JNDE

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vol 10 issue 1 June 2011Journal of Non Destructive Testing & Evaluation

from the Chief Editor

DDDDDrrrrr. Krishnan B. Krishnan B. Krishnan B. Krishnan B. Krishnan BalasubramaniamalasubramaniamalasubramaniamalasubramaniamalasubramaniamProfessor

Centre for Non Destructive EvaluationIITMadras, Chennai

[email protected]@gmail.com

URL: http://www.cnde-iitm.net/balas

The second issue in 2011 continueson the previous issue with the severalrecently introduced features such asIQ Forum, Probe, NDT Puzzle, etc.In this issue, the HORIZONSfeatures new applications in the fieldof NDT of a rather well knowntechnique of photoacoustics. TheBASICS covers some of thefundamental learnings and issues inthe field of Digital Radiography.

The 4 Technical papers in this issue ofJNDTE includes an experimentalreport on the use of high frequencyC-scans for the characterization of thegrain structure of as-cast steel billetsand using this information for theoptimization of the magnetic stirring.The second paper discusses the use ofRadiometry measurements for thecharacterization of Nuclear FuelElements from BARC authors. Thepaper on the Health Assessment ofStructure reviews the comprehensiveapproach by the nuclear industrytowards assurance of safety of thevarious components in the reactor.The final paper from IISc presents anew approach for the computedtomography reconstruction using afan-beam approach for radiographicalimaging of the internals ofcomponents.

During March 2011, an internationalworkshop on Electromagnetic

Nondestructive Evaluation ENDE2011was held in Chennai,co-organized by IGCAR and IITM. TheENDE series is and international eventand held every year. The NDE2011edition boasted of the highest attendanceof more than 150 participants to thisworkshop series with participation fromUSA, UK, France, Germany, Japan, Korea,China among other countries. Thetechnical presentations and posters were ofvery high quality. The next ENDE2012will be held in Brazil.

The NDE2011 will be held between 6-10Dec 2011 in the Chennai Trade Centerand augers to be a very grand conference,which will be augmented by a largetechnical exhibition. It is hoped that allauthors will submit their technicalabstracts to the conference well in advancein order to avoid any disappointments. Itis anticipated that there will beapproximately 200 technical papers (bothoral and posters) presented in theconference. In addition, 4 pre-conferenceworkshops are also planned. For moreinformation, visit www.nde2011.com.

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vol 10 issue 1 June 2011 Journal of Non Destructive Testing & Evaluation

PresidentShri K. Thambithurai

President-ElectShri P. Kalyanasundaram

Vice-PresidentsShri V. Pari

Swapan ChakrabortyShri D.J.Varde

Hon.General SecretaryShri R.J.Pardikar

Hon. TreasurerShri T.V.K.Kidao

Hon. Joint SecretariesShri Rajul R. Parikh

Immediate Past PresidentShri Dilip P. Takbhate

Past PresidentShri S.I.Sanklecha

MembersShri Anil V. Jain

Shri Dara E. RupaShri D.K.Gautam

Shri Diwakar D. JoshiDr. Krishnan Balasubramaniam

Shri Mandar A. Vinze

Shri B.B.Mate

Shri G.V.Prabhugaunkar

Shri B.K.Pangare

Shri M.V.RajamaniShri P.V. Sai Suryanarayana

Shri Samir K. Choksi

Shri B.K.Shah

Shri S.V.Subba Rao

Shri Sudipta DasguptaShri N.V.Wagle

Shri R.K.Singh

Shri A.K.Singh (Kota)

Shri S. Subramanian

Shri C. Awasthi

Brig. P. GaneshamShri Prabhat Kumar

Shri P. MohanShri R. Sampath

Ex-officio MembersManaging Editor, JNDT&E

Shri V. Pari

Chairman, NCB &Secretary, QUNEST

Dr. Baldev Raj

Controller of Examination, NCBDr. B. Venkatraman

President, QUNESTProf. Arcot Ramachandran

All Chapter Chairmen/Secretaries

Permanent InviteesShri V.A.Chandramouli

Prof. S. RajagopalShri G. Ramachandran

& All Past Presidents of ISNT

I S N T - National Governing Council

Chapter - Chairman & SecretaryAhmedabadShri D.S. Kushwah, Chairman,NDT Services, 1st Floor, Motilal Estate,Bhairavnath Road, Maninagar,Ahmedabad 380 028. [email protected] Rajeev Vaghmare, Hon. SecretaryC/o Modsonic Instruments Mfg. Co. Pvt. Ltd.Plot No.33, Phase-III, GIDC Industrial EstateNaroda, Ahmedabad-382 330 [email protected]

BangaloreDr. M.T. Shyamsunder, Chairman,NDE Modelling & Imaging Lab.,Cassini Building, GE Global Research,John F. Welch Technology CenterEPIP Phase 2, Whitefield Road,Bangalore-560066. [email protected]

ChennaiShri T.V.K. Kidao, ChairmanMadras Metallurgical Services Pvt. Ltd.14, Lalithapuram Street, RoyapettahChennai – 600 014 [email protected] R. Balakrishnan, Hon. Secretary,No.13, 4th Cross Street, Indira Nagar,Adyar, Chennai 600 020. [email protected]

DelhiShri Ashok Singhi, Chairman,MD, IRC Engg Services India Pvt. Ltd612, Chiranjiv Tower 43, New [email protected] Dinesh Gupta, Hon.Secretary,Director, Satya Kiran Engg. Pvt. LtdBU 3 SFS Pitampura, New Delhi [email protected]

HyderabadShri G. Narayanrao, Chairman,Chairman & Managing Director, MIDHANI,Kanchanbagh, Hyderabad 500 [email protected] J.R. Doshi, Hon.Secretary,Scientist, Project LRSAMDRDL, Hyderabad 500 [email protected]

JamshedpurDr N Parida, Chairman,Senior Deputy DirectorHead, MSTD, NML, Jamshedpur - 831 [email protected]. GVS Murthy, Hon. Secretary,MSTD, NML, [email protected] / [email protected]

KalpakkamShri YC Manjunatha, ChairmanDirector ESG, IGCAR, Kalpakkam – 603 [email protected] BK Nashine, Hon.SecretaryHead, ED &SS, C&IDD, FRTGIGCAR, Kalpakkam – 603 102 [email protected]

KochiShri CK Soman, Chairman,Dy. General Manager (P & U),Bharat Petroleum Corporation Ltd. (Kochi Refinery),PO Ambalamugal 682 302. [email protected] V. Sathyan, Hon. Secretary,SM (Project),Bharat Petroleum Corporation Ltd. (Kochi Refinery),PO Ambalamugal-682 302. [email protected]

KolkataShri Swapan Chakraborty, ChairmanPerfect Metal Testing & Inspection Agency,46, Incinerator Road, Dum Dum Cantonment,Kolkata 700 028. [email protected] Dipankar Gautam, Hon. Secretary,4D, Eddis Place, Kolkata-700 [email protected]

KotaShri R.C. Sharma, ChairmanAssociate Director (QA),Rawatbhata 323 307 [email protected] S.V. Lele, Hon. Secretary,T/IV – 5/F, Anu Kiran Colony, PO Bhabha Nagar,Rawatbhata 323 307. [email protected]

MumbaiShri R.S. Vaghasiya, Chairman,B 4/7, Sri Punit Nagar, Plot 3, SV Road, Borivile West,Mumbai 400 092. [email protected] Samir K. Choksi, Hon. Secretary,Director, Choksi Brothers Pvt. Ltd.,4 & 5, Western India House, Sir P.M.Road,Fort, Mumbai 400 001. [email protected]

NagpurShri Pradeep Choudhari, ChairmanParikshak & Nirikshak, Plot M-9, LaxminagarNagpur - 440 022Mr. Jeevan Ghime, Hon. Secretary,Applies NDT & Tech Services,33, Ingole Nagar, B/s Hotel Pride, Wardha Road,Nagpur 440 005. [email protected]

PuneShri PV Dhole, ChairmanNDT House, 45 Dr Ambedkar Road,Sangam Bridge, Pune- 411 [email protected] VB Kavishwar, Hon Secretary,NDT House, 45 Dr Ambedkar Road,Sangam Bridge, Pune- 411 [email protected]

SriharikotaShri S.V. Subba Rao, Chairman,General Manager, Range OperationsSDSL, SHAR CentreSriharikota 524124. [email protected] G. Suryanarayana, Hon. Secretary,Dy. Manager, VAB, VAST, Satish Dhawan SpaceCentre, Sriharikota-524 124. [email protected]

TarapurShri PG Behere, Vice Chairman,AFFF, BARC, Tarapur-401 [email protected] Jamal Akftar, Hon.Secretary,TAPS 1 & 2, NPCIL, Tarapur. [email protected]

TiruchirapalliR.J. PardikarAGM, (NDTL)BHEL Tiruchirapalli 620 014. [email protected] A.K.Janardhanan, Hon. Secretary,C/o NDTL Building 1, H.P.B.P., BHEL,Tiruchirapalli 620 014. [email protected]

VadodaraShri P M Shah, Chairman,Head-(QA) Nuclear Power Corporation [email protected] S Hemal Mehta, Hon.Secretary,NBCC Plaza, Opp.Utkarsh petrol pump, Kareli Baug,Vadodara-390018. [email protected]

ThiruvananthapuramDr. S. Annamala, ChairmanGroup Director, Structural Design & Engg Group,VSSC, Thiruvananthapuram [email protected]. Imtiaz Ali KhanHon.Secretary, Engineer, Rocket Propellant Plant,VSSC, Thiruvananthapuram 695 [email protected]

VisakhapatnamShri Om Prakash, Chairman,MD, Bharat Heavy Plate & Vessels Ltd.Visakhapatnam 530 012.Shri Appa Rao, Hon. Secretary,DGM (Quality), BHPV Ltd., Visakhapatnam 530 012

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Contents

Chief EditorProf. Krishnan Balasubramaniame-mail: [email protected]

Co-EditorDr. BPC [email protected]

Managing EditorSri V Parie-mail: [email protected]

Topical EditorsDr D K BhattacharyaElectromagnetic MethodsDr T Jayakumar,Ultrasonic & Acoustic EmissionMethodsSri P KalyanasundaramAdvanced NDE MethodsSri K ViswanathanRadiation Methods

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Basics - Digital Industrial Radiography

Horizon - Photoacoustics - Can we hear Photosynthesis?

Chapter News

IQ forum

NDE events

NDE patents

NDT puzzle

Technical papers

Development of an Immersion-based UltrasonicC-Scan Technique to Evaluate the Performance of theElectro-Magnetic Stirrer for Improving Internal Quality ofContinuously Cast High Carbon Steel BilletsManish Raj, E Z Chacko, Sanjay Chandra, Issac Anto,Krishnan Balasubramaniam

Quality control of Nuclear Fuel Elementsby Gamma Radiometry AssayM.S.Rana, Benny Sebastian, Sanjoy Das, D. Mukherjee,B.K. Shah

Health Assessment of Structures, Systems and Components(SSCs) beyond initial design life: Role of NDE during LicenseRenewal of Tarapur Atomic Power Station-1&2; NuclearPower Corporation of India LimitedA.Ramu, C.S.Mali, J.Akhtar, V.S.Daniel, Ravindranath, B.K.Shah,S.Bhattacharjee, R.K.Gargye

Analysis and computer simulations of fan-beam algorithmswith no backprojection weight for equi-space linear arraydetectorA.V. Narasihmadhan and Kasi Rajgopal

Probe

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About the cover page:

Editorial BoardDr N N Kishore, Sri Ramesh B Parikh,Dr M V M S Rao, Dr J Lahri,Dr K R Y Simha, Sri K Sreenivasa Rao,Sri S Vaidyanathan, Dr K Rajagopal,Sri G Ramachandran, Sri B Ram Prakash

Advisory PanelProf P Rama Rao, Dr Baldev Raj,Dr K N Raju, Sri K Balaramamoorthy,Sri V R Deenadayalu, Prof S Ramaseshan,Sri A Sreenivasulu, Lt Gen Dr V J Sundaram,Prof N Venkatraman

ObjectivesThe Journal of Non-Destructive Testing &Evaluation is published quarterly by the IndianSociety for Non-Destructive Testing for promotingNDT Science and Technology. The objective ofthe Journal is to provide a forum fordissemination of knowledge in NDE and relatedfields. Papers will be accepted on the basis oftheir contribution to the growth of NDE Scienceand Technology.

Journal of Non DestructiveTesting & Evaluation

Published byShri RJ Pardikar,General Secretary on behalf ofIndian Society for Non Destructive Testing (ISNT)

The Journal is for private circulation to membersonly. All rights reserved throughout the world.Reproduction in any manner is prohibited. Viewsexpressed in the Journal are those of the authors'alone.

Modules 60 & 61, Readymade GarmentComplex, Guindy, Chennai 600032Phone: (044) 2250 0412Email: [email protected] at VRK Printing House3, Potters Street, Saidapet,Chennai 600 015 [email protected]: 09381004771

Volume 10 issue 1June 2011

Image shows two snapshots of the contour ofdisplacement magnitude obtained from FiniteElement (FE) simulation of the scattering of bulkultrasonic shear (SV) waves from a horizontalcrack. In the first snapshot, we see wavesreflected from the crack front, diffracted at thecrack tips and transmitted across the crack.However, the scattering is a complicated process,involving multiple passes of waves that can travelalong the crack also, causing interference patternsin the scattered signals. The second snapshottaken from a simulation with a much larger crackillustrates the power of modern numericalsimulation; we are able to observe the cylindrical‘primary’ diffraction, as well as Rayleigh-likewaves that are introduced along the crack facesand make multiple trips across the crack. Theseimages were obtained using ABAQUS commercialpackage.

Courtesy: this picture comes from research carriedout by Dr Prabhu Rajagopal, Assistant Professor,Centre for NDE, IIT-Madras during his PhD at theNDT Laboratory, Imperial College London.

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39

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50

Finite element (FE)simulation of multiple

scattering of bulk ultrasonicshear waves from a

horizontal crack

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Classifieds

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digital image which are discussedbelow.

Spatial resolution. The dots that makeup a digital image are called “pictureelements” or pixels. A pixel has adefinite size. In high resolution imagesa pixel may have a size of 50 μm x 50μm. Actually, this size is about the bestresolution the human eye can achieveand again, when we view such animage, we would think it is continuousin space and not broken down toindividual elements. If we take astandard 5 cm by 20 cm radiographat 50 μm pixel size (i.e. 200 Pixel percm), this image requires 5 x 200 x 20x 200 or 44 million pixels.

