condition monitoring through non destructive technique seminar

8/6/2019 Condition Monitoring Through Non Destructive Technique Seminar

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ABSTRACT

Condition monitoring of components and plants are of great importance for safe

and reliable operation and for increasing productivity of plants. The challenges towards

the condition monitoring can be successfully met by employing non-destructive

evaluation (NDE) techniques. Vibration monitoring techniques are applied for periodic /

continuous assessment of machinery parts and plants. Acoustic emission technique is

used for leak detection and for structural integrity monitoring applications. Infrared

thermographs are employed for condition monitoring applications in steel, electrical and

petrochemical industries. Lubricant analysis by ferrography, and filed signature

mapping are also used for condition monitoring applications. Here, applications of these

NDE techniques could help to properly diagnose faults in plants components, enables

taking timely decision about repair / replacement of components / plants, thus ensuring

increased safety, reliability and productivity.

INTRODUCTION

The successful operation of structures / components during their entire life

requires the implementation of a dedicated programme for condition assessment through

in-service inspection (ISI) of all critical components of the plants / structures. The

condition assessment through ISI and life prediction approaches enable uninterrupted

operation, avoidance of unplanned shutdowns and taking decision on repair, up-

gradation, modernization and replacement of necessary components for extension of the

overall life of plants beyond their design lives. This is achieved through meticulous

planning and incorporation of non-destructive evaluation (NDE) techniques which aims

at detection and characterization of defects, stresses, corrosion micro structural

degradations and dimensional changes that occur in components during service life, due

to exposure to high temperature, pressure, static and dynamic loads, hostile environment

etc.

1. SIGNATURE ANALYSIS

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ness etc . . . . Condition assessment of plants through vibration analysis is a very

important method in spite of relatively higher initial cost of instruments. Acoustic

Emission Technique (AET) is an advanced technique for real time monitoring

application. An AE transducer or sensor acoustically coupled to a sample detects elastic

(Acoustic) energy emitted by the sample and gives information about the dynamic

changes taking place in the sample. AET is widely used for assessing structural integrity

of critical components, such as pressure vessels, pipe line, storage vessels and gas

cylinders. Infra red thermography (IR) is the mapping of IR radiations arising from the

natural or stimulated thermal radiations of an object and can be used for online

monitoring applications. Lubrication monitoring is carried out at periodic intervals to

identify the condition for the lubricant and to access the likely damages to the

machinery parts, through debris analysis by ferrography and quality assessment of

lubricants. More recently for condition monitoring and life extension problems, a new

dimension has been added to the existing NDE approaches with the availability and

adoption of procedure like field signature mapping.

1. VIBRATION MONITORING TECHNIQUES

Vibration is referred to as oscillation of an object about some equilibrium point.

VB monitoring technique has gained wide interest and acceptance for condition

monitoring applications. This is based on exciting vibrations in component by local

external impact or recording the vibration generated in a components under operating

conditions the most common source of vibration are gear gear-mesh, vane passing ,

rotor imbalance, misalignment, eccentricity, damaged bearings or gears, loose

components, rubbing components ,bend shafts, cavitations.

Vibration of a machinery is accessed with a help of transducers by measuring

the amplitude of vibration in terms of their parameters i.e. displacement velocity and

acceleration.

1.1 VIBRATION MONITORING INSTUMENTATION

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Following figure shows a measuring and analysis system that may be used for

monitoring the vibration signals from machines.

Following table gives general guide lines for identifying the causes of vibrations.

The relation between the fault and frequency, amplitude and direction of vibration, are

given. This is a useful guide for pin-pointing the cause in case vibration levels at certain

frequency are seen to increase.

Sl.

No FAULT FREQUENCY

DIRECTION OF

VIBRATION

1. ROTATING UNBALANCE SAME AS RUNNING SPEED RADIAL

2. MISALIGNMENT OF

BEARINGS

2*SPEED RADIAL AND AXIAL

3. ROLLER BEARING DEFECT

AT BALL OR ROLLER SPEEED

ULTRA SONIC FREQUENCIES (20-

60KHZ)

RADIAL AND AXIAL

4.

