintenance was introduced in the 1950s, after the recognition of the need to prevent failure. As an alternative to breakdown maintenance, preventive maintenance was adopted for emerging technologies since such systems were normally more complex than those based on the use of hand tools. The basic principle of preventive maintenance is that it involves pre-determined maintenance tasks which are derived from equipment functionalities and component lifetimes. Accordingly, tasks are planned to change components before they fail and are scheduled during the equipment stoppages or shutdowns.
Preventive maintenance is a time-based maintenance (periodic) which reduces the equipment downtime. The practice is used for reducing the age-based failures of the equipment. The practice is less expensive and need lesser manpower than breakdown maintenance but it has slightly higher initial deployment cost, and computational cost. The preventive maintenance needs a schedule which is based on the standard useful life of the equipment or the history of the failures. Action needed for maintenance is inspection, repair, or replacement at pre-determined intervals, forecasted by design and updated through experience. There is no prediction involved for maintenance such as needed for the predictive maintenance.
As the name suggests, preventive maintenance is maintenance which is regularly performed on a piece of equipment to prevent the equipment failure and unexpected downtime. It is performed while the equipment is still working (rather than after it has broken down). Preventive maintenance is planned on a time-meter, or usage-based trigger. It is carried out at pre-determined intervals or corresponding to prescribed criteria and intended to reduce the probability of failure or the performance degradation of the equipment.
The preventive maintenance programme is normally based on the several factors such as (i) impact of the worst-case scenario, (ii) lost production, (iii) likelihood of failure, (iv) cost involvement, (v) statutory compliance, and (vi) workplace safety. It is performed when the benefits of the maintenance outweigh the risks and costs. The optimum frequency of the preventive maintenance plan is developed by plotting the maintenance cost against maintenance frequency and finding a balance as shown in Fig 3.
Fig 3 Graph between maintenance cost and maintenance frequency
The purpose of preventive maintenance is (i) to improve system reliability, (ii) to decrease the cost of replacement, (iii) to decrease system downtime, and (iv) to improve spares inventory management. The primary objective of the preventive maintenance is to prevent the failure of equipment before it actually occurs. It is designed to preserve and improve equipment reliability by replacing worn parts of the equipment before they actually fail. It is a type of maintenance which includes cleaning, inspection, oiling, and re-tightening operations.
Normally, preventive maintenance is planned and performed after a specified period of time, during which the equipment has been used. It is done in order to reduce the probability of its failure. The majority of the equipments are maintained while a considerable quantity of their useful life remains in the case of this maintenance practice.
Preventive maintenance is a means to increase the reliability of the equipment. It is an easy-to-follow and economically feasible approach for keeping equipment and facilities healthy. It involves a basic trade-off between the two aims, which are to minimize total maintenance costs and to maximize the overall reliability of the equipment and facilities. It can be defined as, ‘actions performed on a time or machine-run-based schedule that detect, preclude, or mitigate degradation of a component or system with the aim of sustaining or extending its useful life through controlling degradation to an acceptable level’.
Preventive maintenance consists of a schedule of planned maintenance actions aimed at the prevention of breakdown failures. The primary objective of the preventive maintenance is to prevent failure of the equipment. It is designed to preserve and improve equipment reliability by replacing worn components before they fail. The activities under preventive maintenance include inspections, equipment checks, partial or complete overhauls at specified periods, oil changes, lubrication, and so on.
Preventive maintenance is an equipment maintenance strategy based on replacement, or restoration of an equipment at a fixed interval regardless of its condition. Scheduled restoration tasks and replacement tasks are examples of preventive maintenance tasks. Preventive maintenance is basically time-based maintenance since maintenance is done at a regular interval while the equipment is still functioning with the objective of preventing failure or reducing the likelihood of failure.
Preventive maintenance can be defined as ‘actions performed on a time- or machine-run-based schedule that detect, preclude, or mitigate degradation of a component or system with the aim of sustaining or extending its useful life through controlling degradation to an acceptable level’. By simply expending the necessary resources to conduct maintenance activities intended by the equipment designer, equipment life is extended and its reliability is increased. In addition to an increase in reliability, expenses are reduced over that of a programme which just uses break-down maintenance.