Depth resolution. One more propertyof a digital image is important. We canassign intensities or shades of grey toeach pixel. If only black and white isrequired, we can represent this interms of 0 or 1. We would describe itas every pixel having a depth of onebit (2**1). More shades can berepresented with a larger pixel depth.If we take an 8 bit pixel depth, wehave 2**8 = 256 shades. Mostly,instead of bit, the unit byte is used, 8bit = 1 byte. In this case one pixelhas the storage requirement of onebyte.

Again it is interesting to take thehuman vision as a reference. We candistinguish two shades of grey, if theirdifference is at least 2%. This is alsocalled visual contrast resolution. Forthe whole range of greys from blackto white, at best we can recognize only50 separate shades, each 2% apart.This means that a digital image thatis based on 8 bit resolution appearsas a continuous image to the humaneye. However, a digital system iscapable to meaningfully resolve andrecord as many as 12 bit (4096shades) or 16 bit (65536 shades). Thisalso increases the storagerequirement. If we take the radiographof the above example and assign 12bit (= 1.5 byte) for every pixel, 44million pixels require 66 million bytesor roughly 63 MB of storage for asingle 5 cm x 20 cm radiograph.

Temporal resolution. For complete-ness, we look at the resolution in time,which could be important for real timeradiography. Movies take advantageof the fact that we cannot resolveindividual images, if we see more thanabout 25 frames per second. A movieappears to be continuous, thoughobjectively, we are presented with asequence of still photographs.

Considering these fundamentals ofdigital imaging, we can understand

Computers require discrete numericalvalues for processing and storing. Theconversion of an analog signal orintensity to a number means that afixed step value is assigned to a smallcontinuous range. The process is calledA/D conversion or digitization. Thequality of digital conversion dependson the number of steps we assign to acontinuous range of values.

In the case of radiographs, a film isoften considered analog. This is it notquite correct. The darkening of the filmafter exposure and development is dueto very tiny silver crystals, also calledthe film grain. It is only because theeye cannot normally resolve theindividual grains that a radiograph isconsidered continuous. Actually thesegrains are randomly arranged,separate particles, a few micrometersin size. When viewing a film the grainscan normally not be seen individually,but are perceived as a continuousvariation in density.

2.2 Digital images

Digital images are made up of a fixedrectangular arrangement of squaredots. The requirement of storage of adigital image can be very largedepending on the parameters of a

1. Introduction

In the previous issues, the physicalprincipals of industrial radiography(RT) and high resolution radiographywere discussed. Digital radiography(DIR) is the topic of this article. DIRis based on the same principles ofimaging as RT, i.e. the recording ofspatially resolved radiation intensities.The only difference is that the methodof recording and visualization followsa digital route. We always have to keepin mind that we deal with X-rayabsorption images and not opticallyfocused photographs.

Digital images are nowadays found inmany applications. In photographythey almost completely replaced filmimaging. In RT, the process oftransition to digital methods is slower,mainly for economic considerations.

2. Fundamentals –

2.1 Analog and digital

When discussing images, often timesthe distinction between analog anddigital is made. Analog meansproportional or continuous. Digitalmeans discrete, or stepwise.

DDDDDrrrrr. H. H. H. H. Helmut elmut elmut elmut elmut WWWWWolfolfolfolfolfAnna University Chennai

DDDDDrrrrr.Theobald F.Theobald F.Theobald F.Theobald F.Theobald FuchsuchsuchsuchsuchsFraunhofer Development Center X-ray Technology, Fuerth, Germany

Basics

DDDDDigital Iigital Iigital Iigital Iigital Industrial ndustrial ndustrial ndustrial ndustrial RadiographyRadiographyRadiographyRadiographyRadiography

Converting an analog range to digital values. Each signal is assigned to theclosest discrete value out of a finite number of values at typically equidistantly

sampled positions.

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how digital radiographs can containmore information than what can beseen with the naked eye. They can besuperior with respect to all resolutions- space, depth or time. All we need issufficient memory space and accurateconversion devices. In this way we canobtain more information that isimmediately visible. Digital images canbe numerically evaluated or visualisedby digital processing. The image canbe magnified (spatial, also called pixelmapping), a limited tone range can beconverted to a larger range of shades(depth mapping, contrast adjustment)or the time intervals of display can beincreased (time mapping, slowmotion).

Digital images are also required forautomated systems where featuresare automatically detected andevaluated. In Computed Tomography(CT) images are superimposed forreconstruction of the inspectedvolume. Without digital technology CTwould not be possible.

3. Creation of digitalradiographs

There are different procedures toarrive at a digital radiograph.Conventional film can be a startingpoint. Real time systems often useconversion by scintilization (lightflashes) combined withphotomultipliers. Computedradiography uses storage phosphorsthat are read out after exposure. Onlyrecently directly converting flat paneldetectors have become available.

3.1 Conversion ofconventionalradiographic film

Conventional radiographic film isconverted into digital images for anumber of reasons. An importantreason is that radiographic filmcontains more information than canbe seen, as discussed earlier. We candetect more details in an image.

When ISNT held a first DIR workshopin India in 1999, the cost of storagemedia (DVDs, Hard Disks etc) was sohigh, that it was not economical tokeep scanned image files for storagepurposes. However, the advantages ofprocessing and evaluation weresufficient reason to digitize films. Anumber of digitization procedureswere developed:

Point scanners. The digitizationprocess reads the film density andconverts it to a numerical value. Thefirst digitizers worked with a singlelight source one side and a light sensor

on the opposite. The principle is thesame as in a film densitometer, exceptthat the density is recordedelectronically and within smaller areas.To read an entire film, the film ismoved point by point by a mechanicalX-Y scanner and the pixels with thedensity values are assembled to forma digital image.

Line scanners became available, wherean image is read line by line. Thescanner consists of many sensorsalong one line. The sensor is movedby an index value and the pixelscovering a complete film area areassembled into a digital image. Thisprocedure is very much like in an officescanner, except that office scannerswork in reflection. X-ray film scannerswork in transmission mode and needthe ability to process larger densityranges, as much as 1 to 10000,corresponding to densities of 4.

2-D scanners. The film can be read ina whole area. The pixels are definedby the resolution of the optical sensor.These are often CCD cameras. SinceCCD sensors have a limited dynamicrange, X-ray images are oftenprocessed with multiple exposures,each exposure in a different dynamicrange, to preserve the maximumdensity nuances of a film image.

3.2 Computed Radiography

Computed radiography (CR) is amethod that uses imaging phosphorplates. The radiation received is storedin the phosphor and read out bythermoluminescence effect. The workflow is very similar to conventionalradiography. The plates can behandled like film, even bent around a

weld. In principle, the plates can bereused more than 1000 times, but inpractical applications this is hardlyreached, because any mechanicaldamage or finger print shows up onsubsequent images. CR is ideal forlaboratory environments where theplates are not handled, but placed incassettes and automatically processedin reader scanners.

A laser beam is stimulating visible lightemission proportional to the radiationexposure of the plate. In a special readout scanner, the laser beam is focusedon one spot. The laser stimulates theemission of light at one spot. The spotis shifted by a rotating prism andcovering the entire area of a film.

This readout process can only beperformed once. By reading the plate,the latent image is removed. Theprocess cannot be repeated. Theparameters of the digital image,especially the pixel size is dependenton the focal spot of the laser. Eachspots becomes one pixel of the digitalimage.

3.3 Digital Flatpanel DetectorArrays - What is a flatpanel detector array?

A Flat-panels detector array (FDA) issubdivided into pixels already. Eachchannel of the flat panel matrix canbe considered a separate X-raydetector, comprising

- a photo-diode/capacitor

- a TFT switch for read-out,

- followed by an amplif ier, amultiplexer and an analogue-to-digital converter (ADC).

Projection imaging geometry

Basics

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There is a strong similarity to aninstrument in nuclear physics: A largenumber of individual detector channels(105 up to 107) are assembled withinthe same electronic device – thedetector matrix.

Signal characteristics of real-world flat panel detectordevices

FDAs have to be understood as acomplex electronic instrument forsignal acquisition and processing: thesignals contain thermal electricalnoise; often there are bad channels(black or white pixels); there mightoccur some coupling withelectromagnetic fields in the cablesand the electronics; there is a finitedigitization depth (number of bits ofADC); there is a read-out time (deadtime) and a cycle time (given asframes per sec); the signal from eachpixel of the matrix (“intensity” in greyvalues) is a measure of the number ofphotons absorbed by that particularpixel during integration time.

A FDA is usually not one single pieceof amorphous silicon of 200 mm or400 mm lateral size, but the detector

matrix is made up of several tiles witha read-out chip assigned to each.Thus, the “raw” images reflect theinternal structure of the device. Thethere can be overlaying patterns thatare characteristic for a particulardetector arrangements of detectors.

Since quality of semi-conductormaterial and processing of the micro-electronics may be inhomogeneous,the sensitivity of the channels mayvary from chip to chip, from line toline, and in large irregularly shapedareas (clouds). If we want to obtain auniform image output, for a uniforminput, we have to calibrate every pixelelectronically to compensatedifferences in linearity and sensitivity.

Gain-offset-correction

Each pixel has to be treated as anindependent measurement channel.The electrical signal from an individualdetector pixel can be written in a linearapproximation:

V(I) - Vdark + I.g

Thereby, I denotes the X-ray intensityreaching a single pixel. Each individualchannel is characterized by its dark

current vdark and gain g. Theseparameters are generally unknownand have to be determined bycalibration measurements.

The dark current (offset) is measuredwith zero X-ray dose:I = 0.

The bright image is measured with theprimary intensity I0 applied duringmeasurement. Its calibrated value canbe chosen arbitrarily, e.g. vcalibrated (I0)= 40.000 grey value level.

Usually, the intensity (e.g. dose orphoton flux) is not measured directlyby an additional instrument. Thus, forreasons of practicability, the gain isnot measured directly. The variationin gain between different channels iscorrected by applying a scaling factor.

Commercially available FDAs

There are various types of flat paneldetectors commercially availabletoday. The devices offered by severalmanufacturers vary in pixel size, pixelformat, the type of X-ray conversion,read out frequency and – last but notleast – price.

pixel size: 50 μm up to 400 μm

area: 50 mm x 50 mm up to 400mm x 400 mm

read out cycle between 5 and 30frames per second

indirect conversion (scintillator CsI,Gd2O2S:Tb)

amorphous silicon (Perkin-Elmer,Varian, Trixell, GE)

CMOS (Hamamatsu, Rad Icon)

direct conversion

Cadmium-Telluride (Ajat, MediPix)

Gallium-Arsenide (MediPix)Arrangement and Internal structure of a typical FDA

Uncorrected dark image. The thermal noise caused by the read out electronics can be seen clearly(left hand side: full panel, right: zoom).

Basics

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CCD-based

Selenium

The costs for a FDA range between10.000 and 100.000 Euro today, butprices are decreasing as the numbersof sold systems increase. The life-timeof a FDA is limited due to the inevitableradiation damages to the micro-electronics. According to theexperience of the authors the life-timeof a device which operated in a 24/7-mode is between 12 and 36 months.

4. Digital image processing

Exactly the same way as in digitalphotography, nowadays, there arecountless methods for digital imageprocessing, which can be applied tothe X-ray images.

One of the most simple options is theenhancement of the images by use oflocal or global filters. A very commonexample is the median filter which

helps to smoothen regions of theimage where the dectability of detailssuffers from high image noise. As wellmedian filters serve in removingirregular pixels while preserving edge-like structures. Another example ofcommon tools for the enhancement ofimages are look-up tables which serveto adapt the grey scale range forvisualization purposes. The same,contrast and brightness of digital X-ray images can be modified easily andrepeatedly.

Moreover, the digital technology allowsfor a computer aided analysis of anykind of X-ray images. Algorithms forpattern recognition and featureextraction can be applied, for instancein order to detect automatically voids,cracks or inclusions in various kindsof materials and components.

Data fusion with other NDT methodsis possible as well as more complexoperations like the reconstruction of3D volume data sets from projections

Digital output signal as a function of the X-ray intensity measured for everydetector pixel. Each of the three lines stands for a particular detector pixel.

Commercially available FDAs – PerkinElmer (left), Hamamatsu (center), Vidisco (right).

in Computed Tomography. A detailedtreatment of the latter techniques isfar beyond of the scope of thispublication, but of course they and allother image processing methodsrequire digital images as input data.

5. Automatic DefectRecognition (ADR) inindustrial production

As an example for a fully automaticinspection system, the FraunhoferISAR system is capable of acquiring asingle digital radioscopy image within200 milliseconds. Typically, for eachpart 3 to 14 different images areacquired, and evaluated, therebykeeping up with a production cycle ofabout 10 seconds per part or less.Subsequently, the software makes adecision, if the current part can beaccepted as defect-free, according tothe limits which are prescribed to thecomponent manufacturer by the OEM.

6. Digital images, issues ofarchival, durability andintegrity

6.1 Archival and durability

Films deteriorate over time. Films thathave not been washed well or arestored in humid places develop spotsand patches soon, but there are wellprocessed and stored films that havesurvived more than 100 years.

As for digital images, it is true thatthere is no deterioration of images.The data can be copied any numberof times and there is no loss of quality.However, if a set of data becomesunreadable, the loss is total. This canbe due to mechanical damage ofmedium such as a hard disk or CD.

If long term archiving is required, it ismore l ikely that data becomeunavailable because the readingdevices become technically outdated.Just consider diskettes or data tapes.

Basics

9


Today you really have to search forreaders to recover old data. 20 yearsfrom now CD and DVD drives may behard to find.Experts consider this tobe the more important issue.Accidental loss of data can be takencare of by multiple copies, stored atdifferent locations, but the loss of datadue to obsolescence also has to beaddressed.

6.2 Data compression

It is obious that the availability ofdigital X-ray images leads to apreviously unknown amount of data.In particular, 3-D volume data afforda large amount of storage, a challengethat is to be addressed in medicalimaging but as well as in industrialinspection. On the other hand amanifold of algorithms for datacompression is available today. Ingeneral, these algorithms can bedevided into two classes: lossy andlossless compression techniques. Thedecision on which type of compressionis to used has to be made case bycase. Although the efficiency of lossycompression algorithms in terms ofstorage saving is higher than withlossless methods, there may be legalrequirements or safety issues whichprohibit any reduction of informationwithin the digital X-ray images.

6.3 Data integrity

X-rays are often required for legalpurposes and digital images have thereputation is that they can be alteredor manipulated easily. Commonsoftware allows to add or removeimage details. This is also possible indigital X-rays. Today there is nouniversal standard or a fool proofsystem that can guarantee that therehas not been an alteration of animage. In principle authentificationsystems are possible, but have notbeen standardized.

7. Summary

This paper discusses the basicprinciples of digital X-ray imaging,further techniques like film digitizationand computed radiography (CT). Thelatest development of flat panel arrays(FPA) is explained in detail with respectto possibilities and challenges. Anumber of applications of digital X-rayimages are pointed out, as well as theissues of image processing,compression and archiving.

