Sudharsan Engineering CollegeSathiyamangalam, Pudukkottai DEPARTMENT OF MECHANICAL ENGINEERING ME1012 MAINTENANCE ENGINEERING STUDY MATERIAL Prepared by M.PUGALENTHI M.E., ASSISTANT 2. Stress analysis of rectangular L bracket PROFESSOR/MECH MAINTENANCE ENGINEERING(ME1012) ME1012 – MAINTENANCE ENGINEERING (Common to Mechanical and Production) L 3 T 0 P C 0 3 10 UNIT I PRINCIPLES AND PRACTICES OF MAINTENANCE PLANNING Basic principles of maintenance planning – Objectives and principles of planned maintenance activity – Importance and benefits of sound maintenance systems – Reliability and machine availability – MTBF, MTTR and MWT – Factors of availability – Maintenance organization – Maintenance economics. UNIT II MAINTENANCE POLICIES – PREVENTIVE MAINTENANCE 9 Maintenance categories – Comparative merits of each category – Preventive maintenance, maintenance schedules and repair cycle – Principles and methods of lubrication – TPM. UNIT III CONDITION MONITORING 9 Condition monitoring – Cost comparison with and without CM – On-load testing and off-load testing – Methods and instruments for CM – Temperature sensitive tapes – Pistol thermometers – Wear-debris analysis. UNIT IV REPAIR METHODS FOR BASIC MACHINE ELEMENTS 10 Repair methods for beds, slide-ways, spindles, gears, lead screws and bearings – Failure analysis – Failures and their development – Logical fault location methods – Sequential fault location. UNIT V REPAIR METHODS FOR MATERIAL HANDLING EQUIPMENT systems –Use of computers in maintenance. 8 Repair methods for material handling equipment – Equipment records – Job order Total: 45 NPRCET/MECHANICAL 2 MAINTENANCE ENGINEERING(ME1012) TEXT BOOKS 1. Srivastava, S.K., “Industrial Maintenance Management”, S. Chand and Co., 1981. 2. Bhattacharya, S.N., “Installation, Servicing and Maintenance”, S. Chand and Co., 1995. REFERENCES 1. Garg, M.R., “Industrial Maintenance”, S. Chand and Co., 1986. 2. Higgins, L.R., “Maintenance Engineering Handbook”, 5th Edition, McGraw Hill, 1988. 3. Davies, “Handbook of Condition Monitoring”, Chapman and Hall, 1996. NPRCET/MECHANICAL 3 A person practicing Maintenance Engineering is known as a Maintenance Engineer. Assessing required maintenance tools and skills required for efficient maintenance of equipment. equipment. MTTR and MWT – Factors of availability – Maintenance organization – Maintenance economics. and availability of equipment. reliability. Maintenance. and hence maintenance engineering. the United States spent approximately US$300 billion annually on plant maintenance and operations alone.MAINTENANCE ENGINEERING(ME1012) UNIT I PRINCIPLES AND PRACTICES OF MAINTENANCE PLANNING 10 Basic principles of maintenance planning – Objectives and principles of planned maintenance activity – Importance and benefits of sound maintenance systems – Reliability and machine availability – MTBF. systems. Assessing required skills required for maintenance personnel. procedures. NPRCET/MECHANICAL 4 . OBJECTIVES AND PRINCIPLES : Analysis of repetitive equipment failures. machinery and structures have grown increasingly complex. Assessing the needs for equipment replacements and establish replacement programs when due application of scheduling and project management principles to replacement programs. machineries and infrastructure. and departmental budgets to achieve better maintainability. Since the Industrial Revolution. Reviewing personnel transfers to and from maintenance organizations assessing and reporting safety hazards associated with maintenance of equipment. Prior to 2006. Maintenance Engineering is the discipline and profession of applying engineering concepts to the optimization of equipment. devices. vocations and related systems needed to maintain them. Estimation of maintenance costs and evaluation of alternatives. is increasing in importance due to rising amounts of equipment. Forecasting of spare parts. requiring a host of personnel. secure file system based on equipment tag numbers. especially on repetitive maintenance tasks. the planner's responsibility is "what" before "how. and ready to execute. The majority of maintenance tasks are repetitive over a sufficient period of time. top level technicians that are trained in planning techniques. The craft technicians use their expertise to make the specified repair or replacement. plan changes. approved. After every job completion. Crew supervisors handle the current day's work and problems. 6. Work that is planned before assignment reduces unnecessary delays during jobs and work that is scheduled reduces delays between jobs. MAINTENANCE 1. or other helpful information so that future work plans and schedules might be improved. tools. parts.2. Supervisors and plant engineers are trained to access these files to gather information they need with minimal planner assistance. instructions. The planners ensure that feedback information gets properly filed to aid future work. The Planning Department recognizes the skill of the crafts. This backlog allows crews to work primarily on planned work. The planner then plans the general strategy of the work (such as repair or replace) and includes a preliminary procedure if there is not one already in the file. planners are experienced. In general.com United States of America (904) 228-5700 . File cost information assists making repair or replace decisions. The Planning Department maintains a simple. The feedback consists of any problems. Any problems that arise after commencement of any job are resolved by the craft technicians or supervisors. or equipment information. The planners are organized into a separate department from the craft maintenance crews to facilitate specializing in planning techniques as well as focusing on future work. Planners use personal experience and file information to develop work plans to avoid anticipated work delays and quality or safety problems. Maintenance Planning and Scheduling Handbook Doc Palmer docpalmer@palmerplanning. travel. coordination with other crafts. Wrench time is the proportion of available-to-work time during which craft persons are not being kept from productively working on a job site by delays such as waiting for assignment. Wrench time is the primary measure of workforce efficiency and of planning and scheduling effectiveness. 5. As a minimum." The planner determines the scope of the work request including clarification of the originator’s intent where necessary. feedback is given by the lead technician or supervisor to the Planning Department. The file system enables planners to utilize equipment data and information learned on previous work to prepare and improve work plans. clearance. PLANNING PRINCIPLES 4. 