Preventive maintenance is an effective approach to improve the reliability and quality of a facility and its equipments. It is done for improving equipment reliability and extending the equipment life in order to prevent failure from occurring. Preventive maintenance practice is able to indicate when a maintenance work needs to be performed. It also provides a critical service function which minimizes interruptions in the facility operation, hence avoiding negative impacts to the organizational performance. The negative impacts can be on the aspects of product output and / or product quality, safety, environmental integrity, system quality, customer satisfaction, and the additional maintenance cost because of breakdowns.
A wisely implemented preventative maintenance programme, designed to correct each problem as or before it occurs is more cost effective than waiting until the problem reaches a magnitude where major overhaul of the equipments and large expenditures are needed to correct it.
The characteristics of preventive maintenance are identified as (i) maintenance personnel, (ii) spare parts and materials, (iii) pre-determined maintenance interval, (iv) failure and maintenance downtime, (v) maintenance equipment and technique, (vi) acquisition of maintenance data, and (vii) monitoring and inspection The characteristics are likely to influence the overall maintenance performance and hence, they are of concern of the personnel connected with the maintenance management. An effective maintenance management practice always put a lot of effort towards these characteristics.
Preventive maintenance is realized from two perspectives, which are known as the managerial and the operational. The managerial perspective refers to the support for decision-making which facilitates the analysis of data. Inputs for the managerial perspective include the determination of the preventive maintenance objectives, planning to perform maintenance actions, and methods involved in solving any problem which occurs with regard to the preventive maintenance as well as the performance of the facilities and equipments. The managerial perspective is also known as an outer process, since it bases decisions on history and analysis prior to the execution of preventive maintenance.
The operational perspective refers to the execution of maintenance actions in order to sustain the capability of a facility or an equipment to perform its intended functions. This perspective is an inner process which consists of technical aspects by which preventive maintenance is carried out based on inputs to the outer process. Both perspectives that pre-figure preventive maintenance are crucial for ensuring its effectiveness and efficiency. However, the managerial perspective plays the more important role in planning and determining suitable and feasible solutions before carrying out the preventive maintenance so that it meets its objectives. This is because without proper planning, the execution of preventive maintenance actions can affect the facility or other connected facilities which can then need further planning actions. Hence, majority of the attention is to be given to planning as the key to connecting the managerial and operational perspectives. With the aid of planning, preventive maintenance can be directed in a structured and systematic way to monitor and increase the lifetime of a facility or an equipment.
Preventive maintenance planning – In the context of preventive maintenance, planning encompasses activities which are undertaken for determining the needed maintenance resources such as material requirements, maintenance personnel requirements, time assignments, and technical references related to the equipment and which are determined and prepared prior to a maintenance work is taken up. In other words, without proper planning, inconsistent and unreliable procedures result, which can lead to interruptions during maintenance and hence can cause delays in maintenance work ultimately affecting the production. Hence, proper planning is an important aspect of the preventive maintenance and basically consists of the preparation for performing necessary maintenance tasks on a priority basis by referring to the needed resources, information, and schedule.
Since preventive maintenance is one of a number of organizational maintenance policies, it is pertinent to that maintenance planning which needs a long-term strategy for executing maintenance actions within a pre-determined interval. This ensures that a facility continues to fulfil its intended function. The scope of preventive maintenance planning covers all the aspects of the preventive maintenance which are to be integrated with planning in order to aid decision-making, in the cases of actions to be taken and the performance of the facility to be monitored and improved.
Preventive maintenance planning is also a feature of the managerial perspective which needs objectives, planning, and methods to be considered prior to the execution of the preventive maintenance of a facility. From the managerial perspective, the process of developing preventive maintenance planning necessitates the incorporation of both preventive maintenance policy and planning to ensure that the preventive maintenance actions are performed in a proven and standardized way. The significance of having proper objectives, planning, and methods is to provide a better understanding and proper guidelines to facilitate the process of developing and improving the preventive maintenance.
In general, the preventive maintenance planning concept is briefly described as the general idea which covers the elements of preventive maintenance in a simple and systematic way. The preventive maintenance concept consists of three aspects namely (i) the objective(s) or the purpose of performing preventive maintenance, (ii) descriptions of the facility’s state in terms of its importance and its functions, and (iii) methods which are divided into several classifications which help in determining the best solutions for the issues highlighted. These aspects are important as they provide a guide on how the preventive maintenance takes place.
The reason for establishing significant objectives prior to the execution of preventive maintenance is to narrow down and focus the maintenance work to be carried out. Significantly, the planning of preventive maintenance is described as an aid to decision-making to determine any action which is to be taken based on the outcome or objective to be achieved from the planning conducted in relation to the issues experienced in the maintenance environment.