Overall, the rapid progress in digitalimaging has also affected the fullspectrum of industrial X-rayinspection. A large variety of newmethods and inspection possibilitiesare emerging with these new devices.

Fully automatic X-ray inspection system of aluminium castings. Casting andthree digital radiographs processed for defect detection.

National Certification BoardIndian Society for NonDestructive Testing

Announcement

ASNT NDTASNT NDTASNT NDTASNT NDTASNT NDTLevLevLevLevLevel III Eel III Eel III Eel III Eel III ExaminationxaminationxaminationxaminationxaminationMumbai 28, 29 & 30November 2011

ASNT NDT Level III Examinationwill be conducted in the followingmethods:

1. Basic2. Radiographic Testing3. Magnetic Particle Testing4. Ultrasonic Testing5. Liquid Penetrant Testing6. Eddy Current Testing7. Neutron Radiographic Testing8. Leak Testing9. Visual Testing10. Acoustic Emission Testing11. Thermal / Infrared Testing

It may please be noted that the basicexamination by itself is not consideredas a method. Basic and methodexamination(s) must be taken tobecome eligible to receive a certificatefor that method(s). The maximumnumber of examinations that can betaken is six during the three days ofthe Examination.

DDDDDrrrrr. B. . B. . B. . B. . B. VVVVVenkatramanenkatramanenkatramanenkatramanenkatramanASNT Level III Examination

Coordinator,Modules 60 & 61,

Readymade Garment Complex,SIDCO Industrial Estate, Guindy,

Chennai 600 032, India

Ph:91 44 22500412 &91 44 42038175

91 44 27480500 Ext.22306

E Mail: [email protected] E Mail:

[email protected]

Basics

VVVVVenue and Renue and Renue and Renue and Renue and Refrefrefrefrefresher coursesesher coursesesher coursesesher coursesesher coursesdate will be intimated laterdate will be intimated laterdate will be intimated laterdate will be intimated laterdate will be intimated later.....PPPPPlease visit lease visit lease visit lease visit lease visit wwwwwwwwwwwwwww.isnt.org.in.isnt.org.in.isnt.org.in.isnt.org.in.isnt.org.in

for application and other detailsfor application and other detailsfor application and other detailsfor application and other detailsfor application and other details

10


PPPPPhotoacousticshotoacousticshotoacousticshotoacousticshotoacousticsCan wCan wCan wCan wCan we hear Pe hear Pe hear Pe hear Pe hear Photosynthesis?hotosynthesis?hotosynthesis?hotosynthesis?hotosynthesis?

Horizon

The photoacoustic effect was firstdiscovered by Alexander GrahamBell around 1880. He was surprisedto discover that a sound wave couldbe produced directly from a solidsample if the incident light wasrapidly interrupted—typically on theorder of kHz. Bell used a spinningslotted wheel to mechanically “chop”the incident sunlight at thisfrequency. He observed that theresulting acoustic signal isdependent on the composition of thesample and correctly conjecturedthat the effect was caused byabsorption of the incident light.Bell’s initial experiments focused onthe solid phase of matter, but JohnTyndall and Wilhelm Roentgenperformed subsequent experimentsdemonstrating the same effect inliquids and gases. Tyndall was thefirst to discover that the intensity ofthe produced sound was directlyproportional to the amount of heatabsorbed, or equivalently, theintensity of the applied light.

The most commonly employedmodel for describing thephotoacoustic effect in condensedsamples was developed in the 1970sby Rosencwaig and Gersho (seeFigure 1). Pulsed light that isincident on a sample is absorbed

and the constituent moleculesbecome thermally excited. Periodicheat flow from the sample to thesurrounding gas causes pressurewaves that are in turn detected byan acoustic sensor. The pressurewaves are characteristic of thesample and are used to determinecomposition, concentration, andother thermophysical properties.

Suppose the incident radiation ismodulated with frequency ω. Thenthe incident intensity, taking intoaccount Beer’s Law with optical

absorption coefficient β, is given by:

The sample and the gas must eachsatisfy the heat-diffusion equation,

which for the case of the sample is

given by:

where σrt is the probability of

radiationless transition, and thermal

diffusivity

where k is thermal conductivity ofthe sample, ρ is the density, and Cp

is the specific heat. Rosencwaig andGersho determined the following

equation for temperature in thesurrounding medium as a function of

both position and time

where the complex temperature

amplitude θ1+iθ2, and thermal

diffusion coefficient .

The equation describes a periodic

wave of temperature thatpropagates through the mediumsurrounding the sample. Thetemperature fluctuation described bythis equation is the cause of thepressure waves that are detected.Since the e-ax term causes the waveto decay away from the sample, the

sensor should be located within the

thermal diffusion length in

order to maximize the strength ofthe acoustic signal.

Surprisingly, modern photoacousticanalysis has not deviated far fromBell’s original “chopped light” setup,apart from the introduction of lasersand generation. Typically, laserpulses on the order of 10 nsec areused for generation of ultrasound inthe order of 10-MHz freqency range.For even higher frequencies, pulsewidths on the order of 100 psec(resulting in ultrasound in the orderof 100-MHz frequency range) oreven femtosecond (for GHz range)laser systems may be necessary.They can be nondestructive if theoptical power is kept sufficientlysmall. In cases where a strongultrasonic signal is needed butablation is unacceptable, a sacrificiallayer (typically a coating or a fluid)is used.

Laser ultrasonic measurementsystems are particularly attractive tonondestructive structural andmaterials characterization of solidsbecause (a) they are noncontact andin situ leading to increased speed ofinspection, (b) they do not requireany couplant, (c) they have a verysmall footprint and can be operatedon curved complex surfaces, and (d)they are broadband systemsproviding information from the kHzto the GHz range, enabling theprobing of macrostructures to verythin films.

Figure 1: Comparison of photoacoustic signal generation in the right-angle (left) and front-face (right) geometries. In the right-angle geometry, the pump beam (green) is shaped witha slit to obtain a planar acoustic wavefront (taken from T.Gensch and C.Viappiani,Photochem. Photobiol. Sci., 2, (2003) 699–721)

Dr. CVK KrishnamurthyCentre for NDE and Department of Physics, IIT Madras

11


HORIZON

On a free surface, a laser pulsegenerates bulk waves (longitudinaland shear) as well as surface waves.Optimized generation of waves ispossible with optical manipulation ofthe laser beam, as shown in Figure2.

Using optical methods to detectultrasound greatly extends the scopeof photoacoustic technique andmakes it completely remote. Anexample is a laser ultrasonic systemthat incorporates cw lasergeneration and superheterodynedetection of acoustic waves. Anamplitude modulated laser source isused to excite high frequency,narrow bandwidth acoustic waves.The resulting surface displacement isdetected using a stabilized Michelsoninterferometer. The detection laserused in the interferometer ismodulated at a frequency that isoffset from the generation laser

modulation frequency by a fixedamount, serving as the localoscillator for superheterodynedetection. Figure 3 shows the resultsobtained through superheterodynedetection.

Photoacoustic (PA) andphotothermal (PT) methods areattractive for modern diagnosticsand imaging of the near surfacestructure where defects may resultin excessively high operational andresidual stresses. Recently, atechnique for nonlinearphotoacoustic imaging of cracks hasbeen reported that is based on laserexcitation with intensity modulationat two fundamental frequenciescombined with detection at mixedfrequencies. By exploiting the strongdependence of the photoacousticemission efficiency on the state—open or closed—of the contactsbetween the crack faces, remarkably

enhanced image contrast isobserved, about 20 times higherthan in linear photoacoustic imagesat the highest of the fundamentalfrequencies.

Photoacoustic Imaging

In the last decade, work onphotoacoustic imaging in biomedicalapplications has come a long way.The motivation for photoacousticimaging is to combine ultrasonicresolution with high contrast due tolight, or radiofrequency (rf),absorption. Unlike ionizing x-rayradiation, nonionizing waves pose nohealth hazard. Unfortunately,however, in the pure optical imagingmethodologies, optical scattering insoft tissues degrades spatialresolution significantly with depth.Since ultrasound scattering is two tothree orders of magnitude weakerthan optical scattering in biologicaltissues, ultrasound can provide abetter resolution than opticalimaging in depths greater than ∼1mm. However, pure ultrasoundimaging is based on the detection ofthe mechanical properties inbiological tissues, so its weakcontrasts are not capable ofrevealing early stage tumors.Moreover, ultrasound cannot imageeither oxygen saturation or theconcentration of hemoglobin, to bothof which optical absorption is verysensitive. These physiologicalparameters can provide functionalimaging. Likewise, pure rf imagingcannot provide good spatialresolution because of its longwavelength. Utilizing operatingfrequencies in the range of 500–900MHz, pure rf imaging can onlyprovide a spatial resolution of ∼1cm. The significance of PA imaging isthat it overcomes the aboveproblems and yields images of highEM contrast at high ultrasonicresolution in relatively large volumesof biological tissues.

It is interesting to note that no otherEM spectrum seems practical for PAgeneration in deep tissues. Forexample, terahertz rays that liebetween the above two EM spectrado not penetrate biological tissuewell due to water-dominatedabsorption. In the short-wavelengthspectrum below the visible region,such as ultraviolet rays, radiationhas high photon energy and,therefore, is harmful to humansubjects.

Figure 2: (a) Crossed beam interferencefor narrowband generation of highfrequency surface acoustic waves.(b) Time-domain signal of a narrowbandsurface acoustic wave on a thin film.(c) Spectrum of the narrowband surfaceacoustic wave showing high frequencygeneration.(taken from Nelson et al,J. Appl. Phys., 53, (1982) 1144–1149)

Figure 3: (left) Time domain signal on a90 μm Al plate with a source-to-receiverdistance of 60 μm obtained through adiscrete inverse Fourier transform offrequency domain data measured from 100MHz to 1.0 GHz. Key: SSL, surface-skimming-longitudinal wave; SAW,surface acoustic wave; L, longitudinalwave; SL, mode-converted SL wave; andS, shear wave. (right) Experimental andtheoretical dispersion curves for two Alfilms of thickness (h) on Si substrates. Thebest-fit Young’s modulus (E

fit) is also

shown. (from Bramhavar et al., Appl.Phys. Lett. 94, (2009) 114102)

12


The spatial resolution of PA imaging,as well as the maximum imagingdepth, is scaleable with the detectedultrasonic bandwidth. For example,PA signals with a 1 MHz bandwidthcan provide approximately 1 mmspatial resolution since the velocityof sound in soft tissues is ∼1.5 mm/s. If the bandwidth is increased to10 MHz, approximately 0.1 mmresolution can be achieved at theexpense of ultrasonic penetration.

In a simple case where a wide beamof light pulse heats a layeredmedium, the detected PA signalreplicates the light energy depositionprofile throughout the depth. Then,the depth-dependent information ofthe sample, such as the depthstructure and properties (e.g., theabsorption coefficient in anonscattering medium) can bedetermined directly from thetemporal PA signal. As shown inFigure 4, it is possible to have acombined photoacoustic andultrasonic imaging configuration.

In this hybrid method, the signals of64 transducer elements aresimultaneously recorded with anultrasound system and passed ontoa computer. The computerreconstructs an absorptiondistribution image and displays it ona screen with a repetition rate of 7.5Hz. One single laser pulse is enoughto get a complete image on thescreen in less than 100 msreconstruction time. Classical echoultrasound images can also beacquired for side by side comparisonor for mixed mode imaging.

However, to image more complicatedstructures, a more complex imagingmethod referred to as PAtomography (PAT) is preferred. PATmakes use of PA signals measuredat various locations around thesubject under study as shown inFigure 5. PAT is also calledoptoacoustic tomography (OAT) orthermoacoustic tomography (TAT),with the term “thermoacoustic”emphasizing the thermal expansionmechanism in the PA generation.OAT refers particularly to light-induced PAT, while TAT is used torefer to rf-induced PAT. Depthprofiling can be regarded as one-dimensional (1D) PAT.

PA imaging with a laser can bescaled down for microscopicimaging. A laser system can easily

PA microscopy imaging does not relyon ballistic or quasiballistic photonsand can, therefore, penetratedeeper.

To generate PA signals efficiently,two conditions, referred to asthermal and stress confinements,must be met. The time scale for theheat dissipation of absorbed EMenergy by thermal conduction canbe approximated by

τth ∼ Lp 2/4DT,

where Lp is the characteristic lineardimension of the tissue volumebeing heated (i.e., the penetrationdepth of the EM wave or the size ofthe absorbing structure). Actually,heat diffusion depends on thegeometry of the heated volume, andthe estimation of τth may vary. Uponthe absorption of a pulse with atemporal duration of τp, the thermaldiffusion length during the pulseperiod can be estimated by,

δT = 2(DTτp)½,

where DT is the thermal diffusivity ofthe sample, and a typical value formost soft tissues is DT ∼ 1.4×10"3

cm2/s. The pulse width τp should beshorter than τth to generate PAwaves efficiently, a condition that iscommonly referred to as thermalconfinement where heat diffusion isnegligible during the excitationpulse. For example, for a rf pulse ofτp = 0.5 μs, δT ≈ 0.5 μm, which ismuch less than the spatial resolutionthat most PA imaging systems canachieve. Therefore, the thermalconfinement condition is typicallymet. Similarly, the time for thestress to transit the heated regioncan be estimated by

Figure 4: Combined optoacoustic andultrasound real-time imaging setup. Thissystem can image several millimeters belowthe skin with 0.4 mm and 0.3 mm lateral andaxial resolutions, respectively (taken fromC.Li and L.V. Wang, Phys. Med. Biol. 54(2009) R59–R97)

Figure 5: (left) Schematic for Photoacoustic Tomography (from http:// en.wikipedia.org/wiki/ Photoacoustic_imaging_in_biomedicine). (right) A cross-sectional photoacousticimage of a rat brain. RH, right cerebral hemisphere; LH, left cerebral hemisphere; L,lesion; MCA, middle cerebral artery (from X. Wang et al., Nat. Biotechnol. 21,(2003) 803.

HORIZON

generate laser pulses with a pulseenergy of 100 mJ and a pulseduration of 10 ns or shorter, whichcan sufficiently excite PA signals athigh frequencies up to 100 MHz inlarge-area soft tissues with a goodSNR. Therefore, laser-based PAscanning tomography can performmicroscopic imaging with an axialresolution of 30 μm or less.

PA microscopy has criticaladvantages over other optical-contrast imaging methods, includingcurrent high-resolution opticalimaging techniques such as confocalmicroscopy and optical coherencetomography (OCT). These opticalimaging techniques can image onlyapproximately one transport meanfree path (∼ 1 mm) into tissuebecause they depend on ballistic orquasiballistic photons.