OIL FILM WHIRL IN HIGHSPEED

TURBO MACHINES0.5*SPEED RADIAL

5. DAMAGED OR WORN GEARS NO: OF TEETH* RPM RADIAL

TABLE 1.1 (a): VIBRATION CAUSES IDENTIFICATION

1.2 APPLICATION OF VIBRATION MONITORING TECHNIQUES

Figure 1.2(b) shows one typical example of the failure rate of components of

different machineries in plants which are maximum for rolling bearings as compared to

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Fig 1.2(a): detection m ethods of failures

vibration

45%

others

4%

acoustic

emission

3%

fluorescence

3%

torque

6%

rotational speed

6%

temperature

10%

oil analysis

23%

vibration

oil analysis

temperature

rotational speed

torque

fluorescence

acoustic emission

others



CM Through NDE

other components. One of the reasons why machinery problems are caused by failure of

rolling bearings is that the number of rolling bearings assembled into machinery is a few

orders of magnitude larger than any other machine elements. Among various NDE

techniques, vibration technique is the most commonly used method for the detection of

failure of rolling bearings as shown in figure 1.2 (a)

1.3 CONDITION MONITORING THROUGH VIBRATION

ANALYSIS IN STEEL INDUSTRY

In steel industry, maintenance cost accounts for nearly 10%-15% of the

production cost. Maintenance affects the target, quality and profitability of the plant.

Implementation of modern concepts of condition based maintenance (CBM) can

appreciably reduce the maintenance costs and enhance reliability of machine

performance and quality of the output.

5

Fig1.2 (b): failure rate of different machineries of plant

others

24%

rolling bearing

29%

slide way

13%

valve

6%sliding bearing

6% seal

7%

gear

7%

oil pump

8%

valve

sliding bearing

seal

gear

oil pump

slide wa y

rolling bearing

others



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The effectiveness of CBM through vibration analysis can be understood by the

example of the Rourkela Steel Plant (RSP). With implementation of CBM activities at

RSP, there has been substantial growth in all aspects encompassing the maintenance

system Figure 1.3 (a) was responded that the programme for condition monitoring in

RSP has grown from 40 to 140 critical equipments in a span of last three years. There

has been significant increase in the number of major breakdown prevention cases from

10 to 102, which is more than 10 times, during the previous five years, resulting in

substantial financial savings.

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0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

94-95 95-96 96-97 97-98 98-99 99-00

breakdownsprevented

savings

insitu balancing

trend line

N

o

:

o

f

m

a c

h i

n

e

s

7

FIG 1.3(A): CONDITION MONITORING IN R S P



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2. ACOUSTIC EMISSION TECHNIQUE

Acoustic emission is the class of phenomenon whereby transient elastic waves

are generated by the rapid release of energy from localized sources within a material.

The energy released travels as spherical wave front and can be picked up from the

surface of a material using highly sensitive transducers, usually electro-mechanical in

nature, placed on the surface of the material.

Figure 2 (a): A E Technique

The wave thus picked up is converted into electrical signal which on suitable

processing and analysis can reveal valuable information about the source causing the

energy release. In metals the different sources are generation and-propagation of cracks,

movement of dislocations, formation and growth of twins, decohesion and fracture of

brittle inclusions, phase transformations etc. In composites, the sources of AE are

matrix cracking, debonding and fracture of fibers.

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2.1 ACOUSTIC EMISSION SET UP

Fig: 2.1(a). TESTING SET UP

The diagnostics can be performed without the product pumping-over

interruption.

Among the existent non-destructive control methods, the acoustic-emission

method is the only one that provides to exclude completely the sudden damage of

constructions, pipelines, and vessels. Originally conceived as an NDT tool for pressure

vessels, Acoustic Emission testing (AE) has become much wider in scope. We now

apply it to all types of process monitoring as well as for its original purposes of flaw

detection and structural integrity inspection. AE sensors respond with amazing

sensitivity to motion in the low ultrasonic frequency range (10kHz - 2000kHz).

Motions as small as 10-12 inches and less can be detected. These sensors can hear the

breaking of a single grain in a metal, a single fiber in a fiber-reinforced composite, and a

tiny gas bubble from a pinhole leak as it arrives at the liquid surface. By detecting

sources as small as these, or as large as brittle crack advance, AE technology warns of

danger, informs about structural health and watches over costly and critical processes.

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http://www.eltest.ru/video/pip.mpg



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2.2. A E DURING HYDRO TESTING OF A HORTON SPHERE

AE monitoring during hydro testing of a 17 m Horton sphere was carried out.

Figure 2.2 (a) shows typical locations of AE sensors (150 kHz resonant frequency each)

mounted on the Horton sphere, along with a typical AE source location map. The hydro

test of the vessel was carried out to a maximum pressure of 22 kg/ cm 2, with periodic

holds at different pressures. A reloading cycle from 20 kg/cm2 to 22 kg/cm2 was

immediately carried out. During the hydro test, AE signals were generated only during

the pressure rise. With increase in pressure, AE signals were generated in newer areas

and the areas where AE occurred in the previous pressure steps do not generate AE inthe subsequent pressure steps. These signals were attributed to local micro-plastic

deformation of the material. A few AE signals were also generated from cracks in

concrete columns that were supporting the vessel. AE monitoring during hydro test was

useful to confirm the integrity of the vessel.