3. The planners and technicians work together over repeated jobs to develop better procedures and checklists. The Planning Department concentrates on future work-work that has not been started--in order to provide the Maintenance Department at least one week of work backlog that is planned. The probability of an item to perform a required function under stated conditions for a specified period of time. NPRCET/MECHANICAL 5 . produced or maintained items to perform as required over time. produced or maintained item to perform as required over time.g. The capacity of a designed. In the most discrete and practical sense: "Items that do not fail in use are reliable" and "Items that do fail in use are not reliable". Propose mitigations by which the risks may be lowered and controlled to an acceptable level. the basic Failure mechanisms and root causes) by specific analysis or tests. possible based on cost-benefit analysis. The resistance to failure of an item over time. The basic sorts of steps to take are to: First thoroughly identify as many as possible reliability hazards (e. In line with the creation of safety cases for safety. the goal is to provide a robust set of qualitative and quantitative evidence that an item or system will not contain unacceptable risk. Select the best mitigations and get agreement on final (accepted) Risk Levels. Assess the Risk associated with them by analysis and testing. relevant System Failure Scenarios item Failure modes.MAINTENANCE ENGINEERING(ME1012) Reliability may be defined in several ways: The idea that an item is fit for a purpose with respect to time. The capacity of a population of designed. lack of repair facilities. spare part availability. Improving maintainability is generally easier than reliability. it is likely to dominate the availability (prediction uncertainty) problem. However. none of the others are of any importance and therefore reliability is generally regarded as the most important part of availability A Fault Tree Diagram NPRCET/MECHANICAL 6 . When reliability is not under control more complicated issues may arise. because the uncertainties in the reliability estimates are in most cases very large. like manpower (maintainers / customer service capability) shortage. Only focusing on maintainability is therefore not enough. If failures are prevented. Maintainability estimates (Repair rates) are also generally more accurate.MAINTENANCE ENGINEERING(ME1012) AVAILABILITY A Reliability Program Plan may also be used to evaluate and improve Availability of a system by the strategy on focusing on increasing testability & maintainability and not on reliability. extensive retro-fit and complex configuration management costs and others. logistic delays. even in the case maintainability levels are very high. The problem of unreliability may be increased also due to the "Domino effect" of maintenance induced failures after repairs. the product is expected to fail in the lab just as it would have failed in the field—but in much less time. where is the failure probability density function and is the length of the period of time (which is assumed to start from time zero). NPRCET/MECHANICAL 7 . To predict the normal field life from the high stress lab life. Mathematically. ACCELERATED TESTING: The purpose of accelerated life testing is to induce field failure in the laboratory at a much faster rate by providing a harsher. this may be expressed as. environment. . RELIABILITY THEORY Reliability is defined as the probability that a device will perform its intended function during a specified period of time under stated conditions.MAINTENANCE ENGINEERING(ME1012) One of the most important design techniques is redundancy. In such a test. but nonetheless representative. The main objective of an accelerated test is either of the following: To discover failure modes. A good software development plan is a key aspect of the software reliability program. software has become an increasingly critical part of most electronics and. operators and procedures. software metrics and software models to be used during software development. Since the widespread use of digital integrated circuit technology.MAINTENANCE ENGINEERING(ME1012) An Accelerated testing program can be broken down into the following steps: Software reliability is a special aspect of reliability engineering. by definition. the higher the probability that it will eventually be used in an untested manner and exhibit a latent defect that results in a failure (Shooman 1987). includes all parts of the system. As with hardware. System reliability. Traditionally. (Denney 2005). NPRCET/MECHANICAL 8 . peer reviews. Software reliability engineering relies heavily on a disciplined software engineering process to anticipate and design against unintended consequences. configuration management. design and implementation. software reliability depends on good requirements. Despite this difference in the source of failure between software and hardware. hence. unit tests. supporting infrastructure (including critical external interfaces). There is more overlap between software quality engineering and software reliability engineering than between hardware quality and reliability. (Musa 2005). The software development plan describes the design and coding standards. software. reliability engineering focuses on critical hardware parts of the system. including hardware. nearly all present day systems. several software reliability models based on statistics have been proposed to quantify what we experience with software: the longer software is run. Define objective and scope of the test Collect required information about the product Identify the stress(es) Determine level of stress(es) Conduct the accelerated test and analyze the collected data. the formula will be: The MTBF is often denoted by the Greek letter θ. greater than) the moment it went up. the MTBF is the sum of the operational periods divided by the number of observed failures. downtime is the instantaneous time it went down. NPRCET/MECHANICAL 9 . which is after (i.MAINTENANCE ENGINEERING(ME1012) MEAN TIME BETWEEN FAILURES Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a system during operation.