Total Quality Maintenance and Trouble Shooting - A Case Study

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Total Quality Maintenance and Trouble Shooting - A Case Study

Mahesh Sharma1, Alok Khatri2

1Department of Mechanical Engineering, Government Engineering College, Ajmer, India. 2Associate Professor, Department of Mechanical Engineering, Government Engineering

College, Ajmer, India.

International Journal of Research in Mechanical Engineering Volume 3, Issue 2, March-April, 2015, pp. 13-23

ISSN Online: 2347-5188 Print: 2347-8772, DOA : 27032015 IASTER 2014, www.iaster.com

ABSTRACT

Total quality maintenance plays a wide role in any industry. Preventive cum shutdown maintenance is very necessary to overcome production loss in any industry. Lead time of maintenance should be less in any industry. It should be less by visualization of graphs and plots and take reading of equipment time to time. So maintenance team plays an important role in any organization. Total quality means quality should be maintain in any overhaul or maintenance. By applying optimization techniques lead time saving in preventive as well as shutdown maintenance will be 10-15% and production loss saving will be 15-20% approximately. Finally we conclude that total quality maintenance and trouble shooting is necessary in term of turnover and production capacity. Keywords: Cause & Effect Diagram, Total Quality Maintenance, Maintenance Forecasting, Lead Time. I. INTRODUCTION Past and current maintenance practices in both the private and government sectors would imply that maintenance is the actions associated with equipment repair after it is broken. From this point of view maintenance as follows: the work of keeping something in proper condition; upkeep. This would imply that maintenance should be actions taken to prevent a device or component from failing or to repair normal equipment degradation experienced with the operation of the device to keep it in proper working order. Unfortunately, data obtained in many studies over the past decade indicates that most private and government facilities do not expend the necessary resources to maintain equipment in proper working order. Rather, they wait for equipment failure to occur and then take whatever actions are necessary to repair or replace the equipment. Nothing lasts forever and all equipment has associated with it some predefined life expectancy or operational life [1]. Total quality maintenance is known as total predictive maintenance. Total predictive maintenance (TPM) originated in Japan in 1971 as a method for improved machine availability through better utilization of maintenance and production resources. Whereas in most production settings the operator is not viewed as a member of the maintenance team, in TPM the machine operator is trained to perform many of the day-to-day tasks of simple maintenance and fault-finding. Teams are created that include a technical expert (often an engineer or maintenance technician) as well as operators. In this setting the operators are enabled to understand the machinery and identify potential problems, righting them before they can impact production and by so doing, decrease downtime and reduce costs of production [2].

International Journal of Research in Mechanical Engineering Volume-3, Issue-2, March-April, 2015, www.iaster.com ISSN

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II. PROBLEM FORMULATION OF AMMONIA PLANT Any breakdown or stoppage would lead to huge loss in terms of production and efficiency. So it is necessary to find problems occur in ammonia plant(Urea Plant) and their cause and effects. In this section we also studies how we reduce maintenance cost or production loss. First we study problem identification. II.1 Problem Identification Basically three types of problem occur in the plant can be classifying according to ABC analysis: (i) Critical problem: Such types of problem are called A type problem. By this type of problem complete stoppage of plant occur. So these are called critical problem or shutdown maintenance problem. These problems occur in multistage compressor. In which co2 compressor does not compress the ammonia as required pressure. (ii) Sub critical problem: Such type of problem occurs in single stage and multistage centrifugal pumps. These problems are called sub critical problem or preventive maintenance problem. Because these are standing by pumps in spare. We do not purchase these pumps by OEM (original equipment manufacturer). Since its cost near about 40000 for impeller of KSB pumps and 10000 by local party indenigation pumps. (iii) Non critical problem: Such type of problem occurs in dosing pumps and chemical injection pumps. This type of problem is called preventive maintenance problem. But if pumps are failed due to some reason the ph of water in boiler does not less than 7. It remains near about 9. By injection of hydrazine and phosphate it remains near about 11 ph. So failure of dosing and chemical injection pumps it does not affect the process of plant and production shut down and production stoppage does not occur so such type of problem is called non critical problem or C type problem. Basically total quality maintenance is of three types: (i) Preventive Maintenance: Preventive maintenance is basically two types: running and standby maintenance. Running maintenance consume one day for maintenance of multistage compressor and centrifugal pump. Standby maintenance consume one and two days for maintenance of both machinery. Preventive maintenance is not optimum maintenance programmed so problem formulation is not done by preventive maintenance programmed.