Fig: 2.2(a). A E monitoring during hydro testing of Horton sphere

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3. INFRARED THERMOGRAPHY

Infrared thermography is based on the principle of detection, and measurement

of infrared radiations QR) arising from the natural or stimulated thermal radiation of an

object. All objects around us emit electromagnetic radiations. At ambient temperatures

and above, these are predominantly infrared radiations.

Figure 3 (a): setup for infrared testing of lap joints

3.1 INFRARED TESTING OF LAP JOINTS

This image depicts the setup for infrared testing of lap joints. The images below

are of a such a lap joint with a three poor spot welds in the middle.

Here is the raw thermo graphic data.

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Here is the same data after removing the noise and vertical gradient.

Here is the same data processed for the local gradient in surface temperature.

The above series of images from thermographic data show that sophisticated

post processing of the raw data offers advantages in identifying good spot welds from

poor ones. Processing the matrix data with FFT algorithms and numerical

differentiation brings out important details that are hidden in the raw infrared data. The

strong change in the surface temperature gradients at the two spot welds on the outside

corresponded to high strength welds. The location of the three spot welds in the middle

can be determined and the weak temperature gradients correspond to low strength

welds.

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4. FERROGRAPHY

Ferrography is a state-of-the-art predictive maintenance technique based on wear

debris analysis. It provides a comprehensive non-intrusive evaluation of the health of

lubricated components while the equipment is in running condition. In today’s modern

power generation, manufacturing, refining, transportation, mining and military

operations, the cost of equipment maintenance, service, and lubricants are ever

increasing. Parts, labor, equipment downtime, lubricant prices and disposal costs are a

primary concern in a well run maintenance management program. Machine condition

monitoring based on oil analysis has become a prerequisite in comprehensive

maintenance programs the ferrography laboratory plays a key role in such programs. It

separates and concentrates wear and contaminant particles for microscopic examination.

Particle size, surface characteristics and composition are then used to determine wear

modes inside a machine so that maintenance recommendations can be made.

4.1. WEAR DEBRIS ANALYSIS

The mechanical systems used in plants have interacting surfaces in relative

motion which are lubricated by oil or grease. During operation, there is a steady

generation of wear particles at interacting surfaces caused by load and relative motion.

These wear debris are carried away by lubricant, which give very useful information

regarding the health of the equipment. Over a period of time, various abnormalities,

such as, excessive load, fatigue, corrosion, abrasion, misalignment, lubrication

starvation and capitation, may arise influencing the wear mechanism and formation of

wear debris. The four major findings from ferrography are the mode, rate, severity and

location of wear. A particular wear mechanism typically generates a particular type of

wear debris. The identified wear modes include abrasion, impact, fatigue, erosion,

corrosion, scuffing and severe sliding. The concentration of wear debris indicates the

rate of wear and the size of debris indicates the severity of wear. The color of the

particles identifies the type of material which pinpoints to the affected component.

Thus, an accurate analysis of all these features of 'the wear debris provides a powerful

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means of knowing the actual wear mechanism based on which, suitable corrective

measures can be taken well in advance.

METAL WEAR POSSIBLE ORIGIN.

ALUMINIUM BEARINGS, BLOCKS, BLOWERS, BUSHINGS,

CLUTCHES, PISTONS.

CHROMIUM BEARINGS, PUMPS, RINGS, RODS.

COPPER BEARINGS, BUSHINGS, CLUTHES, WASHERS.

IRON BLOCKS, CRANK SHAFTS, CYLINDERS,DISCS.

SILVER SOLDERS.

TIN PISTONS.

Table 4.1.(a) wear metal origin table

4.2. ANALYSIS OF OIL SAMPLES

Spectrometric analysis is the most commonly used method for trending

concentrations of wear metals. Spectrometric analysis determines the elemental

concentration of various wear metals, contaminants, and additives present in an used oil

sample. But spectroscopy is less sensitive to the larger particles. A spectrometer is an

instrument with which one can measure the quantities and types of metallic elements in

a sample of oil. The operating principle is as follows. A diluted oil sample is pulverized

by an inert gas to form an aerosol, which is magnetically induced to form a plasma at a

temperature of about 9000°C. As a result of this high temperature the metal ions take on

energy, and release new energy in the form of photons. In this way, a spectrum with

different wavelengths is created for each metallic element. The intensities of the

emissions are measurable for each such element by virtue of its very specific

wavelength, calculated in number of ppm (parts per million). A special spectrometer can

detect the very small metal particles in suspension in the oil, i.e. with a size between 0

and 3 microns. Those small particles are a good indication of general wear. The human

eye can detect particles of a size starting from 50 microns, which allows them to be

visualized using more conventional means. Complementary analysis of such larger

particles can be done by spectrometry, by ferrography or by optical or electronic

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- Reduce or eliminate scaffolding costs

- Eliminate costs

- Eliminate unnecessary pipe replacement

- Widely expand possibilities for monitoring

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Fig 5.1(b). Field signature mapping with

Ideal field pattern and

Corrosion distorted field pattern.