13


τs = Lp /c,

where c is the speed of sound. Thepulse width τp should be shorter thanτs, a condition that is commonlyreferred to as stress confinement.Under the stress confinementcondition, high thermoelasticpressure in the sample can build uprapidly. For example, to achieve aspatial resolution at Lp=150 μm, if c=1.5 mm/μs and DT ∼ 1.4×10-3 cm2/s, then τth∼ 40 ms and τs ∼100 ns.Hence, τp must be less than 100 nsto guarantee the more stringentstress confinement. When boththermal and stress confinements aresatisfied, thermal expansion causesa pressure rise p0 that can beestimated by

p0 = (βc2/Cp)μaF = ΓA,

where β is the isobaric volumeexpansion coefficient in K-1, Cp is thespecific heat in J/(K kg), μa is theabsorption coefficient in cm-1, F isthe local light (or rf) fluence in J /cm2, A is the local energy depositiondensity inJ /cm3: A=μaF, and Γis referred to asthe Grüneisen coefficient expressedasβc2/Cp.

Figure 6 shows a recent effort toprovide high-resolution 3D images ofvascular structures to depths of upto 5 mm based upon a Fabry–Perotpolymer film ultrasound sensor.

Can we hear Photosynthesis?

We all know that energy taken up byabsorption of light by the leafpigments is mainly used up forphotosynthesis. What is less well

known is that a smaller part of thisabsorbed energy is transformed intochlorophyll (Chl) fluorescence andthermal dissipation (i. e. heat). Thethermal dissipation leads to theheating of the gas surrounding thesample. Heating the gas leads to anincreased pressure inside the tightlyclosed measuring chamber (the“photo-acoustic cell”). If themodulation frequency of theilluminating light is chosen withinthe audible range, pressure changescan be measured by a microphone.This photoacoustic (PA) signal isstored or recorded after specificallyamplifying by means of a lock-inamplifier only those microphonesignals which were detected with thefrequency of the modulated light.

Figure 7: (left) Scheme of the Open Photoacoustic Cell (OPC) (from P. R. Barja, RevistaPhysicae, (2000), 1) . (right) Photoacoustic (PA) signal of a tobacco leaf in the millisecondtime domain after a 0.72 ms light pulse (light-emitting-diode: peak wavelength 650 nm) appliedat time = 0. The photothermal component (thin continuous line) was deduced from a separatemeasurement with continuous, non-modulated light saturating photosynthesis and normalizedto fit the overall PA signal (thick continuous line). The photobaric component (thin dottedline) was calculated by subtracting the deduced photothermal signal from the overall PAsignal (from Kolbowski et al., Photosynth. Res., 25, (1990) 309–316).

Figure 6: In vivo photoacoustic image of the vasculature in the palm using an excitationwavelength of 670 nm. Left: photograph of the imaged region, Middle: volume renderedimage. Right: lateral slices at different depths. The arrow ‘A’ indicates the deepest visiblevessel, which is located 4 mm beneath the surface of the skin. (taken from E Z Zhang etal., Phys. Med. Biol. 54 (2009) 1035–1046)

K. L. Muratikov and A. L. Glazov,Photoacoustic effect in stressedelastic solids, J. Appl. Phys. 88,(2000) 2948

J. P. Monchalin, Laser-Ultrasonics:From The Laboratory To Industry,CP700, Rev. of Quan. Nondest. Eval.23, (2004) ed. by D. O. Thompsonand D. E. Chimenti, 3

Minghua Xu, and Lihong V. Wang,Photoacoustic imaging inbiomedicine, Rev. Sci. Instrum. 77(2006) 041101

N. Chigarev, J. Zakrzewski, V.Tournat, and V. Gusev, Nonlinearfrequency-mixing photoacousticimaging of a crack, J. Appl. Phys.106, (2009) 036101

HORIZON

Figure 7 shows the schematic of theopen photoacoustic cell thatfacilitates working with livespecimens and a typicalphotoacoustic response of a leafinvolved in photosynthesis.

Photoacoustic imaging offers uniqueadvantages over existing imagingmodalities. The imaging field isbroad with many excitingapplications in biology, chemistry,and material science.

References

A. Rosencwaig and Gersho, Theoryof the Photoacoustic effect withsolids, J. Appl. Phys. 47 (1976) 64

A.C.Tam, Applications ofPhotoacoustic sensing techniques,Rev. Mod. Phys. 58 (1986) 381

14


Chennai ChapterChennai ChapterChennai ChapterChennai ChapterChennai ChapterUT Level-II (ASNT) course wasconducted from 22.04.11to 30.04.11.No. of participants were 1.R.Balakrishnan was the course directorand Mr.E Sathya Srinivasan was theexaminer.

In – house training MT – Level -II(ASNT),M.M.Forgings Ltd course wasconducted from 24th Apr ,08th ,15th ,22nd

May 2011 No. of participants were 9.Mr.M S Ramachandran was the courseDirector and Mr.E Sathya Srinivasan wasthe examiner.

Surface NDT ( MT & PT) Level - II (ASNT)course was conducted from 20.05.2011to 26.05.2011. No. of participants were20 for course and 18 for examination.Mr. G Jothinathan was the courseDirector and Mr.P.N.Udayasankar wasthe examiner.

ISNT DAY had been celebrated on 21stApril 2010 at Hotel Radha Regent. About190 members along with their familiesattended the function. Mr.S.Swaminathan, was the Convener of themeeting. Mr.M.V. Rajamani Chairmanpresided over the meeting and the ChiefGuest of the day was Mr.N. Balakrishnan,Vice President, M/s.Sundram FastenersLimited, Chennai. The faculty, theexaminers and the dignitaries who wereassociating with Chapter were honored

CHAPTER NEWS

Dr. Amitava Mitra, Life Fellowof ISNT and Sr. DeputyDirector (Scientist –G) andgroup Leader of NDE andMagnetic Materials of NationalMetallurgical Laboratory,Jamshedpur received theprestigious Materials ResearchSociety of India Medal (MRSIMedal) for his outstandingwork on nanostructuredmagnetic materials and use ofmagnetic NDE for materialscharacterization. He receivedthe award at the AnnualGeneral Meeting of MRSI held

* Dr. Narayan Parida, LifeMember of ISNT and Sr. DeputyDirector (Scientist –G) hastakenover as the Head ofMaterials Science and TechnologyDivision at NationalMetallurgical Laboratory-Jamshedpur

and presented mementos by the ChiefGuest. Gifts were distributed to spouseand children. Three awards, the BestMember Award, Thambithurai Award &Best Achievement Award which waspromoted by Shri.M.V.Rajamani andShri.S.Swaminathan were presented toMr.B.Ram Prakash the recipient of TheBest Member award and to Dr.KrishnanBalasubramaniam, I.I.T., Chennai therecipient of Thambithurai award andMr.Suresh Kaushal, Caterpillar IndiaLimited, Tiruvallur the recipient of BestAchievement Award. Magic Show andTattos to children were conducted byMr.S. Swaminathan for the children. Itwas well received

EC Meeting 01.05.2011EC Meeting 11.06.2011

UT L- II (ASNT) course was conductedfrom 30.05.2011 to 05.06.2011. No. ofparticipants were 14 for course and 18for examination. Mr.R.Subburathinamwas the course Director andMr.P.N.Udayasankar was the examiner.

RT L- II (ASNT) course was conductedfrom 10.06.2011 to 16.06.2011. No. ofparticipants were 17 for course and 18for examination. Mr. M S Ramachandranwas the course Director.

Bangalore ChapterA Technical Talk NADCAP NDT & Trainingby Mr. James Bennett, PerformanceReview Institute, USA was held on May10, 2011 in ASI Building of AeronauticalSociety of India

CCCCCongrongrongrongrongraaaaatulatulatulatulatulatititititionsonsonsonsons

Chief Guest Mr. N. Balakrishnan along with Council Members during ISNT Day

15


Problem:

06-2011-Detection of inclusions and cracks beforemachining.

Posted by :

AQUASUE ENGINEERING, Tudiyalur post, Coimbatore - 641034

Problem:

Steel rods are machined as stepped bar specimens. Whatis the bet method to detect cracks and inclusions to satisfythe acceptance criteria given?

Material:

Steel EN 8

Raw Material:

The bar stock used for machining is shown in Figure 1.

Machining:

The finished machined specimen should satisfy the acceptancecriteria given below.

ACCEPTANCE STANDARD FOR INCLUSION & CRACKCONTENT:

1. THREE - STEP STEP - TURN DOWN METHOD:

1 a. For diameter below 60mm, minimum 5 bars shall bedrawn from each lot for estimating the indusion content. Onlyone test specimen shall be cut as per drawing from each barfor step turning.

1 b. For diameter above 60mm, minimum 3 bars shall bedrawn from each lot for estimating the, inclusion content.Only one test specimen sample shall be machined as perdrawing from each bar.

2. ACCEPTANCE STANDARD:

Under Visual inspection,

2.1 a: For the diameter below 60mm, 4 out of 5 specimensshall be free from any steak/ inclusion. If present, indicationsless than or equal to 3mm in length is taken to be acceptable.

2.1 b: For the diameter above 60mm, 2 out of 3 specimensshall be free from any steak / inclusion. If present, indicationsless than or equal to 3mm in length length is taken to beacceptable.

2.2 Remaining specimens can have maximum two indications.

2.3 The maximum length of an indication shall not exceed 10mm.

2.4 The total length of two indications, when added, shall notexceed 15mm.

2.5 In case of any doubt in 2.2,2.3,2.4 retest may beconsidered.

3. RETEST:

3.1 Two more specimens are taken for retest. If both theretest results conform to the specification the lot is acceptedotherwise rejected.

The Query:

Which is or are the suitable NDT techniques to test the barstock before machining so that after machining the acceptancecriteria will be satisfied?

Reader’s are encouraged to send replies to the query [email protected]

“To establish a connect between the Researchers andPractitioners in NDE, this new forum INDUSTRIAL QUERY(IQ) FORUM is being created in our journal.

We wish to bring together the underlying scientificprinciples, engineering and technological aspects and themost probable solutions for a NDT problem posed by ourreaders and members.”

If you are in the industry and have a IQ, send an MSWorddocument with associated drawings [email protected] with subject title “IQ Problem” forconsideration for publication in a future issue. Also includeany attempts at solving this problem.

If you have a suggestion or solution for this, issue of IQ,please send it to [email protected] with subject title“IQ Solution- 03-2011” along with your contact information.Selected responses will be published in the June 2011 issue.All responses will be forwarded to the person posing theIQ.

“Readers are welcome to contribute their own experiencesin this kind of problems.

ISNT would select the best answer for a possible reward.”

-Prof. O. Prabhakar and-Prof. Krishnan Balasubramaniam

iqforum

Figure 1 : Steel rods used for machining

Figure 2: Machined steel specimen

Figure 3: Dimensions of the stepped bar

The steel rods are machined into a stepped bar whosedrawing is given in Figure 2.

Note: Tolerance on all diameters: ±0.30

NDT Required:

16


July 2011

5th ECCOMAS Thematic Conference on“Smart Structures and Materials”(SMART’11) July 6 to 8, 2011 ;Saabruecken, Germanyhttp://www.izfp.fraunhofer.de/smart11/

EPRI Buried Pipe Integrity Group OpenDoor Meeting and Vendor ExpoJuly 11 to 12, 2011 ; St. Louis,Missouri, USAhttp://www.cvent.com/events/buried-pipe-integrity-group-open-door-meeting-and-vendor-expo/event-summary05da397431e246c0a6453b2da9972dd1.aspx

Digital Imaging XIVJuly 18 to 20, 2011 ; Foxwoods Resort,CT, USA http://www.asnt.org/events/conferences/digital/digital.htm

38th Annual Review of progress inQuantitative NDE July 17 to 22, 2011 ;Burlington, VT, USAhttp://www.qndeprograms.org/2011/Conference2011.html

August 2011

World Conference on Acoustic EmissionAugust 24 to 26, 2011 ; Beijing, Chinahttp://www.wcae2011.org/

September 2011

International Congress on Ultrasonics(ICU 2011) September 5 to 8, 2011 ;Gdansk, Polandhttp://icu2011.ug.edu.pl/ocs233-1/index.php/icu/icu2011

8th International Workshop on StructuralHealth Monitoring (IWSHM 2011)September 13 to 15, 2011 ; Stanford,CA, USAh t t p : / / s t r u c t u r e . s t an f o r d . edu /workshop/

Materials Testing 2011September 13 to 15, 2011 ; Telford,UK http://www.bindt.org/Events/Exhibitions/MT_2011

5th Conference in EmergingTechnologies in NDT (ETNDT)September 19 to 21, 2011 ; Ioannina,Greece http://www.etech-ndt5.uoi.gr/

2011 ATA NDT ForumSeptember 26 to 29, 2011 ; Charlotte,

We hope that this new feature added tothe journal since the last issue was founduseful by the readers to plan theiractivities in terms of paper submissions,registering for seminars, etc. Pleasesend your feedback, comments andsuggestions on this section [email protected]

NC, USA ht tp: / /www.a i r l i nes .o rg/S a f e t y O p s / E M / P a g e s /2011NDTForum.aspx

October 2011

V Pan American Conference on NDTOctober 2 to 6, 2011 ; Cancun, Mexicoh t t p : / /www. copaend5 . c om/en /index.php

VIth International Workshop NDT inProgress, October 10 to 12, 2011 :Prague, Czech Republic h t t p : / /cndt.cz/ndt_in_progress2011/

2011 IEEE International UltrasonicsSymposium (IUS) October 18 – October21 ; Orlando, FL, USAhttp://ewh.ieee.org/conf/ius_2011/

2011 ASNT Fall Conference & QualityTesting SHow October 24 to 28,2011 ; Palm Springs, CA, USAh t t p : / / w w w . a s n t . o r g / e v e n t s /conferences/fc11/fc11.htm

November 2011

International Workshop on SmartMaterials & Structures and NDT inAerospace, November 2 to 4, 2011 ;Montreal, Quebec, Canadahttp://www.cansmart.com/

Singapore International NDT Conference& Exhibition (SINCE 2011)November 3 to 4, 2011 ; Singaporehttp://www.ndtss.org.sg/

41st International Conference and NDTExhibition; NDE for Safety 2011 /Defektoskopie 2011, November 9 to 11,2011, Ostrava, Czech Republichttp://cndt.cz/nde_for_safety2011/

Malaysia International NDT Conference& Exhibition 2011 (MINDTCE ‘11)November 21 to 22, 2011 ; Malaysia

http://www.aindt.com.au/images/stories/page_images/conferences/i n t e r n a t i o n a l /mindtce_11_brochure_revision_1.pdf

2011 Aircraft Structural Integrityprogram Conference N o v e m b e r29 to December 1, 2011 ; San Antonio,Texas http://www.asipcon.com/

NDE eventsMaterials Testing show to host ‘NDThall of fame’ Which person or eventhas made the single biggestcontribution to non-destructivetesting and condition monitoring?That’s the question which the BritishInstitute of Non-Destructive Testing(BINDT) is asking practitioners in therun-up to its 50th anniversarycelebrations later this year.