Preventive maintenance consists of technical operations, the execution of which is frequently associated with a wide range of issues. These issues are regarded as technical problems taking place on the production floor which affect production processes and the maintenance of product quality. Several issues have been highlighted such as facility downtime, facility deterioration, imperfect preventive maintenance actions, improper time estimation for preventive maintenance, insufficient numbers of maintenance personnel, and non-availability of the facility for maintenance.
The major issues with regard to the maintenance environment is that of facility breakdown, which can lead to other problems such as facility or equipment deterioration, unplanned failures, and interruptions in production processes. These can be caused by improper planning before undertaking preventive maintenance actions and the improper conduct of preventive maintenance of a facility.
The issue of minimizing facility downtime, particularly its reliability and availability, setup times, product quality, spare parts and the complexity of preventive maintenance actions need careful study. Here, preventive maintenance planning plays an important role by establishing objectives or purposes in order to solve issues regarding facility breakdown. The time intervals for preventive maintenance actions such as replacement are important since it predetermines when to replace an equipment or component before they fail. Further, proper job scheduling which gives the job-to-job sequencing of preventive maintenance actions within the range of a time interval is necessary. Also, planning of preventive maintenance tasks and actions to take n for performing them is important.
Other than defining objectives, the preventive maintenance concept encompasses the description of the facility’s state, its function and importance. A facility is envisaged as an assembly of inter-connected equipments arranged to carry out a process. From an operational perspective, the facility is defined in terms of its state, which refers to its condition with respect to its attributes. The purpose of considering the state of the facility is to represent it as operating normally, as operating in breakdown mode or as having failed completely. Hence, the decision-making for preventive maintenance is based on the state of the facility, which seeks to base an analysis on the condition of the facility with respect to its function.The state of the facility is categorized in two ways, i.e., as single-unit facility and multi-unit facility. A single-unit facility consists of either one equipment or multiple equipments. By contrast, multiple or multi-unit facilities consist of several facility units with several equipments. Also, the elements of each facility are arranged mechanically into two configurations, namely the serial and the parallel. In a serial configuration, the entire facility fails if any one of the facility equipment fails. By contrast, for a parallel configuration, the entire facility works as long as not all the units or equipments fail. Hence, if any problem occurs in any one facility, the other facilities or equipments can also be affected.
Without a proper preventive maintenance system, the maintenance personnel can replace the entirety of a facility’s equipment on its failure, which is very costly. By representing a facility in terms of its state, preventive maintenance can be conducted with the aid of methods applied for solving the issues which have caused the breakdown. As a facility becomes more complicated, more sophisticated preventive maintenance planning is needed to solve the maintenance issues related to the facility’s performance. Hence, suitable methods which can deal with maintenance issues dynamically are to be considered as part of the development process for optimal preventive maintenance. Hence, the state of facilities is to be a focus for the preventive maintenance planning and proper attention is to be given to the condition of facility.
Methods – Another important element of the preventive maintenance is the methods applied to find the best solution for maintenance. The method is the description of any particular procedure followed to determine an optimal preventive maintenance under certain maintenance requirements or constraints. The purpose is to assist with related analysis through an established and systematic procedure, which can facilitate the achievement of certain accurate and efficient results. Hence, the decision-making in preventive maintenance is based on the methods applied, which can be affected by the outcomes. Hence, the most suitable and applicable methods for solving maintenance problems are to be used.
Planning based preventive maintenance – Planning based preventive maintenance is all about the essential analysis of comprehensive planning for preventive maintenance. It involves the fundamental maintenance criteria of the facilities and equipments as the basis for an analysis which derives the best preventive maintenance plan. Planning-based preventive maintenance is categorized in three ways namely cost-based planning, time-based planning, and failure-based planning.
Cost-based planning analyzes the capital cost and benefits to the organization, as well as the revenue it helps to generate. It is important to have cost-based planning as a fundamental assessment as it compares the costs of preventive maintenance solutions with the economic benefits which are to be gained if the solution is put into effect. The cost-based planning takes into account the cost involved when evaluating maintenance factors, such as the costs for repair, replacement, spare parts, tools and manpower. Maintenance costs depends on the cost of downtime, reliability characteristics and the redundancy of equipments. The methods are conducted based on the maintenance factors which affect the effectiveness of preventive maintenance.