Fig 5.1(c). Sensing pins

(electrodes) are distributed in an

array over the monitored area to

detect changes in the electrical field

pattern. The voltage measurements

(the signature).



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Fig 5.1 (d). FIELD PATTERN

The field proven FSM technique detects metal loss due to corrosion by detecting

small changes in the way an induced current flows through a metallic structure. The

system presents graphical plots indicating the severity and location of corrosion, and

calculates actual corrosion and metal loss. Both sensitivity and accuracy are typically

better than 0.5% of remaining wall thickness, but may vary with the application.

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6. CONCLUSION

The implementation of condition monitoring methodologies to components and

plants is very essential for ensuring safety and reliability and for increasing productivity

of plants. Nondestructive evaluation techniques which aim at detection and

characterization of defects, fatigue, stresses, corrosion, dimensional changes and micro

structural degradations in materials, bear unique potential for applications related to the

condition monitoring of components and plants.

It is probably safe to say that most organizations with a significant capital

investment in plant equipment are, these days, employing some form of Condition

Monitoring technology in order to predict at least some failures. This is the time from

which an incipient failure can first be detected, until functional failure occurs. The

primary determinant of frequency of a Condition Monitoring task is the lead time to

failure, or PF Interval. For example, the time interval from when overall bearing

vibration levels reach an "alarm" limit, until the bearing seizes completely. In order to

be completely sure that the failure is detected prior to the functional failure occurring,

the bearing must be monitored at a frequency less than the PF Interval. So far so good-

in theory. Unfortunately, the practice is that the PF Intervals for sophisticated Condition

Monitoring techniques are highly variable. For example, for Vibration Analysis on a

bearing, the PF Interval will vary depending on the type of failure detected, the type of bearing installed, the severity of its operating cycle, the type of lubrication applied,

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ambient temperature conditions and many other factors. To date, no Condition

Monitoring organization can give anything but the most approximate estimate of the PF

Interval. Any error tends to be on the conservative (i.e. too frequent) side.

6.1 SUMMARY OF APPLICABILITY AND CAPABILITY OF

VARIOUS NDT TECHNIQUES

NDT

TECHNIQUE

DETECTION

CAPABILITY

NON CONTACT

INSPECTION

AUTOMATED

INSPECTION

DEFECT

SIZING

VIBRATION VOLUMETRIC POSSIBLE POSSIBLE POSSIBLE

ACOUSTIC

EMISSION VOLUMETRIC POSSIBLE POSSIBLE

NOT

POSSIBLE

I R THERMO-

GRAPHY

SURFACE ,

NEAR

SURFACE

POSSIBLE POSSIBLE POSSIBLE

FERROGRAPHY VOLUMETRIC POSSIBLE POSSIBLE POSSIBLE

F S M

SURFACE,

NEAR

SURFACE

POSSIBLE POSSIBLE POSSIBLE

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7. REFERENCES

1. Dr. C K Mukhopadhayay, Dr. T Jayakumar, Dr. Baldev Raj, ‘Non-Destructive

Evaluation Techniques for Condition Monitoring of Components and Plants’ .

Institute of Engineers (India) Journal, vol.15 , 2005, PP 144-155.

2. B C Nakra & K K Choudhry, ‘Instrumentation Measurement and Analysis’, Tata

Mc Graw Hill, 14th reprint, ISBN : 0-07-451791-0, pp 350-366

3. Sushil Kumar Srivastava, ‘Industrial maintenance management’, S.Chand &

company Ltd, 2002 Reprint, ISBN : 81-219-1663-1, pp 62-106,202-213.

4. Dr. Baldev Raj, NDT for realising better Quality of Life in Emerging Economies

like India, www.ndt.net/article/wcndt00.

5. http://www.engr.du.edu/profile/Marvin.htm

6. http://www.applied-infrared.com.au/thermography

7. http://lubricants.s5.com/index.htm\

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http://www.ndt.net/article/wcndt00

http://www.engr.du.edu/profile/Marvin.htm

http://www.applied-infrared.com.au/thermography

http://lubricants.s5.com/index.htm%5C

http://www.ndt.net/article/wcndt00

http://www.engr.du.edu/profile/Marvin.htm

http://www.applied-infrared.com.au/thermography

http://lubricants.s5.com/index.htm%5C

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