The institute is inviting NDTprofessionals from around the worldto nominate the characters and theevents that have had the greatestinfluence on the industry’sdevelopment. They will becommemorated in a ‘hall of fame’ atMaterials Testing 2011, the bi- annualexhibition, which takes place this yearon 13-15 September in Telford, UK.

To enter, you should name a person(living or dead), an event, or both,along with a brief explanation as towhat you believe they contributed tothe industry and why it was soimportant. BINDT is also keen toreceive memoirs and photos relatingto the industry to be part of a displaytelling the story of NDT through theyears.

Send your contributions [email protected] - allcomments will be collated and theinstitute will set up a panel to discussthe contributions. A special award willalso be made by the BINDT president-elect Steve Lavender at the 50thannual dinner which is part of theannual conference running alongsidethe exhibition.

John Hansen, chairman of theMaterials Testing organisingcommittee, said: “Although it playssuch a critical role in industry, NDTremains a relatively new industry withmany of the key developments havingtaken place within living memory.We’d like practitioners’ views on whatthey believe have been the keyinfluences which have shaped theindustry - both people and events sowe can commemorate these andcapture them for posterity.”

Materials Testing 2011 is free ofcharge for visitors and will featureover 50 exhibitors from around theworld along with a programme of talksand seminars. The show, which takesplace once every two years, isrecognised as one of the mostcomprehensive internationalexhibitions in NDT and relateddisciplines. The venue - theInternational Centre in Telford, in theWest Midlands - is less than one-and-a-half hours from three internationalairports and only five minutes fromrail and motorway networks.

For further information, seewww.materialstesting.org

<http:www.materialstesting.org><http://www.materialstesting.org>

Materials Testing 2011

17


National NDT Awards No. Award Name Sponsored by 1. ISNT - EEC M/s. Electronic & Engineering Co., Mumbai

National NDT Award (R&D)

2. ISNT - Modsonic M/s. Modsonic Instruments Mfg. Co. (P) Ltd.,National NDT Award (Industry) Ahmedabad

3. ISNT - Sievert M/s. Sievert India Pvt. Ltd., Navi MumbaiNational NDT Award (NDT Systems)

4. ISNT - IXAR M/s. Industrial X-Ray & Allied RadiographersBest Paper Award in JNDE (R & D) Mumbai

5. ISNT - Eastwest M/s. Eastwest Engineering & Electronics Co.,Best Paper Award in JNDE (Industry) Mumbai

6. ISNT - Pulsecho M/s. Pulsecho Systems (Bombay) Pvt. Ltd.Best Chapter Award for Mumbaithe Best Chapter of ISNT

7. ISNT - Ferroflux M/s. Ferroflux ProductsNational NDT Award (International recognition) Pune

8. ISNT - TECHNOFOUR M/s. TechnofourNational NDT Award for PuneYoung NDT Scientist / Engineer

9. ISNT - Lifetime Achievement Award

Note-1: The above National awards by ISNT are as a part of its efforts to recognise and motivate excellence in NDT professionalenterpreneurs. Nomination form for the above awards can be obtained from ISNT head office at Chennai, or from the chapters. Thefilled application are to be sent to Chairman, Awards Committee, Indian Society for Non-destructive Testing, Module No. 60 & 61,Readymade Garment Complex, SIDCO Ind. Estate, Guindy, Chennai-600 032. Telefax : 044-2250 0412 Email: [email protected]

MMMMMalaysian alaysian alaysian alaysian alaysian IIIIInternational nternational nternational nternational nternational NDTNDTNDTNDTNDTConferConferConferConferConferenceenceenceenceence and E and E and E and E and Exhibition 2011xhibition 2011xhibition 2011xhibition 2011xhibition 2011

(MINDT(MINDT(MINDT(MINDT(MINDTCE 11)CE 11)CE 11)CE 11)CE 11)November 21-22, 2011, Thistle Port Dickson Resort

www.msnt.org.my

The Malaysian Society for NDT (MSNT) cordially invitesyou and your staffs to participate and present your paper inthe 2011 Malaysian International NDT Conference andExhibition 2011 (MINDTCE 11). We expect there will bea lot of participation from NDT professionals and with yourparticipation we look forward to sharing knowledge andexperience in the field of NDT. MINDTCE 11 is jointlyorganized with the Malaysian Welding and Joining Society(MWJS) and strongly supported by PETRONAS,International Committee for NDT (ICNDT), MalaysianNuclera Agency and SIRIM.

The organizers invite scientists, engineers, educators,researchers and managers to submit paper to this wonderfulconference.

“WCAE-2011”World Conference on Acoustic Emission–2011 Beijing(WCAE-2011) is organized by the Chinese Society for Non-Destructive Testing (ChSNDT) and undertaken by TechnicalCommittee on Acoustic Emission of ChSNDT (TCAE).

ConferConferConferConferConference Dence Dence Dence Dence Date: Aate: Aate: Aate: Aate: August 24 to 26, 2011ugust 24 to 26, 2011ugust 24 to 26, 2011ugust 24 to 26, 2011ugust 24 to 26, 2011Venue: Beijing International Convention Center and BeijingContinental Grand Hotel, No.8 Beichen Dong Road,Chaoyang District, Beijing 100101, P.R. ChinaRoomReservations:Tel: ++86-10-84980105 ; Fax: ++86-10-84970106E-mail: [email protected] Website: www.bcghotel.comwww.bicc.com.cn

Contact Conference-secretariat and Mailing AddressMrMrMrMrMr. Zhanw. Zhanw. Zhanw. Zhanw. Zhanwen en en en en WWWWWu, u, u, u, u, WCAE-2011 SecretariatChina Special Equipment Inspection and ResearchInstituteBuilding 2, Xiyuan, Hepingjie, Chaoyang District,Beijing 100013, ChinaEmail:[email protected]: +86-10-59068313 ; Fax: +86-10-59068666

Revised Final date for full paper submission 5th September 2011Notification of acceptance : 15th July 2011Final date for full paper submission : 5th September 2011

18


Here are some interesting snippetsfrom the world of patents :

- The Indian Institute of Technology,Madras has recently won the awardfor securing the highest number ofpatents in the last five yearsamongst the educational institutionor university It is reported that thepremier institute has filed 78patent applications in the last fiveyears. The award was instituted bythe Confederation of IndianIndustries in collaboration with thecentral department of industrialpolicy and promotion and theIndian Intellectual Property Office.In addition, Lalit Mahajan, analumnus of IIT Madras, won theaward for an individual securing thehighest number of patents in thelast five years. (Source : Times ofIndia. April 30, 2011)

- Filing of an application for a patentshould be completed at the earliestpossible date and should not bedelayed until the invention is fullydeveloped for commercial working.A provisional application can befiled with a brief synopsis disclosingthe essence or the nature of theinvention.

Publication or disclosure of theinvention anywhere by the inventorbefore filing of a patent applicationwould disqualify the invention to bepatentable. Hence inventors shouldnot disclose their inventions beforefilling of the patent application. Whendisclosing, the number and the dateof the patent application should begiven by way of information to public.The date of patent is the priority date,which is the date on which firstapplication (provisional / Complete /PCT) filed disclosing the invention .However, the date of publication is alsoimportant because it is from this datethat the legal protection of aninvention disclosed in the patent takeseffect. The term of the patent iscounted from this date of application.A patent can expire in the followingways ; The patent has lived its fullterm i.e. the term specified by thepatent act of the country ; The

NDE patentsWe hope that the section on NDE Patents, which featured in the March 2011 issue of thisjournal, has continued to trigger your curiosity on this very important topic of Intellectualproperty. We continue this section with a few more facts on patents and a listing of a fewselected NDE patents. Please send your feedback, comments and suggestions on thissection to [email protected]

Compiled by Dr. M.T.Shyamsunder, GE Global Research, Bangalore, India

patentee fails to pay the renewal fee.A patent once granted by theGovernment has to be maintained bypaying annual renewal fee ; Thevalidity of the patent has beensuccessfully challenged by anopponent by filing an opposition ; Thepatent is revoked. (Source : http://www.rkdewan.com )

Listed below are a few selected patentsin the area of Liquid / Dye Penetranttesting, which were issued by USPTOsince 1976. If any of the patents areof interest to you, a complete copy ofthe patent including claims anddrawings may be accessed at http://ep.espacenet.com/

UNITED STATES PATENT7,215,807

NONDESTRUCTIVE INSPECTIONMETHOD AND APPARATUSInventors: Nomoto; Mineo,Katsuta; Daiske, Asano; Toshio,Sakai; Kaoru , Taguchi; Tetsuo ,Tanaka; Isao

Assignee: Hitachi Ltd. (Tokyo, JP)

The present invention relates to amethod for inspecting a crack in ametal surface or the like, and,particularly, to an inspection methodand apparatus for nondestructiveinspection such as liquid penetrantinspection and magnetic particletesting. The present invention providesa flaw inspection method thatessentially comprises the steps ofilluminating a surface of a sample tobe inspected, obtaining an image ofthe surface, characterizing a potentialflaw on the inspected surface byprocessing the obtained image,displaying an image of the potentialflaw, verifying that the potential flawis a true flaw, and storing an image ofthe verified flaw in memory.


METHOD FOR NON-DESTRUCTIVE TESTING OFMATERIALS AND WARES

Inventors: Beriozkina; Nadejda G,Leipunsky; Ilia O, Maklashevsky;Victor J

Assignee: Marvic Ltd. (Moscow,RU), Marotta Scientific Controls,Inc. (Montville, NJ)

A non-destructive testing method forrevealing surface and through defectsin materials and articles. The methodcomprises filling up defects with avolatile penetrant, applying indicatormaterial to a surface to be tested,removing the indicator material fromthe surface and registrating defectsaccording to the presence color spots,shapes and dimensions which arefunctions of shapes and dimensions ofreal defects. The indicator materialcomprises a gas-permeable base withapplied sulfonephthalein indicator inthe range of 0.0001 to 0.001 gramsper 1 cubic centimeter of the base.


EXTENDED BIODEGRADABLEDYE PENETRANTCOMPOSITIONInventors: Molina; Orlando G.

Assignee: Rockwell InternationalCorporation (El Segundo, CA)

A liquid dye penetrant composition foruse in non-destructive testing ofobjects to locate cracks and otherdefects or flaws therein, saidcomposition comprising (1) a nonionicsurfactant, such as an oxyalkylatedaliphatic alcohol, (2) a small amountof a dye soluble in the surfactant and(3) a substantial and preferably amajor proportion, of an N-alkyl-2-pyrrolidone, preferably N-methyl-2-pyrrolidone, as extender. Suchcomposition is applied to the surfaceof an object containing cracks andother defects, water is applied to thesurface of the object to remove excessliquid dye penetrant composition fromthe surface without removing suchpenetrant from such cracks and otherdefects, and with or without adeveloper, the surface of the object is

19


viewed under suitable l ightingconditions, e.g. ultraviolet or blacklight when the dye in the penetrant isa fluorescent dye to locate any cracksor other defects in the surface of thebody as indicated by colored tracesfrom the dye penetrant remaining insuch cracks and other defects.


HIGH TEMPERATUREPENETRANT SYSTEMInventors: Garcia; Vilma A.

Assignee: Magnaflux Corporation(Chicago, IL)

A method and composition for non-destructive testing using the dyepenetrant technique, and adapting theuse of this technique at hightemperatures. The invention isinvolved with using a marking crayonwhich includes a carrier composed ofa solid which melts at a temperaturebelow the temperature at which thework piece is to be inspected and avisible or fluorescent dye. Uponapplication of the crayon to a hot workpiece, the solid penetrant compositionbecomes molten and the visible orfluorescent dye penetrates into anyflaws in the surface in the usualmanner. A remover, also consisting ofa crayon composition, is used toremove excess penetrant, leaving onlypenetrant entrapped in the flaws.Upon removal of the excess penetrantand remover, the entrapped penetrantdeposits are drawn to surface by theapplication of a finely divideddeveloper either in dry form or as anaerosol. Inspection of the piece is thencarried out under visible or ultravioletlight, depending upon the nature ofthe penetrant.


FLUORESCENT STANDARD FORSCANNING DEVICESInventors: Schiffert; Phillip W.


A standard specimen for calibrating anultraviolet scanning system of the typeused to detect surface flaws in workpieces by penetrant testing includinga piece of glass which has thecharacteristic of emitting fluorescentradiation upon excitation by ultravioletlight, and a heat conductive carrierelement rigidly supporting the pieceof glass therein. The standard

specimen provides a means forconfirming instrumentation stabilitydespite changes in temperature.


FLUORESCENT PENETRANTSYSTEMInventors: Mlot-Fijalkowski; Adolf


A method for non-destructive testingfor flaws on the surface of a workpiecewhich includes the step of applying apenetrant composition including afluorescent dye in a liquid vehicle ontothe surface to permit the penetrant tobecome trapped in the flaws and thenremoving excess penetrant from thesurface while leaving penetrantentrapped in such flaws. A remover isthen applied to the surface, theremover composition including asolvent, at least one surface activeagent which serves as an emulsifierfor the liquid vehicle of entrappedpenetrant, and a fluorescent materialwhich is more readily soluble in theliquid vehicle of the penetrant than itis in the solvent. Upon contact of theentrapped penetrant with the remover,the fluorescent material from theremover is preferentially absorbed inthe penetrant vehicle entrapped in theflaws thereby enhancing thefluorescent indication provided by theentrapped penetrant. The indicationsare developed in the usual way byapplying a developer to the surface todraw the entrapped penetrant to thesurface of the workpiece where it iscontrastingly visible to the surface andis observable by viewing the surfaceunder ultraviolet light.


RED-VISIBLE DYE PENETRANTCOMPOSITION AND METHODEMPLOYING SAMEInventors: Molina; Orlando G.


A liquid dye penetrant composition foruse in non-destructive testing ofobjects to locate cracks and otherdefects or flaws therein, saidcomposition comprising a liquidvehicle, preferably a nonionicsurfactant such as an oxyalkylatedaliphatic alcohol, and a single phaseliquid red azo dye compositionconsisting essentially of C5-C12 alkyl

beta naphthols, particularly C7-H15beta naphthols, and containing a liquidorganic viscosity depressantcompatible with the azo dyes, such asxylene, as represented by the dyecomposition marketed as AutomateRed “B”, and which is substantially freeof insolubles. The dye penetrantcomposition may include an extender,preferably an isoparaffinic solventconsisting essentially of a mixture ofisoparaffins having a chain length ofabout 10 to about 17 carbon atoms,and an average chain length of about13 to about 14 carbon atoms. Suchdye penetrant composition is appliedto the surface of an object containingcracks and other defects, water isapplied to the surface of the object toremove excess liquid dye penetrantcomposition from the surface withoutremoving such penetrant from thecracks and other defects, and with orwithout a developer, the surface of theobject is viewed under visible light tolocate any cracks or other defects inthe surface of the body as indicatedby brilliant red traces from the dyepenetrant remaining in such cracksand other defects.


