IME/04 Restri Restricte cted d Circu Circulat lation ion Onl Onl
MAINTENANCE PLANNING
Power Management Institute Noida
CONTENTS S.No.
Description
Page No.
1
Introduction Introduct ion to Maintenance Planning
1
2
Maintenance
13
3
Preventive Maintenance Maintenance
23
4
Predictive Maintenance
35
5
Design Features and Maintenance
43
6
Maintenance Management System in NTPC
48
7
Overhauling Philosophy
55
8
Time & Outage Period
72
9
Long Term Planning
80
10
Maintenance Planning System in NTPC
94
11
Spare Parts Planninq
118
12
Outage Planning
126
13
Maintenance Maintenance Contracts
130
14
Condition Monitoring
144
15
Condition Based Maintenance in NTPC Thermal Power Stations
148
16
Model Session Plan
152
INTRODUCTION Maintenance can be considered as a combination of actions carried out in order to replace repair, service (modify) the components of an industrial plant so that it will continue to operate to a specified availability for a specified time. Maintenance work raises the level of equipment performance and availability but at the same time it adds to more running costs. Hence, the maintenance management objective will be to achieve the optimum balance between these effects, i.e. the balance which maximize the department’s contribution to profitability. The planning provides the guidelines within which maintenance actions can be carried out. Before considering the procedure for determaining the ‘best’ maintenance plan, we see the “policies” which lays the foundation for it. There are a number of maintenance policies that can be specified individually or in combination for each unit of plant. The rationalized sum of such specified policies for the whole plant constitute the maintenance plan.
TYPES OF MAINTENANCE – POLICIES (a)
Fixed time maintenance (Individual or group replacement).
(b)
Condition Based Maintenance (continuous or periodic.)
(c)
Operate-To-Failure (corrective maintenance by repair to replacement).
(d)
Opportunity Maintenance
(e)
Design-out Maintenance.
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Fixed time Replacement or Repair This is only effective where the failure machanism of the item is clearly time dependent, the item being expected to wear out within the life of the unit. The total costs of such replacement are substantially less than those of failure replacement-repair i.e. replacing just before failure.
An attractive concept is that the proper time for performing corrective maintenance ought to be determinable by monitoring condition or/and performance, provided, of course, that a readily monitorable parameter of deterioration can be found. The probabilistic element in failure prediction is, therefore, reduced or eliminated and the item life is maximized and the effect of failure is minimized.
At the extreme complex replacement items, the sophisticated condition monitoring, e.g. vibration, shock pulse oil analysis, thermography can be used to great advantage. The cost of instrumentation may be justified by high repair and unavailability costs.
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Operate-to-Failure Operate-to-Failure Maintenance and Corrective Action No predetermined action is taken to prevent failure. Corrective maintenance arises not only when an item fails but also when indicated by condition-based criteria. The basic task is the esablishment of the most economic way of restoring the unit to an acceptable condition by (i) Rapid repair (ii) replacing with the reconditioned or new one. This type of system will work well if the decision makers, at their respective levels, have a thorough understanding of the plant for which they are responsible and provided with needed information, it is useful where no preventive maintenance is effective or desirable, the ‘item’ is operated to failure.
Opportunity Maintenance
This term is used for maintenance actions, taken after failure or during fixed time, or condition based repair, but directed at items other than those that are the primary cause of the repair. The policy is most appropriate for complex replaceable or continuously operating items of high shut-down or unavailability costs and typically, might take the form of operation to failure and specification of critical items to be dealt with that time.
Design Out Maintenance By contrast with the preceding policies which aim to minimize the effect of failure, design out maintenance aims to eliminate the cause of maintenance (failure). Clearly this requires engineering action rather than maintenance action, but is is often part of maintenance department’s responsibility. This is usually a policy for areas of high maintenance costs which exist either because of poor design or the equipment is being used outside its specifications thus designed condition monitoring helps and the choice is then between the cost of re-design or the cost of recurring maintenance.
THE DETERMINATION OF A MAINTENANCE PLAN The maintenance plan for a plant should be built by selecting for each unit, the best combination of the policies outlined earlier and then by coordinating these policies in order to make the best use of resources and time. Many factors affect selection of policy appropriate for each item, and this, together with the large number of items usually
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involved, gives rise to the need for some systematic procedure for determining the ‘best plant’ for a particular period of time.
CLASSIFICATION AND IDENTIFICATION OF EQUIPMENT This is important but usually tedious and difficult because of complexity and size. It is suggested that the classification into units and items should be based on replace ability and function. Identification is usually in some for m of numerical coding.
PLANT PERFORMING THE OVERALL FUNCTIONS Units
Performing major plant functions e.g. a compressor, vehicle
Non-replaceable (Vehicle Chassis) Replaceable complex
Items
(engine) Replaceable Simple (break pad)
Components
Individual Parts
COLLECTION OF INFORMATION Acquisition of all information which might be relevant to maintenance planning is essential for every unit. Equipments work, whether continuous or fluctuating.
a.
Manufacturer’s recommendations
Actions, periodistics etc.
b.
Equipment factors (which assists
Failure characteristics, repair time after
in prediction of maintenance)
failure before plant function affected; level of redundancy.
c.
Economic Factors
Consequences of failure, cost of replacement, item material cost, monitoring etc.
d.
Safety Factor : (Constraints on
Internal, environmental, statutory
decision)
regulations.
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2.
MAINTENANCE MANAGEMENT
Routine
Annual
Defect
Work
Management Management
Production
Maint.
Overhaul
Rectification
Request
Ratios
Calculations
WORK
INPUT
Work Complete
Define
Quality
Jobs
Control
OBJECTIVE
Effective Utilisation Of Resources
Measure Work
Issue Work
Schedule Work
*
Overall time and resources
*
Reduce plant outage
planning of the project
*
Reliable forecast
*
Scheduling of resources
*
Issue and work control
*
Improve resources Utilzation
*
Progress monitoring
*
Monitor accumulating
*
Assessment of productivity
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Target dates
Maintenance Cost.
5
SPECIAL ASPECTS OF MAINTENANCE OF THERMAL PLANTS The main objects of a Thermal Power Plant Maintenance Organisation is to ensure the greatest availability and reliability of the operating units at an optimum cost. Reliability is defined as the probability of the system or a machine unit performing its purpose adequately for the period of time intended, under the operating conditions encountered. A fairly high degree of reliability can be achieved by several means such as a mature design, which takes care of all possible operating variables and abnormal transients; (b) redundancy techniques which use dual elements in series such as dual valves in certain steam and water lines. (c) redundancy, by switchover by means of stand by equipment; (d) periodic marginal testing of certain types of equipment; (e) reliability specifications specify the requirements of spare parts to meet the most adverse operating conditions.
The means by which a maintenance manager can improve the reliability and availability of the equipment are :
(a)
By ensuring that the quality of maintenance work carried out is the best possible.
(b)
By ensuring that regular periodic inspections are carried out on the most vulnerable equipment and failure of which can result in partial or total shutdown of the operating units.
(c)
By specifying the correct quality of spare parts to meet the operating conditions.
(d)
By periodically reviewing the spares inventory to avoid a stock-run-out condition.
(e)
By ensuring that the lubrication schedules are adhered to strictly.
To Briefly Analyse tthe he above Requirements
Quality of Maintenance Work Maintenance work carried out on the different equipments must ensure that the design criteria like turbine wheel clearances, bearing and clearance sizes, expansion allowances etc. are restored to the original specified values. Any repairs carried out should take note of the cause of the wear and whether any means can be developed to
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abate the wear in order to prolong its life. It may be by a change in material, change in construction, or fabrication, change in design, change in operating practices or a combination of these. Welding technology has in the recent yeas advanced to such extent that there is no machine item which cannot be satisfactorily fabricated to give a long life.
Periodic Inspection This is where the greatest importance should be given to predictive maintenance is inefficient, work is done on an emergency basis without any planning, resulting, in inefficient utilization of manpower and excessive downtime of equipment. Preventive maintenance, though ensures the objectives of reliability, entails greater costs. But predictive maintenance ensures to extend the availability and reliability, eliminates unnecessary work and cost by usage of advanced scientific techniques. Equipment is run to a point just short of failure. The entire maintenance work is planned on that equipment at a suitably planned shutdown during that point. The concept used in this technique is that “similar equipment operating under similar conditions will have similar life-death curves and thus will have similar predictable maintenance requirements”. If the prediction is made correctly by statistical means this technique can obtain the maximum life from the machine. To make this prediction fairly accurate, some of the requirements are :(a)
Establish the maintenance requirements of all equipments.
(b)
Determine the optimum maintenance schedules.
(c)
Make data collection, storage and retrieval systematic.
(d)
Measure the maintenance efficiency.
(e)
Involve the craftsman in implementing the system.
There are many predictive maintenance instruments available in the market today – in our country as well as abroad – like vibration analysers, monitoring equipment, ultrasonic flaw detectors, leakage detectors, corrometers (thickness detectors for monitoring wear) ultrasonic flowmeters, shock tubemeter, gas chromotograph for transformer gas analysis etc. With the aid of these, the maintenance requirement and the time can be fairly accurately predicted.
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Maintenance Spares The specification of the maintenance spares items which have worn out or had premature failure must be studied in detail so that a better one aimed at giving a longer availability consistent with costs may be specified subsequently.
It is not merely enough to specify the item unless care is taken to check those specification when the material is received. Facilities are needed for this purpose by means of a testing laboratory attached to the plant or at least nearby.
Due to the import restrictions for the import of sometimes even critical spares, a greater need has arisen for the development of these items indigenously. But this process is not so easy and requires a great initiative and capability on the part of local manufacturer and co-operation from the buyer. It takes sometimes years to establish the usefulness of the indigenous substitute. The main bottlenecks in the indigenous development are :-
(a)
Non availability of certain types of alloy steels.
(b)
Certain testing facilities.
(c)
Exorbitant development costs.
Some technically less competent but enterprising manufacturers come forward to supply certain items at a lower cost compared to that of established manufacturer’s, who are not very keen on developing certain items for which there is not a large annual demand. The use of these spares manufactured by such parties invariably lead to premature failures which sometimes prove very costly.
A properly maintained inventory control system should ensure against stock run out position at all times.
Lubrication Aspects Most of the operating and maintenance troubles with the rotating equipments can be overcome if the correct lubrication aspect is taken note of. Every component of the machine that needs lubrication, must have a lubrication schedule and that schedule must
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be adhered to and strictly implemented. The correct lubricant must be chosen for every type of application. The lubricant must be periodically examined and tested for decay sludge and oxidation etc. all of which will indicate the type of abnormally existing in that component. Also the tests will indicate whether the lubricant has completed its useful life and needs replenishment.
With the nature of maintenance work known, the actual job should be well planned break-up of the job contents should be made, resources analysed and then schedules made. In a complete unit overhaul the percentage survey should be made from the data available by performance checks, operating conditions and physical evaluation. This survey will reveal the quantum of work involved and will give a reasonable estimate of the job to be carried out based on this survey, the materials required for repair and replacements should be listed out and ordered for timely procurement. A detailed Gantt (Bar) Chart should be made identifying each major activity and the likely duration of the work, taking into account the resource available. A thorough inspection should be carried out immediately after the shutdown of the machine to ascertain the abnormalities and find out whether the scope of the work is more or less the same as what has been made in the earlier survey. Sometimes the work may be more also. This inspection will indicate the vital critical areas where the resources need to be mobilized and optimized. After complete mobilization of resources, a detailed PERT programme should be made to ascertain the critical activity and slack activities. This will enable to control the progress of the outage work and optimization of resources as the job progresses. A constant review should be made to ensure that the job progresses as per schedule. Network can be made for large turbo-generator overhauls in order to optimize the resources and complete the overhaul in time.
In a thermal plant, the main areas of maintenance on boiler are the fuel burning equipment, ash handling equipments, soot-blowing system and the auxiliaries which handle corrosive gas and erosive dust particles. Turbo-generator maintenance is again based on predictive methods and performance checks during operation. The major repairs and maintenance is normally in the boiler.
The fuel burning equipment consists of the coal silos, feeders, pulverisers, exhauster of primary airfan (as the case may be), P.F. Pipes, burners, air registers need to be thoroughly overhauled during the boiler overhaul which is governed by statutes. The pulverisers, exhausters and feeders should be periodically inspected according to the statistically predicted lives so that the parts are replaced just in time. Light load periods
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and weekend outages should be made use of, as far possible, for this purpose and also for carrying out preventive maintenance.
Ash handling equipments equipments need maintenance maintenance because of the highly erosive nature nature of ash. Items like ash conveyance mains, branch and hopper gates, ash pumps need to be inspected periodically to ascertain their performance.
A thorough check of all pressure parts during a boiler overhaul will reveal all abnormalities like internal corrosion external corrosion and erosion. Steam impingement due to soot blowing steam should be guarded against.
Air heaters, especially of the lyingstorn type, need thorough overhaul during unit outages; the corroded elements must be replaced, the seals must be adjusted properly and the caring should be made free fr om leaks.
The drafts fan must be thoroughly inspected periodically to check any corrosion or erosion and necessary precautionary measures should be taken. Weekend outages can be utilized for the inspection of ID Fans, Dust collectors and Air preheaters in a planned manner.
In turbo-generator overhaul, again a thorough inspection is carried out soon after dismantling to find out may abnormalities.
(a)
All high pressure parts like turbine blades, nozzle blocks shrouds, flange bolts, stop vale and control valve bolting, control valve stems, rotor etc. must be subjected to ultrasonic test to detect any flaw. Casings must be subjected to dye penetration checks at every change in cross section to reveal any cracks.
(b)
Wheel clearances, bearings – sleeve and thrust – their condition and clearance, alignment etc. must be checked properly and must be restored to manufacturers specification.
(c)
All the control mechanisms, governing system and protective devices must be thoroughly overhauled and set to the recommended values.
(d)
The turbine oil system must be checked and oil analysed to ensure that is good for resume.
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(e)
The insulation specifications must be strictly adhered to in order to avoid any undue differential expansion and the consequence thereof.
In all the jobs listed above, continuous research and development is possible to improve the life of the components. After all, a chain is only as strong as its weakest link. Even if one component in an equipment has a very poor life, the availability of that equipment becomes limited to that extent. The cause of every failure should be studied whether it is because of corrosion, erosion, vibration, overheating, poor workmanship, improper material etc. With certain improvements in materials, the life can be definitely improved and a good workmanship can ensure the reliability. Continuous research will enable to improve the design. This is where the ‘TEROTECHNOLOGY’ comes into the picture. This is defined as “Insulation, Commissioning maintenance and replacement of plant machinery and equipment and of feed back to operation and design thereof and to related subjects and practices”. This comprises of systems approach of multi-disciplinary engineering and management facets and includes the designing out of maintenance. Modern plant of recent times is engineered to automatic operation of several components and is designed in such a manner that a large regiment of competent engineers and techniques are required to maintain it to give optimum results.
One of the causes of poor design is traced out to lack of practical knowledge and poor orientation of the plant designers. Emphasis is always laid on the performance design of the equipment but the dewings for easy maintenance (known as maintainability of the plant) have been absent. The only way of eliminating the trouble is to study the failures and to redesign the plant and incorporate modifications to eliminate or minimize the frequently occurring breakdowns due to faulty design. Theses changes must be communicated to the manufacturer/designer so that he can take care of the same through such feedbacks and incorporate them in the subsequent designs. Core organization carrying out such feedback is GETSCO who is always in touch with the uses of their equipment and periodically advise them about the expected troubles which might have been encountered by one of their clients. This enables the other users to incorporate the precautionary measures to overcome that trouble. It is hoped that similar feedback systems are being developed by our Indian Manufacturers like BHEL and HE(I)L which will enable the units to operate at a high availability.
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AIMS & OBJECTIVES OF MAINTENANCE Broadly the objectives of maintenance are as follows :-
(a)
To maintain plants and equipments at is maximum operating efficiency ensuring operational safety and reducing down time.
(b)
To safe guard investment by minimizing rate of deteriorating and achieving this at optimum cost through budgeting and control.
(c)
To help management in taking decisions on replacement or new investment and actively participate in preparation of specifications, equipment selection, its installation and commissioning.
(d)
Implementation of suitable procedures for procurement of spares, consumable etc. and to control their storage conservation and consumption.
(e)
Development of resources for equipment and spares promotion of suppliers by technical help and import substitution.
(f)
Running of captive workshops for repairs and reconditioning.
(g)
Manpower Planning, recruitement, training and development of skilled workforce and officer cadre.
The Short Objectives of Maintenance are: (a)
Reduce Plant outage time.
(b)
Make best use of resources.
(c)
Maintain work quality.
For achieving these we need to examine our requirements. In a thermal power station the maintenance ranges from a pattern of breakdown maintenance coupled with annual overhauls to meet statutory and other requirements to more elaborate schemes of preventive maintenance and detailed planning of major overhauls.
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INTRODUCTION Rapid development of a country calls for a creation of increased power generation capacity on an exponential rate. But present economic conditions characterized by the difficulties on account of inflation, unfavorable balance of payment, shortage of investable resources and unemployment, necessitates that our strategy should be not only to increase the installed capacity but to make optimum use of generation capacity already created. It is in this context maintenance assumes greatest importance. Maintenance is therefore, vital to the power generation activity. It not only calls for a high degree of technical acumen but also a great benefit from the co-operation and experience of operators and engineers. So for effective maintenance well defined objectives are necessary.
TYPES Maintenance can be classified broadly as:-
a.
Running Maintenance or Routine Maintenance.
b.
Breakdown Maintenance.
c.
Diagnostic or periodical Maintenance
Routine Maintenance can be sub-divided into
i.
Preventive maintenance
ii.
Scheduled maintenance
Preventive Maintenance It is carried out on each of the sub-assemblies of the unit in turn and comprises of repetitive jobs like lubrication, changing of fast wearing parts etc. Preventive
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maintenance is a process of eliminating emergency repairs. It involves thorough inspection of plant items, which may or may not directly affect plant output. The time of such inspection is judged by analyzing the plant history records. The advantages of such analysis are:-
a.
It allows for systematic planning of maintenance works; and
b.
It eliminates the operating lossed by reducing machine idle hours.