(ii) Shut down Maintenance: Shut down maintenance is done for plant equipment service. Shut down maintenance is done only for effectiveness of plant machinery so it is not use in optimum maintenance programmed.

(iii) Predictive Maintenance: Predictive maintenance is used for optimize machine operation so we formulate LPP with the help of table 1 as given below.

Table 1: Maintenance Data for A, B &C Type Failure

Machine Maintenance Time Per Tonne NH3 (In days)

Capacity (Per day) Machine Operation

Impeller(Casing) Maintenance Leakage Problem A Multistage compressor 12 days 20 hrs(5/6 days) 24 hrs(full day)

B Centrifugal pump 10 days 1 day 24 hrs(full day) C Dosing pump __ __ __


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Step -1 For year 2012 ammonia cost is 32400 Rs/Tonne so production loss function as stated below (according to table 4.1): Min Z = 32400 x1 + 32400 x2 Where x1 and x2 are amount of ammonia loss due to casing maintenance and leakage problem. C1 &C2 are cost coefficient for year 2012 which is 32400. Step -2 According to table 4.1 constraints are: X1/12*420 + 6 X2/ 5* 420 1 X1/10*420 + X2/420 1

Where 420 is ammonia production rate per day. In a category problem we do regular monitoring of compressors and spare inventory should become 100% or one set. II.2 Cause and Effect Diagram In multistage compressor basic maintenance problem occurs due to surging, surging can occur shaft alignment and excessive vibration occur so diffuser and guide vanes damage. Effects are complete plant shut down occur so production loss occur and high maintenance cost pay to organization.

Fig.1: Cause and Effect Diagram of Ammonia Plant Maintenance In centrifugal pump basic maintenance problem occur due to cavitations on impeller and reduced flow deflection and shearing of shaft, seizure of pump internals and excessive bearing failure. The effects are production loss due to change pump which are taken in standby. III. REMEDIES STEPS USED TO REDUCE MAINTENANCE COST (i) In multistage compressor highly loaded journal bearing can be unstable at high speed so tilting pad bearing is used. Each shoe tilts independently to maintain to maintain load carrying hydrodynamic pressure wedge. (ii) Engineers should check rotor response curve displacement, relative bearing force curve verses speed curve time to time for multistage compressor. (iii) Avoiding recirculation in centrifugal pumps. (iv) Operating characteristics curve head verses flow rate study properly on computer so minimum flow rate maintain in centrifugal pump.

NH3 and urea supply

Low productivity

High maintenance cost

Surging in diffuser so stresses develop in impeller, Change shaft alignment in multi stage compressor

Cavitations on impeller, due to reduced flow seizure of pump internals in centrifugal pump


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Visualization of Flow Characteristic curves & Use Remedies

Fig.2: Visualization and Remedies Concept of Engineers

IV. REDUCTION OF PRODUCTION LOSS BY L.P.P. In urea plant we want to do minimum production loss by doing minimum lead time of preventive and shut down maintenance. So we formulate the L.P.P. of problem and applying optimization technique we do minimum production loss. Step-1 Formulate the L.P.P. according to problem formulation data we state the actual problem: For year 2012: minimum Z =32400 y1 + 32400 y2 Here c1=32400, c2 =32400 are cost coefficient for year 2012.Y1, Y2 are amount of ammonia loss due to casing and leakage problem. . Now we are solving minimum production loss for year 2012. Step-2 By apply simplex method we solve the L.P.P. : Optimization function: Minimum Z =32400 y1 + 32400 y2(i) Constraint according to problem formulation stated below. X1/12*420 + 6 X2/ 5* 420 1(ii) X1/10*420 + X2/420 1(iii) To solve this L.P.P. we apply simplex method. So L.P.P. is solved as stated below. Maximum Z= -32400 y1 -32400y2 + 0s1 +0s2 Subjected to y1/5040+ y2/350+ s1=1 y1/4200+ y2/420+s2=1 Basic feasible solution if y1=y2=0 then s1=1, s2=1 Step-3 iteration-1formulate the table according to basic feasible solution

cj -32400 -32400 0 0 cB Basis y1 y2 s1 s2 b b/a 0 s1 1/5040 1/350 -1 0 1 350 0 s2 1/4200 1/420 0 -1 1 420 cj-zj -32400 -32400 0 0