WATER WASHABLE DYEPENETRANT COMPOSITIONAND METHOD FOR UTILIZINGSAMEInventors: Molina; Orlando G.


A water washable substantiallybiodegradable dye penetrantcomposition having excellentsensitivity and high stability, for usein non-destructive testing of objectsto locate voids and defects therein,said composition consisting essentiallyof an organic dye, preferably afluorescent dye, and a carrier orsolvent for said dye, in the form ofcertain ethoxylated linear alcohols,particularly the biodegradable nonionicsurfactants comprised of ethoxylatesof a mixture of secondary alcoholshaving linear alkyl chains of from 10to 17 carbon atoms. In the method ofapplication of the dye penetrantcompositions, such composition isapplied to the surface of an objectcontaining cracks and flaws, water isapplied to the surface of the object toremove excess liquid dye penetrantcomposition from the surface withoutremoving such penetrant from thecracks and defects, and with orwithout a developer, the surface of theobject is viewed under suitable lighting

20


conditions, e.g., ultraviolet or blacklight when the dye in the penetrant isa fluorescent dye, to locate any cracksor defects in the surface of the bodyas indicated by colored traces from thedye penetrant remaining in the cracksand flaws.


PENETRANT FLAW INSPECTIONMETHODInventors: Molina; Orlando G.


A water washable substantiallybiodegradable dye penetrantcomposition having excellentsensitivity and high stability, for usein non-destructive testing of objectsto locate voids and defects therein,said composition consisting essentiallyof an organic dye, preferably afluorescent dye, and a carrier orsolvent for said dye, in the form of a

mixture of certain ethoxylated linearalcohols, particularly a combination ofbiodegradable nonionic surfactantseach comprised of ethoxylates of amixture of secondary alcohols havinglinear alkyl chains of from 11 to 15carbon atoms, one of which containsan average of 5 moles of ethyleneoxide, and another of which containsan average of 9 moles of ethyleneoxide. In the method of application ofthe dye penetrant compositions, suchcomposition is applied to the surfaceof an object containing cracks andflaws, water is applied to the surfaceof the object to remove excess liquiddye penetrant composition from thesurface without removing suchpenetrant from the cracks and defects,and with or without a developer, thesurface of the object is viewed undersuitable lighting conditions, e.g.ultraviolet or black light when the dyein the penetrant is a fluorescent dye,to locate any cracks or defects in thesurface of the body as indicated bycolored traces from the dye penetrantremaining in the cracks and flaws.


METHOD OF LUMINESCENCEDETECTION OF SURFACEDISCONTINUITIES

Inventors: Kuzmina; NadezhdaVasilievna, Vanina; LjudmilaIvanovna, Vdovenko; NadezhdaVasilievna, Melikadze; LeonidDavidovich, Malkes; LeonidYakovlevich, Vasiliev; NikolaiGrigorievich, Borovikov; AlexandrSergeevich

A method for detection of surfacediscontinuities by luminescence whichconsists in the successive treatmentof the surfaces of materials subject totesting and inspection with thefollowing compositions of a penetrant,cleaning fluid and a developer,whereupon they are inspected underan ultraviolet light at wavelength of340-420 nm. Liquid constituents arein volume percent. The inventionenables the revealing of surfacediscontinuities with a minimum widthof 1-4 micrometers and providesadequate contrast and reliability inflaw detection.

DiscountinuitiesReferenceDefectsPorositiesThermographyFerromagneticAmplitudeContrastPenetrantSensorProbesReliabilityIridiumCobaltmaxwellKrautkramerultravioletGaussborescopeweldsfrequencylongitudinalbeamtransversevolumetric

AcousticCalibrationDelaminationCracksUltrasonicRadigraphyThresholdPhaseFlourescentTransducerImpedanceGammaSeleniumOerstedRoentgenFaradayElectromagneticCastingsindicationsrayleighanglewavesurface prodyoke

AnswAnswAnswAnswAnswers for Pers for Pers for Pers for Pers for Prrrrrevious issue - NDT evious issue - NDT evious issue - NDT evious issue - NDT evious issue - NDT WWWWWororororord Sd Sd Sd Sd Searearearearearch Qch Qch Qch Qch Quiz 1uiz 1uiz 1uiz 1uiz 1

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Contact

Mr. D. Simon Amallaraja | 0 9866343309,9848043309|

Ms.Gomathi Ramasamy | 0 7702733309 |

Mr. Frank Edwin Vedam | 0 8978517118 |

[email protected]

[email protected]

[email protected]

24


We hope you enjoyed solving the “NDTWord Search Puzzle” which waspublished in the last issue. We receivedmany entries from the readers andbased on the maximum number ofcorrect words identified, the followingare the WINNERS

- TK Abhilasha, CNDE, IIT, Madras

- P Selvaraj, ISRO-SHAR, Shriharikota

- Sunita Thomas, BARC, Mumbai

- TK Manoj Kumar, Brahmos AerospaceLtd, Thiruvananthapuram

Congratulations to all the Winners. Theywill receive their prizes from the ChiefEditor of the journal shortly. The correctanswers to the Puzzle are published inpage 20 of this issue.

In this issue, we have another puzzle tocontinue stimulating your brain cells! Wehope you will f ind this sectioninteresting, educative and fun filled. Inthe next issue, we will be featuring acrossword puzzle. Please send yourfeedback, comments and suggestions onthis section [email protected]

IntroductionThe “Word Search Puzzle”, contains forty(40) words related to “Liquid / DyePenetrant Testing”. These includeterminologies commonly associated withthe technique. These words are hiddenin the puzzle and may be presenthorizontally, vertically, diagonally in aforward or reverse manner but alwaysin a straight line.

InstructionsAll you have to do is identify these wordsand mark them on the puzzle with ablack pen. Preferably you may take aphotocopy of the Puzzle sheet and markyour answers on that. Once completedplease scan your answered puzzle sheetas a PDF file and email the scanned sheetto [email protected] along with yourname, organization, contact number andemail address

Rules & Regulations- Only one submission per person is

allowed

- The marked answers should belegible and clear without anyscratching or overwriting

- The decision of the Editor-in-Chief,Journal of NDT &E is final and bindingin all matters

The correct answers and the names ofthe prize winners will be published in thenext issue of the journal.

Conceptualized & Created byDr. M.T. Shyamsunder,

GE Global Research, Bangalore

NDT WORDSEARCH - 2

NAME : ___________________________

ORGANIZATION : ___________________________

PHONE : ___________________________

EMAIL ID : ___________________________

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29


32 Technical Paper

Journal of Non destructive Testing & Evaluation Vol. 10, Issue 1 June 2011

Development of an Immersion-based UltrasonicC-Scan Technique to Evaluate the Performance of the

Electro-Magnetic Stirrer for Improving InternalQuality of Continuously Cast High Carbon Steel Billets

Manish Raj*, E Z Chacko*, Sanjay Chandra*, Issac Anto #, Krishnan Balasubramaniam$

* Tata Steel Ltd., Jamshedpur, India

# M/s Dhvani R & D Solutions Pvt. Ltd., IITM Research Park, Chennai, India

$ Centre for Nondestructive Evaluation, Indian Institute of Technology, Madras, Chennai

ABSTARCT

Effect of electro-magnetic stirring on soundness of continuously cast billets and slabs can be assessed by many methods like visualinspection of macro-etch & sulphur print evaluation. But ultrasonic assessment provides through thickness information of thetest samples, whereas, macro-etching and sulphur print methods provide information in one plane only. An attempt has beenmade to evaluate the effect of electro-magnetic stirring on soundness (inhomogeneities / flaws as well as effect of columnar /equiaxed grains) of continuously cast low carbon and high carbon continuously cast steel billets by ultrasonic attenuation as wellas high gain pulse-echo technique in transverse cut slices. With increasing demand for steels for drawing at higher speeds, thequality, in terms of internal defects and macro structural features (central porosity, equiaxed zone, etc.), of billets has becomeof paramount importance. By optimizing the Electro Magnetic Stirrer (EMS) parameters viz., EMS current and frequency theseverity of defects, area of columnar zone as well as central porosity, in continuously cast billet can be effectively minimized.The result would be an increase in equiaxed zone area and improved internal soundness. In the present work attempts have beenmade to determine the best combination of EMS current as well as frequency to ensure good internal soundness of billets. TheEMS current and frequency were changed to different values in the range of 300A to 350 A and 4Hz to 6Hz respectively.Corresponding billet samples were collected for macro structural evaluation. The samples were scanned using an immersionultrasonic C-scanner to get images of samples. Macro structural features revealed by ultrasonic C-Scan were analysed fordetermining the best combination of EMS parameters. It was observed that in the range under trial, % equiaxed zone and %central void area were not affected significantly by varying the EMS parameters.

Keywords: Billet Casting, EMS Current, EMS Frequency, Ultrasonic C-scan, Columnar Zone, Equiaxed Zone, Central Porosity

1. INTRODUCTION

With improvements in wire drawing processes, wiredrawing plants are taking continuous steps to increasedrawing speeds. Wire drawers are thus demanding betterquality steels with lower inclusion ratings and lower fractionof hard phases (cementite and martensite). Apart fromgoing for closed casting to reduce inclusion content, billetcasters are under pressure to reduce segregation in theirproducts.

The Steel Plant located in South East Asia has a threestrand billet caster producing low carbon, high carbonand cold heading quality grades equipped with a MouldEMS. The high carbon billets produced are rolled at theplants rolling mill and sold to wire drawing customers.For the purpose of the study billets of a high carbon PC(pre-stressed concrete) grade steel were selected.

1.1 Electro Magnetic Stirring

The principle of the EMS is similar to that of an ACmotor. The rotating magnetic field (B) produced by thestirrer penetrates across the solidified shell into the liquidsteel (Fig 1). The liquid steel is thus rotating at a speed‘u’ relative to the magnetic field and an electric current ‘j’

is induced in it. The induced current (j) and magnetic field(B) further induce an electromagnetic force (F) whichputs the liquid metal into rotation. By controlling the EMScurrent and frequency, the force of rotation can be varied.

The primary benefits obtained with EMS have beenthoroughly treated in literature (1). Simply put, the purposeof EMS is to homogenize the steel melt in order to obtaina favourable solid structure after solidification. The benefitsare :

Fig. 1 : Schematic diagram of an EMS showing the direction of j,B, u, F inside the mould

33Technical Paper

Vol. 10, Issue 1 June 2011 Journal of Non destructive Testing & Evaluation

1. Improvement in cast structure through increasedvolume of equiaxed grains.

2. Reduced degree of macro-inclusions, especially in thecentral portion of cross sections.

3. Improved surface quality and

4. Reduced shrinkage porosity.

Effect of EMS frequency and current on stirring force :

The following relationship describe the effect of EMSfrequency and current on stirring force, F

f α B2M(f)f (1)

Where, BM = magnetic flux intensity in the consideredpoint inside the mould (in Gauss)

f = Frequency of rotation of the magnetic field

The magnetic flux intensity (BM) decreases with increasingfrequency due to “skin effect” according to which eddycurrents are more concentrated on the outer part of theconductor as the frequency increases. At frequency zerothe force is zero and at higher frequency the forceapproaches to zero again because the term B2

M(f) becomesvery small. In between, there is a specific frequency, atwhich the stirring force is maximum. The current of theEMS coil has a more direct effect on the rotational forceas the magnetic flux (BM) is proportional to the current.

During any metallurgical improvement obtained by EMS,a low rotational force gives insufficient improvements whilea too high rotational force may give practically no furtherimprovement. Moreover, too high rotational force maygive rise to negative effects. Consequently, the optimumcurrent and frequency settings are desired to be foundout.

2. MATERIAL AND METHOD

2.1 Chemical Composition of Material Used

The chemical composition of steel grade considered in thepresent work is shown in Table 1.

Table 1 : Chemical composition of HC Grade selected forstudy

Grade Chemical Composition (Wt %)

C Mn S P Si Al Cr V

HC 0.79- 0.63- 0.030 0.030 0.20- 0.050 0.18- 0.064-0.82 0.68 Max. Max. 0.25 Max. 0.22 0.068

2.2 Measurement of Magnetic Flux in the Mould

A ‘Link-Magnetic Magnetic Fieldmeter MPU-ST’, was usedto measure the strength of the magnetic field produced bythe EMS. The design range for the current of the EMScoil was from 0 to 400 A and the design range of thefrequency was from 4 Hz to 12 Hz. The intensity along

the length of the mold tube was measured by suspendingthe measuring probe at various heights along the length ofthe empty mold tube in a mold fitted on the caster. Theprimary cooling water was running at its standard flowrate of 2000 lpm. The intensity at a particular height wasobtained by positioning the tip of the probe at the requiredheight manually, in the centre of the mold. Thesemeasurements were carried out at six different currentsand three different frequencies in strand 1 of the caster asshown in Table 2.

Table 2 : Setting for magnetic flux density measurementinside the mould

200 250 300 320 350 380Amps Amps Amps Amps Amps Amps

4Hz

5Hz

6Hz

The magnetic flux density measured is illustrated in Figures2 (a) and 2 (b) for varying frequencies and currentsrespectively. The intensity of magnetic field decreases withincreasing frequency and increases with increasing current.

3. EXPERIMENTAL SET-UP

Two sets of trials were conducted for the purpose of thestudy. In order to ensure comparability of readings, each

Fig. 2 : Variation in magnetic flux density at(a) 320 A current with varying frequency, and(b) 4 Hz frequency with varying current

34 Technical Paper


trial was conducted across the same heat and in the twostrands i.e., strand 1 and strand 2, simultaneously. Thenormal casting duration of a heat is around 56 minutes.EMS settings were changed at an interval of 10 minutes.At each setting, one sample of six inches length was cutfor the study. In the first trial, the EMS current was keptconstant at 320 amps and the frequency was varied. Inthe second trial the EMS frequency was kept constant at4 Hz and the current was varied. The details of the trialsconducted are given in Table 3. The settings for thesetrials were chosen considering that higher currents andlower frequencies gave higher magnetic flux values asdepicted in Figs. 2 (a) and 2 (b). Prior to this work, thebillet caster used a setting of 320 A EMS current and 4Hz EMS frequency for all the close casting grades.

Table 3 : Setting for samples collection

Trial Heat Trial Sample Sample SampleNo. No. 1 2 3

1 001069 Constant current320Amps andvarying frequency 4Hz 5Hz 6Hz

2 001070 Constant frequency 300 320 3504Hz and varying Amps Amps Ampscurrent

Each six inch long billet sample was further machine cutinto two one inch samples as shown in Figure 3.

