1

Training report

On

Condition Based Maintenance on Plant

Components Using Vibration Analysis

MMU Section in Power Plant

(KAKRAPAR ATOMIC POWER STATION)

Checked By: Submitted By:

S B Patel Harvish K. Sonar

(SA/F)

2

The Following Report Has Been Prepared By

Name : Harvish K. Sonar

Course : B-Tech, Mechanical

Year : 3rd year

Semester : VI semester

Institute : BITS, Pilani

Training Period : 22/05/2015 TO 20/06/2015

Section Allotted : Mechanical Maintenance Unit

Guided By : Mr. S. B. Patel & G..Pramanik MMU, KAPS.

3

PREFACE A theoretical student/person cannot become perfect without practical understanding of his branch. That's why training is called as a bridge between theory and practical. It makes practical person and hence provide a golden opportunity for all theoretical student to interact with the working environment.

The principal activity of training is that the student should expose to an industrial atmosphere, attitude and discipline before actually working in any industry in feature.

On behalf of successfully completion of my training here, I am realizing that I have made the right choice.

KAPS is what has inspired me to opt for this industry as a first step of knowledge which will lead me to success in future.

Harvish K. Sonar

B-Tech, MECHANICAL,

BITS, Pilani

4

Acknowledgement

The presented project report is a result of team effort to carry out a formidable work in the field of "Turbine-Generator and its auxiliary systems", which would not have got its present shape without appreciable support and guidance of SHRI H.SAPRE SE (MM)

At the moment of submitting this work, I seize the opportunity to express my deep gratitude towards esteemed guide SHRI. A.R.SUBBARAO, SM/E (MMU) for his utmost support and care.

I express my deep gratitude to the whole team of Turbine and Auxiliary systems maintenance group who provided me with valuable guidance and suggestions for preparing this project, indeed they have helped me with their best knowledge to sharpen and refine my knowledge about the subject.

To make anything successful, one needs help and co-operation from people involving directly and indirectly with the company. It's my great pleasure that I got vocational training at KAKRAPAR ATOMIC POWER STATION. So, last but not least, I am greatly thankful to Mr. S. B. Patel, Mr. G. Pramanik who guided me to select this project for studying at KAPS.

Finally, I am grateful to each and every official who knowingly or unknowingly helped me for completing this training .It was really a good experience for me.

Harvish K. Sonar

B.Tech. (MECHANICAL), 6 TH SEMESTER

5

INDEX

Sr. No. Content Page No.

1 Importance of nuclear power plant 6

2 Introduction 8

3 Brief Discussions on Thermodynamics 12

4 Important rotating components of steam cycle

14

5 Maintenance Strategies 24

6 Systematic approach to CBM 35

7 Abbreviations 38

6

Importance of nuclear power plant Each country has to plan its strategy for sustainable long-term development in accordance with its socio-economic condition, natural resources and technological capability. The level of development in a society depends upon the availability of energy and growth rate in energy use in turn depends on its level of development.

The overwhelming energy need of Indian Industry and agriculture is in the form of electricity. A very fast growth in electricity generation in India is necessary to improve the standard of living of our people. India has to look at all sources of energy to ensure long-term availability of energy.

Revival of nuclear energy in different parts of the world is expected to occur sooner or later. Nuclear power plays a major role in most of the sustainable scenarios associated with long-term energy prospects.

Power or energy consumption is now one of the indexes of living of mankind today. Today there is a large demand of electricity and to meet the requirements, large amount of power producing devices have been developed. Nuclear power plant is one such successful system which is used to convert heat energy of Uranium fission to produce the electricity.

Uranium 235 is inserted into calandria and fission reaction takes place which releases energy as shown in the reaction. Calandria is a cylindrical vessel having 306 channels having 12 number of fuel bundles so that total 12 X 306 fuel bundles are loaded. The reaction is

92U235 + 0n1 fission product + avg. 2.5 neutrons + Heat + radiation

7

Above diagram indicates the general layout of a nuclear power plant. The heat energy produced by fission in calandria is carried to the boiler by heavy water (D2O). This heat is then used to convert water into steam which in turn is used to rotate turbine. Turbine shaft is coupled with generator and electricity is produced. The steam loses temperature and pressure in turbine and is returned to condenser. If plant has a cooling tower facility, water is sent to cooling tower or, hot water is disposed into the river. Fresh water is taken into the condenser and inserted to the cycle.

8

Introduction

KAKARAPAR ATOMIC POWER STATION (K.A.P.S) is situated on the left bank of river in South Gujarat. It is a unit of NUCLEAR POWER CORPORATION OF INDIA LIMITED (NPCIL). Which is a wholly owned under taking of Government of India under the administrative control of Department of Atomic Energy (DAE) Government of India. The mission is to develop nuclear power technology and produced in a self-reliant manner nuclear power as a safe environmentally benign and an economically viable source of electrical energy to meet the growing electricity needs of the country. NPCIL has its vision to have an installed nuclear power capacity of 20000MW (e) by the year 2020 AD.