[1] MTBF can be calculated as the arithmetic mean (average) time between failures of a system. If the "Down time" (with space) refers to the start of "downtime" (without space) and "up time" (with space) refers to the start of "uptime" (without spMean time betMean time between failuresween failuresace). FORMAL DEFINITION OF MTBF By referring to the figure above. The difference (downtime minus uptime) is the amount of time it was operating between these two events.e. uptime. or The MTBF can be defined in terms of the expected value of the density function ƒ(t) where ƒ is the density function of time until failure – satisfying the standard requirement of density functions – The Overview For each observation. these "prediction" methods are not intended to reflect fielded MTBF as is commonly believed. or restore. is also subject to interpretation. Mean time to repair Mean time to recovery/Mean time to restore Mean time to respond Mean time to replace In an engineering context with no explicit definition. respond. mean or maximum.UTE 80-810 (RDF2000). Siemens Norm. mean time to repair would be the most probable intent by virtue of seniority of usage. with greatly differing meanings. FIDES. as there are many different ways in which a mean can be calculated. It is wise to spell out exactly what is meant by the use of this abbreviation. the engineering figure of merit. The M can stand for any of minimum. mean. etc. However. less in the case of respond. Telcordia SR332.MAINTENANCE ENGINEERING(ME1012) MTBF value prediction is an important element in the development of products.). It is also similar in meaning to the others above (more in the case of recovery. often utilize Reliability Software to calculate products' MTBF according to various methods/standards (MIL-HDBK-217F. rather than assuming the reader will know which is being assumed. The most common. Reliability engineers / design engineers. NPRCET/MECHANICAL 10 . The intent of these tools is to focus design efforts on the weak links in the design MTTR MTTR is an abbreviation that has several different expansions. repair. the latter being more properly styled mean "response time"). and the R can stand for any of recovery. 1. Objectives: may include profit maximization.10 and 1. and coordinating activites to perform maintenance tasks IMPLEMENTING Executing the plans to meet the set performance objectives Figure 1. minimizing costs.11 present education and training.2 Maintenance Organization Objectives and Responsibility A maintenance organization and its position in the plant/whole organization is heavily impacted by the following elements or factors: • • • • • Type of business. PLANNING Setting performance objectives and developing decisions on how to achieve them CONTROLLING Measuring performance of the maintained equipment and taking preventive and corrective actions to restore the designed (desired) specifications Leader’s Influence ORGANIZING Creating structure: setting tasks (dividing up the work). safe and clean environment. whether it is high tech.9.g. Sections 1. specific quality level of service or products. It is clear that all of these . and Range of responsibility assigned to maintenance. labor intensive. arranging resources (forming maintenance crews). or human resource development. and management and labor relations.12. production or service. Culture of the organization. 1..Maintenance Organization 5 Section 1. respectively. increasing market share and other social objectives. Size and structure of the organization. e. A summary of the chapter is provided in Section 1. Maintenance organizing as a function of the management process Organizations seek one or several of the following objectives: profit maximization. equipment. since the maintenance load is uncertain. In this section the main issues that must be addressed when forming the maintenance organization’s structure are presented. This backlog can also be cleared when the maintenance load is less than the capacity. Techniques for maintenance forecasting and capacity planning are presented in a separate chapter in this handbook. The maintenance capacity is heavily influenced by the level of centralization or decentralization adopted. Making long run estimations is one of the areas in maintenance capacity planning that is both critical and not well developed in practice. Haroun and S. well configured and safe to perform their intended functions. 2. however they generally include the following according to Duffuaa et al. The above responsibilities and objectives impact the organization structure for maintenance as will be shown in the coming sections.6 A. The issues are: capacity planning. Conserve and control the use of spare parts and material. Critical aspects of maintenance capacity are the numbers and skills of craftsmen required to execute the maintenance load. centralization vs decentralization and in-house vs outsourcing. . design modification and emergency maintenance in an efficient and effective manner. Commission new plants and plant expansions. 4. corrective. The principal responsibility of maintenance is to provide a service to enable an organization to achieve its objectives. Perform all maintenance activities including preventive. and Operate utilities and conserve energy.O. In order to have better utilization of manpower. It is difficult to determine the exact number of various types of craftsmen.1 Maintenance Capacity Planning Maintenance capacity planning determines the required resources for maintenance including the required crafts. Therefore accurate forecasts for the future maintenance work demand are essential for determining the maintenance capacity. administration.E. tools and space to execute the maintenance load efficiently and meet the objectives of the maintenance department. This is likely to result in a backlog of uncompleted maintenance work. Keeping assets and equipment in good condition. organizations tend to reduce the number of available craftsmen below their expected need. The specific responsibilities vary from one organization to another.3 Determinants of a Maintenance Organization The maintenance organization’s structure is determined after planning the maintenance capacity. 1. predictive. 3.3. 1. (1998): 1. overhauls. 5. Duffuaa objectives are heavily impacted by maintenance and therefore the objectives of maintenance must be aligned with the objectives of the organization. 4. Allows more effective on the job training.3. The main sources or options available are in-house by direct hiring. 