Cost-based planning provides an optimal preventive maintenance interval based on the minimum total expected costs which eases the decision to perform preventive maintenance. Based on the cost-based planning, an optimal preventive maintenance interval which minimizes the cost per unit of time, or maximizes the equipment availability can be selected. Cost-based planning integrates quality, production, and maintenance parameters for an imperfect process in a multi-period, multi-product, capacitated, lot-sizing context. It is seen that an increase in the preventive maintenance levels lead to reductions in quality control costs.
Cost-based planning addresses the inventory of spare parts by grouping identical components which proves to be economical for preventive maintenance. It considers two alternatives namely with and without considering preventive maintenance and also considers two maintenance criteria namely the reliability and resource utilization to determine the optimum time interval for preventive maintenance by minimizing the failure repair cost of the facility as well as the preventive maintenance costs. Also, there exists possibility of grouping the facilities as per the optimum preventive maintenance interval to improve the reliability and utilization of the facility. Hence, the preventive maintenance which provides a considerable improvement in terms of system reliability and total cost reductions can be implemented.
Overall, the cost-based planning is used aggressively to evaluate the total anticipated cost and effectively provides the costs and benefits of the proposed method with regards to preventive maintenance. However, there are a number of arguments against cost-based planning as a decision-making tool. The ambiguity and uncertainty involved in quantifying and assigning a monetary value to intangible items can lead to inaccurate analysis. Hence, it can increase risks and cause inefficient decision-making.
Time-based planning involves the measurement of the subject analysis in terms of the allocation and information of a certain period or duration of an operation. The time basis is crucial in planning, as it serves up an analysis which indicates the quantity of time spent on preventive maintenance jobs. The analysis encompasses a wide perspective, which needs a lot of information and data concerning maintenance factors such as the time spent for repair and replacement, the time lost because of failure, the time allocation for gathering spare parts, shift times, and time for a facility’s operation.
\There are several methods conducted in regard of maintenance factors which affect the effectiveness of preventive maintenance planning. Methods grouped under the mathematical formulation category have received tremendous attention. One of the methods deployed is dynamic programming, which is known as an optimization method which transforms complex problems into sequences of simpler problems.
One of the methods developed consists of a framework for an integration of optimization, which consisted of priority setting, planning and combining preventive maintenance tasks. In the priority setting, the order of preventive maintenance tasks’ execution is determined. The analysis involves a dynamic programming which depended on the rolling horizon presented in the planning and combining of preventive maintenance tasks. Multiple objective criteria and the uncertainty of the preventive maintenance interval leads to optimal solutions. Hence, a properly scheduled job for preventive maintenance is the outcome of the analysis based on the optimal integration of the combination of preventive maintenance tasks and planning.
A rolling-horizon approach is for preparing a properly scheduled job, and hence it minimizes the costs. The rolling-horizon approach for grouping preventive maintenance actions is based on component usage. The approach is founded upon long-term planning, which is to be updated by incorporating short-term information which can change over time. However, because of the complexity of practical situations, it is difficult to achieve real optimal solutions.
Dynamic programming is used to formulate and get an implementable solution with regards to preventive maintenance actions and emergency maintenance. With dynamic programming, maintenance personnel aim to develop a schedule for job assignment by minimizing delays and maximizing the utilization of resources such as manpower, spare parts, and tools through the exploitation of integer and stochastic programming. The solution provides a decision-making tool for assigning manpower, which is reserved for anticipated jobs based on the schedule developed.
Dynamic programming is also used to determine the optimal stochastic interval of a critical reliability level for a single-unit system with multiple components, subject to degradation. The parameter adopted to undergo the analysis is the time interval for the preventive maintenance and its hazard rate. By using dynamic programming for the analysis, criteria such as the hazard rate, reliability, availability, and cost are compared with the operational time. The outcome of the analysis supports the decision-making on the preventive maintenance actions based on the value of the acceptable critical reliability level with an optimal time interval in the preventive maintenance cycle.
Dynamic programming with the rolling horizon is used to determine the effectiveness of grouping in the preventive maintenance for a multi-equipment facility. In it, the preventive maintenance durations and the scheduling of maintenance occurrences are taken into account. This methodology for dynamic programming is with positive economic dependence, which suggests that the grouping of preventive maintenance is cheaper rather than performing preventive maintenance on components in isolation.