KAPS has two-unit module with the capacity of 220MW (e) each belongs to CANDU family of reactors, which is pressurized heavy water reactor (PHWR). The reactors use heavy water as moderator and natural Uranium as a fuel in a sophisticated form, which is available in large quantity in India.

The science and engineering design, manufacturing, fabrication, erection, commissioning and operation of this station are totally executed by Indian engineers and scientists.

The studies in the nuclear science on a systematic basis began in India during late forties with the establishment of TATA INSTITUTE OF FUNDAMENTAL RESEARCH CENTRE at Mumbai. After that the atomic energy commission (AEC) was formed. The scope and magnitude of the atomic energy program has grown considerably in this five decades which has made us to join the pool of countable countries which proved the technology excellence in administrating nuclear energy in the civil and defense line for peace full development.

Research and development in many advance technologies has taken place. Exploitation of nuclear energy for generation of electricity has supplied the country with nearly 75000 million unit so far. The peaceful, moral and disciplined research activity taken up by BHABHA ATOMIC RESEARCH CENTER (BARC)

9

encompass fields like agriculture, isotopes, medicines, computers and R&D in area directly relevant to nuclear energy.

The research reactors APSARA, CIRCUS, ZERLINA provide insight into science, technology and engineering for the atomic power programmers. BARC, in addition provide over the past 35 years the nucleus of the manpower for atomic power programs through its scientific and engineering training. BARC has contributed widely in various aspects like physical engineering, material selection, fabrication and testing for their behavior and production. Spent fuel re processing, radioactive waste management also taken up by BARC. Design analysis and simulation have also been taken up to improve the design manufacturing aspect of Indian reactor technology.

BARC is also responsible for development and applied development of various device, equipment and system of nuclear power plant to complete with the emerging safety requirement. Further developments of specialized (including robotics) tools and tackles also have been helpful in the operation, maintenance and surveillance of the reactor equipment.

The atomic act was enacted in the year 1948 with the objective of providing for the development, control and use of atomic energy for welfare of people of India and for other peaceful purposes. NUCLEAR POWER CORPORATION OF INDIA LIMITED was incorporated as a public limited company wholly owned by Government of India, under the companies act 1956 and commenced its business with effect from Sept, 17, 1987.

Kakrapar Atomic Power Station (KAPS) is one of the nuclear power plant under NPCIL.It has a mission to develop nuclear power tecnology in a self-reliant manner as a safe and economically viable source of electrical energy to meet the growing electricity needs of the country. KAPS is located in mandvi taluka of surat district in state of Gujarat and is fifth nuclear power station of country. It has currently two units running which gives approximately (2 X 220 MWe) power. The construction work of another two units is under progress, which are decided to give nearly (2 X 700 MWe) of power supply.

In view of the limited fossil fuel availability with the country, the relevance of Nuclear Power in meeting the short and long term needs of our energy was

10

recognized right at the initial stage. From the very beginning, as a long term strategy, the Nuclear Power Program formulated by Dr. Homi Bhabha embarked on the three stage nuclear power program, linking the fuel cycle of Pressurized Heavy Water Reactor (PHWR) and Fast Breeder Reactor (FBR) for judicious utilization of our limited reserves of Uranium and vast Thorium reserves. The emphasis of the program was self-reliance and thorium utilization as a long term objective. The PHWR was chosen due to extensive research and development facilities covering diverse areas for supporting technology absorption. The 3-stage of our Nuclear Power Program is:

Stage - I: envisages, construction of Natural Uranium, Heavy Water Moderated and Cooled Pressurized Heavy Water Reactors (PHWRs). Spent fuel from these reactors is reprocessed to obtain Plutonium.

Stage - II: envisages, construction of Fast Breeder Reactors (FBRs) fuelled by Plutonium produced in stage-I. These reactors would also breed U-233 from Thorium.

Stage - III: would comprise power reactors using U-233 / Thorium as fuel.

K.A.P.S TECHNICAL DATA

Type of reactor CANDU, Pressurized Heavy Water Reactor (PHWR)

Gross electric generation 2 x 220 MWe

Type of fuel Natural uranium in oxide form (UO2)

Number of coolant channels 306 channels

Number of fuel bundles 3672 bundles

11

Primary coolant Heavy water (>95% isotropic purity)

Primary coolant temperature

2930C at outlet header

Primary coolant pressure 87 kg/cm2

Primary coolant flow 3173*103 kg/cm3

Moderator Heavy water (>99.97% isotropic purity)

Reactor vessel Calandria integral with end shield

Calendria and end shield material

Stainless steel 304-L

Coolant tube material Zircalloy + Niobuim (2.5%)

Calendria tube material Zircalloy-2

End fitting Stainless steel

Steam generator Tube steel material –low alloy

Tube material –incolloy

Steam condition Saturated steam at 2500C, 40 kg/cm2, 0.26% moisture

Turbine Horizontal tandem compounded. One high pressure and one double flow low pressure turbine.

