U N I T - 3 C O N D I T I O N M O N I T O R I N G

16 mark questions:

1. Define Condition monitoring and explain its types and levels. State its advantages and disadvantages.

Condition Monitoring: Condition monitoring (CM) is one of the maintenance methods which are used to access the health and condition of equipments, machines, systems or process by absorbing, checking, measuring and monitoring several parameters. It is also called as Equipment Health Monitoring (EHM). It is the process of measuring the temperature, noise, vibration, etc. to find out the condition of the equipment. Types of Condition Monitoring:

i. Subjective condition monitoring ii. Aided-subjective condition monitoring

iii. Objective condition monitoring

i. Subjective condition monitoring: The monitoring person uses his perception of senses and judgment to note any change from the normal condition. The four senses are seeing, hearing, smelling and feeling which can detect smoke by sight, bearing noise by hearing, burning of oil/rubber due to heat by smelling and excessive heating and vibration by touch. No gadget/ instruments are used to sense the abnormal condition.

ii. Aided-subjective condition monitoring: In this type, monitoring person uses gadgets, instruments, etc. to find out the abnormal condition and its causes. The instruments are used as an additional confirmation only when the person thinks that the machine is abnormally working.

iii. Objective condition monitoring: In this type, instruments are used to monitor the machines continuously. The maintenance person uses the instruments even on perfectly working machines. In some cases, the instruments are always mounted on the machines so that they indicate when the machine works abnormally. So, the maintenance person need not waste time in checking machines which works normally.

Levels of Condition monitoring:

Parameters and Instruments on Condition monitoring:

S. No. Parameters to measure Instruments used

1. Temperature Pistol Thermometer, IR thermographs,

Pyrometers, Temperature sensitive tapes.

2. Speed and distance Tachometer, Odometer,

Accelerometer.

3. Vibration Vibration analyzer, Frequency analyzer.

4. Electrical quantities (Amp, volt, ohm)

Voltmeter, ammeter, etc.

5. Wear Thickness gauge

6. Corrosion Corrosion meter

7. Fits and clearances Proximity sensors

Advantages of Condition monitoring:

Improved availability of the equipment

Minimized breakdown costs

Visual Inspection

Sensor-Assisted Inspection

Indicator analysis

Integrated monitoring applications

level 1

level 2

level 3

level 4

i. seeing ii. Hearing

iii. Touching iv. Smelling

Different instruments given below

i. Lubricant analysis ii. wear debris Analysis

Remote sensors and alarm system, microprocessor based instruments, etc.

Improved morality of the operating personnel and safety

Improved reliability

Improved planning

Disadvantages of condition monitoring:

Gives only marginal benefits

Increased running cost

Difficult to organize

2. Explain the costs of condition monitoring and compare the cost with and without condition monitoring with examples.

The following two costs are the prime factors incurred in any industry.

i. Installation cost: It is the amount spent on infrastructure, buying machines and other equipments and services. It includes creating access, installing foundations, covering or protection, power supply, services and consultancy. It also includes the cost of training the workers.

ii. Operating cost It includes the manpower cost, resources, inventory, fuel or power, etc. The installation cost along with the operating cost may lead to early cash outflow. But, if things are perfectly planned and money is spent on right things at the right time, it will yield good profit within an acceptable period.

Cost comparison with and without condition monitoring: The cost of a maintenance engineering department should be clearly planned and documented. It should include wages, spares, overheads, instruments, etc. Generally the cost of maintenance will increase the total cost of the plant. Also, this cost will further increase as the instruments need more maintenance after certain years since their life and working conditions will be weaker year by year.

When the plant is new, the equipments are in good condition and the maintenance cost will be less. After some time, the instruments will significantly fail because of continuous working for some time and wear of moving parts. The above graph shows that the maintenance cost will increase exponentially with time.

The above graph shows the cost and profit (savings) due to condition monitoring. The upper curve is the actual cost incurred without condition monitoring. It is high and increasing steeply with respect to time. The below curve represents the running cost with condition monitoring and it steadily increases with time. The shaded portion indicates the savings (profit) due to the implementation of condition monitoring.

The above graph shows the cost (money) spent on implementation and operation of condition monitoring system in an industry. Initially the condition monitoring instruments are purchased which results in high initial cost (installation). Then, because of this condition monitoring, the equipments will work better and their running cost decreases (pay-off cost). After a particular time, the equipments will steadily work without failure due to regular and continuous condition monitoring and hence the cost of routing operation will almost be a constant.

Some examples of the benefits of implementing condition monitoring system:

i. A 25 year old flour mill implemented a planned condition monitoring system and achieved a 43% savings within 12 months.

ii. An estimated benefit of Rs.160million has been reported by Imperial Chemicals Industry (ICI) after implementing permanent vibration monitoring systems at a number of sites.

iii. The successful implementation of an overall condition monitoring system by British Petroleum (BP) on one site alone has saved a considerable amount of money.

iv. Taxaco’s Pembrock refinery saved nearly Rs. 40lakhs perpendicular year by implementing an effective energy monitoring and management programme.