Step-4 iteration-2 formulate the table towards optimality

cj -32400 -32400 0 0 CB Basis y1 y2 s1 s2 b b/a -32400 y2 35/504 1 -350 0 350 5040 0 s2 154/5040 0 350 -420 70 2290.9 cj-zj -2250 -30150 0 0

ENGINEERS& OPERATORS

REDUCED MAINTENACE COST

REDUCED PRODUCTION LOSS


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Step-5 iteration-3 formulate the table towards optimality

cj -32400 -32400 0 0 CB Basis y1 y2 s1 s2 B b/a

-32400 y2 0 1 -1145.45 954.54 190.97 -32400 y1 1 0 11454.54 -13745.4 2290.9 cj-zj -32400 -32400 -334014516 -360217670

This is optimum solution so production loss by casing problem for multistage compressor and centrifugal pump is 190.97 tones of ammonia and production loss for leakage problem for both machinery is 2290.9 tones of ammonia. IV.1 Graphical Reduction of Production Loss by L.P.P. Optimization function: Minimum Z =32400 y1 + 32400 y2..(i) Constraint according to problem formulation stated below. X1/12*420 + 6 X2/ 5* 420 1(ii) X1/10*420 + X2/420 1(iii) When x1=0 then x2 = 5/6* 420= 349.99 350 tonnes say A (0,350) When x2=0 then x1=12*420=5040 say B (5040, 0) When x1=0 then x2=420 say c (0,420) When x2=0 then x1=4200 say D (4200, 0)

450

400 350 300 250 200 150 100 50 0

1000 2000 3000 4000 5000 6000

Fig.3: Graphical Representation of Production Loss Problem

IV.2 Analysis of Problem by MATLAB Optimization function: Minimum Z =32400 y1 + 32400 y2(i) Constraint according to problem formulation stated below. X1/12*420 + 6 X2/ 5* 420 1(ii)


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X1/10*420 + X2/420 1(iii) To solve this L.P.P. we apply simplex method. So L.P.P. is solved as stated below. Maximum Z= -32400 y1 -32400y2 + 0s1 +0s2 Subjected to y1/5040+ y2/350+ s1=1 y1/4200+ y2/420+s2=1 First, enter the coefficients f = [-32400; -32400] a = [1/5040 1/350 1/4200 1/420]; b = [1; 1]; lb = zeros(2,1); Next, call a linear programming routine. [x,fval,exitflag,output,lambda] = linprog(f,a,b,[],[],lb); Entering x, lambda.ineqlin, and lambda.lower gets x =

190.97 lambda.ineqlin = 0 1.5000 lambda.lower = 1.0000 0 Nonzero elements of the vectors in the fields of lambda indicate active constraints at the solution. In this case, the second and third inequality constraints (in lambda.ineqlin) and the first lower bound constraint (in lambda.lower) are active constraints (i.e., the solution is on their constraint boundaries). V. MULTI STAGE COMPRESSOR MAINTENANCE FORECASTING Basically multistage compressor forecasting is dividing in two stages: (a) For impeller maintenance (b) Leakage maintenance (A) For impeller maintenance: we use simple smoothing forecasting formula as stated below: Ft+1 = Dt + ( 1- ) Ft Where Ft+1: Forecast for next period maintenance Dt : Actual maintenance demand for present period Ft : Previously determined forecast for present period : Weighting factor smoothing constant Total impeller maintenance time for multistage compressor is 12 days. It is predictive maintenance or emergency maintenance. The maintenance demand for June is 2 days and 4 days for July. We use forecasting method which takes average method maintenance demand forecast for June is 4 days (smoothing coefficient 0.7 to weight the recent demand most heavily) and we manipulate the maintenance demand for august and thus we manipulate for other month also.


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For July Ft+1 = 0.7 * 2 +(1- 0.7) * 4 = 1.4 + 1.2 = 2.6 days For August Ft+1 = 0.7* 4 + ( 1- 0.7) *4 = 2.8 + 1.2 = 4 days and so on.