Condenser vacuum 696.5 mm of Hg

Generator Rating 250 MVA, terminal voltage 16.5 KV

Quantity of steam 1340 tonnes/hr

Type of governing Throttle governing

12

Brief Discussions on Thermodynamics The saturated steam in PHWR type Indian NPP is supplied to HP turbine from Steam Generator (SG) through MSIVs, main stop valves and HP governor valves at a supply pressure of 41.03 kg/cm2(a), temperature of 2500C & wetness of 0.26% at SG outlet. The inlet pressure at HP Turbine is 40.33 kg/cm2(a).. After expansion in HPT the wetness of HP exhaust steam is about 9-10% and exhaust pressure is about 7 kg/cm2(a) in PHWR type of NPPs. The HP exhaust steam is passed through MSR. MSR is a single shell construction houses Moisture separator (MS), 1st stage steam to steam reheater (BSR) and 2nd stage steam to steam reheater in series. In MSR, the moisture is separated out first (0.5% wetness at MS outlet), then reheated to 2330C (superheated) prior to entering in LP turbine. The reheated stem enters to LP turbine through inceptor stop & governor valves placed in series. These inceptor valves are provided to control over-speed of turbine. Another design philosophy to control the turbine over-speed is to provide LP bypass system in place of interceptor valve arrangement or even the combination of both are used for this purpose depending upon the quantum & quality of steam being dealt. The inlet steam to LPT is superheated and LP exhaust steam after expansion is having of the order of 11-13% wetness. LP exhaust steam is condensed in surface type condenser. Condensate thus formed is circulated back to SG through different stages of feed heating and de-aeration.

Following Enthalpy-Entropy (H-ф) diagram shows the cycle & thermodynamic behavior of steam while expanding in Turbine cylinders. Carnot cycle is not the working cycle for a steam power plant because it is difficult for a pump to suck a mixture of water and vapour simultaneously and discharge saturated water only. This difficulty is eliminated in Rankine cycle where in there occurs complete combustion of steam and then when it turns into water; it is sucked into compressor isentropically at boiler pressure. Nuclear power plants are basically steam power plants and hence operate upon Rankine cycle. But efficiency is very low in original Rankine cycle and hence reheating and regenerative Rankine cycle is employed which is as below.

13

Water enters at 4200C. This water is then heated to 1300C isentropically. At this stage, further sensible heating is done and temperature gets as high as 1700C. Steam now reaches saturated state with a temperature of 2500C is achieved. At this stage, moisture is 0.26%, flow rate of steam is 1330 tonne/hr and steam pressure is 40 kg/cm2. Steam then enters into turbine and both pressure and temperature drop considerably. Modification is done here in original Rankine cycle that the steam at this low pressure and temperature is reheated in moisture separator and reheater. Moisture content increases to 11% at this stage and pressure gets as low as 5.6 kg/cm2. This reheating and regeneration gives us extra work. Hence it increases efficiency of power plant as a whole. Thus modified Rankine cycle is employed for its operation.

14

Important rotating components of steam cycle

Steam turbine:

It is a prime mover (equipment) which converts Thermal energy in to Rotational energy (torque). They are required to drive the generator to produce the electricity.

The factors affecting the design of the turbine are called features. The features which have to be taken in mind while designing the steam turbine are as follows:

1. Low Heat Drop: Turbines are operating with saturated steam with low inlet parameters hence it has very low heat drop across HP and LP cylinder.

2. Moisture Control

3. Turbine Governing System

MW - 237

RPM – 3000

Steam Pressure – 40 Kg/cm2

Steam Temperature - 250ºC

Reheat Temperature - 233ºC

15

16

General description:

The turbine is of the horizontal impulse-reaction design, on a single axis and consuming low pressure wet steam supplied from a heavy water moderator and heavy water cooled, uranium dioxide fuelled reactor. At stop valve, pressure and temperature condition of systems are 39.71 Kg/cm² and 250.3°C with 0.26 % wetness.

The turbine is suitably compound so that the expansion of the steam takes place in two cylinders,

[1] High pressure single flow (H.P) &

[2] Double flow low pressure (L.P) cylinder.