3. Explain ON-load and Off-load testing (or) Explain two types of Condition monitoring tests.

Condition monitoring can be done in two methods namely,

On-load condition monitoring

Off-load condition monitoring

i. On-load monitoring:

It means monitoring or adjusting the parameters of the machine of equipment when it is running.

It is done for superficial, easily accessible, non-interfering parts of the equipment which can be carried out without interruption to the operation.

It is a continuous monitoring technique in which the machines are always under inspection and the problems are detected immediately.

It prevents severe damage as it identifies the problem immediately

The cost of maintenance is high because continuous monitoring is performed.

ii. Off-load monitoring:

It is the monitoring process done when the machine is switched off.

The machines may be temporarily stopped to check their working conditions

It may be performed continuously or periodic.

Periodic off-load monitoring is done when the machines are connected during monitoring process and then switched off.

In continuous off-load monitoring, the machines are connected as long as they operate well. When a fault is detected by the operator, the condition monitoring personnel will come and check its conditions.

Desktop conputer

process insturments

•key entry data collector

Integrated vibration data collector

Permanently intalled transducers

4. Describe various methods and instruments for condition monitoring.

Type Method On/Off-line

Comments

1. Visual Inspection

Human Eye On/Off Wide range of conditions by checking and surface inspection methods

Human Eye Off Used for internal inspection of machines, detecting surface corrosion, wear and severe cracks

CCTV (Closed circuit

television)

On/Off Detailed inspection of inaccessible/ hazardous environment machine parts. Image recording and high resolution analysis is a post-processing possibility

2. Vibration monitoring

Overall Vibration level

On Represents the vibration of a rotating or reciprocating part Fault diagnosis is not possible

Frequency (spectrum)

analysis

On Represents the vibration of a rotation or reciprocating part as a frequency spectrum which reveals discrete frequency component content of vibration. Fault detection, diagnosis and severity assessment are possible

Shock pulse monitoring

(Spike energy and kurtosis)

On Uses high frequency vibration signals to detect and diagnose a range of faults including rolling element bearing damage, lubrication failure and leak.

Structural monitoring

Off A variety of vibration-based techniques for detection and location of structural faults. Imparting a known vibration into structure and analysis the resulting response.

3. Temperature Monitoring

Temperature crayons, paints

and tapes

On Simple and effective Can resolve body temperature at a glance

Thermometers, Thermocouples

On Range from stick-on thermometric strip to permanently installed thermocouple sensors. Can give visual temperature readout on

electrical input.

Infra-red meter On Non-contact device which measures body heat to estimate the surface temperature. Only a small area can be measured accurately

Infra-red Camera

On Same as the above, but measures a larger area by taking a detailed picture of the body.

4. Lubrication Analysis

Magnetic Plugs and filters

On/Off Analysis of debris picked by plugs of filter in oil washed system. Debris size (100-1000 microns)

Ferrography N/A Analysis by separating ferrous debris followed by microscopic examination. Smaller Debris size (3-100microns)

Spectrography N/A Analysis by determining the chemical composition of the oil and debris. Smallest debris size(0-10 microns)

5.Crack monitoring

Dye penetrant On/Off Detects cracks which breaks the surface of the material

Magnetic Flux On/Off Detects cracks at/near surface of ferrous material

Electrical Resistance

On/Off Detects cracks at/near to surface and can be used to estimate the depth of crack

Eddy current On/Off Detects cracks near to the surface. Also detects inclusions and hardness changes

Ultrasonic On/Off Detects cracks anywhere in a component Suffers from directional sensitivity and so lengthy. It is used as an additional technique to other NDT

Radiography Off Detects cracks and inclusions anywhere. Access to both sides of the component is necessary. Radiation hazard is involved

6. Corrosion Monitoring

Weight loss coupons

Off Coupons are weighed and weight loss is equated to material thickness loss due to corrosion

Incremental bore holes

On A series of fine plugged holes of incremental depths which are periodically unplugged and scrutinized for leakage

Electrical Resistance

On Electrical element and potentiometer are used to assess resistance changes due to material loss. Capable of detecting material thickness reduction of less than 1 mm.

Polarization resistance

On A good indicator of corrosion by is unreliable as a means of estimating material loss rate

5. Explain temperature sensitive tapes and pistol thermometers.

Temperature crayons and tapes: Temperature monitoring by feel of hand or by simply measuring instruments like thermometer, temperature crayons and tapes is an age-old practice to find out defects or defective components. The subjective of temperature monitoring is touching the motor, etc. and assessing if over-heated. Also, temperature sensitive stickers are the most common and cost effective. A sticker having four or five 10mm dia dots of special paints, each of which changes its color a t a particular temperature is stuck to the heat prone parts of the machine. The operators or supervisors can identify its temperature by looking at the sticker from a distance during periodic patrol. Temperature sensitive chalks, thermal paints with which larger parts of the heat prone are is painted fall under this category. The main objective of temperature monitoring is pyrometers, thermometers, pistol thermometers, etc. Depending upon the convenience, these instruments can be thermostat type or connected to a warning system in case of overheating.