3. In a decentralized maintenance organization. and Permits the purchasing of modern equipment. size of the plant and skills of craftsmen. The cascade system organizes maintenance in areas and what ever exceeds the capacity of each area is challenged to a centralized unit. Allows more efficient line supervision. In some cases a compromise solution that combines centralization and decentralization is better. Capability of the source to achieve the objectives set for maintenance by the organization and its ability to carry out the maintenance tasks.3. Supervision of crafts becomes more difficult and as such less maintenance control is achieved. decentralized or a hybrid form depends to a greater extent on the organization is philosophy. (1998) and Niebel (1994). Less specialization on complex hardware is achieved since different persons work on the same hardware. This tends to reduce the flexibility of the maintenance system as a whole. This type of hybrid is called a cascade system.3 In-house vs Outsourcing At this level management considers the sources for building the maintenance capacity. technological and economic factors. maintenance load. 3. Availability and dependability of the source on a long term basis.Maintenance Organization 7 1. and More costs of transportation are incurred due to remoteness of some of the maintenance work. outsourcing. Provides more flexibility and improves utilization of resources such highly skilled crafts and special equipment and therefore results in more efficiency. 1. Less utilization of crafts since more time is required for getting to and from jobs. 2. However it has the following disadvantages: 1. The following are criteria that can be employed to select among sources for maintenance capacity: 1. 2. 2. The criteria for selecting sources for building and maintaining maintenance capacity include strategic considerations. The range of skills available becomes reduced and manpower utilization is usually less efficient than in a centralized maintenance. For more on the advantages and disadvantages of centralization and decentralization see Duffuaa et al. or a combination of in-house and outsourcing. . The advantages of centralization are: 1. In this fashion the advantages of both systems may be reaped. departments are assigned to specific areas or units.2 Centralization vs Decentralization The decision to organize maintenance in a centralized. 4. What is Mean Failure Rate? 06. 07. What are the objectives of maintenance organization and what different types of organizations are in use in Indian industries? (16) 4. State the benefits of reliability analysis in industries. MTBF. 02. What do you mean by maintenance job planning? Discuss various steps of maintenance job planning. Define failure rate. PART-B (16 Marks) 1. (16) 2.MAINTENANCE ENGINEERING(ME1012) UNIT. (16) NPRCET/MECHANICAL 11 . What is Mean Time Between Failures (MTBF)? 08. Define Failure Density. 09. MTTR and failure rate? (16) 6. (16) 5. 10. Define Mean Time to Repair (MTTR). Define reliability. 04. MTTF. Define Mean Time to Failure. 03. Explain briefly different types and classes of maintenance cost. What is long term plan? Discuss few long term planning? (16) 3. Define maintenance. 05. Explain MTBS. What is equipment availability and what are the three basic approaches to define and quantity availability. Define Maintenance Action Rate.I PRINCIPLES AND PRACTICES OF MAINTENANCE PLANNING PART-A (2 Marks) 01. a liquid-liquid dispersion (a grease) or. NPRCET/MECHANICAL 12 .g. graphite. The science of friction. maintenance schedules and repair cycle – Principles and methods of lubrication – TPM. In the most common case the applied load is carried by pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces. LUBRICATION Lubrication is the process. a liquid. MoS2) a solid/liquid dispersion.MAINTENANCE ENGINEERING(ME1012) UNIT II MAINTENANCE POLICIES – PREVENTIVE MAINTENANCE Maintenance categories – Comparative merits of each category – Preventive maintenance. (e. Lubrication can also describe the phenomenon such reduction of wear occurs without human intervention (hydroplaning on a road). lubrication and wear is called tribology. or technique employed to reduce wear of one or both surfaces in close proximity. exceptionally. and moving relative to each other. a gas. by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces. The interposed lubricant film can be a solid. Boundary lubrication (also called boundary film lubrication): The bodies come into closer contact at their asperities. Boundary lubrication is also defined as that regime in which the load is carried by the surface asperities rather than by the lubricant. and there is an elastic deformation on the contacting surface enlarging the loadbearing area whereby the viscous resistance of the lubricant becomes capable of supporting the load. and the exact design of the bearing is used to pump lubricant around the bearing to maintain the lubricating film. This design of bearing may wear when started. or film on the moving solid surfaces (boundary film) which is capable of supporting the load and major wear or breakdown is avoided. which are called regimes of lubrication: Fluid film lubrication is the lubrication regime in which through viscous forces the load is fully supported by the lubricant within the space or gap between the parts in motion relative to one another (the lubricated conjunction) and solid–solid contact is avoided. the heat developed by the local pressures causes a condition which is called stick-slip and some asperities break off. to maintain the fluid lubricant film where it would otherwise be squeezed out.[3] NPRCET/MECHANICAL 13 .[2] o Hydrostatic lubrication is when an external pressure is applied to the lubricant in the bearing.MAINTENANCE ENGINEERING(ME1012) The regimes of lubrication As the load increases on the contacting surfaces three distinct situations can be observed with respect to the mode of lubrication. as the lubricant film breaks down. At the elevated temperature and pressure conditions chemically reactive constituents of the lubricant react with the contact surface forming a highly resistant tenacious layer. stopped or reversed. o Hydrodynamic lubrication is where the motion of the contacting surfaces. Elastohydrodynamic lubrication: The opposing surfaces are separated. but there occurs some interaction between the raised solid features called asperities. TOTAL PRODUCTIVE MAINTENANCE TPM is a maintenance process developed for improving productivity by making processes more reliable and less wasteful. turbines. pumps. TPM is an extension of TQM(Total Quality Management). NPRCET/MECHANICAL 14 . To implement TPM the production unit and maintenance unit should work jointly. such as piston engines. In some applications. preventing combustion gases from escaping into the crankcase . preventive and predictive maintenance is required. bearings.MAINTENANCE ENGINEERING(ME1012) Besides supporting the load the lubricant may have to perform other functions as well. Lubrication is required for correct operation of mechanical systems pistons. cams. cutting tools etc. While carrying out these functions