Scheduled Maintenance It is carried out at predetermined fixed periods with the works planned in advance and is scheduled with due regard to maintenance and availability of other stations in the grid. It also covers the statutory inspection and maintenance of equipment under the Boiler Act and Factory Act.
Breakdown Maintenance The timing of the individual job can not be foreseen in this case. Restoring the equipment back into operation speedily is the over riding consideration here and procedures are designed to expedite rendering of such services.
Diagnostic or Periodical Maintenance Major overhauls, inspection etc. which are done when indicated by monitoring of plant performance. This is called capital maintenance and is carried out at periodical intervals of two or three years depending upon the type of the equipment and its usage.
GUIDELINES TO SELECTION OF MAINTENANCE POLICY Let’s face it, machine break down – Production management must provide for this eventuality in a way that maintains the reliability of the production system at reasonable levels without “going broke” just keeping machines running. We are faced with another problem of attempting to strike a balance between cost factors. When machines break down, these kinds of costs occur, machine down time and possible loss of potential sales, idle direct and indirect labour delays in other processes that may depend for
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material, supply on the machine that is down, increased scrap, customer dissatisfaction from possible delays in deliveries, and the actual cost of repairing the machine.
We can view the problem as one of maintaining the reliability of the entire production system. In general this reliability r eliability can be maintained and improved by:-
a.
Increasing the size of repair facilities and crews so that average machine down time is reduced because maintenance crews are less likely to be busy when a breakdown occurs.
b.
Utilising preventive maintenance where practical parts are replaced before they fail. It is often possible to do this on second and third shifts and, thereby, not interface with normal production schedules. Whether preventive maintenance is worthwhile or not depends on the distribution of breakdowns and the relation of preventive maintenance time to repair time, as we shall see.
c.
Providing for slack in the system at critical stages so that we have parallel paths available. This means excess capacity so some machines can be down without affecting the delay costs to any great degree.
d.
Making individual components within a machine or the machines within the system more reliable through improvements in engineering design. For example, special lubrication systems may be used that may extend the life of working wor king parts.
e.
Decoupling successive stages of the production system by inventories between operations. The resulting independence of operations localize the effect of breakdown, so operations proceeding and following the machine that is down are less likely to be affected.
To accomplish increased reliability by any of these means is costly, therefore, we can justify it only in so far as the costs of attaining it are offset by cost reduction in idle labour, scrap, lost business, etc. Number 4 may be regarded as an engineering design problem coupled with economic analysis. Number 5 interacts with problems of layout and inventory control. Below is discussed the approaches to these problems which can guide maintenance policy.
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BREAKDOWN THE DISTRIBUTIONS Breakdown time distribution data are basic if we hope to be able to formulate any general policies concerning maintenance. Break down time distributions show the frequency with which machines have maintenance free performance for a given number of operating hours, and are ordinarily shown as distributions of the fraction
of
breakdowns that exceed a given run time. Breakdown time distributions are developed from distributions of run time free of breakdowns, such as Figure 2, Figure-3 shows three breakdown time distributions. These distributions take different shapes, depending on the nature of the equipment with which we are dealing. For example, a simple machine with few moving parts would tend to break down at nearly constant intervals following the last repair. That is, exhibits minimum variability in breakdown item distributions. Curve of Figure-2 would be fairly typical of such a situation. A large percent of the breakdowns occur at the extremes. If a machine were more complex, having many parts, each part would have a failure distribution., When all of those were grouped together in a single distribution of the breakdown time of the machine for any cause, we would expect to find greater variability because the machine breakdowns could occur shortly after the last repair or any time. Therefore, for the same average breakdown time T a, we would find much wider variability of breakdown time as in curve ‘b’ of Figure 2.
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To complete the picture of representative breakdown time distributions, curve ‘C is representative of distributions with the same average breakdown time ‘T’, we would find much wider variability. A large proportion of the other hand, a large number of machines have a long running life after repair. Curve ‘C’ may be typical of machines that require ‘ticklish’ adjustments. If the adjustments are made just right, the machinery may run for a long time; but it is not, readjustments and repair may be necessary almost immediately.
FIGURE – 3
In models for maintenance, we normally deal with distributions of the percentage of breakdowns that exceed a given run time, such as in Figure 3. They are merely transformations of the distributions of free run time typified by those in Figure 2. Taking curve ‘a’ of Figure 2 as an example, we may convert it to the breakdown time distribution of curve ‘a’ in Figure 3 in the following way. It the vertical scale of Figure 2 is converted to the percentage of breakdowns that occur instead of the frequency of breakdowns, we can then easily plot the percentage of breakdowns that exceed a given run time. First, we know that all the breakdowns or 100 percent, exceed an average run time of zero. To
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obtain curve a in Figure 3, we simply subtract successively the percentages that occur at different free run times. We can see by examinations of Figure 3 that almost 60 percent of the breakdowns exceeded the average breakdown time ‘Ta’ and that very few of the breakdowns occurred after 2 Ta.
In practice, actual breakdown time distributions can often be approximated by standard distributions, three of which are shown in Figure 3. Curve ‘b’ is actually the exponential distribution which we discussed in connection with waiting line theory. From this point, on our reference will be to the breakdown time distributions would be accumulated as distribution of the frequency of free run time as in Figure-2.
PREVENTIVE
MAINTENANCE
VERSUS
REPAIR
(SINGLE
MACHINE) Let us assume a preventive maintenance policy which provides for an inspection and perhaps replacement of certain critical parts after the machine has been running for a fixed time. ‘Tm’ to accomplish the preventive maintenance cycle. A certain proportion of the breakdowns will occur before the fixed cycle has been completed. For these cases the maintenance crew will repair the machine, taking an average time ‘T s’ for the repair. This is the repair cycle. These two patterns of maintenance are diagrammatically shown in Figure 4. The probability of occurrence of the two different cycles depends on the specific breakdown time distribution of the machine and the length of the standard preventive maintenance period. If the distribution has low variability and the standard period is perhaps 80 percent of the average run time without breakdowns. ‘T a’ actual breakdown would occur rather infrequently and most cycles would be preventive maintenance cycles. If the distribution were more variable, for the same standard preventive maintenance period, more actual breakdowns would occur before the end of the standard period. Obviously, shortening the standard period would result in fewer actual breakdowns and lengthening it would have the opposite effect for any distribution.
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BREAK DOWN
% that of Std. Period is of A verage mtc free down time.
FIGURE - 5
Assuming that either a preventive maintenance or a repair put the machine in shape for a running time of equal probable length. More (6) has shown that the percent of machine running time depends on the ratio of the standard maintenance period and the average run time. ‘T a’ for the breakdown time distribution. Figure-5 shows the relations of the percent of time that the machine is working and the ratio of the standard period to average run time ‘T a’ for the three distributions of breakdown times shown in Figure-3. Note that, in general when the standard period is short, say less than 50% of ‘T a’ the machine is working only a small fraction of time. This is because the machine is down so often owing to preventive maintenance. As the standard period is lengthened more actual breakdowns occur which require repair. For curves ‘b’ and ‘c’ this improves the fraction of time the machine is running because the combination of preventive maintenance time and repair time produces a smaller total down time.
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Curve ‘a’ however, has a peak in it, or an optimum preventive maintenance period which maximize the percent of machine working time. What is different above curve ‘a’ / it is based on the low variability breakdown time distribution from Figure 3. For curve ‘a’ lengthening the maintenance period beyond about 70 percent of ‘T a’ reduces the fraction of machine working time because actual machine breakdowns are more likely. For the more variable distributions of curves ‘b’ and ‘c’ this is not true because breakdowns are more likely throughout their distributions than they are in curve ‘a’. Comparable curves can be constructed showing the percent of time that the machine is in a state of preventive maintenance and the percent of time machine is being repaired because of breakdown (6).
GUIDE TO A PREVENTIVE MAINTENANCE POLICY Some generalizations about preventive maintenance policy can be made through the concepts we have developed. First, preventive maintenance is generally applicable to machines with breakdown time distributions that have low variability then the exponential, curve ‘b’ are in this category. The reasons is that low variability means that we can predict with fair precision when the majority of breakdowns will occur. A standard preventive maintenance period can then be set which anticipates breakdowns fairly well.
Equally important, however, is the relation of preventive maintenance time to repair time. If it takes just as long to perform a preventive maintenance as it does to repair the machine, there is no advantage in preventive maintenance, which has the effect of reducing the amount of time that the machine can work. In this situation, the machine spends a minimum amount of time being down for maintenance if we compare the percent of the time a machine is working when repair time is greater than preventive maintenance time and when the two times are equal. Both curves are based on the lowvariability distribution curve of Figure 3. Note that curve ‘d’ exhibits on optimum, but curve ‘a’ does not. For curve ‘e’, the percent of time that the machine works continues to increase as the standard maintenance period is lengthened which result in more repairs and fewer preventive maintenance cycles. Clearly, there is no advantage in preventive maintenance when ‘T m’ = ‘T s’ from the views point of maximum machine working time. To sum up at this point, preventive maintenance is useful when breakdown time distributions exhibit low variability and when the average time for preventive maintenance is less than the average time for repair after breakdown.
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The Effect of Down time Costs: Can modify the conclusions just just stated, however, suppose that we are dealing with a machine in a production line. If the machine breaks down, the entire line may be shut down, with very high idle labour costs resulting in this situation, preventive maintenance is more desirable than repair if the preventive maintenance can take place during second or third shifts, vacations, or lunch hours when the line is normally down any way. This is true even when T
m
= T s. The determination of the standard preventive maintenance
period would require a different, but similar analysis in which the percent of machine working time is expressed as a function of repair time only, since preventive maintenance takes place outside of normal work time. An optimal solution would be one that minimised minimised the
total of down time costs, preventive maintenance costs, plus
standard preventive maintenance periods and to justify making repairs more quickly (at higher cost) when they do occur, job would not speed it up.
FIGURE - 6
In such cases, total down time might be shortened by overtime on multiple shifts and weekends, with attendant higher costs. Optimal solutions would specify the standard preventive maintenance period, the machine idle time, and the repair crew idle time, striking a balance between down time cost and maintenance costs.
A special case exists when sales are such that the plant must operate at full capacity to meet demand. Under circumstances, reduced machine working time due to repair and preventive maintenance reduces the number of units that can be sold and, therefore,
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affects income. Optimal maintenance policy is then even more heavily weighed in favour of shortening standard preventive maintenance periods and pouring in more effort to repair machines quickly when break-downs occur. Morse has developed basis models which fit this special case in which an income less maintenance cost function is maximised.
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INTRODUCTION Total maintenance planning embraces all activities to plan, control and record all work done in connection with keeping an installation to the acceptable standard. This includes Preventive Maintenance and Corrective Maintenance, Breakdown Maintenance, Periodic Overhaul, Planned Replacement, Spares Provisioning, Workshop functions, Repair Policies, Plant History Compilation, Plant Modification to facilitate maintenance of spare parts etc. In a fully controlled situation only, the time spent on emergency work is ‘unplanned’ and this could well be less than 10% of available man hours in the Maintenance Department. The three basic requirements of a Planned Maintenance System are :
a.
A Programme of maintenance activity for Plant and Equipment.
b.
A method of ensuring that the programme is fulfilled.
c.
A method of recovering and assessing results.
In order to have systematic maintenance programming and scientific way or recording the plant performance data for analysis, the BRADMA system for Preventive Maintenance is being followed at Badarpur Thermal Power Station.
The System Facilities a.
Reduction in breakdown/down time by carrying out scheduled Preventive Maintenance and thereby increasing the productivity and life of the Plant.
b.
Systematic and timely manpower and material planning thereby curtailing the overall Maintenance cost. In addition, the analysis of the systematic documented performance data of the plant will enable to have an idea of works requiring modifications and special attentions.
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Forms and Methodology In order to have systematic compilation of the performance data of the Power Station equipments and systematic preventive maintenance scheduling, certain forms have been designed. In all there will be 9 forms, all listed below, to start with the system individual forms are described and represented in the f ollowing pages :
a.
Plant Data Card.
b.
Running Hours Record Card.
c.
Breakdown Job Card.
d.
Plant Performance Card.
e.
Annual Preventive Maintenance Schedule.
f.
Preventive Maintenance Inspection Record.
g.
Preventive Maintenance Progress Schedule.
h.
Default Report
i.
Breakdown Information Slip
Plant Data Card Each equipment has its separate card. Similar equipments, say six I.D. Fans in the Power Station have only one card. The card will contain Information about equipment specifications, manufacturer and its catalogue No. & purchase order reference etc. The reverse side of the Card has information regarding Equipment Assembly, Drawing Number, Lubricant details and Spare Parts specification details etc.
Running Hours Record Card Individual Equipment have its separate Card for logging its Running Hours. This Card contains information about Monthwise Running Hours, Cumulative Running Hours since
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last maintenance, Cumulative, Total Running Hours, Idle Hours, Breakdown Hours and Type of Maintenance Due and Done. The Card is printed on both sides. Each Card has 2 years Running Hours Record for the equipment.
Breakdown Job Card This Card contains information for :
a.
Nature of Breakdown
b.
How rectified
c.
Assembly wise Hours spent for breakdown on the equipment. In the reverse of the Card, it contains information about Reporting Time, complete Repair Time, Down Time, Main-hours and Cost Details etc. Each breakdown has a separate card.
Plant Performance Card This Card contains information regarding Number of Breakdown and the time spent on breakdowns on a particular equipment during a month and also year wise. Each card has information for 8 years. On the reverse of it, it has yearwise record of assembly wise breakdowns and total maintenance cost details etc. Each equipment has separate card.
Annual Preventive Preventive Maintenance Schedule Schedule This Form contains yearly information about monthwise breakdown numbers and time spent on breakdowns, type of maintenance when due and done, and cumulative Running Hours after Maintenance. Space has been provided for six equipments in one sheet. Information of identical equipments irrespective of the Unit is recorded for analysis in this sheet.
Preventive Maintenance Inspection Card This card has information about the points to bee checked, periodically to the Preventive Maintenance and Advance Intimation Ticket. On the reverse of the card it has
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information about the man and Material and Period spent details. Each Equipment has a separate Card for individual periodically.
OBJECTIVES Breakdown Job Cards Provides at a glance :
a.
Major Assembly wise breakdown Data for each plant item.
b.
The frequency of such breakdowns.
c.
Generation time lost due to such breakdowns.
d.
Down time of individual items because of Breakdowns.
e.
The importance of each composite part of the item based on the above factors.
f.
Down time of individual items because of breakdowns.
h.
The importance of each composite part of the item based on the above factors.
From the above data, priorities, nature and frequency of PREVENTIVE MAINTENANCE JOBS for each assembly of every item can be determined on a very objective basis, as also Cost Data of each Breakdown.
Plant Performance Cards : A complete behavioural pattern of the Equipment is available for a number of years to make managerial decisions like major overhauls, replacements, purchase disposal etc. Data available to prepare PREVENTIVE MAINTENANCE PLANTS and PROGRESS, YEAR WISE comparative analysis of Cost Data of PPM and Overhaul.
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ANNUAL PREVENTIVE MAINTENANCE SCHEDULE a.
Provides an Annual Programme for the Maintenance Division for the job to be carried out at every week for the whole year.
b.
Provides the type of maintenance, i.e. A, B, C or D based on the Number of Running Hours of the equipment.
c.
Gives at one glance not only the Maintenance Plan for the year but also the work done at any given time during the year, like jobs, not done, jobs pending to be done, number of breakdowns and the Man and Machine Hours lost.
d.
A basis for revising and Maintenance Schedules for the coming years, rescheduling of the programme etc.
PREVENTIVE MAINTENANCE INSPECTION RECORD
Advance Intimation Intimation Ticket / Maintenance Maintenance Job Card
a.
To ensure that the Maintenance Staff’s time is not lost in planning and the Machines are made available by providing an Advance Intimation to the operation Department to spare the Equipment.
b.
To provide specific type written instructions for all the Maintenance Jobs to be done.
c.
To fix responsibility for any lapses.
d.
To work out the cost of the Maintenance Spares etc. for each Maintenance Job done.
e.
To programme SPARES Procurement Plan.
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Preventive Maintenance Progress Schedule a.
To instruct the Maintenance Department the details of Equipment that are to be serviced during the week / month.
b.
To provide an effective written Reminder system.
c.
To enable the Maintenance Division to programme proper Man power Planning.
Default Report a.
To help the Department to keep a watch on those equipment that are not serviced so that at the time of next servicing more attention is paid.
b.
To analyses the reasons for the programme NOT being carried out.
c.
A follow up system against possible overlooking of Maintenance of critical items.
d.
To enable top management to know the exact position of overdue maintenance jobs in the plants.
e.
To enable the Management to take timely corrective action, when programme are not followed either by re-scheduling the plan or endorsing stricter control.
Breakdown Information Slip This contains information about the nature of breakdown, reporting and completion time of the breakdown on a particular equipment. All slips are in triplicate serially numbered and bound.
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BADARPUR THERMAL POWER STATION BREAK DOWN JOB CARD
Detailed Report of Work Done Time taken & Initiates ---------------------------------------------------------------------------------------Equipment Ref.
:
Information Slip Ref. : -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Nature of Break Down -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------1. Rotor 6. Frame & Foundation 2. Stator 7. Cable & Cable Box 3. End Shields 8. Power Circuit 4. Fan 9. Control Circuit 5. Bearings -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Hours spent for breakdown Total Hrs. MTCE on equipment -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Equipment No. Location Date 1 2 3 4 5 6 7 8 9 10 Man M/C
Ball Cleaning Cleaning Motor 1-3 1-3 - 4 – M
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PREVENTIVE MAINTENANCE INSPECTION BOARD BADARPUR THERMAL POWER STATION (To be Returned By Control Room to Maintenance In charge) -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Week No. Week Commencing -----------------------------------------------------------------------------------------------------------------------------Badarpur Thermal Power Station TO CONTROL ROOM
Advance Intimation Ticket
Following Equipment is required for Maintenance as per Schedule shown S.E. (O) S.C.E -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------The above Equipment: From Day / Date …………. Hrs…………… Will be available for Maintenance To Day / Date ……………. Hrs. …………… -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Week No. Week Commencing ----------------------------------------------------------------------------------------------------------------------------Maintenance Job Card ----------------------------------------------------------------------------------------------------------------------------Check ( ) it OK – Mark Mark (X) if further Repair needed needed -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------INSPECTION LIST
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Names / TKT Nos./Grades
STARTED COMPLETED Man Hrs. M/C Down Remarks ---------------------------------------- ----------------------------------------------------- -----------Spent Time spent Date Time Date Time -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Spares and Consumables Used
Cost of Total Initial -----------------------------------Spares Cons. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Additional Notes
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BADARPUR THERMAL POWER STATION
P.M. Progress Schedule
For the Month ……………………….. ………………………..