A better planning for preventive maintenance can be implemented in the actual operation by improving the stock control system and ensuring efficient communication and teamwork throughout the facility. Also, an effective joint production, setup and maintenance control policy can be made for inflexible and unreliable single equipments which produces two types namely the hedging corridor policy (HCP) and the block replacement policy (BRP). Aiming to maximize machine availability and to reduce the risk of shortages, it integrates the concept of opportunistic maintenance by taking advantage of the machine stoppages for setup operation to carry out preventive actions.
Overall, time-based planning has been used widely to evaluate the total anticipated time for preventive maintenance and its impacts in decision-making. It has been quickly and easily applied from the planning perspective, but the value of time assigned for maintenance can be varied and inconsistent.
Failure-based planning is another basic analysis for deriving a good preventive maintenance planning. It involves analysis which takes into account information about facility or equipment deterioration. It involves a detailed definition of failures which occur with facilities and equipments before any analysis is carried out. There are several failure-based planning methods which affect the overall effectiveness of the preventive maintenance.
In failure-based planning, in order to anticipate the characteristics of a failure mechanism, critical analyses involving the objectives of analysis and evaluations of failure issues are carried out and extensively quantified. This ensures that preventive maintenance is conducted properly, hence reducing failure. Methods of critical analysis normally used are tree diagrams, failure mode and effect analysis (FMEA), and failure mode effect and critical analysis (FMECA).
In a case study on planning for preventive maintenance with the aid of tree diagrams, the outlined problems faced by the organization have been outlined, which included the insufficiency in numbers of maintenance personnel available to perform the preventive maintenance and the facilities breakdowns which has led to inefficient preventive maintenance. Based on the data of prior failures and equipment breakdowns, a root cause analysis of the issues involved in the ineffective preventive maintenance has been done as an affinity diagram. Then, a preventive maintenance planning model has been developed and the analysis has been presented in the form of a tree diagram which enabled possible solutions to be generated. The generated has been validated at the organization and provided the maintenance personnel with a solution to perform preventive maintenance by focusing on the critical equipments instead of the non-critical equipments and this improved the preventive maintenance processes in the plant.
In one processing plant, a study has been done on a single-unit facility with a single equipment. In this study, a preventive maintenance model has been developed, which consisted of three general steps consisting of problem identification, evaluation of the present condition of the facility, and maintenance decision. FMECA has been used in the model developed to identify possible external factors which contributed to the equipment failure. Once the external factors and failure modes have been identified, the critical equipment has been evaluated using a PHM (prognostics and health management) before determining the preventive maintenance interval in the present state of the facility by means of an age replacement model. Hence, the replacement of equipments based on the preventive maintenance interval for the present state of the facility implied a reasonable decision to improve reliability of the facility.
In a study in a plant, a failure analysis planning methodology has been proposed for preventive maintenance, where the evaluation has been conducted using a reliability model, which permitted the use of flexible intervals between maintenance interventions. The study has focused on the failures and accidents to achieve the best possible safety levels at the lowest possible cost.
Another study has been conducted on the state of a single unit with multiple equipments in a fuel oil facility. Evaluation of the failures using FMEA analysis has been structured based on feedback, brain-storming, and expert judgment resulting in preventive maintenance planning which increased the reliability of the facility. Hence, preventive maintenance tasks can be assigned properly based on the priority of critical equipments.
One study in a plant has presented a new, critical-based maintenance methodology for decision-making in preventive maintenance planning by integrating the issue of reliability with safety as well as with environmental issues. The critical-based method involves risk and failure analyses which is intended to inform decisions about the needed level of facility design features, and to evaluate the safety and risk of the facility. The methodology comprises of three main modules namely estimation, evaluation, and planning. In the estimation module, the consequences as well as the probability of failure is identified. The evaluation module consists of aversion and acceptance analyses which reduces incidences of failure amongst components prior to designing the preventive maintenance. This is done to reduce the level of risk resulting from facility failure in the final module of preventive maintenance. Based on the results obtained from the analyses, the preventive maintenance interval time for the facility is determined.
Overall, as per failure-based planning, prior to any further evaluations of failure, thorough assessments and analyses are crucial for defining the criticality of failure. This is because failure evaluation can have an impact on decision making which pertains to preventive maintenance. However, it is difficult to evaluate failure as the subject matter of any analysis because of the difficulty of gathering information on the time lost and the costs paid because of failures. Having said that, even though determining the root causes of failure mechanisms is time-consuming, it affects further analysis if a failure’s cause is not properly determined, especially in real-world scenario.