After expansion in single flow HP cylinder, the steam is exhausted to two moisture separator–cum re-heater units where moister is extracted and steam is reheated to 233°C before it enters the double flow low pressure cylinder.

The turbine has a maximum continuous rating (MCR) of 236 MW economical continuous rating (ECR) of 227.5 MW at a generator terminal at 3000 rpm. Steam is extracted from suitable stages of expansion to provide for 6 stage regenerative feed heating, with a final feed water temperature of 170.7°C.

Steam is supplied to the machine through two Combined Isolating and Emergency Stop valves (CIES valves) housed in two chest cast integral and then through two governor valves located on the either side of the center line of the machine and each consisting of a steam strainer and two throttle valve housed in two separate chests. For initial runs temporary strainers having holes of size 3.2 mm are fitted in CIES valve. After initial run permanent strainers having holes of size 5 mm are fitted for regular operation of turbine.

The TG equipment are tandem compounded in the order HPT – IPT(in case it exists) – LPT – Generator – Exciter (in case rotating exciter). In all Indian NPP the TG sets are full speed machine (i.e., rotating speed 3000 rpm) having 2 pole generators. The Turbine generator shafts are rigid coupled. A typical layout arrangement of TG is shown in following figures:

17

The advantage of tandem compounding is, there is no separate gear box arrangement for transmissions of power/torque, which reduces loss and capital & maintenance costs of gear box.

HP turbine:-

18

HP cylinder casing is cast from 2.25 % Cr Mo steel and made of two halves: top and bottom, which are bolted when assembled by the heat tightened bolts made of 1.25 % Cr and 0.7 % mo steel to ensure an effective seal against steam leakage. It consists of 5 stages.

There are five stages in the HP cylinder. From HP cylinder, steam is extracted for steam reheating before stage 4 & for feed heating before stage 5 from the exhaust of cylinder. The exhaust steam is led in to two separators cum reheated units positioned in parallel on either side of center line of the machine. Most of the moisture is recovered in the two stages in the reheater part, employing bled steam and live steam as the heating medium.

The steam from the reheaters passes through two interceptor steam chests, each housing an interceptor emergency valve & an interceptor governor valve before entering the LP cylinder, from where it is finally exhausted to the condenser.

LP turbine:-

The LP cylinder is a double shell construction and the outer and inner casings are fabricated from mild steel and 1.25 % Cr 0.7 % Mo steel respectively. As the LP outer cylinder halves are too large in dimension, each of them is divided into three sections to facilitate transportation. The fixed point of the rotor system is the collar of the LP rotor held in place by the thrust bearing, which takes all the axial thrust. The vertical and axial keys maintain alignment between inner and outer LP cylinders. The LP cylinder is supported on steel sole plates, which in turn rests on spherical packers (wedges).

It is a dual flow and dual admission turbine i.e., the steam enters from two sides and flows in opposite sides of the LP turbine (as it has 5 blades on either side).

There are five stages in each flow of LP cylinders & steam is extracted from four stages 2, 3, 4 & 5 for feed heating to de-aerator combined into a common exhaust chamber welded to a rigidly supported condenser.

19

TG rotor system

The direction of rotation of the rotor system is clockwise, if viewed from the front pedestal end. All the rotors in the turbine generator system are mono-bloc rotors and coupled by solid (flange) couplings. Both the turbine rotors are machined from the 3.5 % Ni, Cr, Mo, forgings and the blades from stainless steel billets containing 12-14% Cr. The blades are of impulse reaction type in HP and LP first three stages whereas LP last two stages blades have high % of reaction. The LP last stage blades are 940 mm long and the 4th and the 5th stage LP moving blades roots are of curved side entry fir tree type.

Except for the last two stages of LP cylinder, in all the other stages, the blades are shrouded to minimize the steam leakage between the moving blades and the diaphragm baffle rings. Each rotor is supported on two main bearings. The thrust bearing is in pedestal between the HP and LP.

20

Main Oil Pump (MOP)

It is a centrifugal pump, bolted to the front end and is directly driven by the turbine shaft. It delivers 4455 lpm of oil at 24.6 kg/cm2 in to the pump discharge line through a non-return valve when the turbine is running at 3000 rpm. A portion of this tapped off from the discharge line and passed through an air operated control valve and duplex filter and supplied to the control gear and seal oil system at 21 kg/cm2.

Jacking Oil Pump (JOP)

It serves two purposes:-

Reduces the torque required by the barring gear.

Prevents metal to metal contact at the initial stages of rotation, thus avoiding any damage to the bearings.

It is brought into operation in conjunction with the barring gear during turbine start up and shutdown. It supplies oil at a pressure of 140 kg/cm2 to each of the turbine and generator bearings in sufficient quantity to establish an oil film on which the heavy rotors may float at low speeds of rotation when the normal oil wedge would not be formed.