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Code Cat. Trade Type FreqRunning ESTD Week Man M/C Remarks No. of uency Hrs. Hrs. work Done Date Hrs. Down MTCE ---------------------------------------------- ---------------------------- Spent Time 1 2 3 4 Start Finish --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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BADAR THERMAL POWER STATION PLANT PERFORMANCE CARD -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Year 1981 1982 1983 1984 1985 1986 1987 1988 TOTAL -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Month B/D H rs. B/D H rs B/D H rs B/D H rs B/D H rs B/D H rs B/D H rs B/D H rs B/D H rs ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- April May June July August September October November December January February March -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------TOTAL -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EQUIPMENT DETAILS SPECIAL NOTINGS --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Equipment
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Location
33
BADARPUR THERMAL POWER STATION DEFAULT REPORT
Code No.
Type of FreqRunning Eat. Over due Remarks Maint. Uency Hours Hrs. Since ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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Cat.
Trade
34
INTRODUCTION With advancement advancement of modern science and technology, dynamic dynamic problems concerning concerning machines and plants, designed for optimum weight and requirements are becoming increasingly important. It is not just enough, if machines are looked after through preventive maintenance alone, but predictive maintenance is also as essential for smooth running of machines and plants without causing unexpected breakdowns, thus endangering both life and economy. There is a remarkable parallelalism between machines and human systems. Periodic testing of blood, blood-pressure heart pulse rate etc. goes a long way to predict forthcoming dangers and thus prevent health failures. A similar technique will help to predict potential machine failures, well ahead of a breakdown. These are general observational techniques changes. This technique has been found technically feasible as an effective tool for predictive maintenance. Quite a deal a work has been put in this area particularly in U.S.A. and material published. Unless recorded extensive data is available about malfunctioning of a machine or a plant operating under varied conditions, it will not be possible to pin point the source of trouble. Since it may be a costly affair to try-out such tests on costlier machines and plants, it would be better they are done on models through simulation techniques. In the succeeding prographs this and other observational technique including signature analysis are briefly discussed with regard to their application, utility and limitations.
Simulation Techniques Model study has been a major tool in design. An intensive Model-study is required for studying or preparing models in order to apply the results obtained on them to the prototypes of the actual systems. Models Models are broadly classified under under iconic, analog and symbolic.
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SIGNATURE ANALYSIS Introduction As people responsible for maintenance of power plants – whether it be a steam turbine used in power generation or a gas turbine used on the aircraft – we are aware of the need for periodic strip of the unit for repair replacement of worn components. Our maintenance objective in this context is two fold. One is to achieve the maximum life on the units between scheduled strips. The second is to detect in time any signs of failure while the power plant is running to its scheduled life so that a shut down or major disaster can be avoided. With the increasing cost of power plants and their idle time, the observational techniques available to ensure their continued serviceability is being greatly expanded. Some of these techniques require basic provisions to be built into the unit for observation such as tapings for parameter measurement or boroscope holes to view internal component conditions. Others have been developed on the basis of data already available. One such later technique is Signature Analysis.
What is Signature Analysis ? Signature Analysis is truly an age old technique. Our primitive fore fathers made use of foot prints to track down animals while hunting in the forest. In aircraft maintenance, we use this technique to track down sick or potentially sick engines on the basis of their parameter plottings. It is been estimated that nearly 44 percent of machinery problems appear as vibration problems. This may be true for a particular type of plant, but in general, this is true with respect to most of the machines and plants. The machinery signature analysis is a sophisticated and detailed technique of using machinery vibration to aid in the detection of developing failures. Within critical processmachinery. Through a good vibration amplitude and pattern history in addition to a history of regular thermodynamic performance checking, provide plant engineering and management personnel with the data they need, to decide if preventive maintenance by expensive inspection is immediately required. The main task in this type of analysis consists in transducing machinery vibration and noise and converting them on to a frequency, domain graph, thus showing important
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frequencies attributable to particular events. No doubt this technique requires sophisticated instrumentation and it may be generations before, we adopt this to every plant in this country. Maintenance, preventive maintenance and predictive maintenance are the three stages, every engineer has to understand well to know the limitations and scopes. Signature analysis is on the horizon as a significant tool of potential. In the near future it may well develop the capability of pinpointing early internal abnormalities before damage results, thus permitting optimum repair scheduling. A data bank cataloging all vibration and noise changes w.r.t. all the variables will help the future signature analysis work, since much of the effort depends upon relating subtle vibration-pattern changes to previously identified vibration causes. The figure below shows a schematic diagram of the implementation.
IMPLEMENTATION OF SIGNATURE ANALYSIS
A.
Caution Signal
B.
Experts Attention
C.
Automatic cutoff of power.
The diagram helps in detecting a fault before a defined limit of severity has reached with the help of secondary effects viz. Signatures, generated in the system in running conditions. Observations relevant to signature analysis may lead to detection of
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malfunctions of various components, such as windings of a transformer or turbo generators, rotors, bearings gears and foundations. Signature, as already said are varied in nature like vibe rational, acoustical, thermal and/or chemical. Charts providing limits and tolerance are available for different type of machinery for different capacities. All these will help to a greater extent, but one should regard the technique ‘signature analysis’ as intuitive and derived from experience.
Applications and Newer Newer Techniques In recent times the technique of signature analysis is effectively used for predicting both machine component failures as well as overall machine or plant malfunctioning. As already pointed out many of the troubles result in excessive vibration and noise. These, therefore form powerful signatures in the diagnosis. A brief account of the technique applied for various machines are illustrated below:
Machine Components a.
Bearings Rolling element bearings, which are inherently more noisy than slider bearing have tendency to fail by fatigue rather than wear out. This is due to the contact load being very high between balls/rollers and the race. The local defects, generate impacts periodically when ball or roller rolls over it. These are more or less shock pulses and contain not only the low frequency components but also high frequency ones. By detecting the latter, through special instruments like shock pulse meters (developed by SKF), one can assess the magnitude of damage. By mounting the sensors close to the bearing, right from the beginning of operation will help to trace the history. There are also different techniques to detect bearing malfunctions in operating machinery like spectroscope or radiographic analysis of the oil contamination, measurement of oil temperature and overall noise level. However these techniques do not fore-warn the occurring danger. Impulse signatures are more effective and reliable in such cases. One advantage of vibration analysis is mathematical modeling and analysis is possible incorporating various malfunctions. Slider bearings operating under different lubrication principles and lubricant, are known to produce different forms of vibration like oil Whirl or whip, half frequency whirl, sub-harmonic, resources etc. For many of these, stability analysis is possible and the working range can be monitored to prevent such oscillations, which will result in machine failure.
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b.
Gears A pair of properly operating gears running at constant speed and load can be expected to generate a signal which is periodic with the meshing frequency. The signal can be sound, vibration, stress and strain or something else and all the machine events are similar when there are no mechanical imperfections in gears. Characteristic wave form depends on gear-profile, load speed, sensor and many other parameters. It is very difficult to calculate. However, certain predictions can be made about the perturbations resulting from both local (cracked or deformed teeth, securing etc.) and distributed (non-uniform load distribution) defects. These distributed defects may be symmetrical or non-symmetrical. A gear condition monitor which has been built as a jet engine diagnostic system, pre-processes the signal by band-pass filtering and wave form averaging to isolate one gear signature from the total signal sensed extremely on the gear box housing. The extracted wave form may then be analysed automatically for the local or distributed defects.
c.
Rotors Generally rotors form a major contributor for troubles in machinery due to their inherent unbalance, their behaviour to certain self excited and parametric excited type oscillations. Etc. All these have studied intensively and norms established to identify the causes. Sensors can detect the limits of vibration and indicate immediate attention. As a result of all this balancing techniques both in field and in plant have been developed to prevent unexpected shutdowns.
Machines a.
Pump Systems: Systems: Both reciprocating and rotary pumps generate repetitive signatures which can be extracted from background noise with signal averaging, performed so that speed vibrations are tracked by the processing system. A failure analysis made at at Esso Refineries, Bombay showed the the following:Bearing Failure
37 percent
Mechanical Seal Failures
28 percent
Packing Failures
28 percent
Long Preventive Overall Pump
22 percent
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It is, therefore, necessary for any machine or plant to establish about a knowledge of failures of various mechanism and components. As one can see the pump failures are essentially due to bearings and one should incorporate predictive sensors for this purpose. b.
Machine Tools and Machining Processes The metal cutting action during machining generates characteristic mechanical signatures which can be used to automatically detect low level tool chatter or cutting edge wear without stopping the machine for visual inspection. This capability is of great importance in developing adaptive machine tool controls. Sonic signals indicate the extent of cutting wear. An analysis of vibrations generated by the cutting processes will help monitoring cutting edge wear. Through understanding the nature of sound profiles of cutting edges as they go from sharp to dull, one could evolve new and improved cutting tool materials, tool holders and cutting-edge-geometries. In general the overall machine tool design may be improved. Electronic mechanical systems have been developed which utilize sonic signals to detect the degree of cutting edge wear in metal working tools and automatically trigger a cutting edge change. A packaged electronic unit reads out sonic vibrations from and instrumented machine tool work piece cutting tool system to determine degree of cutting edge wear during a turning out. At a predetermined comparative sonic ratio, the electronic unit commands stoppage of the machine tool feed, retraction of the tool and automatic index of the cemented carbide inser to the next good cutting edge. The latter function is usually performed by a proto-type mechanical device. Sensors may be suitably mounted to record both high and low frequency components. The low frequency band either for a s harp or a worn cutting edge may be more or less the same. However, the high frequency band for a worn one is considerably higher than for a sharp one. These high frequency vibrations are indicative of magnitude of wear. An adaptive control is therefore possible to detect wornout tool by making energy to the low frequency one. The sonic signals from a given cutting tool machining a work piece, at given cutting conditions may change distinctly from machine to machine. There may be some correlation between these sounds and cutting tool performance, which
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would imply that a basis exists for the development of improvements in machine tool design. c.
Transformers Transformers (oil cooled) and Turbo-generators (hydrogen cooled) are both considered. Discharges or local overheating inside the transformer often lead to decomposition of the insulating oil, generating hydrogen, light hydrocarbons and carbon oxide, as insulation comprises mineral oil and cellulose materials. Buchholz-gas collector relay, based on this fact, cannot respond to all forms of breakdown at an early stage. All gases generated by insulating decomposition are soluble in transformer oil. Hence oil is analysed. The magnitude of normal concentrations depends largely on the age and loading and so limiting values are determined by experimentation. The various gases that are observed are hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide. If two different gases exceed the concentration limits, a potential hazard is suspected. If the gas separated in the Buchholz relay is in equilibrium with the dissolved gases in oil, it indicates a gradual fault over a long period. So after rectifying it, oil is to be degassed eliminating false alarms due to oil saturated with air, fluctuating operating temperature, aging of insulating oil etc. On similar lines hydrogen used for cooling turbo-generators can be analysed periodically to get the chemical signatures of internal failures.
c.
Plants Signature analysis applied to plants like power plants (thermal, hydro or nuclear), steel or rolling mill plants, refineries etc. is really complex and needs elaborate instrumentation and trained manpower for effective control. As already mentioned, the signatures may be vibratory, acoustic, thermal or chemical or of various combinations. A central monitoring system to control the entire network is absolutely essential for quicker diagnosis. One of the estimates made by a large company in States under the programme MACE (Measurement Analysis Corporation Engineering) showed an investment of about 85,000 dollars on instrumentation alone. This investment proved to be economical in the long on compared to the annual maintenance and breakdown costs. Most of the problems connected with turbo-machines are understood today and the r emedies known. Vibration sound, temperature or pressure sensors could be installed permanently and using a telemetry system, signals can be used to indicate the operating conditions of the plants. Proper use of signatures analysis techniques on large machinery is certainly not an easy task, since there are may variables that may change through the normal operation. For a programme to work, it is
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necessary that the controlling element to able to act on critical signals and disregard extraneous data that will be accumulated. Figure below shows a signature analysis system for controlling turbo-machinery operation.
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INTRODUCTION There is growing tendency to relegate maintenance activity to a secondary role in system operation and management, particularly in the current situation of power and energy shortages. The effort is generally directed towards making machines run as long as production demands dictate, with the lurking hope that the machine will behave themselves as a self-sustaining organism. While such an attitude tries to satisfy the immediate requirements, it inhabits a more enlightened and fruitful approach to the world of machines and physical systems.
Maintenance activity cannot cannot be considered as merely merely a breakdown service. It is rather a predictive, diagnostic and corrected function to prevent system incapacity in the first instance. It is therefore a comprehensive activity in the nature of equipment management and not restricted to only those conventionally designated as maintenance function.
EQUIPMENT MANAGEMENT
The close relationship between system design, system operation and system maintenance is amply highlighted in the basic concept of the equipment management function. This function, as any other function, is best defined in terms of its objectives. These are basically : -
i.
To preserve the system against any impairment to its potential in terms of its design capability and optimum service life.
ii.
To keep the system continuously available to perform up to its design capability with the degree of reliability for which it is designed.
The management function must attain these objectives within the constraint of total cost which includes plant investment cost, operating costs and rehabilitation costs. These costs can be categories categories into : -
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a.
Direct costs or actual financial expenditure on the initial plant and on repairs and rehabilitation.
b.
Indirect costs as determined by system non-availability over the period when it is actually required for service.
The basic and interdependent factors that govern total maintenance cost optimization are therefore the initial system specification, quality of plant design and construction and equipment downtime, whether for preventive or breakdown servicing.
EQUIPMENT DETERIORATING AND DESIGN SAFEGUARDS The behaviour of machine systems is governed by fairly well defined cause effect relationships. To this extent their physical state and capability are largely predictable. It is, therefore, possible to slow down equipment deterioration that takes place with time, if sufficient cognizance is taken at the system design, stage, of the process that lead to such deterioration and to ultimate failure.
a.
Wear & Tear Material attribution cannot be altogether eliminated. It can however be slowed down in the interest of saving the costs of spare parts as well as the outage time for the replacement of parts. The three process which basically contribute to material loss are friction, erosion and corrosion. Friction can be minimized by designed the lubricating system for correct lubricating pressures, through pump selection pipe and valve sizing and system layout oil quality must be ensured by providing appropriate conditioning equipment. Abnormal deterioration of bearings can very well result from inadequacies in the lubrication system. To minimize erosion, it is necessary not only to optimize selection of wear resistant materials, but also design the system for lower fluid velocities through tube spacings, pipes, valves, pumps and fans. Frequent replacement of pumps internals, due to cavitation conditions and erosion, can be attributed to improper design of the pump suction system. Excessive coal mill wear calls for selection of mill type, size and materials of construction suited to the characteristics of the available coal. The phenomenon of corrosion calls for a design effort aimed basically at reducing corrosion rates. Selection of materials resistant to chemical attack and galvanic action, application of appropriate protective coatings,
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provisions of cathodic protection and design of environmental control have to be decided at the engineering stage of an installation.
b.
Fatigue Metal properties change with time under cyclic conditions of service, resulting in deterioration of system components. Frequency of component failures and the need for replacement can be minimized if duty conditions are realistically assessed appropriate materials of construction are selected for each component and its application. For this exercise, the designer takes resource to established material test data, statistical information on failure modes and history of service experience.
The system engineer supplements the design optimization by providing monitoring and protective systems through instrumentation and safety controls, to protect components from being stressed beyond their capability limits.
Outage time for replacement of components can be minimized by incorporating plant design features that reduce preventive and breakdown service time and enhance system maintainability. These include adequate work space and access around equipment, selection of equipment designed for optimum maintainability, appropriate material movement systems and effective workshop facilities.
SYSTEM CONCEPT AND DESIGN FOR PLANT AVAILABILITY AND RELIABILITY The modular concept of system engineering facilitates enhancement of plant availability and reliability. This approach recognizes the inevitability of material deterioration in service and the need for component replacements, but exploits and potential of a system to sustain through a structure of alternative modules.
System configuration, sizing of system components and provisions of standby and bypasses are optmised to provide and degree of system maintainability that is required. The principal governing in this optimization are the reliability level and service life of each component and the availability factor which is specified for the system. The designer must therefore be armed with sufficient statistics on the characteristics of each system component and also on the environment which the system is to perform. A classic
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example of the influence of component reliability on system design is the engineering of the boiler plant. Up to the early 50’s the then prevailing boiler reliability and its uninterrupted service capability dictated use of a bank of similar sized boiler units to serve a single turbine-generator. With the advances in boiler plant technology, such an arrangement is now no longer considered either economical or essential for system maintainability.
The above philosophy extends to each of the sub systems of the plant and their respective components, for ensuring overall a system security. Its primary objective is to permit timely rehabilitation of deteriorating components with minimum disturbances to system performance. It must however, be recognized that system and component reliability is a cost factor, impinging on the equipment purchase philosophy of high first cost versus low first cost purchase. Hence the need for optimization of the maintenance function on a total cost basis.
SYSTEM PRESERVATION FOR OPTIMUM SERVICE LIFE A system no matter how well designed for availability, reliability and maintainability, needs to be protected from abnormal deterioration that may result from misuse or maloperation due to operator ignorance or negligence. In addition to providing monitoring and alarm devices at strategic points in the system, the designer incorporates automatic controls and safety interlock to obviate operator actions that can lead to serious component damage or extended breakdown of the total system. The effort is towards localizing faults without jeopardizing the main system.
A comprehensive monitoring system for prompt recording and alarming of plant operating conditions is possible with the application of computers. The system can be engineered to log operational events and identify change of state of equipment with time. The on-line processing of the logged data by the computer facilitate reliable fault analysis, prompt identification of system deficiencies and timely servicing of the affected plant components. The facility therefore contributes towards extending plant running hours by optimizing outage rate for preventive or breakdown repairs.