the lubricant is constantly replaced from the contact areas either by the relative movement (hydrodynamics) or by externally induced forces. To achieve this objective. causing seizure. where without lubrication the pressure between the surfaces in close proximity would generate enough heat for rapid surface damage which in a coarsened condition may literally weld the surfaces together. the film between the piston and the cylinder wall also seals the combustion chamber. The objective of TPM is to maintain the plant or equipment in good condition without interfering with the daily process. By following the philosophy of TPM we can minimize the unexpected failure of the equipment. for instance it may cool the contact areas and remove wear products. will increase productivity within the total organization. this next methodology was called lean manufacturing. where: (1) A clear business culture is designed to continuously improve the efficiency of the total production system. Finally TPM will provide practical and transparent ingredients to reach operational excellence. Japan. An accurate and practical implementation of TPM. influencing productivity.MAINTENANCE ENGINEERING(ME1012) Original goal of total productive management: ―Continuously improve all operational conditions. the focus was stretched. where all losses are prevented and/or known all departments. not as a quick menu. NPRCET/MECHANICAL 15 . (2) A standardized and systematic approach is used. by stimulating the daily awareness of all employees‖ (by Seiichi Nakajima. After TPM. This sheet gives an overview of TPM in its original form. within a production system. JIPM) TPM focuses primarily on manufacturing (although its benefits are applicable to virtually any "process") and is the first methodology Toyota used to improve its global position (1950s). and also suppliers and customers were involved (Supply Chain). (5) Steps are taken as a journey. (4) A transparent multidisciplinary organization in reaching zero losses. will be involved to move from a reactive to a predictive mindset. office TPM. early-phase management. equipment breakdown time. Seiketsu (Standardisation). autonomous maintenance (Jishu Hozen). Then through a clear understanding of this Gap Analysis (Fishbone Cause-Effect Analysis. Few organisation also add Pillars according to their Work Place like: Tools Management. Equipment Failures and Accidents. These 8 pillars are the following: focussed improvement (Kobetsu Kaizen). idling and minor losses.MAINTENANCE ENGINEERING(ME1012) IMPLEMENTATION TPM has basically 3 goals . quality maintenance (Hinshitsu Hozen). Seition (Systematic Arrangement of the required items). Seiri (Sorting out the required or not required items). namely set-up and initial adjustment time.Zero Product Defects. speed (cycle time) losses. The Pillars & their details a) Efficient Equipment Utilisation b) Efficient Worker Utilisation c) Efficient Material & Energy Utilisation NPRCET/MECHANICAL 16 . Seiso (Cleaniness). Zero Equipment Unplanned Failures and Zero Accidents. planned maintenance. health. TPM identifies the 7 losses (types of waste) (muda). Information Technology & more. Shitsuke (Self Discipline). It sets out to achieve these goals by Gap Analysis of previous historical records of Product Defects. and in process quality losses. and safety. start-up quality losses. each being set to achieve a ―zero‖ target. Why-Why Cause-Effect Analysis. training and education. TPM has 8 pillars of activity. The Base for the TPM Activity is 5S. and P-M Analysis) plan a physical investigation to discover new latent fuguai (slight deterioration) during the first step in TPM Autonomous Maintenance called "Initial Cleaning". and environment. and then works systematically to eliminate them by making improvements (kaizen). called the repair cycle. Rather than bear the cost of completely replacing a finished product. Ultimately. spare parts. repaired. and replaced. a model of the life cycle of parts in a supply chain can be developed. Spare parts that are needed to support condemnation of repairable parts are known as replenishment spares. when they have failed. This type of model allows demands on a supply system to ultimately be traced to their operational reliability. enabling cheaper replacement. in particular. A rotable pool is a pool of repairable spare parts inventory set aside to allow for multiple repairs to be accomplished simultaneously. This allows components to be more easily removed. repairables typically are designed to enable more affordable maintenance by being more modular. This can be used to minimize stockout conditions for repairable items. allowing for analysis of the dynamics of the supply system. this sequence ends with the manufacturer. This model. usually by virtue of economic consideration of their repair cost. NPRCET/MECHANICAL 17 . consists of functioning parts in use by equipment operators. either by production or repair. and the entire sequence of suppliers or repair providers that replenish functional part inventories.MAINTENANCE ENGINEERING(ME1012) REPAIRABLE Repairable parts are parts that are deemed worthy of repair. REPAIR CYCLE From the perspective of logistics. MAINTENANCE ENGINEERING(ME1012) UNIT-II MAINTENANCE POLICIES – PREVENTIVE MAINTENANCE PART-A (2 Marks) 01. What are the functions of lubrication and gives the tips on lubrication. Classify various planned maintenance approach. What is meant by Reliability Centered Maintenance (RCM)? 09. What do you understand by maintenance categories? Explain common types and explain the basis of their selection. 03. What is Total Productive Maintenance (TPM) and discuss it's similarities with TQM? 10. Give the merits and demerits. Explain the repair cycle of metallic materials. Define Corrective maintenance approach. . (16) NPRCET/MECHANICAL 18 . List out the objectives of Corrective maintenance. What is meant by preventive maintenance approach? 05. .(16) 2. What are all the steps involved in preventive maintenance why preventive maintenance is better than reactive maintenance. 04. Briefly explain the procedure for TPM. Distinguish between fixed time maintenance and connect based maintenance. List out some condition based monitoring techniques and briefly discuss on them. What is. .(16) 5. 08. (16) 6. What is meant by Breakdown maintenance approach? 02. (16) 3. Health and Environment pillar of TPM aims at? PART-B (16 Marks) 1. What does Safety. 06. . . meant by Reliability Centered Maintenance (RCM)? 11. (16) 4. What is meant by Predictive Maintenance? 