Pistol Thermometer:

It is an ideal, professional diagnostic tool for maintenance professional. High end Fluke-576 is a non-contact pistol grip thermometer which enables the capture of simultaneous, time-stamped digital photographic image as a temperature reading. The logged results and images from up to 100 locations are uploaded via USB connection into a PC using windows-based software that comes with the thermometer. Thus, the temperatures can be stored, presented graphically and analysed and the photographic images can be displayed on screen for improved documentation and maintenance follow-up. The Fluke-576 measures surface temperatures, helping to quickly locate lubrication problems, overloads, short-circuits or misaligned and overheated equipments, reducing the work and follow-up time and improving performance.

Fluke 567 is an IR thermometer which features a true dimension laser sighting system for precise targeting. It is most advanced and accurate. It measures a temperature between -30 and 900*C to a 0.1*C resolution with a very fast response time and a distance to spot ration of 60:1. Features include max/min readings, difference and average readings, and audible alarm for high and low readings in comparison with 30 preset levels. A bargraph on the backlit LCD screen displays the last 10 readings.

6. Explain Wear Debris Analysis (WDA).

WDA is related to oil analysis only in that the particles to be studied are collected through drawing a sample of lubricating oil. Wear debris analysis provides direct information about the wearing conditions of the machine train, where as the lubricating oil analysis determines the actual condition of the oil sample. Particle in the lubricant of the machine can provide sufficient information about the condition of the machine. The information is obtained from the study of particle shape, composition, size and quantity. WDA is normally conducted in two stages. The first method is routine monitoring and trending of the solid content of machine lubricant. The continuous trending of wear rate monitors the performance of machine and provides early warning and diagnosis. The lube oil is indicative of the mechanical conditions of the machine. A normal machine will contain low levels of solids with size less than 10microns. Difference mechanical systems have different life and minimum component wear. International Organization for standardization (ISO) set up cleanliness codes for proper lubricating analysis defined as the number of particles per mm greater than 5, 15, 25, 50, 100 microns. The second method involves analysis of the particulate matter in each lubricating sample. In this, the sample is run through a particle counter. The counter passes the lubricant stream through a beam that measures the number and sizes of the particulate matter. If the debris concentration indicates that there are too many particles in the given size range, then further investigation is required. The solid components are then inspected under a microscope. The result of this test includes a particle identification, possible sources, suggestion on correction and picture of the particle. There are basic types of wear as explained in the following table:

S.No Type of wear Description

1. Rubbing wear Particle size <20micron Chord dimension, 1 microns thick results from flaking of pieces from mixed shear layer mainly benign.

2. Cutting wear Swarf like chips of fine wire coils. Caused by abrasive cutting tool action

3. Rolling fatigue Chunky, several microns thick Eg: gear wear (20-50 microns) chord width. Primary result of rolling contact bearing failure

4. Combined rolling and sliding wear

Typically ferrous. 1>10 microns dia generated when micro cracks occur under rolling contact fatigue condition

5. Severe sliding wear Large >50 microns chord width several microns thick Surfaces heavily striated with long straight edges. Typically found in gear wear. Caused by excessive loads or heat in gear systems

1. Rubbing wear:

It is caused by normal sliding wear in a machine.

A unique layer is formed at the surface when normal breaking of wear surface. If this is stable, normal wear occurs. If this layer is removed faster than it is generated, rate increases and maximum particle size increases.

Excessive quantity of contaminants in lubricant can cause this,.

The machines wear out rapidly. 2. Cutting wear:

It is generated when one surface penetrates another.

They are produced when a misaligned or fractured hard surface produces an edge that cuts the below layer.

It also occurs when abrasive contents in lubricant oil cuts the surface.

They are abnormal and require attention

If they are few microns long and fraction of microns wide, failure may occur soon

3. Rolling fatigue wear

Occurs in rolling contacts such as bearing and may produce three kinds of particles namely, Fatigue spall particles, spherical particles and laminar particles.

Fatigue spall particles are the material removed when a pit or spall opens up on a bearing surface.

Laminar particles are very thin and thought to be formed by the passage of wear particles through a rolling contact.

Spherical particles indicate pits and holes in bearing. 4. Combined rolling and sliding wear:

They result from moving contact of surface in gear systems.

These larger particles result from tensile stresses on the gear surface.

They cause the fatigue crack to spread deep before pitting.

Scuffing of gears is caused by too high load or speed.

The excess heat generated by this condition breaks down the lubricant film and cause adhesion of the mating gear teeth. As the surface becomes rough, wear rate increases.

5. Severe sliding wear:

It is caused by excessive load or heat in a gear system.

Large particles break away from the wear surfaces and cause an increase in wear rate. If the stresses applied to the surfaces increases, a second transition point is reached. The surface breaks down and wear occurs.