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CONCLUSION In a developing country with severely restricted resources, its machine wealth represents an invaluable national asset which has to be diligently guarded against misuse and neglect. Machine systems should be designed to permit continuous monitoring of machine health, facilitate timely implementation of diagnostic and corrective measures and contribute thereby to higher system availability and reliability. This is essential if equipment management is to prove effective in securing both immediate and long term economic returns from the country’s c ountry’s limited machine wealth.
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INTRODUCTION Power being a basic infrastructure for economic growth. India’s Five Year Plans have given high emphasis for its developments at a very rapid pace. The installed power capacity in India in 1947 was in the region of 1100 MW which has now reached to about 42000 MW. This capacity is planned to be increased to 11000MW by the 2000 AD. To meet thee challenge of power shortage NTPC was formed in the year 1976 with an objective to plan, design, construct and operate coal pit head Super Thermal Power Stations with an aggregate capacity of about 13000 MW which is planned to be increased to 56000 MW by the year 2017 AD. This will be approx. 25% of country’s total power production at that time.
The power plants being set up by NTPC would comprise large power generating units of 200 & 500 MW of capacity. To keep pace with the recent developments in technology, NTPC is using sophisticated equipment and instrumentation for effective operation of the Units. Investments on high technology high value equipments are to be justified by an effective maintenance which is yet to emerge as a vital management function in Indian Power Industry. The average availability of thermal power units in the country presently is as low as 65% which allows a capacity utilization of only about 50% in thermal units.
The down time of 200 MW unit in the form of revenue loss to the utility is as high as Rs. 20 lakhs per day and consequential loss in industrial, agricultural production is 12 to 15 times of this loss. Equipment availability of 85 to 90% and capacity utilization of around 70% in thermal units is considered well within the realm of feasibility, provided effective and scientific maintenance management systems are developed and rigidly followed. Keeping high availability as the basic objective NTPC has tried to develop and implement an effective maintenance management system in all NTPC thermal power stations. The broad features of this system are highlighted in this article.
DEVELOPMENT OF MAINTENANCE MANAGEMENT SYSTEM IN NTPC NTPC, since its inception had recognized the need of acquiring professionalism in the © PMI, NTPC
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management of power industry for reliable service to customers and has made all possible
efforts
to
standardize
certain
systems
in
Engineering,
Construction,
Commissioning, Project Management, Finance Management, Personnel Management, Materials Management, etc. Implementations of these systems have paid rich dividends in the form of early completion of projects and commissioning of 200 MW units within record time. The units have also achieved full load operation in shortest possible time with appreciable economy in fuel oil and other inputs.
A similar approach has been conceived to manage the operation and maintenance of running power stations of NTPC and achieve a sustained capacity utilization. In the ares of maintenance, an effective system known as ‘Maintenance Management System’ for NTPC has been developed. The system has been received in consultation with experts from British Electricity International (UK) and finalized as suitable for Indian conditions.
Objective The Maintenance System for NTPC has been developed and introduced with following objectives :
i.
To maximize plant availability.
ii.
To minimize maintenance cost through optimization of resource utilization.
iii.
To create safety in work, equipment and environmental.
IMPLEMENTATION STRATEGY The departure from a crisis dominent maintenance culture to the acceptance of data based computerized maintenance was no easy task. From perception of concept to development and its actual implementation, a considerable degree of commitment and input of human resources was needed.
Accordingly 270 mandays training was imparted to NTPC engineers at UK and about 1500 man days of British experts were invested at Singrauli Super Thermal Power Station. Besides this, about 25,000 man days were utilized by the Station and formal work orders, daily planning meetings and present work procedures have been introduced
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to improve the commitment of every individual to achieve reduction in unproductive supervision.
The estimation of mean failure rates, mean repair time and utilization factor of maintenance work force also have a built in feature of accountability at the craftman level which in turn provides sufficient opportunity for maintenance executives to concentrate on engineering problems and development development of expertise in the relevant discipline.
SYSTEM The Maintenance Management System has been development based on work control and feed back concept in which all maintenance activities are predetermined with its standard inputs like work instructions, manpower, tools, spare and estimated completion time. For the purpose of effective work control system, ‘Equipment’ forms the basic maintenance unit. The power station is classified into various systems, sub-systems and equipments. Data regarding man and material are identified for maintenance of each equipment and on job specification cards.
The system has been designed to regulate the total quantum of work in a manner that maintenance work load remains uniform throughout the cycle of year and utilization of available resources of optimum.
WORK CONTROL The concept of work control envelopes all the maintenance activities accrued in the power plants. Normally the maintenance jobs are originated by preventive maintenance of routine nature, defects leading to break downs, major overhauls and statutory inspection, modifications to overcome manufacturing or design defects. All such jobs are reported on Work Order Cards and sent to a centralized place known as Work Control Office where these are scheduled in accordance with the priorities. The priority of the work is defined by the operation engineers who have to play an ownership role. The role of priority is also defined as emergency (E), second priority (A), third priority (B), and the last priority (C). The manning of maintenance of round the clock which undertakes maintenance in accordance with 2,500 mandays by Corporate Core Group in the development, standardization, training and extension of system to various other Super Thermal Power Stations of NTPC.
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About 200 executive were given in short term training at Korba / Ramagundam / Delhi by British experts and their NTPC counter parts for the appreciation of the maintenance management philosophy and actual system. The process of training has become a regular feature at the intake level and as well as at the middle management level. Sr Executives are appraised of the implementation status of the systems during Operation and Maintenance conferences periodically at the Corporate Centre and Projects. Such conferences are attended by the Members of Board, Regional Directors along with senior level Managers responsible for operation and maintenance of NTPC power stations.
One of the major problems encountered during the initial stage of system implementation was to identify the various functional elements of maintenance and define the role of planning vis-à-vis engineering. The following functions were identified :
•
Identification of equipments.
•
Identification of known defects and work procedure.
•
Trouble shooting and Engineering Analysis.
•
Actual Supervision.
•
Identification of resources and their mobilization for maintenance.
•
Documentation and Retrieval system.
The engineering function like trouble shooting, methods and resource identifications have been entrusted to area engineers where as planning, resource mobilization and documentation functions are entrusted to maintenance planning engineerings. engineerings. The maintenance planning cell has an additional responsibility of condition monitoring and spare parts planning which are essential inputs to an effective maintenance. A long term working philosophy has been imbibed to groom the sense of responsibility at grass root level. The stipulated defects reporting system through the pre-scheduled commitment made by the respective area engineers, planning and operation engineers in daily planning meetings at least 24 hours in advance. Under the accepted system, an
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arrangement of permits for work, spares and resources are organized in advance which are listed in the work specification specification already designed designed to attend any any kind of maintenance maintenance work.
The jobs of emergency nature are immediately attended by the maintenance crew, however, jobs which are deferred, waiting for the unit shut down or major overhauls are separately stored. The day to day jobs of routine and breakdowns are planned by the short term planning group and major major overhauls and unit outage details details are planned by the long term planning group. The long term planning group is also responsible for the development of systems in accordance to the Corporate Policy in association with Core group stationed at the Corporate Centre. A small maintenance contract, condition monitoring and spare part planning group is also associated with the long term planning cell.
For 1000 MW plants, 11 executives and 5 non-executives are engaged to develop and operate the system
For work specifications, the area engineers are drawn from respective department for a fixed duration to prepare the work specifications and their indexing.
WORK SPECIFICATIONS The work specification is a step by procedure of trouble shooting and undertaking a complete maintenance work. These specifications have all the relevant information regarding type of craftsman required, estimated time for each activity, tools to be used, spares, engineering details like clearances, set values and other details along with safety procedures to be followed. Whenever a requisition for a maintenance work is raised, a copy of these work specifications is given to the crew members for ready reference. The preparation of work specifications has been the most difficult task, as about 12000 different specifications had to be prepared by the respective area engineers deputed in planning during the course of system development at Singrauli STPS. Copies of these specifications are now transferred in a phased manner to other power stations of NTPC for their guidance. Some of the work specifications are running into 20 sheets. To impress further, about 200 Sq. mtr. Floor area was required to accommodate various lateral filing systems which has at least 6 tiers in each cabinet.
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PLANT HISTORY SYSTEM Initially a manual system for equipment maintenance history has been developed as an interim arrangement. However, a computerization programme is in hand to store the data for easy entry and retrieval. Under the existing system different cards have been designed to register, plant inventory, details of spares and history. These cards are presently stored in the bin cardex.
Plant Inventory Card All the major items of equipment in the plant have been listed out during codification work and the PLANT INVENTORY CARD prepared for each equipment contains engineering details, specifications and name of supplier of the equipment. The Plant Inventory Card is kept in Maintenance Planning Cell.
Spares List Card The equipment contain number of spares. These spares are entered in SPARES LIST CARDS for each equipment which includes the specifications and the relevant drawing number. This card also contains population and inventory level to be maintained in Central Store. Purchase action is initiated by stores department as soon as the minimum stock is reached. However, for slow moving items, the purchase indent is raised by concerned maintenance department, depending upon the requirement.
Equipment History Card A history card is maintained for each equipment, which contains data of commissioning, initial alignment and vibration reading of the equipment. Subsequently up dating is done by recording major breakdown and any modification carried out on the equipment.
In the long run, equipment card helps in technical audit and analysis of the failure pattern of an equipment and initiation of corrective action.
PREVENTIVE MAINTENANCE AND LUBRICATION SCHEDULE It is prepared for all equipment with the objective of :
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a.
Monitoring the plant items i.e. wear and tear of parts.
b.
Preventing its untimely failure e.g. by ensuring that the plant item is properly adjusted and that its lubrication is satisfactory.
c.
Taking the plant item out of service at times.
Out of 52 weeks in a year, preventive maintenance scheduling has been prepared considering only 48 weeks and remaining 4 weeks have been kept free with no schedule for preventive maintenance work. The free work identified are the 13 th/26th/39th / and 52 and during these weeks are arrears in preventive maintenance work are carried out, work taken out from the 2 weekly, 12 weekly, 24 weekly and 38 weekly preventive maintenance cycles. Accordingly preventive maintenance schedules are prepared from itemized maintenance sheet and the standard work specification are attached by planning schedule for giving guidance to the foreman for doing particular job.
The work orders for preventive maintenance and lubrications are to be raised by planning which are including in the daily work schedule known as “Committed Work Plant”. Since this is recurring activity at a fixed interval, the scheduling of preventive maintenance is done with the help of computers. Computerisation of these schedules has helped in eliminating slippages and reducing the time and energy needed from planning efforts. The print out of preventive maintenance schedules are sent to thermal power stations every fortnightly and station’s planning cell return them after entering the actual work done. The data are reprocessed in accordance with the actual work done and schedule for future work is generated in a regular basis.
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INTRODUCTION Power plant operation requires uninterrupted performance of generating systems to optimize its capacity utilization. NTPC, with its present installed capacity of 2720 MW, is planned to increase the installed capacity it to about 56000 MW by 2017. The power generating units, mainly comprising of 200 & 500 Mw capacity, shall use sophisticated equipments and instrumentation. The average availability of thermal power units in the country is presently of the order of 655% and plant load factor around 50%. However, an availability of 80-85% and plant load factor around 75% has been considered to be well within the realm of feasibility, provided scientific maintenance management systems are developed and implemented effectively. NTPC POWER PROFILE
FIGURE - 7 Investment in high technology and high cost equipments is justified only with optimum utilization of power generating units, which can be ensured by the efficient operation and maximum availability. The objective of maximum availability of power generating units inturn means low down time. The increased equipment reliability and low down time can
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be achieved by an effective maintenance management system, which has to emerge as a vital function in a prime power industry like NTPC. PERT net work and bar charts are in vogue in most of the power stations in the country and the planning process of unit outages starts a month or two prior to shut downs. Due to lack of systems support often the planning becomes in isolation and individual approach of outage execution prevails. The success of planning shall be, in its being of continuous in nature supplemented by scientific techniques available to budget the outages with optimum resource level. NTPC, with the objectives of ensuring maximum plant availability and minimum maintenance cost through optimum resources utilization and safe work conditions, has already, accepted a system approach to maintenance management. The auxiliaries which have redundancy, shall have to be periodically attended under a routine or preventive maintenance programme. However, main equipments e.g. steam generators, turbo generators, transformers, and their auxiliaries will be overhauled and maintained depending upon the duty conditions, statutory requirements, availability of resource level and governed by the maintenance philosophy of NTPC. The objective is to introduce a uniform approach for all the power stations of NTPC in evolving their long term maintenance projections and standardize a system to conduct unit overhauls and long outages for major repairs in a planned manner. The daily generation loss to the station due to outage of a 200 MW unit shall be in order of Rs. 18 lakhs (@ Rs. 0.50 per unit and 75% PLF) whereas outage of a 500 MW unit shall cost about Rs. 45 lakhs per day. Therefore it is essential that unit overhauls are meticulously planned to control the outage duration. Stress has been laid to detail out the entire planning process of unit overhauls and long outages for major repairs. It is envisaged that entire outage planning has to start about 18-24 months before unit goes off load. The proposed planning system entails to following: a.
To project plans for major replacements during the life cycle of units.
b.
To develop five year rolling plans.
c.
to develop station annual plans.
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d.
To standardize the detailed planning of unit overhauls.
e.
To develop the system suitable for use with computer programme.
f.
To create a Standard Data Bank for reference.
g.
To interpose engineering judgement between computer programme output and the actual working team
h.
To establish equipment reliability trend and unit merit rating.
The proposed overhaul management management concept is aimed to achieve the following: a.
To reduce overhaul duration.
b.
To reduce duplication of engineering efforts.
c.
To improve definition of work content.
d.
To improve availability of spares and materials.
e.
To improve quality and inspection of maintenance jobs.
f.
To improve monitoring and reporting of overhaul progress.
g.
To improve the re-commissioning interface.
h.
To provide a record of work carried out.
i.
To minimize isolation restrictions.
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MAINTENANCE PHILOSOPHY OF NTPC The maintenance management system, based on the concept of total work control and feed back incorporates judicious planning of all maintenance activities to achieve uniform work load over the year with optimization of resource inputs. The overall objective of the maintenance philosophy is to revive the efficiency and reliability of the units as also to meet the statutory requirement. During the three O&M conferences, a working philosophy was evolved to provide policy guide line for the system development of maintenance management. management. The guideline also aims to stipulate an optimum duration and frequency of unit overhauls and is modeled to achieve the following objectives: a.
To maximize plant availability and reliability.
b.
To optimize maintenance cost.
c.
To create safety in work, equipment and environment.
The proposed policy guidelines are given below: The operation department of the power stations shall have an ownership role where as maintenance shall be a service function with advisory capacity. The maintenance plans shall commensurate to generation plans of the station. The engineering functions related to maintenance e.g. identification of equipments, spares and resources, trouble shooting, execution of job and quality checks shall be the responsibility of area engineer/maintenance engineer. The planning of work and resources, their availability and coordination, work scheduling and documentation shall be the responsibility of planning engineer. All the maintenance jobs jobs shall be executed and documented through work order card. The stations planning group shall develop preventive maintenance and lubrication schedules, of all the mechanical, electrical and C&I Equipments. It is envisaged that equipments having redundancy will be covered under the preventive maintenance
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whereas equipments which do not have standby will be clubbed with the minor and major overhaul. A periodic condition monitoring schedule of major equipments shall be developed by planning group. The signature analysis will establish the trend of machine behaviour and the predictions shall be incorporated in preventive maintenance and lubrication schedules. An operational change over schedule of stand by equipments while unit is in operation shall also be prepared in consultation with operation department. The definition of emergency maintenancy jobs (E) shall limit its implication for situations leading to hazard to human life or equipment or loss of generation. The maintenance jobs of other category shall be priority rated A, B & C as defined below and planned in advance of taking up the work. E.
The defects which immediately involve danger to life of the people, safety of the equipment, immediate loss of generation beyond 20 MW for 200 MW unit and 50 MW for 500 MW unit.
A.
The defects which if not attended attended within 72 hours may result loss of generation. generation.
B.
The defects which if not attended within 72 hours to one week will result loss of generation.
C.
The defect which does not have any significant effect on generation, availability or thermal performance. The concept of unit replacement shall be used, wherever applicable to reduce down time and the criteria shall be components having minimum life cycle. This concept involves the replacement of defective assembly/sub-assembly as a whole with a new spare unit to minimize the down time. The replaced assembly is revived in a planned manner and preserved as a spare unit for future use.
The concept of unit replacement can be progressively extended to turbine cylinders. The servicing or replacement of each module of turbine (HP, IP and LP cylinder) is under taken, one at a time so that outage duration of account of turbine overhaul is evenly distributed over the successive years and matched with the frequency and duration of boiler overhaul. This concept more popularly known as MODULAR CONCEPT although
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involves a high inventory level at initial stage is favorable for increased plant reliability and availability. A five year rolling plan, projecting the generation plans, unit outages and requirement of resources e.g. spares, material and finances, etc. shall be prepared by maintenance planning. The plan shall be updated every year for the duration of next five years. A station annual plan shall be prepared projecting generation targets, unit outages for maintenance, efficiency revival and to meet statutory inspections. The unit outages budgeted under the station, annual plan shall only be termed as “ Planned Maintenance”. Maintenance”. Maintenance planning group shall prepare a Life Cycle Plan with anticipated projections of major replacements of components/assemblies over the entire life cycle of the unit. The frequency and duration of planned unit outages shall be as f ollows:
Minor Overhauls 15 days outage at an interval of six months for inspection and maintenance on critical equipments and to meet statutory requirement.
Medium Overhaul 45 days outage for 200 MW unit at an interval of two years for overhauling of boiler and its aux, revival of unit efficiency and to meet statutory requirements. The proposed duration for 500 MW unit is 60 days.
Major Overhaul 60 days outage for 200 MW unit at an interval of four years for overhauling of boiler, turbo generator and auxiliaries and revival of unit efficiency. The proposed duration for 500 MW unit is 75 days. An engineering declaration for the Unit(s) to be taken for planned outage shall be prepared defining the objective of outage i.e. projected jobs to be taken up and anticipated expenditure, the expected improvement in availability and revival in the unit efficiency after maintenance.