Each sample was then surface ground and scanned usinga computer-controlled immersion ultrasonic C-scanequipment. The samples were then rated with respect tocentral porosity and percentage equiaxed zone by both themethods using the methodology given in Table 4. Centralporosity was rated based on the area fraction of the centralvoid. Percentage equiaxed zone was rated based on thearea fraction of the equiaxed zone.

4. EQUIPMENT USED

The samples were tested in a water tank using a 2 inchesdiameter 5 MHz ultrasonic focused beam probe. The C-scan images were obtained with the help of a computercontrolled immersion ultrasonic C-scan system.

4.1 Ultrasonic Immersion C-scan ImagingTechnique

During the continuous casting process, due to thedifferential cooling from the outside surface to the inside,the grain structure is expected to take the distribution asrepresented by the classic schematic shown in Fig. 4 (a).Here, the chill zone (A) is found on the outer most layerthat is in contact with the mould. The anisotropic columnargrain structure (B) is found below the chill zone. Theinside regions are found to be equiaxed (C). At the centre,owing to the metal shrinkage, central void (D) is found.The relative areas of these zones will depend on variouscasting process parameters. Ultrasonic technique wasapplied to evaluate the above mentioned zones of the billetsamples. This method revealed the four different regionsin the samples, chilled zone, columnar zone, equiaxed zoneand central void, in different gray / colour scale Fig. 4 (b).

Ultrasonic C-scan can image five different intermediatelayers of billet samples and plot the results in twodimensions. Therefore, all the internal defects appear aswell giving an advantage over normal macro-etching where

Table 4 : Quality evaluation methodology

Parameters Unit of measure Measurement system

Central % Area of central void/ totalporosity transverse area x 100

% Equiaxed % Area of equiaxed zone/totalzone transverse area × 100

Fig. 3 : Schematic diagram of CC billet sample collected forultrasonic evaluation.

Fig. 4 : Macro-structure of a continuous cast billet sample(a) Schematic diagram, and(b) Image revealed by Ultrasonic C-Scan

35Technical Paper


only the top etched layer of the sample can be inspected.One major advantage of ultrasonic C-scan over A-scan isthat classification of different kinds of defects is possibleby imaging of the defects by this method.

A series of C-scan tests (24 nos.) were carried out withvarying parameter settings. The instrument variables forthese tests were as follows :

PRF : 100 Hz

Gain : 40 dB

Energy : 50 uj

Damping : 100 ohms

Voltage output (amplitude) : + 3 to - 3 and

Resolution : 0.2 mm x 0.2 mm

Grey scale was used to evaluate and analyze the resultsobtained from the gated area. Referring to ultrasonicC-scan images, and based on a grey scale that depictsattenuated signals darker, one may see clear identificationof different macro structures by the darker areas. Althoughnot very sharp, each and every one of the areas isreproduced with a certain degree of dimensional accuracy.However, the boundary of each defect is not well defined.

Top and bottom surfaces as well as three intermediatelayers of each billet sample were scanned at an interval ofaround 7 mm in the ultrasonic C-scanner. The twodimensional image obtained from the C-scannerdistinguished different macro structural regions such asequiaxed, columnar and chilled zones, and casting defects,if any.

5. RESULTS AND DISCUSSION

5.1 Optimization of EMS frequency

Figures 5 (a), (b) and (c) show the ultrasonic C-Scanimages of transverse section of CC billet sample of HCGrade cast at strand 1 at EMS current 320 A and EMSfrequency 4 Hz, 5 Hz and 6 Hz respectively whereas theC-scan images of transverse section of CC billet sampleof HC Grade cast at strand 2 at EMS current 320 A andEMS frequency 4 Hz, 5 Hz and 6 Hz respectively havebeen illustrated in Figs. 6 (a), (b) and (c). Fig. 7 (a) and(b) show the effect of EMS current on the % equiaxedzone and % area of central void of total area of billetsamples cast at strand 1 respectively whereas 8 (a) and(b) show the effect of EMS frequency on the % equiaxedzone and % area of central void of total area of billetsamples cast at strand 2 respectively. The results havebeen tabulated in Table 5.

It is found, from the above mentioned figures and table,that the % equiaxed zone is quite significant and consistentat EMS frequency 4 Hz and it do not increases significantlywith the increase in EMS frequency. The % area of centralvoid in the billet samples, with respect to the total area of

billet section, also does not change considerably withincrease in EMS frequency. Therefore, EMS frequencywas not raised further and considered optimum as 4 Hz.

Table 5 : % Equiaxed zone and % central void measured inCC billets samples cast in strand 1 and strand 2at EMS current 320 A at EMS frequency 4, 5 and6 Hz

EMS EMS % Equiaxed zone % Central voidCurrent Freq. Strand 1 Strand 2 Strand 1 Strand 2

* S1 S2 S1 S2 S1 S2 S1 S2

320A 4Hz 50.78 51.36 45.01 50.35 0.5 0.6 0.1 0.12

320A 5Hz 49.88 49.12 49.09 47.38 0.6 0.4 3.03 0.21

320A 6Hz 50.42 54.31 47.35 46.03 0.68 0.61 0.12 0.32

* S = sample no.

Fig. 5 : Ultrasonic C-Scan image of transverse section of CC billetsample cast in strand 1 at EMS current 320 A and

(a) Frequency 4 Hz, (b) Frequency 5 Hz, and(c) Frequency 6 Hz

36 Technical Paper


5.2 Optimization of EMS Current

Figures 9 (a) and (b) show the ultrasonic C-Scan imagesof transverse section of CC billet sample of HC Gradecast at strand 1 at EMS frequency 4 Hz and EMS current300 and 350 A respectively whereas the C-scan images oftransverse section of CC billet sample of same grade castat strand 2 at EMS frequency 4 Hz and EMS current 300and 350 A respectively have been illustrated in Figs. 10 (a)and (b). Fig. 11 (a) and (b) show the effect of EMScurrent on the % equiaxed zone and % area of centralvoid of total area of billet samples cast at strand 1respectively whereas Fig. 12 (a) and (b) show the effectof EMS current on the % equiaxed zone and % area ofcentral void of total area of billet samples cast at strand2 respectively. The results have been tabulated in Table 5.

Fig. 6 : Ultrasonic C-Scan image of transverse section of CC billetsample cast in strand 2 at EMS current 320 A and

(a) Frequency 4 Hz, (b) Frequency 5 Hz, and (c)Frequency 6 Hz

Fig. 8 : Effect of EMS frequencies (at current 320 A) on

(a) % equiaxed zone, and (b) % area of central void of totalarea of billet samples cast at strand 2.

Fig. 7 : Effect of EMS frequencies (at current 320 A) on

(a) % equiaxed zone, and (b) % area of central void of totalarea of billet samples cast at strand 1.

37Technical Paper


Fig. 9 : Ultrasonic C-Scan image of transverse section of CC billetsample cast in strand 1 at EMS frequency 4 Hz and (a)Current 300 A, and (b) Current 350 A

Fig. 10 : Ultrasonic C-Scan image of transverse section of CC billetsample cast in strand 2 at EMS frequency 4 Hz and(a) Current 300 A, and (b) Current 350 A

Fig. 11 : Effect of EMS Current (at frequency 4 Hz) on(a) % equiaxed zone, and(b) % area of central void of total area of billet samplescast at strand 1.

Fig. 12 : Effect of EMS Current (at frequency 4 Hz) on(a) % equiaxed zone, and(b) % area of central void of total area of billet samplescast at strand 2.

38 Technical Paper


Table 6 : % Equiaxed zone and % central void measured inCC billets samples cast in strand 1 and strand 2 atEMS frequency 4 Hz at EMS current 300, 320 and350 A.

EMS EMS % Equiaxed zone % Central voidCurrent Freq. Strand 1 Strand 2 Strand 1 Strand 2

* S1 S2 S1 S2 S1 S2 S1 S2

300A 4Hz 49.59 51.08 45.77 48.27 0.91 0.42 0.32 0.47

350A 4Hz 51.72 50.76 46.53 50.03 1.59 0.64 0.05 0.14

It can be observed, from the above mentioned figures andtable, that the % of equiaxed zone is significant as well asconsistent at EMS current 320 A (existing practice) and itdoes not increases significantly with the further increasein EMS current. The % area of central void in the billetsamples, with respect to the total area of billet section,also does not change considerably with further increase inEMS current. Therefore, EMS current was not increasedfurther and considered optimum as 320 A.

6. CONCLUSIONS

It is important to control the EMS motion within themeniscus and bulk regions of the casting to achieve thedesired product quality and operating flexibility. The stirringof molten steel by EMS is effective to improve thehomogeneity of the cast, which solidifies with enoughamounts of equiaxed crystals. Based on the experimentsand analysis it was concluded that

Magnetic flux density (Gauss) inside the mouldincreased with increasing EMS current and decreasingfrequency.

The change in EMS frequency from 4 Hz to 6 Hz,with varying EMS current 300 A to 350 A did notresulted in further improvement in billet quality.

The current setting of EMS i.e. 4 Hz frequency and320 A current is the optimum setting to get goodquality of CC billets.

The qualitative as well as quantitative evaluation ofcentral void and columnar/equiaxed zone in the

continuously cast billets was possible using ultrasonicimmersion C-Scan imaging technique.

7. ACKNOWLEDGEMENTS

The authors are thankful to the management of Tata Steelfor giving permission to publish this paper. The authorsalso acknowledge the assistance of Mr. ThepthemrongWongwiriyakul, Mr. Krittawit Sajawirote and Mr. DhanupolUaapisitwong of Tata Steel Thailand during the course ofthe study.

REFERENCES

1. A. Badidi Buda, S. Liable, A. Enchilada, 2003, Grain size influenceon ultrasonic velocities and attenuation, NDT & E International36, 1-5.

2. J.C. Pandey and Manish Raj, 2007, Evaluation of internal andsubsurface quality of continuously cast billets & slabs byultrasonic techniques, Ironmaking and Steelmaking, Vol. 34, No.6, 482-490.

3. J.C. Pandey, Manish Raj, T.K. Roy and T. Venugopalan, June2008, A Novel Method to Measure Cleanliness in Steel UsingUltrasonic C-scan Image Analysis, Metallurgical and MaterialsTransactions B, Vol. 39B, 439-446.

4. M. Yoshimura, S. Suzuki, S. Takagawa and H. Ueno, Oct. 1980,On the Quality Improvements of Continuously Cast Productsthrough Electromagnetic Stirring at Mold and secondary CoolingZone, 100th th ISIJ Meeting, Lecture No. S802.

5. Manish Raj and J.C Pandey, March 2007, An ultrasonic techniqueto evaluate the performance of the electro-magnetic stirrer forimproving internal quality of continuously cast billets, MaterialEvaluation, Vol. 65, No. 3, 329-334.

6. Manish Raj and J.C. Pandey, 2008, Optimization of ElectroMagnetic Stirring in Continuously Cast steel billet using UltrasonicC-Scan Imaging Technique, Ironmaking & Steelmaking, Vol. 35,No. 4, 289-296.

7. Preeti Prakash Sahoo, Ankur Kumar, Jayanta Halder and ManishRaj, 2009, Optimisation of Electromagnetic Stirring in SteelBillet Caster by Using Image Processing Technique forImprovement in Billet Quality, ISIJ International Vol. 49, No. 4,521-528.

39Technical Paper


Quality control of Nuclear Fuel Elementsby Gamma Radiometry Assay

M.S.Rana, Benny Sebastian, Sanjoy Das, D. Mukherjee and B.K. ShahQuality Assurance Division

Bhabha Atomic Research Centre

Mumbai 400085

ABSTRACT

Determination of fissile material concentration and its variation along length of fuel element is a critical requirement forqualification of nuclear fuel. All the fuel elements are evaluated by non-destructive method to ensure uniform distribution of fissilematerial for reliable performance in reactor. Although several NDT methods such as micro radiographic testing for smallerdiameter fuel pin and conventional radiographic testing for the large diameter fuel pin have been tried, but these methods donot provide adequate quantitative information. An alternative method to mitigate these problems is being tried by observing theattenuation characteristics of gamma photon beam from a radioactive isotope by the fuel. One such technique is radiometricgamma scanning of nuclear fuel element. Radiometry is a procedure in which, gamma rays produced by the radioactive sourcegets attenuated by the material under test and the transmitted beam of gamma rays are detected by the scintillation detector.The detector - photo multiplier tube coverts the radiation beam into weak voltage pulses through a series of opto-electricalphenomena. These pulses are subsequently amplified by the use of amplifier and are processed in Single Channel Analyzer (SCA).The final output for a fuel element is in the form of series counts across the length of fuel element, which are analyzed byapplication software to produce quantitative information about it. The operational procedure of radiometric technique developedfor qualification of fuel has been described in this paper. Effect of different parameter on the scanning and their interdependencyare also discussed.

1. INTRODUCTION

Dispersion type fuel elements are fabricated through powdermetallurgical route where fissile material in form ofintermetallic compound (eg. UAl3) is dispersed in the matrixof aluminium alloy. This method of fabrication involvesdifferent process such as vibro compaction of intermetalliccompound in the clad tube and infiltration of the matrixinto it. Different NDT methods are used for monitoringthe fabrication process. Eddy current testing is done tocheck the continuity of the matrix through out the lengthof the fuel element. Helium leak testing ensures the leaktightness of the element. The linear power rating of a fuelpin in the reactor depends upon the fuel density as wellas its axial distribution. Axial uniformity of fuel density isessential to avoid the formation of hot spots in the fuelpins and form an important quality control requirementduring fabrication. Non destructive technique usingradiometry has been developed for determination ofuniformity of axial distribution of fissile material densityalong the fuel element. Passive gamma scanning is notsensitive to linear density change because of severe selfabsorption of low energy, low intensity gamma rays fromfuel material and can reveal only surface characteristic ofthe sample. Radiometry technique using active gammascanning has been used for such application in which anappropriate external radioactive isotope is used as sourceand scintillation detector for detecting and counting oftransmitted beam of photon. This attenuated beam will beanalyzed to find out distribution of heavy material alongthe fuel column.

2. PRINCIPLE

Radiometry is a technique where gamma rays from aradiation source pass through material and the attenuatedbeam is detected by a radiation detector. The result isavailable in the form of counts, i.e. number of pulsesrecorded in the gamma counting device. The attenuationof gamma rays in a solid medium follows the modifiedBeer-Lambert law.

I= I0 exp(-μg ρx)

Where I0 and I are intensities of incident and transmittedradiation respectively, μg and x are mass attenuationcoefficient and distance traversed respectively, ρ is densityof the material.