Condensate Extraction Pumps:

Two 100% capacity condensate extraction pumps and two 2.5% auxiliary condensate extraction pumps are provided to pump the condensate from hot well to the deaerator. During normal operation one of 100% CEPs will be in operation and the other main CEPP will remain as standby. The auxiliary condensate system is designed to ensure condensate flow to deaerator when CL-IV power fails, to maintain feed to steam generator for removing decay heat during reactor shut down condition. The auxiliary CEPs (normally kept in AUTO) will start automatically when both 100% pumps trips.

21

Main Condensate Extraction Pumps (MCEP):

The main condensate extraction pumps of 100% capacity each make is KBL. It is a vertical 3-stage centrifugal barrel pump. Power is supplied to the pump by an electric motor through a flexible pin bush type coupling. Barrel is lowered in the pit and is bolted on foundation base frame. The distributor casing is mounted on the barrel flange with O-ring required for sealing. The suction and delivery connection are located on distributor casing above which bearing stool is fixed. The pumps are capable of delivering 1100 T/Hr at a delivery head of 125m of water column of 1484 rpm. The motor is of 500 KW rating.

The arrangements for lubrication of the pumps are self-contained. The tilting pad bearings are filled in the oil bath of the bearing, cooled by the cooling coils installed in the bearing housing.

The oil level gauge is mounted on the outer bearing housing from which the oil level inside the bearing housing can be read. A local temperature gauge and thrust bearing metal measure the oil temperature by RTD located in thrust bearing pad. In the event of packing failure, the bearings are cooled by non-active high-pressure water.

Normal cooling water flow for each bearing is 7.5 lit. /min. Main CEPs motors are rated 6.6KV and supplied with CL-IV power supply. 520 watt, 240 volts space heaters are provided in each motor for eliminating the moisture from the air during shut down. The minimum flow required for continuous operation is 220m3/Hr.

Auxiliary Condensate Extraction Pumps (ACEP):

There are two pumps of 2.5% duty. The pumps are vertical 3 stages, centrifugal barrel type and are provided with deep groove ball thrust bearing for which no cooling water is required. The drive of the pumps is affected by an electric motor through a flexible coupling. On the bottom section of the distributor casing suction and delivery nozzles are located.

The condenser pressure is developed by transformation of velocity into pressure through the diffuser; the normal discharge is 32 T/Hr, with the total head of 65m of the water column. The speed of the pump is 2920 rpm. The motor is 15Kw, 415 V,

22

and CL-III power supply. The ACEPs have separate discharge line with a orifice plate and manual globe valve parallel to the orifice and connected to the condensate line at deaerator inlet with check valve (the manual valve is normally closed) for exhaust hood spray one tapping is taken from ACEP discharge line connected at upstream of duplex filter with isolating valve. In case of requirement, exhaust hood spray cooling can be given through ACEP.

Main Boiler Feed Pumps (MBFP):

Three 50% MBFP's each of capacity 630 T/hr take suction from deaerator storage tank and discharge into 4 nos. steam generators through HP drain cooler, HP heater 5, 6 and feed control stations. The MBFP's are horizontal two stages, barrel type and cartridge design. Each pump is provided with mechanical seal circuit consisting of magnetic filter, seal cooler and temperature indicators. NAHP cooling water is supplied to each pump for cooling of lubrication oil cooler, motor cooler and mechanical seal coolers. For isolating each pump manual operated gate valve in suction and MV (gate valve) in discharge line have been provided. Y-type strainers on suction of each BFP are provided for removal of dirt. The check valve are provided in discharge line of each

BFP for preventing reverse flow and thus reverse rotation of pumps. In addition reverse rotation probes are provided on each pump for sensing the reverse rotation and subsequently giving alarm in C/R. The reverse rotation is not permitted as pump suction line has been designed for much less pressure. Each pump is provided with its own independent forced oil lubrication system for the bearings. There are two gear type oil pumps one electric driven and other shaft driven which takes suction from main oil tank and distributes to motor and pump bearings via oil cooler and duplex filter. Flow control to each bearing is achieved by adjustable orifice located in supply line to each bearing. Three pressure switches located within the local control panel are used for start/stop of MBFP motor and stop/ start of auxiliary oil pump. Sight flow glasses have been provided in lubricating oil outlet line of each bearing. The oil recommended is servo system-46 of IOC or equivalent.

23

Each MBFP is provided with an automatic recirculation system consisting of modulating control valve and independent recirculation line leading to the deaerator storage tank with a pressure reducing orifice. This system protects the pump during period of low steam generator demand or when pump is operating against closes discharge valve. Each recirculation line is sized for 240 T/hr flow for ensuring minimum flow for pump protection. No warm up arrangement has been provided and pumps have been designed to accept hot water when starting from cold condition.