07. before the failure occurs. a deviation from a reference value (e. temperature or vibration behavior) must occur to identify impeding damages Predictive Maintenance does not predict failure. Nevertheless. CONDITION MONITORING Condition monitoring is the process of monitoring a parameter of condition in machinery. Once a defect has been identified. NPRCET/MECHANICAL 19 . the failure process has already commenced and CM systems can only measure the deterioration of the condition. Machines with defects are more at risk of failure than defect free machines. Condition monitoring has a unique benefit in that the actual load.MAINTENANCE ENGINEERING(ME1012) UNIT III CONDITION MONITORING Condition monitoring – Cost comparison with and without CM – On-load testing and off-load testing – Methods and instruments for CM – Temperature sensitive tapes – Pistol thermometers – Wear-debris analysis. and subsequent heat dissipation that represents normal service can be seen and conditions that would shorten normal lifespan can be addressed before repeated failures occur.g. The use of conditional monitoring allows maintenance to be scheduled. such that a significant change is indicative of a developing failure. Intervention in the early stages of deterioration is usually much more cost effective than allowing the machinery to fail. or other actions to be taken to avoid the consequences of failure. It is a major component of predictive maintenance. Serviceable machinery includes rotating equipment and stationary plant such as boilers and heat exchangers. g. or screen capture. 3. 4. number of keystrokes per minute) may track the performance of keyboard-intensive work such as word processing or data entry. of the entire [video display] or the content of the screen activity within a particular program or computer application. once every 4 minutes).g. Screen monitoring records video or static images detailing the contents. Keystroke logging captures all keyboard input to enable the employer to monitor anything typed into the monitored machine.. Idle time monitoring keeps track of time when the employee is away from the computer or the computer is not being actively used. NPRCET/MECHANICAL 20 ..g. They may collect images constantly or only collect information while the user is interacting with the equipment (e. Monitoring tools may collect real time video. accelerated or [time-lapse] video or screen shots. Data monitoring tracks the content of and changes to files stored on the local [hard drive] or in the user's "private" network share. capturing screens when the mouse or keyboard is active).. 2. Keystroke monitoring (e.MAINTENANCE ENGINEERING(ME1012) METHODS OF CM 1. or may take video or still image captures at regular intervals (e. g. Keystroke logging captures all keyboard input to enable the employer to monitor anything typed into the monitored machine. o Monitoring tools may collect real time video. or may take video or still image captures at regular intervals (e. number of keystrokes per minute) may track the performance of keyboard-intensive work such as word processing or data entry. of the entire [video display] or the content of the screen activity within a particular program or computer application. or screen capture. o They may collect images constantly or only collect information while the user is interacting with the equipment (e.. o Idle time monitoring keeps track of time when the employee is away from the computer or the computer is not being actively used.. accelerated or [time-lapse] video or screen shots.g.MAINTENANCE ENGINEERING(ME1012) BENEFITS o Screen monitoring records video or static images detailing the contents. once every 4 minutes). NPRCET/MECHANICAL 21 .. capturing screens when the mouse or keyboard is active).g. o Data monitoring tracks the content of and changes to files stored on the local [hard drive] or in the user's "private" network share. o Keystroke monitoring (e. Nevertheless the high cost of these instruments prevent their use in all required locations. . If by assessment. National Seminar of ISNT Chennai.SIMPLE INSTRUMENTS USED IN CONDITION MONITORING Prof. On-load vs off load condition monitoring On load monitoring means monitoring or adjusting the parameters while the machine or equipment is running.org ABSTRACT Condition monitoring is a system of assessing the service condition or the change of service condition of any component or a part of an equipment or a system. In other words the preventive maintenance with condition monitoring is a system in which. Thus it is done for superficial. These have the advantages of being portable. the condition of the part is satisfactory. it is replaced even before its PM schedule and prevent unexpected breakdowns. an assessment is made on the condition of all major parts of an equipment while in operation.Peter’s Engineering College NDE2002 predict. 2. easily accessible & non interfering parts of the equipment which can be carried out without interruption to the operation. D. department of production Engineering. in addition to the programmed stoppages for maintenance work. improve. – 7. On the other hand traditionally used simple mechanical gadgets are being used by the maintenance personnel of today’s industry all over the world. the schedule of stopping the machine or scrapping the part etc. assure.R.nde2002. 2002 www. 5. 12. simple. These. More significantly they can be used to check any location or component suspected to be functioning abnormally. even when a preventive maintenance schedule is on. What is Condition monitoring Condition monitoring is that type of planned maintenance wherein the actual working conditions of major components of an equipment are constantly monitored to give an indication of which parts should be replaced and which need not in the near future. Considerable research has been done in this direction leading to development of several electrical and electronic monitoring instruments. easy to use and economical. This paper discusses some of such instruments used and could be used for condition monitoring of industrial machines as well as process equipment like pressure vessels and heat exchangers 1. is reviewed and deferred .KIRAN Head. Similarly if the condition monitoring finds a certain part may fail in a short time. St. when connected to strategic locations of the systems measure and indicate certain parameters enabling us to monitor the condition and take vital decisions on a continuous basis. inside of narrow mouthed cylinders. Simple gadgets are being used either on-line or off-line. or the pipes of heat exchangers or boilers. dark spots . to aid the perception of the condition. 