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The requirement of manpower during overhaul shall be met from internal resources to the extent possible. However, external resources can be sought under the following conditions: a.
When the required degree of expertise is not available.
b.
When the requirement of human resources is large over a short duration and cannot be met from available manpower at the st ation.
The maintenance cost shall be projected on the basis of feed back from work order cards regarding consumption of spares and materials, tools, and manpower together with generation loss. Maintenance costing shall be done by a costing engineer under maintenance planning group. Documentation of all major maintenance activities shall be done on equipment history cards, by maintenance planning. planning. For overhauls or major repairs cross reference of outage completion report or investigation report shall also be given in the history. The detailed reports shall also be preserved and available for reference. During any maintenance activity the responsibility of work progress, supervision, inspection, quality checks and successful recommissioning of the system under all circumstances shall be of area engineers/maintenance engineer of the station who in turn should be able to fix up the responsibility of every workmen/agency to execute the work with requisite skill and quality.
INTEGRATED OVERHAUL PLANNING
The cost of unit overhauls in terms of generation loss and resource requirement during the planned outage are very high and therefore, decision making process for overhaul of the unit has to be in an integrated manner.
The generation plan should have the provision for unforeseen outages like tube failure, breakdown and trippings on account of external reasons besides planned outages. The declaration of overhaul subsequent to any forced outage has to be avoided because of its undesirable affects on resource availability. With the commissioning of additional units
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to the grid such decision and declaration will upset overhaul plans of other units/stations and dislocate the overall regional plan. The inter-dependency of stations on the services from external agencies like BHEL and ILK, Central Maintenance & Overhauling workshop and power demands or Regional Electricity Boards, an integrated approach to unit outage planning is essential. The assistance of external agencies like BHEL, ILK and Central Maintenance and Overhauling Workshop, etc. can be better coordinated by projecting station’s 5 year rolling plan on their manufacturing and servicing schedule. This will also help in quick mobilization of resources like spares and manpower. The agencies can allocate their facilities and resources to match with the requirement of specific unit of particular station and can generate aggregate aggregate resources to meet meet the overall requirement of the regions. regions. The various regional electricity boards functioning under Central Electricity Authority have to plan the generation of their region. NTPC regional plans for major overhauls and station location plans have to be made supplementary. To this effect a four tier planning system has to be evolved as follows:
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a.
Regional 5 year rolling plan.
b.
Station life cycle plan
c.
Station 5 year rolling plan.
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d.
Station annual location plan.
REGIONAL 5 YEAR ROLLING PLAN NTPC Corporate Centre and Regional Offices would like to have a realistic projection of power generation throughout the year. The sequence of unit and planned outage has to be such that there are minimum number of units under overhaul at any point of time and NTPC commitment to regional grid will largely depend on the effectiveness of these outage plans. It is proposed that NTPC regional plans should be evolved in conjunction with the regional electricity boards. NTPC regional plans for all the station in a region are to be drawn so that capacity outage is spread uniformly throughout the year and matches with the regional grid demand. (Figure-8). These plans shall have projections of five years and reviewed updated every year to project the assessment for the next five years in a rolling manner. Such a rolling plan should be able to project following information: a.
Expected power demand of the region.
b.
Expected generation by individual station of the region.
c.
Total expected generation level inclusive of addition to installed capacity.
d.
Capital investment and revenue budget.
e.
Station merit rating based on efficiency and economics of generation.
STATION LIFE CYCLE PLAN Stations have to develop a major replacement plan of all the generating units for the entire life cycle of 25 years. Such plans will indicate a trend of replacement in the equipment/parts which are likely to fail before the life expectancy of the entire unit such as super heaters, reheaters, high pressure valves, safety valves, gear reducers, ash disposal lines, slurry pumps, chemical piping, resins, conveyor belts and drives, coal crushers, turbine rotor blades, turbine bolts, feed pump rotor, HP heater coil, HT motor,
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transformer, switch gears, cables, etc. These replacement plans have to be conceived on the basis of the following:
a.
Coal quality.
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b.
Creep life of various components.
c.
Duty conditions.
d.
Wear rate.
e.
Behavioural trend of plant equipments.
f.
Plant history
A typical life cycle plan has been given in Figure-9 for reference.
STATION FIVE YEAR ROLLING PLAN The effectiveness of overhaul management shall largely depend on the system approach and accuracy of assessment forming the basis of 5 year rolling plan developed by each station. Stations will develop a 5 year rolling plan for overhaul of all the units, and update every year for next five years. These plans will be developed on the basis of followings: a.
Expected generation of individual units of the station
b.
Total expected generation of the station committed to regional grid.
c.
Unit merit rating based on heat rate and economics of generation.
d.
Feed back on wear and tear of plant and equipment.
e.
Feed back on plant incipient problems, expected action for correction and revival in performance/efficiency as its result.
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f.
Financial scheme for justification of heavy expenditure with better plant availability and efficiency.
g.
Plant engineering status report.
h.
Resource availability.
i.
Fuel cost.
j.
Generation cost.
k.
Capital investment.
l.
Revenue budget.
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Figure No. – 10 shows the part of the typical rolling plan only indicating date of overhauls. These plans have to be supplemented with the text to explain each and every point given above.
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STATION ANNUAL LOCATION PLAN Station annual location plans are the detailed account of operation and maintenance of the proceeding year and plans for the next year. The objective of this plans is to identify all the constraints to achieve the generation level and organize resources for effective operation and maintenance. It is envisaged that station will prepare the review of preceding year and identify all the major activities to be undertaken next year. The plan shall incorporate the following: a.
Generation budget.
b.
Fuel budget.
c.
Manpower budget.
d.
Spares budget.
e.
Revenue budget.
The overhaul plans will form the part of these annual location plans which will give the history of each unit, key problem areas and modifications to be carried out in the following years. The plans will include discussion about the resources like spares, manpower, special tools and tackles and services required from outside agencies. The annual location plan of the station will include details as given below with a text to explain various points:
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a.
Annual planned generation of individual unit of the station.
b.
Annual total generation of station as committed to grid.
c.
Unit merit rating based on its performance in the last one year.
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d.
Wear and tear trend of major components and equipments of each unit.
e.
Justification for heavy expenditure with better unit availability and reliability.
f.
Resources availability.
g.
Fuel cost.
h.
Generation cost.
i.
Revenue budget.
The Figure 11 shows a time schedule for preparations of station annual location plan.
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TIME FOR OVERHAUL The selection of time of overhauls though dependent on several factors, is the best when grid demand is minimum or can be supplemented by other sources such as hydro-plants. The period from August to November may be ideal for unit overhaul, however it is difficult to complete the overhauls of all units within the period. The various factors influencing the selection of time areas follows: a.
Station generation plan and its commitment to grid.
b.
Actual grid demand and peaking requirements.
c.
Plant condition.
d.
Unit merit rating.
e.
Resource availability.
f.
Low outage cost.
Unit merit rating is decided on the basis of its availability performance & reliability over the past years and the cost of generation excluding fuel cost. Since cost of fuel is governed by Government pricing policy from time to time cost of heat input may not be considered as the criteria for merit rating. It is anticipated that by 1991 NTPC shall have an operating capacity of about 7000 MW comprising of 200 & 500 Mw units. The overhauling of NTPC units shall affect the capacity outage by 15-20%. Considering SSTPS (5x200 + 2x500 MW) as typical case, it is estimated that in 1991 about 225 days of outage shall be required by 200 MW unit & 150 days of outage for 500 MW unit to undertake unit overhauls and to meet statutory requirement which shall cause an average capacity reduction of the station by 16.5% (350 MW approx.) throughout the year (Figure-12).
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The above loss of capacity on account of overhauls & statutory requirements alone will result into revenue loss of Rs. 40 lakhs (approx.) per day @ Rs. 0.50 unit) or about 150 Crores (approx.) per annum to the super thermal power station of 2000 MW. Besides the serious financial implication, availability and plant utilization factors are likely to be impaired to meet preventive & routine maintenance and thereby affecting forced outages. The decision for taking the unit for overhauls should therefore be governed carefully for optimum utilization of available resource with uniform work load over the year and strictly adhered, to avoid disruption of plans of other units/stations. An effective maintenance management system can uniformally distribute the workload by careful selection of outage frequency and optimize the utilization of available resources.
OUTAGE DURATION The outage duration shall be deemed from the day unit goes off load for the overhaul till it is resynchronized. Since unit overhauls are to be accomplished within the given time schedule it is essential to identify the objective of shut down and define each maintenance work/activity in detail and arrange matching resources. The duration of different types of nit planned outages is defined and it is aimed to contain the unit overhauls within the stipulated time schedule. All necessary inputs shall be planned and arranged at appropriate time so that the outage is not extended beyond the planned duration thereby disrupting generation as well as resource availability plans of other units, stations and the region. The duration of overhaul shall be governed by the f ollowing factors: a.
Work quantum.
b.
Working pattern.
c.
Resources availability.
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Work Quantum The clear details & accuracy of assessment of the work quantum anticipated to be taken up during the outage is essential to avoid last stage additions leading to shortages or non-availability of resources thereby stretching the outage duration.
Working Pattern
The outage duration shall be fixed on the basis of execution of work whether on all the week days including Sundays/Holidays or not, and daily working hours.
Resource Availability
On the basis of anticipated work load an accurate & detailed projection of requirement of resources, manpower & skill, spares & material, tools & plants etc. should be made and steps taken to ensure their timely availability.
SCOPE OF WORK In order to contain the duration of overhaul, it is essential to anticipate each and every work desired to be undertaken during the overhaul with clarity. These jobs should be enlisted on the basis of f ollowing: a.
Standard work required for statutory inspection
b.
Jobs pending for want of unit shut down.
c.
Jobs arising as a result of system modifications for plant betterment and safety requirement.
d.
Jobs proposed to be taken up on the basis or monitoring of equipment behaviour.
The entire unit has to be divided into sub-areas for the purpose of defining the area of responsibility and each job should be clearly enlisted in consultation with the concerned area in-charge and any last minute additions should be avoided.
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WORK CALENDER It is essential that all the days falling during the span of overhaul should be examined and list of holidays, weekly off days worked out. A decision should be taken in advance whether the maintenance activities will continue on holidays or not and the duration of overhaul planned accordingly. The stipulated duration given in Section-1.3.14 in inclusive of holidays falling within the period of overhaul.
WORKING PATTERN The requirement of work force and duration of outage shall also depend upon the number of working available for overhaul on each day. Thus a decision regarding continuation of maintenance activities for number of working hours (8/12/16 or 24 hours) on each working day should be taken and communicated to all concerned. The intimation has to be be given to the external external agencies also to be agreed upon by them to ensure its eff ective implementation.
INTEGRATED RESOURCE ANALYSIS Once the time of overhaul is determined and quantum of work to be executed as well as working pattern is decided the analysis of resource requirement, its availability and optimum utilization is of prime importance. Any situation leading to non-availability improper utilization or scheduling of resources may have a compounding effect on the plans leading to extension of outage duration or compromise in work quality.
HUMAN RESOURCES The job to be done departmentally and through external agencies are classified based on the availability of manpower. The assessment of requirement of manpower in quantity and quality is essential for different types of work Planned. P lanned. The movement of working crew fr om one job/equipment to another is also planned.
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SPARES & MATERIAL RESOURCES On
the basis of repair and maintenance maintenance jobs jobs planned planned the assessment of spare parts,
consumables & materials, etc. is done. Their availability at station is checked and for the short fall procurement action is initiated to ensure timely availability.
TOOLS & PLANTS The requirement of general & special tools, machines, e.g. cranes, material handling & transportation, welding generators, compressor etc. as decided to be required and/or supplied to external agencies is established and their availability in working condition should be assured during the period of overhaul.
ALLIED SERVICE FACILITIES The station should assess the requirement of other facilities such as fabrication, manufacturing & workshop, radiography & stress relieving, photography etc. during overhaul. In house or external agencies as necessary s hould be tied up for the same.
GENERAL AMENITIES The station should assess the requirement of general amenities to large work force engaged during overhauls such as accommodation & kitchen, toilet, crèches, drinking water, tea, dispensary & medical facilities, stores & office cubicals for contractors etc. and make suitable provisions for the s ame.
SYSTEM SUPPORT The success of any planning activity shall depend on the faith, association & cooperation and the effective coordination among different groups/departments. Each individual has to work individually as well as jointly with dedication to achieve the objective. Planning is a continuous process and should not be considered absolute. Initial failures should not be demoralizing and efforts to combat their recurrence should be termed as innovation. Lack of appreciation at initial stages should not discourage and deviate the institution of planning towards short term gains, instead taken as a challenge.
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The station management should therefore provide all necessary infrastructure & system support to achieve its objective of maximum generation & optimum maintenance through the institution of planning. Indian boiler regulations originally promulgated in 1923 was subsequently modified in 1950, 1962, 1969 & 1980. The basic intent of these regulations has been to ensure safety of personnel and equipments due to failure of pressure and firing parts of the boilers.
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In the last three decades, there has been a considerable advancement in the design, manufacture and control technology of high capacity steam generators, and due to the
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prohibitive cost of outage, there is an increased awareness on the part of owners to go for stringent quality assurance measures from manufacturing stage to erection. The erosion rate of boiler tubes has been reduced by incorporating low fuel; gas velocities through improved design, use of wear resistant, material and higher tube thickness. There has been a major break through in the water chemistry, flue controls and other online monitoring instruments to conduct fail safe operations of high capacity and high pressure boilers. The sophisticated water treatment and monitoring techniques such as on line silica analyzer and pH meter to ensure the drum internals and other heat transfer elements free from any corrosion or scaling. The inherent features of furnace safeguard supervisory system e.g. drum level and furnace pressure trips, use of electromatic safety valves in addition to spring loaded safety valves and other advanced control systems for boiler trippings under adverse operation ensure safety of personnel, pressure parts and firing equipments. Besides above, NTPC boilers are continuously monitored through Data Acquisition System and have capability to display and log any deviation of the operating parameters. In Western countries like U.K. & West Germany the requirement of statutory inspection is stipulated after 30 months for a 200 MW size unit and 36 months for unit size of 500 MW and above. It is established that the effective installed capacity capacity of a 2000 MW size power station will be reduced by an average of 350 MW throughout the year on account of statutory inspections alone (Figure-12). According to annual statistics about 90% of 200 MW units of the country are reliably operating beyond the period of 18 to 24 months without any statutory inspections. In view of above it is proposed that NTPC should take up the matter periodicity of statutory inspection under the provisions of IBR which is far from the today’s relevance because of growing reliance on instrumentation & controls. This will enable NTPC to plan the major overhauls of its units in a more rational manner and step up its generating capacity and maintain the reliability of plants at the same time.
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The planning functions which help the unit to maintain its original level of performance in terms of output, efficiency and reliability and cater to long term needs of the station are considered under the Long Term Planning.
The following are the essential inputs for any successful planned system.
a.
Detailed and defined work activities.
b.
Standard work hour pattern and job duration
c.
Overall time for outage.
d.
Type of crafts men and skill required, their availability and productivity.
e.
Requirement of spares & consumables, tools & plants etc., their souce of availability.
f.
Mobilisation of resources within given time.
g.
Progress monitoring of work.
h.
Quality checks.
i.
Feed back system
j.
Budgets (Finance availability) availability)
For the planning projections to be close to actual, it is essential that feed back data of previous shutdowns/maintenance in quantified terms is available.
The successful execution of major repairs/overhaul will depend upon the easy and ready availability of resources based on the accurate information. LTP management therefore besides planning shall also serve as an information bank.
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RESPONSIBILITIES OF LTP MANAGEMENT Besides the function of serving as an information bank, long term planning shall have the following specifications.
Custodian of all the registration licences under IBR, IEA, Factory Act, Indian Explosive Act and their timely renewal/extension. renewal/extension.
Preparation of station’s life cycle plan for major replacement and renovation.
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Preparation of a realistic annual outage plan considering work load and availability of resources including finances.
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Accurate assessment of resource e.g. manpower, spares & material, tools & tackles etc. for requirement annual unit outages.
Identification of source for resources and to ensure their availability.
Development
and
standardization
of
maintenance
Quality
Assurance
sheets,
recommissioning check sheets, monitoring sheets and other control programme documents for overhauls major repairs/replacements.
Control & Schedules of resources during planned outages to ensure timely execution of work programme.
Coordination among agencies (internal & external) deployed for quality checks, contractors, area engineers and other associated groups for manufacturing, resources, safety, gate passes & housekeeping etc.
ORGANISATION STRUCTURE The maintenance planning of the station has to carry out a wide range of functions, through an integrated planning system, to provide an effective service to maintenance, coordination with operation and organize documentation and feed back service to station Management and Corporate Centre.
The approved organization structure of station maintenance planning group for NTPC Super Thermal Power Station is shown in Figure 13 to 18.
OUTAGE COMMITTEE It is proposed that the entire planning support, monitoring and documentation of overhauls will be provided by the Long Term Planning while actual control of the unit overhaul will be executed by an outage committee. This committee will be exclusively responsible to conduct the overhaul of only one unit and shall change for next unit outages according to availability of personnel and workload of the station. The Outage Manager will be Sr. Superintendent/Superintendent (Maintenance/Operation/Planning). Under the proposed system total overhaul of a unit shall be controlled by the outage manager who will be nominated by an office order of the competent authority of the
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station. He will head the team of inter disciplinary executives responsible to conduct the outage of a particular unit. The outage committee will be responsible for execution of overhaul as per the details planning from unit off load to synchronization and shall ensure that all the jobs are carried out as per laid down specifications and quality plans. The various members of the outage team shall be as follows : a
Outage Manager
E.6/E.5
1
b
Planning and Resource Analysis Engineer
E.4
1
c
Maintenance Contract Engineer
E.4
1
d
Coordinator Boiler and Auxiliaries
E.4
1
e
Coordinator Turbine and Auxiliaries
E.4
1
f
Mechanical Engineer (Boiler)
E.3
2
g
Mechanical Engineer (Turbine)
E.3
2
h
Electrical Engineer
E.4/E.3
1
i
C and I Engineer
E.4/E.3
1
j
Operation Engineer Engineer
E.4/E.3
1
k
Material Engineer
E.3
1
Team members will be nominated from different department/groups at least six months ahead of overhaul and kept informed of the various activities in connection with units planned outage.
