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AbstractNon-Destructive Techniques are used widely in themetal industry in order to control the quality of materials. Eddy

current testing is one of the most extensively used non-destructive

techniques for inspecting electrically conductive materials at very

high speeds that does not require any contact between the test piece

and the sensor. This paper includes an overview of the fundamentals

and main variables of eddy current testing. It also describes the

determination of coating thickness and identification of materials

defects. The experiments were conducted with reference block by

eddy current testing, and also found that defects identification on the

block, plastic coating thickness was measured .Recent advances incomplex models towards solving defects-sensor interaction,

developments in instrumentation , and the evolution of data

processing suggest that eddy current testing systems will be

increasingly used in the future.

KeywordsDefects, Eddy Current, Non-Destructive Testing,Probe.

I. INTRODUCTIONON-Destructive Testing (NDT) is a wide group of

analysis techniques used in science and industry to

evaluate the properties of a material, component or system

without causing damage [1].The common NDT methodsinclude ultrasonic, magnetic-particle, liquid penetrant,

radiographic, remote visual inspection (RVI), eddy-current

testing. Based on particular nature the choosing the right

method and techniques is an important thing of the

performance of NDT.NDT is a highly-valuable technique that

can save both money and time in evaluation of materials,

evaluation of product, evolution of products that have been

put into services, and research[2]. Coating thickness

measurement in metals and inspection of weld scan having

limitation with ultrasonic testing, fluorescent dye penetrate

testing and magnetic particle testing .Easy and faster way of

measurements carried out by Eddy current testing .

The objective of NDT may be simply expressed as the

detection and complete specification of defects and flows. The

Sivaprakasam.Palani is with the Al Musanna College of Technology,

Engineering Department, Al Muladdah, Box: 191, Postal code: 314, Sultanate

of Oman phone:+968-97858336; (e-mail:[email protected] ).

Karthikeyan.S is with Al Musanna College of Technology, Engineering

Department, Al Muladdah, Box: 191, Postal code: 314, Sultanate of Oman

phone (e-mail: [email protected] ).

Hariharen.P is with the Manufacturing Engineering Department, Anna

University ,Chennai ,Pin:600025, Tamil Nadu, India (e-mail:

[email protected] ).

eddy current test was used for internal defect detection and

coating thickness measurements.

II.WORKING PRINCIPLE OF EDDY CURRENT TESTINGIn eddy current testing, electrical currents (eddy currents)

are generated in a conductive material by a changing magnetic

field shown in Fig 1. The strength of these eddy currents can

be measured [5]. Material defects cause interruptions in the

flow of the eddy currents. Interruption of flow alerts the

inspector to the presence of a defect or other change in thematerial.

Fig. 3 Eddy current Testing

III. EXPERIMENTAL EQUIPMENTSGE Phasec3d Eddy current flow detector shown in Fig 2, it

has dual frequency inspection capability. It is light weight

portable and user friendly. Eddy current flow detector suitable

wide range of application like aerospace, automotive,

petrochemical, power generation and rail. Its used for, general

crack detection, sub surface cracking and corrosion,

conductivity measurement, coating thickness measurement.

The general specifications of eddy current instrument asshown in Table 1. Different factors will affect the eddy

current response. To minimize the effects, need to control the

following factors namely material conductivity, permeability,

frequency, geometry etc [3]. Practical testing of eddy current

will need the following, A suitable probe should select based

on application and geometry of the product to be inspected.

An instrument equipped with the necessary capabilities like,

light weight ,portable ,user friendly, interference with

computer large memory and reporting software .Need to find

the nature of defects size , location and type of flaws etc

A Study on Non Destructive Evaluation of

Materials Defects by Eddy Current Methods

Sivaprakasam.Palani, Karthikeyen.S, and Hariharen.P

N

International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2012) Jan. 7-8, 2012 Dubai

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,Important thing in eddy current testing is setup the

equipments with suitable test standards. Skilled and expertise

technician needed for interpret the results.