Development of preventive maintenance programme – There are seven elements of preventive maintenance consisting of (i) inspection which consists of periodically inspecting of equipments to determine their serviceability by comparing their physical, mechanical, electrical, and other characteristics to established standards (ii) calibration which means detecting and adjusting of any discrepancy in the accuracy of the material or parameter being compared to the established standard value, (iii) testing which consists of periodically testing to determine serviceability and detect mechanical or electrical degradation, (iv) adjustment which means periodically making adjustments to specified variable elements to achieve optimum performance, (v) servicing which means periodically lubricating, charging, cleaning, and so on, materials or equipments to prevent the occurrence of incipient failures, (vi) installation which consists of periodically replacing limited-life parts or parts experiencing time cycle or wear degradation to maintain the specified tolerance level, and (vii) alignment which consists of making changes to an equipment’s specified variable elements to achieve optimum performance.
Development of an effective preventive maintenance programme needs the availability of items such as test instruments and tools, accurate historical records of equipment, skilled personnel, service manuals, recommendations of the manufacturer, past data from similar equipment, management support, and user cooperation. A highly effective preventive maintenance programme can be developed in a short time by following certain steps. These steps are described below.
Identification and selection of the areas – It consists of identifying and selecting of one or two important areas on which to concentrate the initial preventive maintenance effort. The main objective of this step is to get good results in areas which are highly visible.
Highlight of the preventive maintenance requirements – It defines the preventive maintenance needs and then develop a schedule for two types of tasks consisting of daily preventive maintenance inspections and periodic preventive maintenance assignments.
Determination of assignment frequency – It consists of establishment of the frequency of assignments and review of the item or equipment records and conditions. The frequency depends on factors such as supplier recommendations, the experience of personnel familiar with the equipment or item under consideration, and recommendations from engineers.
Preparation of the preventive maintenance assignments – It consists of preparation of the daily and periodic assignments in an effective manner and then get them approved.
Scheduling of the preventive maintenance assignments – It consists of the scheduling of the defined preventive maintenance assignments on the basis of a 12-month period.
Expanding of the preventive maintenance programme as appropriate – It consists of the expansion of the preventive maintenance programme to other areas on the basis of experience gained from the pilot preventive maintenance projects.
Preventive maintenance checks and service (PMCS) are to be conducted at the minimum frequency. Normally, each item is to be given a 360-degree visual inspection for any deficiency, visual inspection of overall appearance, surface condition, cleanliness, alignment and operation and performance followed by operator maintenance as per the manufacture’s guidelines. Operator maintenance such as lubrication, filter changing, adjustment, and upkeep is performed as per the PMCS schedule. When deficiencies are determined, the maintenance personnel take immediate, appropriate corrective action.
All the statutory regulations including those for occupational health, safety, and the environment are to be observed. Safety in all its aspects refers to the health and safety of the person, the safe operation of the equipment, and concern to the preservation of the environment. The maintenance team is to comprise at least two persons. The team is to be equipped with all the necessary tools, equipment and instruments to safely and effectively perform their job.
Benefits of preventive maintenance
Effective use of preventive maintenance eliminates much of the maintenance expenditures which are wasted by several manufacturing and production plants. Preventive maintenance is cost effective in several capital-intensive processes. It is flexible since it allows for the adjustment of maintenance periodicity. It increases equipment life cycle and results into energy savings. Fig 4 gives some of the benefits of preventive maintenance.
Fig 4 Benefits of preventive maintenance
Depending on the present maintenance practices, present equipment reliability, and facility downtime, there is little doubt that several facilities purely reliant on reactive maintenance can save much more than 18 % by instituting a proper preventive maintenance programme. While preventive maintenance is not the optimum maintenance programme, it does have several advantages over that of a purely reactive programme. By performing the preventive maintenance as the equipment designer envisioned, the life of the equipment can be extended closer to design. This translates into savings. With preventive maintenance, the equipment can be normally run more efficiently resulting in savings. While equipment catastrophic failures are not prevented but there is decrease the number of failures. Minimizing failures translate into maintenance cost savings.
The initial savings generated by effective preventive maintenance programme fall into several areas which include (i) elimination of unscheduled downtime caused by equipment or facility failures, (ii) increased manpower utilization, (iii) increase in the throughput or production capacity of the plant, (iv) reduction of maintenance expenditures, and (v) increased useful life of the facility and equipments.