Representatives from unit operation shall be drawn to plan the sequence of isolation, permit to work and recommissioning procedure. The representative of material department shall be inducted to maintain a close liaison between procurement, issue and actual users.
The Maintenance Contract Engineer under maintenance planning group will be responsible for coordination & award of contracts, contractor’s mobilization for all the repair/overhaul of the unit. The maintenance contract engineer will operate under the planning group and will be given a short term exposure in the Contract Cell of the project or as deemed necessary by the station authority.
The role of each outages team member should be clearly defined and responsibility of each member clearly fixed up prior to commencement of work.
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FUNTIONS OF AN OUTAGE COMMITTEE The general guidelines for the responsibility and function of outage team is given as follows :
a.
b.
To Assess
To Coordinate
-
Technical viability of Contractors.
-
Skill availability with Contractors.
-
Among different Contractors.
-
Among different departments
-
Among
different
supervisory
executives -
c.
To check & ensure
-
Job quality as per Q.A. plans.
-
Job execution as per technical Specification
-
Observance of safety rules as per laid Down principles
d.
e.
To monitor work progress to
To provide feel back of
-
Reduce cost
-
Reduce down time
-
Optimize man power utilization.
-
Resource utilisation
-
Effective work control.
-
Bottle necks in planning
-
Improvements for effective planning.
Figure-19 shows a coordination flow chart for a Typical overhaul management support system.
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UNIT OUTAGE CONTROL ROOM A unit outage control room shall be set up under outage manager to coordinate various maintenance activities, their resource requirement and transaction of vital informations.
The Outage Control Room (OCR) shall be attended by a representative of maintenance planning group who shall be a member of outage committee. All the communications regarding requirement of resources, manufacturing, and common facilities, coordination, reporting of major events, arrival of critical material & accident etc. shall be complied by this center. It shall be the responsibility of OCR to arrange necessary facilities to the requisitioning agency and coordinate among different agencies.
ENGINEERING DETAILS
It is envisaged that all the documents and manuals, relevant cross-sectional drawings incorporating the modifications and deviations, erection & commissioning protocols. Quality Assurance protocols and assembly passports for rotory equipments e.g. turbo generator, feed pumps, fans etc. shall be handed over to maintenance planning group by project erection group. These documents will be classified according to functional groups and identified by unique codes for easy r eferences.
COMPUTERISATION PLANS
An ambitious plan has been drawn to computerize the entire maintenance systems with the help of real time computers. Under the proposed plan the main frame computer will be stationed at the Corporate Centre which will be linked with the computers located at the power stations. The various stations will be interlinked in such a manner that information can be exchanged between corporate center and stations and also between the two stations. In time to come the minor maintenance will be controlled by the stations and major maintenance like unit overhauls or break down will be additionally monitored from the Corporate Centre and regional head quarters.
The power generating units, equipment sub-assemblies, spares, cost centers, work specifications, defects, outages, etc. have already been identified by unique codes.
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Shortly these will be utilized as effective management tools to understand, equipment behaviour and reliability, maintenance cost benefits utilization of resources and plant inventory.
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1.
SHORT TERM MAINTENANCE PLANNING
Introduction Power being a basic infrastructure for economic growth, high emphasis, for its development at a rapid pace, have been given. To meet the challenge of powershortage, NTPC was formed with an objective to plan, design, construct and operate coal pit head Super Thermal Power Station. The power plants being set up by NTPC would comprise of large power generating units of 200 MW & 500 MW capacity using latest sophisticated Equipment and instrumentations. Investment in high technology high value equipments are to be justified by effective maintenance which can lead to high availability and optimum capacity utilization. NTPC, since its inception, had recognized the need of acquiring professionalism in the management of power industry for reliable service to customers and has made all possible
efforts
to
standardize
certain
system
in
Engineering,
Construction
Commissioning, Project Management, Finance Management, Personnel Management, Material Management etc. Implementation of these system have paid rich dividends in the form of early completion of projects and commissioning of units on or ahead of Schedule. A similar approach has been conceived to manage the operation and maintenance of running power stations of NTPC and achieve a sustained capacity utilization. An effective system known as “Maintenance Management System” has been developed in consultation with experts from BEI (UK) and adjusted to suit Indian conditions. This manual deals with the principle of maintenance management system and short term tactical planning. The long term strategic and overhaul management have been dealt in a separate manual on “overhaul “ overhaul management”.
Objectives The maintenance management system has been developed with the following broad objectives.
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1.
To maximize availability of generating Units with minimum maintenance costs and down time.
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2.
Most effective utilisation of resources.
3.
To carry out maintenance jobs in accordance with the laid down procedures within stipulated time.
4.
To plan for the major and manual ovehaul statutory inspection and to obtain statutory certificate from the competent authority for the safe running of the equipment.
5.
To predict the life cycle of assemblies and sub-assemblies and prepare major replacement plants for next 10 to 15 years.
6.
To ensure safety during isolations, maintenance and recommissioning.
7.
To forecast the plant generation in consulation with grid control and schedule major maintenance in accordance with the generation plan.
In other words the maintenance management system incorporates all the components of maintenance organisation and effective control of Repair and Maintenance.
System The maintenance management system has been conceived based on work control and feed back concept in which all maintenance activities are pre-determined with its standard input like work instruction, manpower tools, spares and estimated completion time. The allocation and arrangement of resources, required for maintenance jobs are the prime objectives of the system. A central controlling office called work control office, permit to work control office and material control office are the main ingradients for implementation of the system. For the purpose of effective work control system ‘equipment’ will form the basic maintenance unit and all its technical specifications/manufacturer’s details etc. will be recorded in plant inventory card. (Chart No. 1).
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The power station has to be classified into various systems, sub-systems/as indicated in annexure under codification chapter. Data regarding man and material have to be identified for maintenance of each equipment and written on work specification cards. The maintenance jobs in the power plants are generally catagorised in the following heads. 1.
Defects (Break down).
2.
Routine maintenance (prev. mtc, Lubrication & inspection).
3.
Annual overhauls and statutory inspection.
4.
Design and operational modifications.
The jobs may come from the above sources only, need to be rationalised and planned according to priority availability of work permit and availability of resources. The system is designed to regulate the total quantum of work in a manner that the maintenance work load remains uniform throughout the day, week, and year and utilisation of available resources is optimum. It enables maintenance personnel to achieve a balance between work-load and the available resources.
Organisation Functionally, operation department is the most significant department directly, responsible to produce power. This department always remains in the forefront of activities and stands accountable for all constraints production including maintenance. Obviously it will play an ownership role and its total participation in the planning process of maintenance is imperative of Maintenance policy and the procedures are directed to meet the production targets, set by the station or corporate management. The maintenance is a service function needs to operate in accordance with the needs and priorities of production department. However operation department will not sacrifice the maintenance to achieve short term gains. The maintenance planning is a service function to maintenance and assistance to station management in meeting their targets by the effective utilisation of resources.
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With in the planning and maintenance, it is essential to identify the various functional elements and clearly define the role of planning vis-à-vis area engineers. The following functions of maintenance have been rationally shared between area engineers and planning engineers. 1.
Identification of equipment.
2.
Identification of known defects and work procedure.
3.
Trouble shooting and engineering analysis.
4.
Actual supervision.
5.
Identification of resources and mobilisation for maintenance.
6.
Documentation and retrieval system.
The engineering functions like trouble shooting, resource identification including spares and quality supervision have been entrusted to area engineers whereas planning, resource mobilisation and documentation will be looked by maintenance planning engineers.
The total sanctioned discipline wise manpower in the maintenance and maintenance planning is given in Chart-1, Chart-2(a), 2(b) and 2(c). In accordance with the basic policy of system, maintenance crew will operate in all three shifts of a day besides the general shift. It is envisaged that there will be multicraft personnel in the shift who can undertake effective maintenance work which do not involve too many resources and coordination. The shift personnel will give priority to the emergency maintenance whereas general shift people will consists of personnel of specialised nature and will undertake major jobs which require precision and close supervision. In this context it is essential that the shifts personnel be given opportunity to be rotated in a small number within the general shift to improve their overall expertise gradually.
According to the proposed system there has to be close co-ordination between the functioning of shift, maintenance planning and respective area engineers. Ideally the control of the shift personnel along with shift store should be under the control of a maintenance co-odinator since success of maintenance largely depends on the effective
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management of resources. However, area engineers find it difficult to give up the control of personnel to other department thus making the task of planning difficult. Provisionally a decentralised concept needs to be introduced to control the electrical, mechanical and C&I personnel by separate group heads. At a later stage a common group head to be known as maintenance co-ordinator assisted by experienced foremen of different discipline can be incorporated
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The shift personnel will also be utilized to assist the operation/maintenance department in the disconnection, connection of electrical connection, coupling and decoupling of rotary drives, repair of minor leakages of coal, steam, water and ash, removal of foreign material from mills etc. In case, of urgent requirement of multi-disciplinary services like mechanical plus electrical or electrical and C&I or any such other combination the operation personnel will co-ordinate between different department outside the normal shift hours. For planned work, matter can conveniently be sorted out by discussion in the daily planning meeting.
Function and responsibilities of long term, short term planning, maintenance department and Corporate centers, maintenance management group:
The function and responsibilities of long term, short term planning, maintenance department and corporate centers maintenance management group along with the function and duties of the executive are given below:
Function of Long Term Planning 1.
Compliation of the station five year rolling plan.
2.
To prepare and ensure all necessary arrangements for the following year’s overhaul work programme.
3.
Produce, distribute and monitor major overhaul and control programme.
4.
Operate section of permit to work system before, during and after major overhaul.
5.
Custody of all licences of equipment covered under Indian Boiler Regulation, Indian Electricity Act, Indian Explosive Act and other safety rules.
Function of Short Term Planning 1.
Development and efficient operation of station work control system.
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2.
Co-ordinate with maintenance sections and apprise them about the plant reports, proposed shut down if any, cooling, drains or the constraints that might delay the availability of permits to start maintenance work.
3.
Liasion with operation for the planning of defects rectification and apprise them about maintenance work and delays if any.
4.
Allocation of station maintenance manpower to achieve short term and long term objectives.
5.
Maintain and improve co-ordination between plant operation and maintenance.
6.
Plant inspection programme and progress.
7
To receive input documentation from the long term planning office and to schedule accordingly.
8.
Co-ordinate and exercise control over the production of power for 24 hours.
9.
To draw committed work programme for all section of maintenance department inclusive of lubrication, preventive pr eventive maintenance schedule and planned outages.
10.
To receive, monitor and integrate work-order cards in accordance with station administration and to ensure that defects which require long term planning are correctly routed to the long term office after diagnostic appraisal.
11.
To maintain on-going lists of priority work and to ensure that short term plant overhaul programme are prepared and issued as required.
12.
Liasion jobs with operation for P.T.W.
13.
Review and improve methods of maintenance equipment and staff-skill and crew size to achieve safe and efficient maintenance. Revise work specification cards accordingly.
14.
Update and maintain the stock of work order cards.
15.
To organize and provide a service to the daily planning meeting.
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16.
To table and confirm committed work programmes, ensure action list, receive feed back information and plan before daily planning meeting and senior executive meeting.
17.
To maintain history of all the equipment, plant inventory cards and spare list cards.
2.
LONG TERM MAINTENANCE PLANNING
Planning Process NTPC philosophy is to imbibe the institution of planning in totality. Therefore, emphasis is to initiate the planning planning process much much before the actual overhaul. This will ensure ensure identification of all events & requirement of resources and inputs in advance. Planning is a continuous process and does not cease after completion of one overhaul or an event. Therefore the planning process which envisages action plans for budgeting, lead time for spares, quality assurance plan, design of work packages and award of contracts on continuous basis i.e. the concept of five year rolling plan has been adopted as a part of NTPC maintenance philosophy. The total cycle takes about 24 months to translate five rolling plan into action while maintaining the dynamics of process and the plan thus overlaps for the subsequent years in a rolling manner.
The detail planning of each unit outage is unique in nature and may not only differ from one station to another put from unit to unit, depending upon the nature and quantum of work, unit condition, load demand and resource availability etc. It is therefore not practical to make any standard st andard plan to suit all variations. However, since large number of the activities are repetitive in nature, an effort has been made to design a “Standard Work Module” for Minor, Medium and Major nature of unot overhaul in the following sections. This may serve as a guide line to decide initially the jobs which are to be undertaken in the successive years of overhaul under the accepted maintenance policy of NTPC.
The planning process of any unit outage has essentially three stages of progression as follows:-
a.
Pre shut down planning activities.
b.
Shut down activities.
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c.
Post shut down activities.
Each stage involves several events for successful execution of planning. The Figure 20 shows the major events of the three stages of planning process.
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PRE SHUT DOWN PLANNING Pre-shut –down planning essentially begins from the time unit is synchronized. The initial information and behaviour of the base line data of plant and equipment form the basis of work plan to be undertaken in future. Similarly data obtained during the previous overhaul will provide sufficient feed back to structure the realistic plan and will help to access the actual quantum of work.
A brief history of unit shall be maintained for reference in the Unit History H istory Record Sheet. The salient points to be recorded are as per format of Unit History Record Sheet enclosed in Chart No. 2. The details may be recorded and updated from O.R.T. reports, monthly performance reports, annual NTPC report, and special investigation reports. Reference of all such reports shall also be made for ease of retrival. With all the available information, quantum of work to be taken up during overhauls is assessed. Since work list forms the basis for analysis and planning of resources, its accurate assessment is of utmost importance.
WORK LIST An accurate identification and and detailed listing of various various jobs to be taken up during shut down is the primary step to predict the requirement of resources and duration of outages.
This list may be prepared on the basis of information to be obtained from following sources:
a.
Standard work module.
b.
Defect work order pending for unit outage.
c.
Plant Betterment works of modification plans.
d.
Outstanding preventive maintenance works.
This work list is compiled by the long term planning in consultation with area engineers and circulated to all the concerned for review and suggestions.
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STANDARD WORK MODULE The quantum of work during the outage will vary from year to year depending upon the operating hours and duty conditions of the unit. However, an effort has been made to develop standard work modules to be undertaken during the outage period of 14, 45 and 60 days. The station maintenance planning group can develop their work plans along similar lines depending upon the actual requirement and local conditions.
PLANT BETTERMENT WORK LIST The list include modification jobs which may arise out of following requirement:
a.
Demand for better unit availability.
b.
Efficient unit operation.
c.
Modifications for design improvements.
d.
Safety requirements, easy accessibility and maintainability.
Jobs enlisted on plant betterment shall be treated as an independent project and all necessary inputs e.g. technical feasibility, approved drawings, cost analysis, material and resource availability, financial provisions and sanction etc. will be obtained and reviewed in advance.
The guidelines for formulation of such proposal are given as follows:
i.
PROPOSAL
-
Modification required.
ii.
PROBLEM
-
Brief history of the problem and how it is affecting unit operation, performance and safety aspects.
iii.
RECOMMENDATIONS
-
Various suggestions to overcome the problem with sufficient technical support.
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iv.
TECHNICAL ASPECTS
-
Selection of recommendations. recommendations. Technical advantages of the selected suggestion and its effect on revival of system efficiency & safety. Approved of the drawings for the modification and technical sanction
v.
FINANCIAL ASPECTS
-
Cost analysis and pay back period. Budgetary provision and financial financial sanction.
vi.
RESOURCES AVAILABILITY
-
Material and skill required for the proposed modification inhouse availability of the material, suggestive action of procurement and lead time. Additional resources required to be supplemented by contractor.
vii.
DURATION OF WORK
-
Proposed duration of the work and its impact on the total outage period of the Unit/System/Sub-system
viii.
EXECUTION AND REVIEW
-
Proposed date of work execution and review of the system performance, after modifications. Feed back of the review after modifications to Engineer for incorporating in the technical specifications for future projects.
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PLANT BETTERMENT WORK LIST S. No.
Equipment/Area
Work Description
Drawing/Document
Agency Agency
Originator
Nos. for detailed
for work
of proposal
abc
ABC
U
Remarks
Reference 1.
ID Fan
Removal of dampers nos……………………..
2.
BOILER
Reheater cutting
def
DEF
V
3.
BOILER
Provision of platform
ghi
GHI
X
jkl
JKL
Y
mno
MNO
Z
near bottom ash hopper
4.
E.S.P.
Provisions of electric vibrators on ESP ash hopper
5.
BUNKER CONVEYOR
Provisions of smoke/ fire alarm
NOTE
Each proposal should carry detailed technical technical feasibility and analysis and should be treated as an independent independent project for evaluation evaluation of Cost benefits.
CHART NO. 5
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A model format of plant betterment betterment work list is enclosed Chart No. 5.
PENDING JOB LIST The various defect jobs pending for want of unit outages or resources and outstanding preventive maintenance jobs are enlisted and incorporated in the worklist for their completion during unit’s proposed shut down.
RESOURCE ANALYSIS Once the total quantum of work is assessed it is imperative to plan & match the availability of resources for effective execution of unit outage within the stipulated time frame. The areas which shall require attention and review are enlisted below:
a.
Availability of manpower in quantity & quality through department as well as external agencies during proposed outage time.
b.
Availability of anticipated spares and other consumable materials at main store and steps to ensure timely arrival of items on order.
c.
Availability of anticipated tools and plants of general and special category.
d.
Availability of material handling facilities e.g. cranes, lifts, transport etc. inhouse or through outside sources and their scheduling.
e.
Availability of manufacturing facilities e.g. stations workshop, central maintenance and overhauling workshop, BHEL works, local workshop etc.
f.
Requirement of communication facilities e.g. telephones, walkie-talkie, PAsystem etc.
g.
Requirement of test facilities e.g. radiography, instrument test bench, hydrotest etc.
h.
Requirement of photography and micro-filming facilities.
i.
Requirement of temporary store & office cubicals.
j.
Requirement of general general facilities for additional work force from outside outside agencies.
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The short fall in each category is analysed and action initiated for their timely availability.
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HUMAN RESOURCE PLANNING Duration of repair & overhauls shall depend on the basis of quantum of work and availability of manpower in sufficient quantity & quality.