(B) Leakage maintenance: Similarly leakage maintenance time for multistage compressor is 20 hrs. It is preventive maintenance. The maintenance demand for June is 1 hrs and 2 hrs for july. We use forecasting method which takes average method maintenance demand forecast for june is 2 hrs ( smoothing coefficient 0.8 to weight the recent demand most heavily) and we manipulate the maintenance demand for august and thus we manipulate for other month also. For July Ft+1 = 0.8 * 1 + ( 1- 0.8) * 2 = 0.8 + 0.4 =1.2 hrs For August Ft+1 = 0.8* 2 + ( 1- 0.8) *2 = 1.6 + 0.4 = 2.0 hrs V.1 Centrifugal Pump Maintenance Forecasting (A) Impeller maintenance (B) Leakage maintenance (A) Impeller maintenance forecasting Total maintenance time for centrifugal pump is 10 days. It is predictive maintenance or emergency maintenance. Maintenance demand for June is 1 day and 3 days for July. We use forecasting method which takes average method maintenance demand forecast for June is 3 days (smoothing coefficient 0.7 to weight the recent demand most heavily) and we manipulate the maintenance demand for august and thus we manipulate for other month also. For July Ft+1 = 0.7 *1 + ( 1- 0.7) * 3 = 0.7 +0.9= 1.6 days For August Ft+1 = 0.7 * 3 + (1- 0.7 ) *3 = 2.1 +0.9 =3 days (B) Leakage maintenance forecasting: Similarly leakage maintenance time for centrifugal pump is 1 day. It is preventive maintenance. The maintenance demand for june is 3 hrs and 4 hrs for July. We use forecasting method which takes average method maintenance demand forecast for June is 4 hrs ( average smoothing coefficient 0.8 to weight the recent demand most heavily) and we manipulate the maintenance demand for august and thus we manipulate for other month also. For July Ft+1 = 0.8 *3 + (1-0.8) *4=2.4+0.8=3.2 hrs For August Ft+1 =0.8 *4+(1-0.8)*4 =3.2+0.8 = 4 hrs Now we draw operation chats for June, July and august month and we alert for august month according to previous trends for predictive and preventive maintenance. VI. OPERATION CURVES FOR FIND OUT CERTAIN PRIOR MAINTENANCE Operation curves mainly divided in to three basic categories: (1) Rotor response curves (2) Efficiency curves (3) Surge curves


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VI.1 Rotor Response Curves

Modern process compressors are built in API specification. One important item of specification is natural frequency of rotor. This natural frequency must not occur in variable speed range of compressor. The dynamics of rotor can be studied with the help of computer and the effect of rotor of operative unbalance due to built up misalignment can be evaluated. The rotor unbalance will load the bearing. Computer analysis allows the engineer to predict these bearing loading and to design a dependable maintenance free machine.

Fig.4: Eight Stage Rotor Response Curve

Fig. 4 shows calculated and measured response curve for eight stage rotor compressor. The measured values were obtained first during the mechanical test of compressor. Although the vibration level was less than 0.7 mils and the bearing forces were below the designed dynamic load limit, the steepness of vibration curve near the maximum operating speed was understandably cause for concern. The rotor was modified and rested.

Fig.5: Eight Stage Rotor for Modified Response Curve


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These results are shown in Fig.5. The shop test shows quite low vibration amplitudes and low bearing loading. The compressor, once in actual service, will become unbalanced due to built-up on rotor. The difference between the calculated and measured response curves shows that this compressor will be tolerant to considerable rotor deposits before it will have to be cleaned. Lightly loaded journal bearings, such as those used in compressor, can be unstable at high speeds, and a number of solutions of this problem have been used. A tilting pad journal bearing is widely used in compressor. Each shoes tilt independently to maintain its load carrying hydrodynamic pressure wedge. By observation it is observed that in month of July and august curve is deflected more so prior maintenance should be done and save the production loss 15-20% respectively. VI.2 Efficiency Curve

Fig.6: Compressor Performance Curve

Compressor performance curves consist primarily of a plot showing the variation of compressor head or pressure ratio and efficiency at various constant rpm conditions at different mass flow rates such as shown in figure 6. It can be seen from figure 6 that increase in rotor speed increases the compressor flow rate. At a particular rotor speeds an increase in compressor pressure ratio can be obtained by reducing the mass flow rate. This is to be expected because an increase in pressure at compressor delivery can only be expected if there is resistance to flow, otherwise, compressor would behave more like a fan or a blower. In a similar fashion, an increase in flow rate at constant rpm can be obtained by a reduction in the resistance at the compressor exit. An enhancement of compressor flow rate at constant delivery pressure is also possible. This requirement however can be met by not only changing exit throttle, but also increasing the compressor rpm. Minimum and maximum flow rates at constant rpm are termed surge line. Similarly, locus of operating points of compressor at various rpm is termed operating line. The compressor rotor should be designed such that constant rpm, its efficiency peaks close to surge line, as indicated in figure 6 that is when compressor ratio is maximum. By observation it is observed that in month of July and august curve is deflected more so prior maintenance should be done and save the production loss 15-20% respectively.