4. These gadgets are discussed more in detail in the following paragraphs. which need to be stopped temporarily to check the condition. may be with respect to corrosion or fatigue cracking or even dust/ sediment collection that is deleterious to the functioning of the component. Posters or figures illustrating different conditions of components may also be helpful ii) Aided subjective or condition monitoring with simple gadgets: Here the monitoring personnel use simple gadgets to add to their ability to perceive conditions better. the equipment can be stopped for detailed check and/or rectification. Subjective. iii) Objective condition monitoring : In objective condition monitoring different instruments and facilities are used for obtaining data giving direct measure of the parametric condition of the components even while the machine is working. 3. bearing play etc. Some of the gadgets are illustrated below: i) Inspection mirrors used to inspect crevices. like seeing (emanation of smoke). It is important that the person carrying out subjective condition monitoring has an adequate qualifications and skills as the result depends on their judgement and experience. hearing (bearing noise). These mirrors can be simple like that of a dentist or . A doctor feeling the pulse (subjective). The four senses a man is bestowed with. guidelines or hints where to look for leakage. aided subjective or objective condition monitoring i) Subjective condition monitoring : Here the monitoring personnel use their perception of senses and judgement to note any change of the condition. In many cases these simple mechanical or complex electronic measuring devices can be mounted on convenient locations for better monitoring and control. Depending upon the extent of change as perceived. smelling (burning of oil or rubber components due to excessive heat). Some of the gadgets and simple instruments used for condition monitoring a) Monitoring of visual condition of inaccessible parts/locations Quite often the visual condition of the components located at inaccessible locations are to be monitored. In subjective condition monitoring it is also possible to use instructions. his using a stethoscope to determine any abnormal heart beat (aided subjective) or looking into the ECG monitor (objective) form the examples of the above three categories.Off load monitoring is for interior or inaccessible parts. feeling (touching the motor to feel the excessive heating or touching the housing to feel a vibrating shaft) are used. However there may be several situations like the two-shift working or the plant’s temporary shut down for other reasons when this class can be conducted without productions loss. for specialised applications or to assist the viewer et.a) with adjustable mirror angle controlled by a wire running along the holding rod or b) illuminated with a light bulb near the mirror of special use in dark spots. c) with telescopic rod. inside cylinders or inside heat exchanger pipes. 2. e) periscopic. enabling an early preventive action. 1 a) a collection of inspection mirrors. which can tell a lot about the working condition of the inside of the tubes about the rusting. These are also called as borescopes. Use of borescopes to inspect heat exchanger pipes. d) mirrors fitted inside a small tube rather than on a rod to prevent damage to the mirror during insertion or other operation. cracking. fig. sedimentation etc. . b) inspection of crevices and c) inspecting the inside of as cylinder Of specific interest to the NDE practitioners is their versatility to inspect the inside of the boiler pipes or heat exchanger pipes. Fig. for adjusting the length of the gadget. Etc. The application of endoscopes in industrial equipment . but are flexible. they are flexible ands are more versatile in several applications illustrated below. Also called optical fibroscopes. They work on the principle of image transfer by total internal reflection in a bundle of glass fibres. Fig. 4. Some times they are permanently fixed for constant monitoring of critical components are inserted when needed into pre-fixed tubular guides leading to the location to be monitored. 3 borescopes and periscopes ii) Endoscopes: These are like borescopes.Fig. They are more popular with gastroenterologists for diagnosing ulcers in stomachs. Fig. 5. Aided subjective Temperature sensitive stickers are the most common ands cost effective. c) Vibration monitoring Subjective By touching and feeling the vibrations in a rotating body or by listening to vibrating sounds. thermometers. The operatives or supervisor can identify its temperature range by looking at the stickers from a distance itself during their periodic patrol rounds. these instruments can be of thermostat type or connected to some sort of warning system in case of overheating. . The principle of endoscope Having illustrated the gadgets for visual perception as above. use of screw driver ends by expert foremen etc. pistol thermometers etc. and assessing if over heated. b) Temperature monitoring Subjective Touching the motor etc. each of which changes its colour at a particular temperature. thermal paints with which larger part of the heat prone body is painted fall under this category Objective Pyrometers. Depending of convenience and need. Aided subjective Stethoscopes. is stuck to the heat prone parts of the equipment. A sticker having four of five 20 mm diameter dots of special paints. classified into the three categories. some of them used in other monitoring functions may be cited as below. Temperature sensitive chalks. Objective Shock pulse meters (SPM). Aided subjective A number of leak detecting techniques are available. d) Leak Monitoring Subjective Listening to and identifying any hissing sound near hydraulic or pneumatic circuits. Use of proprietary preparations can make this method more effective. sound is generated in the frequency range 40-80 Khz. Objective One powerful technique is ultrasonic detection. Ultrasonic leak detector to detect internal & external leaks . including the soap and water methods. Vibration measurements made near the source of vibration might indicate the following: • imbalance • shaft misalignment • damaged bearings (worn or chipped balls or races) • damaged gears another transmission components • mechanical looseness • cavitation and stall etc. vibration measuring instruments etc. Fig. capable of detecting leaks as low as 1 m1/s. When a fluid is forced through a leak under internal or external pressure. The ultrasonic leak detector identifies this very high frequency which is easily separated from the lower frequencies of ordinary machine noise. 