Fig. 3 Eddy current flaw detector

IV. EXPERIMENTAL RESULTSA.Coating thickness measurementAfter setting the all parameters in the instruments [6] like

(frequency, probe mode gain, phase etc), Coating thickness is

measured by comparing the signal from the reference

standards 31A00B shown in Fig 4. Signal from reference

standards were individually scanned using the broadband

testing probe shown in Table 2. The plastic coated test block

shown in Fig 6.Correlated with reference value and signal

obtained from test block shows the coating thickness. Its

observed the coating thickness of plastic was 1.541mm.

TABLE2

CALIBRATION STANDARD REFERENCE

Reference Standard with

plastic slots(0.5 mm each )Signal values

0.5 mm

1.0 mm

19

32

1.5 mm

2.0 mm

38

44

Fig. 5 and Fig 7 show typical screenshots taken from the

inspection system screen of reference standard and coated

plastic respectively.

Fig. 4 Reference Standard

Fig. 5 Signals obtained from reference standard

Fig. 6 Test block coated plastics

TABLEI

GENERAL SPECIFICATION

Frequency 10 Hz to 10 MHz

Probe mode Absolute, locator, bridge and reflection

Mix gain

Mix phase

x/y -60 to 60 dB

0 to 359.9 in 0.1 Step


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Fig. 7 Signals obtained for coated plastics

B.Flaw detectionAfter setting the all parameters in the instruments like

(frequency, probe mode gain, phase etc), Calibrate the

equipment using a test block of similar materials to that

under examination. Record the signal obtained from thecalibration block. The weld scan probe has placed the parent

material scanned fully shown in Fig 9 and also founded the

horizontal flaw detected by eddy current testing and liquid

penetrate testing (LP) shown in Fig 10, and Fig 11

respectively .

Fig. 8 Testing block

Fig. 9 Scanning of Test block

Fig. 10 Flaw detected by eddy current inspection system

Fig. 11 Flaw detected by liquid penetrant test

V.CONCLUSIONThe expected goals for this research were studied. Non

destructive evaluation of materials defects has been found by

eddy current testing. Adequate signal values were successfully

obtained calibration reference standards. Coating thickness of

plastic was measured 1.541 mm and materials defects were

found by both eddy current testing and liquid penetration

testing. The operating performance of the inspecting system

was demonstrated for laboratory conditions

ACKNOWLEDGMENT

This work is being conducted at the Al Musanna College ofTechnology, Sultanate of Oman.

REFERENCES

[1] Cartz,Louis Non destructive testing ASM Intl, ISBN0871705176,USA ,1995, pp 173-187

[2] Charles Hellier , Hand book of Non destructive evolution,McGrawHill, 2001, pp. 1.2.

[3] J. R. Wait Electromagnetic Basis for Non destructive testing ofcylindrical conductor,IEEE Transactions on Instrumentation and

Measurement.1978 Vol 27 pp 235-238.Flaw

Flaw


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[4] A.Bernieri, Crack Shape Reconstruction in Eddy Current Testing UsingMachine Learning Systems for Regression, IEEE Transactions on

Instrumentation and Measurement, 2008, Vol 57, pp 1958-1968

[5] Baldev, Practical non destructive testing, Wood head publication Ltd2002, pp 27-53.

[6] Donizete A, Using Eddy Current NDT to Check Integrity of TRIGAMARK I Fuel Rods Cladding, The e-Journal of Nondestructive

Testing,2008 pp 1-6.

P.Sivaprakasam was born in Tieuvannamalai ,

Tamil Nadu , India , on may 5th in 1983 . Earned a

Bachelor degree, Industrial Engineering at Anna

University, Chennai, India (2005) then earned his

Masters Computer Integrated Manufacturing

engineering from Anna University in 2008, He

Worked at Regency International clothing Pvt Ltd as

an Industrial Engineer from 2005 to 2006.Then

lecturer in Tagore Engineering College in Chennai

from 2008 to 2010. At present working as Faculty in Al Musanna college of

Technology in Oman.


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