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VI.3 Surge Curve

Fig.7: Performance Map with System Curves and Surge Cycle

A typical centrifugal multi stage compressor performance map used in process industry is shown in figure 7. The family of fixed pressure drop, or pressure control in the particular system external to compressor through which the flow is being pumped. However, it should be noted that, to follow any of these system curves, speed must be changed. This, in turn, changes the flow. With system 2 and 3, the head is also changed. These statements are valid only if no changes within system itself occur. Changing setting of control valve, adding another piping loop, or changing catalyst level in a reactor which would modify the system curve. To a large extent, the frequency of surge cycle varies inversely with in volume of system. For example, if the piping contains a check valve located near the compressor discharge nozzle, the frequency will be correspondingly much higher than that of system with a large volume in the discharge upstream of a check valve. The frequency can be as low as few cycles per minute or as high as 20 or more cycles per second. Generally speaking, if the frequency is higher, the intensity of surge is lower. The intensity or violence of surge tends to increase with increase gas density, which is directly related to higher molecular weights and pressures and lower temperatures. Higher differential pressure generally increases the intensity. By observation it is observed that in month of July and august curve is deflected more so prior maintenance should be done and save the production loss 15-20% respectively. VII. EXPECTATION OUTCOME The basic problem occur in multistage compressor (A type problem), centrifugal pump(B type problem) and injection pump (c type problem).


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In A type problem company shut down the plant. But I analysis by optimization techniques, the lead time may be reduced for preventive maintenance by daily monitoring and daily preventive maintenance policy. Reduce by daily monitoring and daily preventive maintenance policy. In B type Problem Company put the centrifugal pump in spare and replaces the pump whenever required. But I also reduced lead time by optimization techniques for preventive maintenance by daily monitoring and daily preventive maintenance policy. C type problem is not affected the production. So injection pump may be change over on the monthly repairing shut down time. By applying optimization techniques lead time saving in preventive as well as shutdown maintenance will be 10-15% and production loss saving will be 15-20% approximately. VIII. CONCLUSION MORA (2002), states that implementing total quality maintenance is not a difficult task. However, it requires some customized training in order to succeed. The results of implementing an effective programmed in terms of increased plant efficiency and productivity are outstanding [3]. According to Kennedy (2005), it should be acknowledged that a TQM implementation is not a short-term fix programmed. It is a continuous journey based on changing the work-area then the equipment so as to achieve a clean, neat, safe workplace through a "pull" as opposed to a "push" culture [4]. Significant improvement can be evident within six months. However, full implementation can take many years to allow for the full benefits of the new culture created by TQM. At this crucial point of global competition the implementation of TQM not a matter of liking it or following the fashion. While TQM in the 60's was just an innovative thing, today it has turned into a survival strategy. TQM is capable of bringing a machine back to original condition and even better. The cost of postponing a decision of implementing TQM that has to make sooner or later can be excessive. It is convincing that the losses for each day of delay are out of imagination. Successful TQM implementation can achieve better and lasting results as compared to other isolated programmers because there is an ultimate change in people (knowledge, skills, and behavior) during the progress. It gives a summary of why companies should consider implementing TQM in their organization, including the motivating factors as well as the resulting benefits. REFERENCES [1] Hopp W. and Wu S., Machine maintenance with multiple maintenance actions, IIE Trans., Vol.

22(3), pp. 226-233, Sep.2002. [2] http:// www.techeduhry.nic.in/syllabus/computer%20engg/6comp.pdf [3] Mora S., Implementing total Quality Maintenance is not a difficult task, IIE Trans., Vol. 23(4),

pp. 330-340, Sep.2002. [4] Kennedy P., TQM implementation is not a short-term fix programmed, IIE Trans., Vol. 26(4),

pp. 231-235, 2005.

Total Quality Maintenance and Trouble Shooting - A Case Study

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