6. e) Corrosion Monitoring Subjective Corrosion cannot be generally judged visually and is not as effective as those discussed below. The corrosion characteristics of the coupon are expected to be same as the base metal to which they are pasted. . and analysed once in a month or as required. the details of which are beyond the scope of this paper. of the same material as the base. b)The coupon mounted in tubes carrying chemicals Objective Electrical and electronic devises can be developed to measure the corrosion characteristics based on the following principles. 7. are pasted at locations suspected to be highly corrosive. Fig. ♦ ♦ ♦ ♦ The basic principle in Corrosion Monitoring is the change in the resistance of special electrical elements in corrosion environment. and hence give an indirect measurement the corrosion of the body. Hydrogen gas formation during corrosion can be detected with a thin walled blind tube which can be analysed to determine the corrosion. The polarisation resistance of the special designed probe indicate the rate of corrosion. which are small pieces say 1 square inch. The potential difference between the reference electrode and the system will indicate the presence and the extent of corrosion. Aided subjective Corrosion coupons.a) A view of the corrosion coupon. it can be visually seen. Depending upon belt looseness. a) pen type tension gage and b) strain gage for bi-directional measurement g) Shaft run-out monitoring: When a lathe is being tested for accuracy. the position of the rubber ring on the graduated scale of the lower part indicates the belt looseness. that can be corrected if necessary. the inner part of the gage telescopes into the upper part. Objective Strain gages or other electronic instruments are used to measure the stresses in metallic parts or components. 8. Fig. On removing the gage. leaving the rubber ring stuck on to the lower part at the lowest point of insertion. a mandrel is fixed in the spindle and rotated and checked for the run-out. Subjective If the run-out is high.f) Belt tension monitoring: subjective Slightly pressing down the V-belt Aided subjective Pen type tension gage as illustrated below is a simple and handy one. Aided subjective - . Electrical resistance or eddy current test (ET). magnetic particle test (MT). A number of crack detection techniques have been developed to a great degree of advancement. Most serious failures are preceded by crack growth from a point of stress concentration or from a material defect at the surface of the component. 5. 9 Run-out checking by optical sensor h) Crack detection This is mostly off-line monitoring and most tests under this category form NDE tests. Objective Optical sensors as illustrated below can be used to check the run-out even at high speeds. vibration. visual. run-out. temperature. the primary function of ISNT specialists. the latter can be categorised as objective Since the purpose of this paragraph is to highlight crack detection as a condition monitoring techniques. Ultrasonic Testing (UT) and Radiographic test (RT). belt tension. Conclusion While only few types of monitoring namely. But this can be done by turning the spindle by hand or at low speeds. leak. the amount of run-out can be measured. a host of simple gadgets are being developed according to their specific use for many other monitoring functions that are not discussed here. and crack monitoring are discussed.By use of dial gages fixed on to the bodies. like dye penetration test (PT). Fig. While the first two of the following can be classified as aided subjective. corrosion. ******** . these NDE methods are only cited but not discussed further. and volume testing. it is known as stress testing. o The load is usually so great that error conditions are the expected result. o Load testing is performed to determine a system’s behavior under both normal and anticipated peak load conditions. o The term is often used synonymously with concurrency testing. although no clear boundary exists when an activity ceases to be a load test and becomes a stress test. o It helps to identify the maximum operating capacity of an application as well as any bottlenecks and determine which element is causing degradation.MAINTENANCE ENGINEERING(ME1012) LOAD TESTING o Load testing is the process of putting demand on a system or device and measuring its response. in order to test the system's response at unusually high or peak loads. reliability testing. o Load testing is a type of non-functional testing. o There is little agreement on what the specific goals of load testing are. NPRCET/MECHANICAL 22 . software performance testing. o When the load placed on the system is raised beyond normal usage patterns. NPRCET/MECHANICAL 23 .Wear Debris Analysis . Using this method. size and morphology. Instruments then reveal the elements contained. the mechanical failure mechanism and the time to eventual failure may be determined. the site. their proportions.MAINTENANCE ENGINEERING(ME1012) WEAR DEBRIS ANALYSIS Using a Scanning Electron Microscope of a carefully taken sample of debris suspended in lubricating oil (taken from filters or magnetic chip detectors). This is called WDA . 10. 8. What is wear debris analysis what are the three wear debris analysis techniques commonly used and compare their performance and uses? . (16) 4. 3. State the applications and limitations of thermisters.MAINTENANCE ENGINEERING(ME1012) UNIT-III CONDITION MONOTORING PART-A (2 Marks) 1. 11. Briefly explain the cost comparison with and without condition monitoring. What is thermal monitoring and what thermal monitoring are used in industries explain principle and uses of thermograph . (16) NPRCET/MECHANICAL 24 . Mention title applications of bimetallic strip. Name the types of pyrometers. State the advantages and disadvantages of condition monitoring. State the methods of measuring vibration. (16) 5. What is equipment health monitoring? 2. Write down the basic steps in condition monitoring. List down the key features of condition monitoring. 13. 12. What is condition monitoring and explain condition monitoring What type of condition monitoring are normally used in industry. What is leakage monitoring? Explain some of the leakage mediums used for condition monitoring. Mention the various costs involved in costing of condition monitoring mainly. 7. (16) 2. (16) 3. 5. Describe briefly pistol thermometer. PART-B (16 Marks) 1. What are three types of condition monitoring? 6. List down the features of RTD. Briefly explain various methods and instruments for condition monitoring. 9. 4.(16) 6. List down the factors for increasing the demand condition monitoring.
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