Auxiliary Boiler Feed Pumps (ABFP):

Two ABFP’s each rated at 36T/hr one operating during CL-IV failure and other standby take suction from the deaerator storage tank, and supply feed water to SG for removal of decay heat from reactor by blowing steam from steam generators. For better reliability and redundancy the ABFP discharge has been taken to the SG's through two alternate paths.

Through a line directly connected to auxiliary feed nozzle of the SG's, which will be the normal route, which ensures decay heat removal even after main feed water line rupture.

Through downstream of HP heater 6 in the main feed line. This is an alternate route for auxiliary feed water when required to take advantage of SG level control.

The ABFP's are 9 stage pumps fitted with mechanical seal. The pump and motor bearings are anti-friction bearings. Seal housings are having jackets which are cooled by NAHPPW. Each ABFP and recirculation is connected back to deaerator. A pressure control valve has been provided in the ABFP discharge header upstream of discharge MV to maintain ABFP discharge pressure to avoid pump tripping on O/L as well as damage to the pump in case of reduction in SG pressure resulting in considerable lowering of pump developed head.

24

Maintenance Strategies

Maintenance Strategy is a long-term plan, covering all aspects of maintenance management which sets the direction for maintenance management, and contains firm action plans for achieving a desired future state for the maintenance function.

Maintenance: The process carried out on any equipment to keep it in running condition is called as maintenance. The maintenance of any equipment can be done in following ways.

Types of Maintenance Strategies are:

• Preventive maintenance Ex.: Condition Based Maintenance, Routine maintenance, Periodic maintenance, Pro-active maintenance

• Break Down maintenance /Corrective maintenance

Merits & Demerits of types of Maintenance:

Advantages of Breakdown Maintenance:

• Low cost of maintenance as compared to other maintenance strategies.

• Process cycle need not be stopped frequently • Human error in case of operating in running condition is eliminated.

Disadvantages of Breakdown Maintenance:

• The production loss is too high when the equipment fails. • The Breakdown maintenance is associated with 3M loss ie, man power,

material and money.

Advantages of Preventive maintenance:

• Improve production by reducing machine downtime

• Mitigate wear and tear on equipment by keeping it clean and lubricated • Detect potential machine/part failures early

25

• Avoid unexpected equipment failures that cause production loss

• Schedule full repairs instead of performing a partial repair • Reduce maintenance and repair costs by eliminating emergency repair

services • Reduce Re-Active Maintenance by increasing Pro-Active Maintenance

Disadvantages of Preventive maintenance:

• Increases investment in diagnostic equipment • Increases investment in staff training • Inefficient operation on equipment may lead to unwanted shut down of

running equipment. • Unplanned downtime cannot be excluded.

Why CBM is selected as Tool for maintenance?

Even though the cost incurred in maintaining equipment is a bit on a higher side CBM is selected as strategy of maintenance because the overall gain obtained by maintaining the equipment frequently is much larger.

On assessing the condition of the equipment a prediction can be made of when the equipment is going to fail and time can be determined for maintenance to be done.

Also as the equipment is very well handled exact cause of problem can be determined and remedial actions can be made at exact location without disturbing the other functional parts of the equipment.

This reduces the manpower involved and this reduces extra effort. It saves the extra money incurred as the preventive action is taken before the system comes to a standstill.

It give extra confidence to operator while operating the machine.

Advantages of Condition Based Maintenance:

• Continuous Maintenance detects the onset of component problems in advance.

26

• Maintenance performed only when needed and may be planned in ahead of time.

• Reduced costs for machine and process downtime. • Reduced costs for manpower and replacement parts.

Disadvantages of Condition Based Maintenance:

• High initial costs for standard-Maintenance systems and/or contracted services to perform them e.g.: as thermography and vibration analysis.

Tools/techniques available for CBM:

The Condition of any equipment can be checked by various senses and indications given out by equipment while it is in operating condition. Some of them are discussed below

Acoustic Analysis: Any abnormal sound produced in the equipment is an indication of any malfunctioning of it. But the main problem is the receptivity and distinguishability of the sound. Many times the source of the sound is too confusing that may lead to ambiguous conclusions. Also analyzing sound needs a fair bit of experience.

Temperature: When any part having relative motion comes in direct contact due to friction temperature rises. This indicates wearing and lack of lubrication.

Vibration: This is the ultimate and the most reliable tool for assessing the condition of operational equipment. Various instruments are designed for vibration data collection and analysis of the collected data.

Ferrography: Oil Analysis of lubricating oil used for the machine is analyzed for any wear debris particles. This indicates the wear and tear of rotating and mating parts.

27

Why vibration is selected as tool for CBM?