It is estimated that for a 200 MW unit medium overhaul the peak requirement of manpower shall be about 950-1000 with a an average deployment of 450-460. A typical manpower deployment pattern for a 200 MW unit medium overhaul is enclosed in figure 21. PERT Network for 45 days overhaul is shown in the Figure 21-22.
The assessment and planning of manpower shall have to be done with care by classifying the scope of work into three groups:
a.
Jobs to be executed & supervised by mobilization of departmental manpower.
b.
Jobs to be executed through outside agencies but supervised by department.
c.
Jobs to be executed through external agencies including responsibility of supervision, work progress and quality control.
It is suggested that the jobs of similar nature should be classified together so that a particular gang can move to undertake similar jobs on various equipments. The total manpower can be divided into number of crews or gangs to be uniquely identified by a number. The movement of each each crew from one equipment equipment to another has to be planned planned over the total duration of unit maintenance. When the total manpower requirement is established, availability of the internal resources should be examined considering the routine maintenance jobs and emergencies of the operating units. The areas of high skill requirement should be catered by the internal human resources to the extent possible and labour intensive jobs can be awarded to outside agencies.
The possibility of external human resource requirement shall mainly arise under following circumstances:
a.
The desired level of expertise is not available within the station.
b.
The requirement of man power is more than the available man power within the station.
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Generally main problem faced by maintenance department is improper management of spare parts. Either needed spare parts are not available or some times they have gone defective because of inefficient storage and handling. Some times spares are procured in bulk which hold excess capital causing loss to organisation, reasons behind it, are difficulty of forecasting the future requirements and due to obsolescence. Apart from these, cost of procurement is very high due to monopolist suppliers or due to insufficient production capacity.
In some organisation spares are also managed as all other materials. Initially the maintenance department indicates their requirement and quantity to be stocked to the Material Management Department. Then they tally the list with their inventory and raise indent to replenish the stock up to inventory level. This kind of management is called replenish Management. But difficulty here comes since the consumption is extremely erratic, purchasing in small quantities is not economical. So this creates some sort of adhoc replenishment process requirement which in turn generates new purchase orders. Management of spares needs attention because of its involvement and direct effect on the performance of the system.
ROLE OF SPARES IN EFFICIENT MAINTENANCE When any equipment of the assembly or sub-assembly mal-functions or wears out or breaks away which does not allow that particular part of equipment or assembly to run its designated form. So far replacement of these parts a new piece of same part is used which we name as spare part. While designing the parts of various assemblies, keeping maintainability and accessibility in view, wear prone parts are designed separately and they have to be replaced by new parts after a particular time which depends on type of service and conditions under which these parts are functioning.
So while ordering for any equipment initial set of compulsory spares are ordered, and while commissioning the equipment depending on the knowledge and technical details available we again order for general spare parts and keep a level of inventory according to convenience of the system and industry.
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While going for any type of Maintenance either break down or preventive one, basic things required for starting the work are proper time and isolation of equipment, skilled man power tools and consumables and spare parts.
While planning for any type of spare part of a equipment we should have detailed engineering drawings from final level assembly to assemblies, sub-assemblies and up to part level. Technical detail, supplier and his catalogue No., the supplier’s reference nos. are also needed. If the facilities are available, one may try for alternate supplier or may develop local vendors for spares supply.
Generally in direct costs of maintenance work we find a considerable share of spare parts. This can be controlled by taking care of various factors involved in the spare parts Management. They are described as follows:
a.
Proper maintenance information system should be established. All engineering drawings, their break-ups’ up to part level, supplier’s reference, catalogue etc. are needed. Their proper feed back system of all type of Maintenance being carried out on various equipments and their details, history and various maintenance information should be available. This facilitates proper planning of spare parts by which exact quantity and type of spares may be decided.
b.
The lead time of various spare parts should be taken care with an adequate level of inventory in the stores. But at the same time excess of storage should be avoided. Particularly for power plant spares, the suppliers are Monopolistic type so one has to take care of their long lead time. So with proper planning well in advance we can optimize the level of stock and cost consideration. Therefore we have to assure the availability of spare parts in the stores as and when required but without blocking excess capital in spares.
c.
There should be proper quality control before taking the spares in the store. The spares should be make of standard material as per the original. The storage should be proper, so that they are not affected by all atmospheric conditions.
If the availability of spares is upto the required standard then the down time can be reduced and the maintenance cost also can be reduced. The quality of maintenance work can be improved resulting in improved operations. It will result in reduction of
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outages and this will increase the generation. If the spare parts are managed properly it improves the maintainability also.
MANAGEMENT OF SPARE PARTS As mentioned in earlier topic the availability of spares directly affects the maintenance work reducing outages which in term improves the plant performance. For efficient Management of spares one has to interact with the various sections of organisation. This is described as follows:
Maintenance Engineer faces a very general problem of unavailability of spares at the right time or the spares do not fit; quality is poor and quite often degraded during storage. Purchase Department asks for spares list and suppliers from maintenance. The Engineer concerned has to spend much of his time in identifying the sources and even inspecting the spares. Then operation department complicates the problem by not giving shut downs for preventive maintenance as scheduled.
This aggravates the wear and tear of various parts and certainly increases the consumption of spare parts in unpredictable manner and thus up sets the inventory situation and planning. So all these problems bring out considerable interaction between operation maintenance and spare parts management. Each segment can help or hurt functioning of others. So proper co-operation between operation, inventory and purchase can assist the maintenance and extensive discussions on problems, can improve the functioning of the system appreciably.
While designing the parts the maintenance aspect is not taken care since if the designer takes care of preventive maintenance, it complicates the design. The concept of maintainability is to be introduced with the component and equipment design. The Maintenance Engineer may interact with the designer; identify the high value failure prove parts which could be redesigned to make them more reliable. Also the small wearing parts may be separated from non wearing more expensive parts. Modular design may also be used with slightly higher initial cost and reducing the down time and maintenance cost. This design interface is very important and now this is being adopted in India. It needs special attention of designer specially with the mechanical equipments.
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Operators can also reduce the problem by proper attention to factors like intensity of operation. Environment, preventive maintenance adopted and intensity of operation affects the spare parts planning. At the time of commissioning, the engineer concerned should take full care of equipment behaviour without any haste of starting production. It affects several critical components.
Operators should be trained enough and they should report any incipient component failure observed as unusual noise or degradation of operation at the earliest. While this may create a small shut down it will save a larger down time in future.
Inventory of spares is most important factor of spares management. The spares are relatively slow moving and only 5-10% have their noticeable consumption. So a very important decision has to be taken for replenishment of various moving parts and also to stock or not to stock. Some parts are stored only as insurance item. If it is left on maintenance department, they would like to have every spare part which is ever expected to be required. So here maintenance department should only assess the likely consumption rate of spares. This estimate should be based on engineering judgments coupled with data or experience of similar items.
The top management has to make decisions about assurance level and budgets. If budget is not permitting high assurance level, they should be ready to accept-stock-outs. But generally it is left to manager of spares and maintenance to sort it out amongst themselves generally top management demands cost effectiveness. This interaction between top management and other section is most important and possibly least understood.
Nature of organisation also effects the material and maintenance interface.
The concept of repair or replace also effects the requirement of spares. If we are going for replacement the spares budget will be high and it will reduce the labour cost and down time. If we go for repair then it will decrease the spares cost but it will increase the down time and labour cost.
Typically at lowest level of maintenance the engineer has to decide, if the repair can be carried out with relatively simpler skill, tools and test equipment and if the failure prone parts are accessible. He has to choose between replacing the assembly or subassembly or part instead.
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Manufacturers are also to be selected carefully. If possible more than one supplier should be kept in contract for reducing lead time and monopoly. Local vendors also can be developed for reducing the cost and controlling the supplies. Manufacturers usually indicate applicability of spares in different models. Maintenance Engineer must kept this in view and should initiate the model, no. of drawing relating to the equipment. Complete documentation of purchased equipments and its accessories, spares etc. should be maintained. There should be recognized substitutes in consultation with maintenance and purchase departments.
Problem of lead time is much evident in an industry like power plant. In a free flowing market where production and consumptions are constant there is no problem. But for industry like power plant where very few or even single supplier is there the planning should be well in advance. An attempt should be made for alternate supplier.
INVENTORY MANAGEMENT Inventory control of spare parts is different from inventory like raw material etc. The spares are slow moving parts and only 5-10% show their noticeable movement of consumption. So while taking decision on stocking of spares many agencies are to be involved. The Maintenance Engineer should give consumption rate of spares based on engineering judgment judgment with the help of the data available for the spares.
Satisfactory material control means that needed parts are available in adequate amount as and when required. A requirement in the form of a list of spares is sent to the spare parts cell by maintenance department which is then procured and stocked in store.
While re-ordering the stock a travelling requisition is used. When the stock of a particular spare part reaches a level, an order is automatically placed to the supplier which supplies the component to the stores.
For selection of spares in quantity joint decision between maintenance maintenance and purchase has to be taken. Here well known A-B-C pattern of annual usage may work well. As thousands of spares are consumed annually only a few (~15%) account for bulk (7080%) of consumption value, these items are called as ‘A’ on the other hand ‘C’ items represent almost 50% range of items but contributes 15% annual consumption value. ‘B’ items are intermediate ones. Since spare parts used are erratic and can occasionally
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greatly exceed the average a large stock has to be kept. Obviously this safety stock has to be kept for ‘A’ items. While this is one way of sharing the cost burden of parts which remain un-utilized. There is another cost which spares may create viz. cost of down time and damage if a spare is not available. This is not very easy to quantify but spares can be given subjective attributes or levels of their criticality e.g. Vital, Essential and Desirable (V-E-D).
The optimization could be done in cost attributes (A-B-C) and criticality attributes (V-ED). It would then be sensible to have an almost guaranteed level of assurance of availability of low cost vital items. This would mean a high safety but low down time losses. On the other hand high value desirable items have the lowest assurance level. Mathematical models in the form of decision matrix can be developed.
The final decision of inventory depends on A-B-C and V-E-D analysis, nature or a repair and assurance level required. Some spares have to be stocked with large safety stock because of their criticality. Lead time has to be taken in due consideration while ordering for spares. Depending on reliability of supplier and alternate resources of getting supply, planning as well as ordering has to be done in well advance. Then only a proper inventory can be maintained.
HUMAN MANAGEMENT It has been experienced that successful execution of any unit overhaul has been many a times governed by environmental factors of the people engaged in the work. A study of human management during several unit overhauls has revealed that often this aspect gets little attention. It is estimated that a careful planning and clever handling of this aspect shall help in a reduction of the outage duration by about 20-25% which is considerable in terms of cost as well as unit availability as compared to the expenses on this overhead.
The various points requiring the attention are enlisted below:-
a.
Clear defined objectives of the executives and decision making process.
b.
Location of site stores.
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c.
Location of contractors store/office sheds.
d.
Routing of the material – It is essential that damaged equipment/parts are unloaded to suitable place so that they do not pose obstruction to movement of resources of other contractors.
e.
Location and numbering of winches, welding sets etc. to avoid confusion and delays.
f.
Suitable facility of drinking water/toilet etc. to large work force.
g.
Large number of service counter for tea/refreshment etc.
h.
Availability of transport and communication facilities e.g. telephone, PA system etc. in adequate number.
i.
Availability of on the spot first aid facility and necessary safety appliances.
j.
Availability of spares & consumables consumables at site stores in adequate quantity. quantity.
k.
Authorisation of area engineers for signing issue slips to draw material from site stores and general stores.
l.
Facility of round the clock availability of electrician, crane operators, jeep drivers, ambulance drivers, with necessary service facilities.
m.
Availability of a spare gang of manpower for jobs such as cleaning of area/equipments, misc. scaffoldings materials handling and other contingencies. The gang may include following:
n.
a.
Unskilled labour
-
20 Nos.
b.
Riggers
-
10 Nos.
Availability of a gang round the clock to undertake repairs of working tools such as jacks, grinders, hand lamps, extension boards and lighting etc.
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The gang may include following: f ollowing:
a.
Electrician
-
3 Nos.
b.
Fitters
-
4 Nos.
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0UTAGE EXECUTION The outage duration begins at the time unit is off load till it is re-synchronised inclusive of both days. From detailed net work for a typical 45 days overhaul, it is evident that 3-4 days are required for initial cooling of boiler and turbo-generator and about 17 days shall be required for the re-commissioning activities considering date of hydraulic test as the reference. Consequently about 24-25 effective days are available for the overhaul activities in all the areas and disciplines viz. electrical, mechanical and C&I. In this context it is imperative to exercise close monitoring of events and inputs. It is envisaged that outage committee with the assistance of members from planning and materials will be able to identify the input constraints and take suitable remedial measures. The mechanism of overhaul control will be exercised though an effective co-ordination of outage committee and information system given as following:a.
Daily outage meeting.
b.
Work progress reporting system.
c.
Quality assurance system.
d.
Manpower reporting system.
e.
Recommissioning checks.
f.
Documentation of data.
DAILY OUTAGE MEETING It is proposed that all the members of outage committee will meet once a day at about 1200 hours to review the progress. The meeting known as outage committee will be chaired by the outage manager. The duration of the meeting should not normally exceed for more than an hour. The representative of major contractors should also be invited to
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attend this meeting for the purpose of better co-ordination. The secretarial assistance like preparation of agenda, minutes of meeting and documentation shall be provided by LTP cell.
WORK PROGRESS REPORTING SYSTEM The reporting of the overhaul work progress will be through formats prescribed. The frequency and the pattern of reporting will be as follows: a.
Daily equipment work progress shall be reported by area engineers to LTP cell discussed in the outage committee meeting. The daily work progress shall be reported to station DGM/GM.
b.
Weekly Unit overhaul progress shall be reported by LTP Cell to Station DGM/Gm, ED, GM (OS) and other concerned authorities at Corporate Center. O.S. will compile the exception report and forward it to board and CMD.
MANPOWER REPORTING SYTEM It is proposed that area engineers/contractor will fill up the manpower reporting sheet prescribed. The planning cell will compile the area-wise and craft-wise statements and copy of the same will be given to outage manager, who will take appropriate measures with the contracting agencies in case of short fall in the number or level of skill.
QUALITY ASSURANCE IN MAINTENANCE The Quality Assurance Sheets prescribed are given as guidelines for the planning. It is proposed that the design values of clearances, alignment and set value will be entered in these sheets in consultation with the area engineers. The inspection of furnace will be undertaken by the area engineers jointly with O.S. & R.D. Once the facilities with R&D are developed, they will undertake the measurement of tubes/headers thickness by ultrasonic equipment and hardness of vulnerable boiler tubes, to establish the pattern. R&D will also raise the microstructure of headers, rotors etc with the help or replicating tapes and carry out other NDT, as necessary.
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RECOMMISSIONING CHECKS It is proposed that recommissioning plan and check lists will be adhered for every equipment during the trial run & commissioning activities. Any deviation from the logical sequence of events or safe procedures will be recorded in the outage completion reports, to avoid recommissioning delays in future. The various operating parameters will also be logged on the sheet which will also form the part of completion report and equipment history.
OUTAGE REPORT An outage report will be prepared after the completion of overhauls. The relevant information should be complied in such a manner that it supplements the overhaul planning and serves as a valuable feed back to future planning process. The main points covered under the report shall be as follows operating hours of the unit for previous overhaul total cumulative operating hours. a.
Major works taken up during overhaul.
b.
The planned and actual outage schedule.
c.
Availability of resources-Deviations from the planned features.
d.
Time analysis of delays.
e.
Comparative study of human resource-planned vs. actual daily development pattern of work force and skill-wise manpower deployment.
f.
Quality checks carried out on equipments and records of major clearances, back lash and alignment values, tube thickness, analysis of transformer oil, calibration records of instruments etc.
g.
Equipment behaviour during recommissioning.
h.
Jobs kept pending/under observation till next outage.
The relevant features incorporated in the report should be used to assess the effectiveness of the planning system and actual overhaul control mechanism.
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a.
Problems faced in resource mobilization e.g. manpower, spares, materials etc. and suggestions for improvement.
b.
Problems faced during equipment trial run.
c.
Suggestive steps for better co-ordination and effective implementation of plans.
This completion report will bear a unique number indicating the project code, unit code, year of outage and number of overhaul. Reference of this outage report, completion report shall be entered into plant history record.
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INTRODUCTION One of the major responsibility of a maintenance planning department is the contracting for maintenance works. The success of any maintenance project like major overhaul, major repairs, renovation and modifications etc. depends to a large extent on the quality of the contract if the work is entrusted to a contractor. It is the job of a maintenance planning department to evaluate various contract proposals and finally select the best one. In this Chapter we discuss some salient features of maintenance contracts.
CONTRACTS FOR MAINTENANCE Objective The objective of contracts is to make the needed equipment material, works and services in the right quantity and quality at the right time and at the right place, after giving fair and equal chance to all tenderers, subject to the Corporate Works/Procurement Policies.
Maintenance Contract Normally contracts are given to outside agencies when:
a.
the skill required for repairing or overhauling certain equipments is not available in maintenance department.
b.
the man power and tools required are not sufficient in the maintenance department.
c.
the work assigned is to be completed before the works undertaken by the maintenance department.
The example, overhauling Boiler and its auxiliaries, the man power requirement varies as given below:
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During cooling of the boiler, the labour required is to collect the necessary tools and materials only.
The next three days more labour is required for scaffolding and after it is over, during cleaning requirement reduces. As here, the fluctuating requirement does not warrant us to have the maximum manpower which will cost more for the personnel department along with many social management management problems. Meanwhile, the Maintenance Department has to look after the other unit’s maintenance works.
Consider the another case. Overhaul of Turbine. It is a specialized job which can only be done by the manufacturer (BHEL) who has more trained specialists and the spare parts needed. Hence, that work needs to be given contract to BHEL.
TYPES OF CONTRACTS If a contract deals with overhauling of certain equipments/auxiliaries, it is known as contract for overhauling – e.g. TG/Boiler/Coal Handling Plant together.
Contract for Repairing Suppose, maintenance of mills or pump or damaged rotor of turbine if given as a separate contract is known as contract for repairing.
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Contract for Renovation If the work is laying of new roads or path ways, erection of new equipment or changing some design or modifications modifications work on the equipment equipment requires a separate contract. contract. e.g. lining the fly ash and bottom ash slurry channels with iron plates to reduce the checking of them by making the flow f low path more inclined.