Any deterioration in machine condition will first indicate in increase in vibration level. As discussed earlier it is the most reliable tool for condition Maintenance of the equipment. Also once the data is collected the analysis would give precise cause of vibration. This would lead to an exact remedial action to be undertaken while maintenance is done.

What is vibration?

It is the response of a system to an external or internal force which causes the system to oscillate. Also it refers to mechanical oscillation about an equilibrium position.

Vibration Analysis is a non-destructive technique which helps early detection of machine problems by measuring vibration.

Basic theory of vibration:

FREQUENCY: Number of oscillations in a given interval of time. It signifies the source of vibration. It answers the question what is vibrating?

Simple Spring Mass System

Upper Limit

Neutral Position

Lower Position

Dis

pla

cem

ent

Max Acc Mim Vel

Max Acc Mim Vel

Max Vel Mim Acc

28

Units: CPS (Hz), CPM AMPLITUDE: It is the magnitude of vibration signal. It signifies the size(severity) of problem. It answers the question how much is it vibrating? Units: micron, mm/sec, mm/s2 PHASE ANGLE: It is the measure of relative time difference between two sine waves. It provides information how one part of a machine is vibrating compared to other. It signifies causes of vibration. It answers the question how is it vibrating?

Amplitude Measurement:

1. Displacement: Total distance traveled by the mass. Unit: Microns. It is Stress indicator. 2. Velocity: Rate of change of displacement. It is the measure of the speed at which the mass is vibrating during its oscillation. Unit: MM/Sec, Inch/sec.It is fatigue indicator. 3. Acceleration: It is the rate of change of velocity. The greater the rate of change of velocity the greater the forces (P=mf) on the machines. Unit: M/Sec2, Inch/sec2.It is force indicator. 4. Spike Energy: It is the repetitive force exerted by a dent in the faces particularly in ball bearing. It is a trade name given to a frequency corresponding to high rpm.

29

What is the advantage of using velocity?

• Flat frequency range compared to displacement & acceleration. • Almost all machines generate fault frequency between 600CPM to 60KCPM • Velocity indicates fatigue. • Velocity is the best indicator of vibration severity.

Vibration transducers: They produces electrical signal of vibratory motion. Proximity Probe: It measures relative displacement between two rubbing surfaces. Frequency ranges from 0 to 60000cpm. Velocity Probe: It produces signal proportional to velocity. It is self-generating and needs no conditioning electronics. Frequency ranges from 600cpm to 60000cpm.It is temperature sensitive.

t

+

a

d v

30

Accelerometer: It produces signal proportional to acceleration of seismic mass. Its extremely linear amplitude sense. It’s having large frequency range.

Scales of Amplitude:

FFT spectrum analysis:

• It is known as Fast Fourier Transformation, developed by J.B.fourier in 1874. • It mathematically converts overall complex signal into individual amplitude

at component frequencies. • Different machinery problems cause vibration at different frequencies. • Overall vibration coming out from machine is combinations of many vibration

signals from various machine parts and its structure.

• FFT is a method of viewing the signal with respect to frequency.

P e a k

Pe

ak to

Pea

k

RM

S

Av.

Peak - a Peak to Peak - 2a RMS - 0.707 a Average - 0.637 a

31

Detection by Vibration Analysis:

• Unbalance • Bent shaft

• Misalignment • Looseness • Eccentricity

• Resonance • Defective antifriction problems • Wear in sleeve bearings • Oil whirl

• Aerodynamic/ hydraulic problems • Belt problems • Electrical problems

• Gear problems

32

Unbalance

� Vibration occurs at a frequency of 1 x rpm. � Radial vibration is reasonably uniform, is not directional. � Unbalance of couplings will reveal comparable amplitudes on both driver

and driven component. � Unbalanced machine component like motor or fan, will show higher

amplitudes.

Bent shaft

� Bent shaft can be due to machining errors/ mishandling / thermal distortion.

� Predominant vibration at 1 x rpm like unbalance. � Radial vibrations will be fairly uniform. I.e., non-directional. � But unlike unbalance axial vibrations exceeds 50% of the radial

vibrations. � Can be confirmed with phase analysis of axial vibration. � Bent shaft conditions:

• Rotor with a simple bow • Shaft having a bend near a particular bearing

� Bent shaft problems cause high axial vibration • 1x rpm dominant if bend is near shaft center

• 2x rpm dominant if bend is near shaft ends � Phase difference in the axial direction will tend towards 1800 difference

Misalignment

� Misalignment can be due to • Operating temperature • Settling of the base of foundation

• Deterioration or shrinkage of grouting

33

� The forces resulting from coupling misalignment are shared by the coupled machine components. Amplitudes of the vibrations on the driver and driven units shall be same.