CONTRACTS PLANNING AND SCHEDULING As bulk of project work or the maintenance work may be carried out, more attention is given to contracts. Experience would indicate that the system of contracting in projects may be set with delays. Frequently, contracts may not provide for adequate internal control and fail to rebate payments to the performance on the milestones envisaged in the project plan/maintenance or overhaul plan. The contracting process consists of three broad steps namely:
*
Preparation of the contract.
*
Selection and award of contract.
*
Execution of the contract.
Contract Preparation The contract should define precisely the obligations of the contractors and the project authorities and include the schedule of work and milestones selected from master plan and schedule. Some of these milestones may need to be related with the effort of other related contractors. To be able to obtain effective control over the contractors, there should be incentive and penalty clauses which may be linked with the achievement of the tasks.
Selection and Award of Contract In regard to selection and award of contractors, there appears to be need to reduce the time in scrutiny of tenders, selecting a contractor on the basis of the lowest bid only, would not ensure that a competent contractor is chosen. Besides the price, past
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performance and the capability should be the criteria for selecting a contractor. It is worth considering whether the letters of intent need be issued at all and whether fairly standard contracts cannot be developed which can be issued along with the tender.
Execution of the Contract After the contracts are awarded, document are signed and the project enters the construction phase, a certain amount of control needs to be exercised over the contractor and the contract should provide the authority for exercise of this control. This would enable the project management to monitor all contracts regularly and maintain an upto date master schedule and cost plan t o facilitate evaluation and review.
CONTRACT PACKAGING Objective As the first activity, the total work should be broken down into smaller, well defined packages. This is done with a view to optimize the number of contracts to be handled for better planning coordination and implementation of the whole project.
Package Design In breaking down the total project works into smaller packages, the factors to be considered:-
The contents of a package should be interplated that prospective bidders can tie up with suppliers of the various elements (equipments) and services involved in order to be able to quote for the entire package. This will ensure adequate competition in bidding and consequent procurement at optimum cost.
The packages formed should include such combinations of equipment and services that can be advantageously/engineered for the preparation of specification for bid documents and subsequent product design and drawings.
The terminal point of each package should be clearly defined and the proper tie ups of these between packages ensured.
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Package Description A complete description of a contract contract package shall include: include:
a.
A list of all equipment and services contained in it.
b.
Full details of its terminal points and then tie up with other packages.
c.
Classification and contract number assigned to it.
CONTRACT SCHEDULING To ensure timely execution of the work, a contract schedule shall be developed. This will identify the major milestone events in the contract works and indicate their scheduled date of completion. This will enable the co-ordinators to evaluate the progress of works. If found lagging, reviewing and updating of schedule shall be necessitated.
CONTRACT BUDGETING Estimating the cost of the services/equipments will enable the finance department to allocate its funds to various expenditure outlays efficiently. The normal rule is:
Basic price of equipment/service Ex-works + Price of shares @ 4% + Freight and Insurance @ 8% + erection charges @ .8% + contingencies @ 3%.
Alternatively budget estimates may be arrived at by using actually quoted values for similar contracts in some other projects, with suitable price adjustments for changed conditions.
Enlistment Activity shall be initiated by issuing an advertisement asking interested parties to enlist themselves for specific works.
PRE QUALIFICATION OF CONTRACTS In order to avoid frivolous tenders, a pre-qualification procedure may be adopted for obtaining offers from reliable parties. The interested parties shall be required to present
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documents for pre-qualification and their merits judged on the basis of the criteria mentioned below:
CRITERIA
Past Performance
DOCUMENTS REQUIRED
-
Past suppliers, quantity, nature
-
Satisfactory performance certificate.
-
Balance Sheets.
-
Profit & Loss Statements.
-
Fund Flow statements.
-
Technical nature of past service.
-
Quality Assurance Progress Details.
Organisation
-
R & D Structure.
Capability
-
Engineering man power.
-
Regional set up.
-
Factory locations.
Financial Soundness
Technical Competence
PREPARATION AND CONTENTS OF BID DOCUMENTS The bidding set to give to the tenderer shall consists of:
a.
Covering letter.
b.
Project synopsis.
c.
General conditions of contract & special conditions.
d.
Amendments, if any.
e.
Bid proposal sheets/six copies/tracing.
f.
Technical specifications.
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g.
Data requirements.
h.
Drawings.
Bidders will be asked to submit their offers in five copies.
Tendering and Bidding For the purpose of delegation of powers one of the following methods of tendering shall be used:
Open Tendering
a.
Bidder are invited to quote through a general advertisement.
b.
Bids are invited from contractors on the approved list made after prequalifications.
Limited Tendering
The following shall be treated as limited t ender:
1.
Contracts of value less than Rs. 50,000/- and where bids are invited from at least four parties from the approved list of enlisted contractors.
2.
Bids are invited from a limited nos. of parties for valid reasons and for emergency project work. The approval of competent authority is sought.
Single Tendering
Where bid is invited from single party (BHEL, Railways) if monopoly exists or rules are in services.
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Bid Document Pricing It is imperative that frivolous bidding is avoided and only various contenders bid. Moreover it is possible to cover if not recover, part of the cost incurred in the bid documents.
CONTRACT VALUE IN LACS
0-1
1-5
5-7
7-10
10-15
BID DOCUMENT PRICE RS.
250
500
750
1000
1250
APPROVING AUTHORITY Approving authority for bid issue issue shall be as follows construction/erection construction/erection activities.
Type of Tender Authority
Open
Limited
Up to Rs.
Up to Rs.
Sr. Engineer
5 Lacs
Dy. Manager
Single
--
--
10 Lacs
1 Lac
--
Manager/DGM
25 Lacs
5 Lacs
10,000
DGM/GM
50 Lacs
15 Lacs.
1 Lac
Bidding Time Extension Requests of extension of bidding time shall be taken up from case to case in consultation with the competent authority.
The factors which may affect the decision are:
a.
affect on overall schedule,
b.
no. of bidders asking for extension,
c.
organisation guidelines.
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CONDITIONS OF CONTRACTS This chapter deals with the techno-economic conditions/clauses which must be incorporated in the document/contract.
BID GUARANTEE To ensure that the Contractor Contractor executes the work after the contract has has been awarded to him, he shall be required to pay a bid guarantee of value 2% of the contract price at the time of submission of bids. For Non-IDA contracts the above shall normally be subject to a maximum of Rs. 50,000/-
Validity The bid guarantee shall normally be valid for 30 days more than the required validity of offer.
a.
Bid evaluation time required.
b.
Time required for negotiation and preparation of contract agreement. Normal period is 120 days.
Forfeiture The bid guarantee shall be forfeited if;
a.
tender is revoked, or if prices are increased after bid opening and during validity of offer.
b.
Contractor refuses to enter into contract after the contract is awarded to him.
Submission The bid guarantee shall be submitted in the original and four copies of the bid or equivalent US dollars and along with the bid document but in a separate envelope.
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Return The successful bidder’s bid guarantee shall be returned after he submits the “Contracts Performance Guarantee”.
Bid Guarantee of all unsuccessful bidders except the second most responsive bidder shall be returned after the issue of Letter of Tender.
And it will be returned after signing of the contract agreement or at the expiry of guarantee whichever is earlier.
CONTRACTS PERFORMANCE GUARANTEE The Performance Guarantee provided by the contractor is intended to ensure;
a.
Performance of the contract in accordance with the terms and conditions.
b.
Successful and satisfactory operation of the equipment furnished and erected under the contract.
c.
Rectification of all defects which might occur during the warranty period.
Value and Text The value of the performance guarantee shall be 10% of contract price. It should be provided in the designed Performa to the NTPC and normally given at the time of signing the contract.
Return This money will be returned at the end of warranty period. The return shall be subjected to satisfactory performance and guarantee tests.
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LIQUIDATED DAMAGES FOR DELAY Normally the liquidated damaged will be payable at the rate of half percent (1/2% of the contract price per WEEK and subject to a maximum of 5%.
However if the delay is not attributed to the contractor these dates may be shifted.
PRICE BASIS If the execution period is less than one year or so, firm base for price is included, otherwise escalation conditions are taken into contract.
SPARES Usually for maintenance contracts, spares, consumables are supplied by NTPC.
PERFORMANCE AND GUARANTEE TESTS Performance is guarantee tests shall be carried out at site to stick compliance with stipulated conditions.
a.
Detailed lists and methods of carrying such tests.
b.
Value of liquidated damage for non-compliance. non-compliance.
c.
Relevant standards for tests.
REPEAT ORDER AND QUANTITY VARIATION This clause is added, if:
a.
The need to place a repeat order because of the situations.
b.
The saving by NTPC due to discount by contractor. Generally NTPC keeps 20% as the variation in quantity at the same unit price quoted.
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PAYMENTS The payment for the equipment/service say overhaul shall be normally paid in the following stages.
a.
Initial advance at the time of order
15 to 20% of contract price.
b.
Interim Advance
20%
c.
Progressive Payments
Depending on the work completed.
d.
After successful completion
10%
BID OPENING The people who will normally be present at the bid opening are:-
1.
Bidders
2 representatives each.
2.
Engineering
1 representative.
3.
Finance
2 representatives
4.
Contracts
2 representatives
After opening the offers, one evaluation evaluation report is prepared.
NOTE 1.
Lumpsum prices (with break up)
2.
Alternative offers.
3.
Discount offered
4.
Guaranteed technical specifications
5.
Delivery and completion dates.
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6.
Taxes, levies and duties if any.
Finally, Evaluating Committee, prepares the most economically, technically sound, capable to complete the work satisfactorily in time, offers and selects the lowest responsive bidder.
Clarifications and some alternate offers and concessions are, then, discussed and settled with that contractor.
AWARD OF CONTRACTS Approval Requirement Requirement The recommendations of Tender Committee as contained in the evaluation report have to be approved by the competent authority within their financial limits.
Then contractor is asked to prepare the work schedule and if suits with NTPC’s estimated schedule, NTPC will agree to it. OR, necessary alternations are made.
The following are settled with the successful bidder before the award of contract.
1.
Progress Reporting.
2.
Payment Schedule.
3.
Settlement of extra rates.
4.
Hire Charges for NTPC Services.
Then Letter of Intent (LOI) is prepared and given to the bidder in duplicate. When returned from the bidder after duly signing on each page of LOI, NTPC authority will sign. Now the contract DOCUMENTS are signed and the contract is awarded.
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Post Award Activities The Engineer-in-Charge shall have the rights to supervise and inspect the work while in progress. Through better co-ordination between the contractor and the Engineer-inCharge the work/service is completed. c ompleted. Periodic evaluation of the work is necessitated.
Sub-Contracts Normally for the maintenance contracts sub contracts are not given. It is the responsibility of the contractor to look after his sub-contractor and complete his work satisfactorily.
Required tools (Welding sets, crane, Power) and consumables are supplied by NTPC, NTPC’s man power also some times used for the completion of the work.
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INTRODUCTION NTPC has been entrusted to set up pit head Super Thermal Power Stations in the country. Main objective of forming NTPC is to boost up country’s total generation capacity to such a great extent to defuse the power crisis within the coming decade. To meet this challenging job, NTPC has to ensure high standard level of performance, availability and efficiency of the power stations being installed. In order to achieve high availability and reliable performance of plant and equipment, some modern maintenance techniques have to be adopted in the maintenance management system.
General practice now relies on preventive maintenance system i.e. time based overhauls, based on previous experience and the expected life of wearing components. As a result, action is often taken before it is really necessary. The built-in-reliability of the equipment is ignored and replacement etc. are carried out unnecessarily, since initial faults are not discovered at a sufficiently early stage to prevent un-planned breakdowns. This procedure significantly reduces the likelihood of catastrophic failure, but does not guard against unexpected deterioration/damage between overhauls. In brief time based maintenance will not provide high availability of the equipment or in turn reliable power generation.
Therefore, turn-to-break and time based preventive maintenance can be avoid by regularly measuring the machines “Condition” and only interfering with it, when it is shown to be necessary by measurements. This technique, known as “Condition Monitoring” virtually eliminates unexpected failures and gives better plant availability and economy. Typical machine condition pattern using condition monitoring techniques is shown in Figure-24.
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OBJECTIVES The plant maintenance department can hold machinery in good running order with a minimum of intervention by applying monitoring techniques. Condition Monitoring is used in two distinct ways, for “non-condition maintenance”, also known as predictive maintenance and in “permanent monitoring”.
Major objectives of the condition monitoring are as follows:
On Condition Maintenance a.
Increase the average time between overhauls.
b.
Decrease the likelihood of sudden unexpected breakdown between overhauls, i.e. gives increased reliability.
c.
Avoids unnecessary replacement of perfectly good machine components.
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d.
Removes the necessity to have an extensive range of spare parts in stock-wise required can be ordered in time.
e.
Decrease the duration of the overhauls, the maintenance staff having planned the necessary action in advance.
f.
Warns the operation or maintenance personnel regarding machine condition deteriorated to a preset warning level.
g.
Ensures the safety of machine against total damage.
CONDITION MONITORING METHODS There are various methods of condition monitoring of machines. Following are the major methods – mainly applied for power plant equipment:-
Vibration Monitoring Vibration analysis is the most widely used dynamic technique for monitoring condition of moving machinery. By continuously or regularly checking, machine vibration level and character, i.e. its signature, the condition of machine can be kept continuously under surveillance.
Shock Pulse SPM measures and evaluates the shock pulses caused by mechanical impacts in rolling element bearings to check the condition of antifriction or its lubrication or installation.
Thermography Thermography is a temperature surveillance technique and useful for locating hot spots in transmission system and the areas where heat generation in equipment is suspected.
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Wear Debris Monitoring The rate of deterioration of a fluid lubricated wearing component is monitored by analysis the fluid for wear particle content.
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The sophisticated equipment equipment installed in power plants always stand the r isk of failure due to improper maintenance or by natural deterioration of machine. Therefore it is necessary to introduce the condition monitoring techniques in maintenance organisation. This technique will be applied on machineries and other critical equipment on priority basically and later as a regular monitoring system on all improvement equipment.
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CBM shall be implemented in plant maintenance in following three distinct ways:
i.
Condition Monitoring
ii.
Trend Analysis and
iii.
Permanent Monitoring.
The function of CBM in our plant maintenance will be as shown schematically in Figure25.
All critical items of individual equipment will be brought under this scheme for one time t ime and periodic monitoring of equipment condition and trend analysis of its parameters like ‘output’, ‘pressure’, ‘temperature’, ‘flow’, ‘vibration’, ‘properties of oil’, ‘erosion/corrosion’ etc. for each equipment, in trend analysis, initial parameters will be recorded. Periodic readings of all these parameters will be recorded and any change in the trend will be analysed to identify the defects for necessary corrective action.
Condition Based Maintenance will be applied in following major areas for detecting any changes:
i.
Structural components.
ii.
Fixed joints, such as welds, fasteners.
iii.
Pressure parts such as tubes, headers.
iv.
Rotating parts such as fans, pumps and motors etc.
For detecting the changes or any flaw development in above areas few Non-Destructive Testing techniques such as radiography, magnetic and liquid particle and ultrasonic inspection etc. will also be employed. The deterioration will be regularly monitored and when exceeds the limits (as established by the manufacturer of the equipment) immediate advance warning for necessary action will be conveyed to concerned division.
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MAINTENANCE STAFF In a Thermal Power Station most of the critical equipments are rotating machines which require the efficient efficient maintenance maintenance using condition monitoring techniques.
At the
beginning stage vibration analysis (as it has wide application) shall be used to determine the health of the machine. When vibration measurements are introduced into a maintenance system, it is most common to use personnel already in the system or having some background of this technique. This is possible because the skills required are easily learned and developed from experience, and goods instruction material is available.
Two types of personnel will be necessary. One is the operator who will perform the actual measurements following a well laid out measurement procedure. In a fully developed scheme he has only to record the vibration signals with preset instruments and turn over the data in the form of taped signals or graphs of spectra to the maintenance engineer at the end of the day for analysis or evaluation by the latter. The maintenance engineer is responsible for preparing the measurement procedure and performs analysis and evaluation himself, particularly during the development period.
The measurement procedure should include which points on the machines should be measured, in what sequence, the manner in which instruments should be used and the desired running conditions of the machines. The points on the machines should be prepared for easy attachment of the vibration tranducer and market with a reference number.
The engineer should instruct the operator the purpose and the execution of the programme. It is advisable to gain experience by taking the measurement many times on a small number of machines. This will also reveal the repeatability of the procedure.
The engineers should also gather technical details to help him diagnose any faults detected. These are details such as rotational speeds, bearing geometry, numbers of rolling elements, gear teeth, turbine blades etc. This information can be set up in diagnostic reference sheet for each machine.
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CONCLUSION To improve the plant availability, reliability and efficient maintenance system, Condition Monitoring is the only economical technique which if implemented will lead to benefits to the organisation. Condition Monitoring has already been used and proved well in western countries. Using this technique it is reported that improvement in output to the extent of 45% have been achieved in some power stations in Western Countries. Therefore, looking into the benefits of Condition Monitoring, NTPC has taken it as a policy to introduce this programme in all its projects. For this purpose training to executives are being provided and necessary instruments are being obtained. To provide guidelines in the application of Conditions Monitoring to the projects. Operation Services Division has already issued a number of condition Monitoring Memoranda and also issued a ‘Specification for Laboratory Testing Instruments’ covering also Condition Monitoring instruments.
It is hoped that with these efforts in a short span of time, it will be possible to switch over the existing maintenance programme to predictive maintenance using Condition Based Maintenance Management Systems.
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MODULE : MAINTENANCE PLANNING MODULE NO. : 1 ME/03
DURATION : ½ WEEK
Day
SESSION – I
SESSION-II
SESSION-III
Day – 1
Introduction to
Maintenance Management
Preventive and Predictive Maintenance.
Maintenance Planning
System in NTPC
Day-2
Day-3
SESSION-IV
Short Term-Outage Planning, Long Term
Organisation of major overhaul, Human Management,
Maintenance Planning
spare part planning.
Condition Monitoring and Reliability
Contracting of major
Written Test/
Maintenance Work and
Viva-Voce.
Maintenance of Records ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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