� Misalignment occurs in certain direction. Hence directional vibration.

Vibration frequencies:

• Axial misalignment: 1 x rpm( normally)

• Offset or parallel misalignment : 2 x rpm

• Combinations: 1x , 2x and 3x

Axial vibrations exceeds 50 % of highest radial vibration.

Will reveal a phase difference up to 60°-180° between the driver and driven.

Looseness

� Looseness is not an exciting force. Other exciting forces such as unbalance or misalignment cause the vibration.

� It is a loss in stiffness of the system. � Looseness of rotating shaft cause series of impacts and will give multiple

harmonic frequencies. � Looseness of supporting system result in highly directional radial

vibration. Vertical amplitude equal or greater than horizontal.

Eccentricity

� No rotor can be made perfectly round. � Normal balancing procedures can be carried to minimize the effect of

eccentricity. � But eccentricity can result in reaction forces that cannot be compensated

by balancing.

34

� Eccentric belt pulley or chain sprocket will cause variation in belt/ chain tension.

� Vibration frequency at 1 x rpm of the eccentric element with a directional force between the centers.

� Highly directional nature of vibration � Slow motion studies with stroboscope or run out checks will confirm

eccentricity problem.

Resonance

� Natural frequency of the system ω = √k/m � Excessive vibration can result if a machine component has natural

frequency close to some exciting force inherent to the machine. This is termed as resonance.

� There are no. Of components of a machine with different natural frequencies. Stiffness of each component is also different in different directions. So each machine component has several different natural frequencies.

� Resonance problem will usually cause highly directional vibration � Resonance problem can be verified by :

• Changing the exciting force frequency

• Change the mass of stiffness • Performing bump test

Wear in sleeve bearings

� Vibration problems are associated because of excessive bearing clearances, looseness of bearing shells and misalignment of sleeve bearings.

� Excessive bearing clearance / looseness: 1 x rpm is the vibration frequency.

� Actual bearing wearing in the load zone causes increase in vertical vibration amplitude.

� Wear in plain bearing for : • Gear boxes: vibration frequency is gear meshing frequency

35

• Centrifugal pumps: vane passing frequency

• Large motors: electrical problems � Excessive wear of sleeve bearings may result in sub harmonic vibration

frequencies such as ½ x rpm � Later stages of sleeve bearing wear will give a large family of harmonics

of running speed � A minor unbalance or misalignment will cause high amplitudes when

excessive bearing clearances are present

Systematic approach to CBM:

Step-1: Collect useful information:

• History of Machine. • Control room data-speed, feed, temperature, pressure etc. • Name place details-bearing no, no of gear tooth etc. • Design operating parameters, critical speed. • Limits of vibration level.

Step-2: Identifying the type of measurement procedure:

• Identify measurement type-Disp, Vel, Acc.

• Measurement direction: Horizontal, Vertical, Axial.

36

Step-3: Analysis:

• Evaluate overall vibration reading of the entire machine. (a) Identify 1x RPM peak. (b) Locate highest amplitude. (c) What is the direction of the highest amplitude? (d) What is the frequency of the highest amplitude?

• See the values of Shock pulse, HFD etc. • See the trend - in case of sudden increase the problem severity increases. • Analyze the frequency for possible defects. • Analyze the phase readings for confirmation if necessary.

37

Collect history and other useful information of equipment

Identifying the type of measurement procedure

Taking measurement using suitable technique

Analysis of the obtained data

Equipment is ok Equipment is not ok

Analysis

Corrective action

Bring back to Normal

Routine Maintenance

38

Abbreviations

D.M.Water De-mineralised Water J.O.P Jacking Oil Pump M.O.P Main Oil Pump M.O.T Main Oil Tank B.F.P Boiler Feed Pump

A.C.E.P Auxiliary Condensate Extraction Pump M.C.E.P Main Condensate Extraction Pump H.P.T High Pressure Turbine L.P.T Low Pressure Turbine D.P.R Differential Pressure Regulator Mo.V Motorised Valve

A.P.R.V Automatic Pressure Regulating Valve I.A.C Inter After Cooler G.S.C Gland Steam Condenser

L.P.D.C Low Pressure Drain Cooler H.P.D.C High Pressure Drain Cooler N.R.V Non Return Valve M.S.R Moisture Separator and Reheater B.S.R Bleed Steam Reheater L.S.R Live Steam Reheater C.V Control Valve

H.P H High Pressure Heater L.P.H Low Pressure Heater

C.I.E.S.V Combined Isolating and Emergency Stop Valve L.P.G.V Low Pressure Governing Valve H.P.G.V High Pressure Governing Valve N.D.C.T Natural Draught Cooling Tower C.C.W Circulating Cooling Water

N.A.H.P Non Active High Pressure