Taking natural logarithms both sides of Beer-Lambertequation yields.

ln (I) = ln (I0) - μg ρx

Since photon flux recorded in a detector is proportional tothe intensity of radiation, the above expression can bewritten as,

ln (counts) = ln (counts)0 - μg ρx

In the above equation, the counting of incident beam isfixed for given setup and mass attenuation co-efficient isalso constant for a given material and is independent ofit’s physical form. The diameter of fuel pin is also fixedfor a given type of fuel. Therefore ln (counts) is a directlinear function of density of fuel pin.

40 Technical Paper


3. RADIOMETRY SETUP

A schematic of the radiometry mechanical setup is shownin Fig. (1). The radiometry setup consists of the followings

a) Mechanical Scanning unit and its control electronics

b) Nuclear data acquisition system.

c) PC Hardware and Application software.

3.1 Scanning unit

Scanning unit consist of lead shielded source and detectorassembly and mechanism for translational (linear) androtational motion of the fuel element. The collimatingaperture would always be smaller than the diameter of thefuel element. Thus some material on periphery will lieoutside the radiation beam. Rotation is necessary to bringthis into the field of testing. The mechanical scanner shouldsatisfy the following criteria for precision in results:

i) Uniform speed, i.e. equal linear or angular movementshould occur in equal time interval.

ii) No slippage, i.e. it should not happen that during somesmall time interval, the fuel element remains stationaryat a place with only rotation and no linear motion.

iii) Vibrations should be minimum.

The control electronics consists of motor drives andcontrol, sensors logic. The control electronics takes care

of mechanical movements in proper sequence as requiredby the system. It provides start signal and linear motionsignal to data acquisition electronics for synchronization.This synchronization of data acquisition by scintillationdetector and linear motion start is vital because it correlatebetween the coordinates of fuel element and radiationabsorption data.

3.2 Nuclear data acquisition electronics

It consists of detector front end electronics, single channelanalyzer (SCA) with programmable dwell time, lower leveldiscriminator (LLD) and upper level discriminator (ULD)and scalar. The front end electronics consists of voltagesensitive preamplifier, amplifier and high voltage bias tothe detector. The output form detector assembly is lowamplitude – short duration current pulse. Preamplifierconverts this current pulse into voltage pulse whoseamplitude is proportional to energy deposited in detectormedium during gamma ray interaction. The signal frompreamplifier is not suitable for processing in SCA. Forthis, shaping of output signal from preamplifier is required.The amplified pulses are fed into SCA in order todiscriminate pulses of different heights, which in-turnshows different energies. The analyzer consists of twodiscriminators with independent voltage thresholds. Unlessthe pulse height is greater than the setting of LLD, it isdisregarded. If the pulse larger enough to exceed the LLD,

Radiometry Scanning Unit (Plan view)

Fig. (1)

Fig (2)

41Technical Paper


but not too large to exceed the ULD, SCA produces anoutput. SCA is connected to scalar and the scalar willcount all gamma rays in a selected energy interval.

3.3 Computer Hardware and Application software:

Computer is connected to nuclear data acquisition unit bya USB cable or through RS232 cable. Integrated applicationsoftware is designed and developed to analyze the countsobtained from the counter electronics. The applicationsoftware not only supports the acquisition but also controlsthe system mechanical operation.

4. RADIATION DETECTOR

Detector used for the application mentioned above is1" dia. x 1" length NaI(TI) scintillation detector. Selectionof detector material is governed by the followingrequirements.

i) Detector should possess good resolution. Resolutionis the ability of detector to distinguish between twoclosest energy levels. High resolution gives moreaccurate assay. The resolution of germanium detectoris 0.5 to 2.0 Kev where as resolution of NaI(TI)detector is 20 to 60 Kev.

ii) Efficiency means probability with which detector candetect in-coming photons. Efficiency can be achievedat the cost of resolution. A given efficiency is lessexpensive to obtain in low resolution NaI (TI) crystalthan in high resolution germanium detector.

iii) Other parameters such as space and coolingrequirement and portability must be considered andmay be prime criteria in detector selection.

5. RADIATION SOURCE

The selection of proper radiation source for the applicationis necessity for good quantitative resolution. In otherwords, a minute change in heavy material density shouldresult in as large count rate variation as possible. Otherfactors such as diameter of the fuel element, packingdensity and source properties such as half life, availabilityand cost have to be considered. In case of uranium bearingfuel, an isotope of Cobalt is generally used as source. Theenergy of the source selected is close to K-edge absorptionenergy of the uranium atom. This ensures that theabsorption is high in the fuel and sensitivity in quantitativeassessment is high.

6. INTERDEPENDENCE OF OPERATIONPARAMETERS

The operation parameters such as linear and rotary speeds,collimator slit length and width, source strength, acquisitiontime etc need to be properly selected and fixed for theapplication. These selections are done to obtain best possibleresult. The interdependence of the operation parametersare discussed bellow

6.1 Collimator slit dimensions

The collimator slit is present on both side i.e. source anddetector. The dimension of the slit is very important, sinceit significantly affect the sensitivity of the result. Lengthof the slit should be such that it can detect the smallestlocal variation in the linear density as per the acceptancestandard. On the other hand many factors are to beconsidered in the selection of the width of the slit. It cannot be too wide, or else so called ‘direct shine’ will occur,which means that the external radiation will by-pass thefuel and directly enter the detector. This can greatly reducethe counting accuracy.

6.2 Linear and Rotational Speeds

At the outer periphery, radiation path lengths vary greatlywith distance from the centre of the fuel and hence someof this portion will be left out of the slit. To test thisportion of the fuel element rotation motion is very importantparameter. Linear and rotational speeds for scanning aresynchronized to ensure that no portion of fuel, particularlyfrom the periphery, escapes coming in line with the sourceand detector. Higher linear speed and low rotational speedwill result in this situation. Pitch can be defined as theaxial length moved per rotation. If l mm/sec is linearspeed and r revolution/sec is rotational speed.

Pitch p = l / r

6.3 Acquisition time

Acquisition time is nothing but the counting time perchannel. It also plays part in coverage of the volumeinspected. If counting time is t then fuel length travelledin one acquisition is l x t. To ensure that counts arecollected at least for every mm of the fuel length, it is tobe ensured that magnitude of l x t i.e.

| l x t| ≤ r

6.4 Source strength

Source type and strength is very important parameter,which dictates all the parameters discussed above. Asdiscuss earlier source type is selected by ensuring that theabsorption is high in the fuel and sensitivity in quantitativeassessment is high. It is well known that the countingstatistics improves with the count rate and hence properselection of source strength is required. The linear speedl and the acquisition time t are to be selected in such away that the count rate is high enough to satisfy therequirement of precision laid down in the specifications.

7. RADIOMETRY SCANNING PROCEDURE

In order to use the radiometry system for quality evaluation,the equipment has to be calibrated with standard fuel pin.After the standardization of the system, the machine isready for inspection.

42 Technical Paper


7.1 Calibration

Radiometry testing discussed here is an indirect methodfor determination of heavy material linear density and hencecalibration of the counting system is necessity for thisapplication. Calibration of the gamma ray spectroscopysystem is done to establish relationship between countsand linear density of the material under examination. Tocalibrate the system, a set of standard elements are scannedfirst. The standard elements are made up of same fissilematerial as that of actual fuel but with slight variation inits linear density. The variations in linear density of thestandard elements are required so that the equation betweencounts and the linear density can be established. Thevariation of the linear density must be such that it coversthe entire range of inspection values set by the designer.The standard must contain minimum three elements ofvariable density for calibration but for better accuracy oneshould always use more numbers of standards. One ofthe standard elements must have linear density very closeor equal to the nominal value. After all the standard elementsare scanned, the counts are stored for calibration. Thecalibration is performed by plotting graph of linear densityversus natural logarithm of counts {ln (counts)} as shownin Fig. (3). The by using least square method therelationship between linear density and count can achieved.

Linear Density = - m {ln (count)} + C

Where, m = Slope of the curveC = Constant.

Negative (-m) slope indicate that the linear density isinversely proportional to the counts.

7.2 Inspection

Radiometry inspection of nuclear fuel elements is done byscanning the elements one after the other. The purpose ofthe inspection is to check the distribution of fissile materialthroughout the active length of the element. There arelarge number of variables whose value needs to be fixedeither at design stage or during operation. These are linearand rotary speeds, collimator slit length and width, sourcestrength, acquisition time etc. As they influence the overallaccuracy of the result, their interdependence should be

understood. These variables are selected to obtain the bestpossible result.

The data obtained in terms of counts are fed to thecalibration equation and the distribution of linear densityof that element can be obtained by using analyzing softwareas shown in Fig. (4). The various measurement parametersare derived after data processing and analysis throughspecial algorithms. These measurement parameters are thencompared and based on the specification accept or rejectdecision is taken.

8. CONCLUSION

Though passive gamma scanning is much simpler inoperation, but it is a surface or sub-surface technique.

Fig. (3)

The information obtained in passive scanning is qualitative.Active gamma scanning has an added advantage of fullcross sectional examination and information obtained isprecise and quantitative. The variables in active scanningare more than the passive gamma scanning. Hence processparameter needs to be standardized before operation.Radiometry using active gamma scanning is currentlyadopted for quality control of dispersion fuel element.

9. ACKNOWLEDGMENT

The authors acknowledge the support and constantencouragement from Shri H.S. Kamath, Director, NuclearFuels Group and Shri. R.P. Singh, Associate Director,Nuclear Fuels Group for carrying out the work. The effortof our colleges in Quality Control Section is dulyacknowledge.

REFERENCES

1. Hastings Smith Jr. and Phyllis Russo in Chap 9 of “Passive non-destructive assay of nuclear materials”, NUREG/CR-5550 Ed:Dong Reilly et al (1991).

2. Sanjoy Das, P.R.Vaidya & B.K.Shah “Assessment of pipe wallthickness radiation technique”, Inspectioneering Journal July/August 2007.

3. Robert C. Mc Master, Non-destructive Testing Hand book,Volume-3, 2nd edition, The American Society for Non-destructiveTesting, (ASNT), Ohio, USA.

Fig. (4)

43Technical Paper


Health Assessment of Structures, Systems andComponents (SSCs) beyond initial design life:

Role of NDE during License Renewal of TarapurAtomic Power Station-1&2; Nuclear Power

Corporation of India Limited

A.Ramu, C.S.Mali1, J.Akhtar1, V.S.Daniel1, Ravindranath1, B.K.Shah2, S.Bhattacharjee1 and R.K.Gargye1

1Tarapur Atomic Power Station, Tarapur Maharashtra Site; Nuclear Power Corporation of India Limited

PO: TAPP; Dist: Thane; Maharashtra: State; Pin: 401 5042 Head, Quality Assurance Division, Bhabha Atomic Research Centre, Mumbai, India.

E-mail : [email protected]; [email protected]

ABSTRACT

Tarapur Atomic Power Station-1&2 (TAPS) is one of the Boiling Water Reactors (BWRs) operating in the world and belongsto earlier generation of BWRs. These units were commissioned in late 60’s and have successfully completed 40 years ofcommercial, reliable and safe operation. Ageing of plant Structures, Systems and Components (SSCs) important to safety needto be effectively identified using various Non-Destructive Testing (NDT) methods to ensure their integrity and functionalcapability throughout their service life. The process of license renewal of Tarapur – BWR units was initiated well in advancewith the Indian regulatory authority, the Atomic Energy Regulatory Board (AERB) before the license expires. A systematicapproach has been devised and followed in identifying & addressing the critical areas/components important to nuclear safety.Comprehensive assessment of SSCs and material condition of the station has been identified as key factors to determine fitnessof Systems, Structures and Components (SSCs) for continued operation beyond its initial designed life of 40-years. The expertisegained from the operation and maintenance of both the units for the past four decades has strengthened the capabilities of thestation personnel to develop various inspection methodologies & their application in the field. The inspection programmes hasbeen revised based on the feedback obtained from In-Service Inspection results and ageing management related comprehensiveinspection & testing programmes. In addition to this, TAPS has developed and established many of the inspection techniques/procedures to assess the component’s integrity using various non-destructive testing methods. In some of the critical areas,independent review from various governmental research agencies has also been sought. TAPS had also taken up corrective stepsin this regard and a comprehensive study was conducted in association with the expertise from NPCIL Directorates and variousR&D agencies such as Bhabha Atomic Research Centre (BARC) and Indira Gandhi Centre for Atomic Research (IGCAR).

This paper gives a brief of various Non-Destructive Evaluation (NDE) methodologies followed during Condition Assessment ofvarious critical nuclear components during license renewal of TAPS for Long Term Operation (LTO) beyond its initial designlife.

Keywords: AMP, SSCs, PSI, ISI, Integrity, NDE, BWRs, License Renewal, LTO.

1. INTRODUCTION-TARAPUR BWRS

Tarapur Atomic Power Station-1&2 is one of the LightWater Reactors – BWR type design constructed andcommissioned in late ‘60s with an installed capacity of220MWe. Tarapur-BWRs is one of the vintage reactors(BWR-1/Mark I)which were built on turnkey basis byGeneral Electric, USA. These units were designed tooperate with load following characteristics with the helpof secondary steam generators. As per the design 70% ofthe power output was from the Reactor (Boiler) corethermal power and the balance 30% power was from theSecondary Steam Generators (SSGs). Due to the frequenttube leaks of SSGs, these were isolated from the systemin the year 1985 and units were re-rated to 160MWe andoperating since then at this re-rated capacity. Both theunits have completed 40 years of commercial operation till

date and still giving excellent performance with a stationcapacity factor close to 90%. The performance of bothunits improved over the years. Tarapur reactors weredesigned in early 60’s with the technology and standardsavailable at that time giving considering more safetymargins while designing plant layout, selection of materialof construction, following best engineering practices duringfabrication and maintaining the appropriate qualitystandards. Three more reactors are in operation in theworld which belongs to similar age of Tarapur-BWRs andthese are Tsuruga of Japan and Oyster Creek & Nine MilePoint of USA which belongs to BWR-2 design and alsooperating since 1969.

The design life of most of the components is 40 years andhence a detailed review was carried out to ascertain thebalance life of Structures, Systems and Components

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(SSCs). Most of the components in conventional systemsare replaceable including piping, equipments and variousstructurals. Therefore, as part of plant ageing managementprogramme, a comprehensive study & review of all thesafety systems was carried out and modificationsimplemented to improve the plant safety and reliability.Various degradation mechanisms were identified usingappropriate NDE methods and replacements with suitablematerial/design modifications were implemented. However,the non-replaceable components such as Reactor PressureVessels (RPVs) and Civil Structures - Containment metallicvessels were subjected to both comprehensive inspectionsand analytical evaluation. In this regard, various inspectionmethodologies were developed and examination techniqueswere established on full-scale mock-up facilities with thehelp of the expertise from NPCIL-HQ and various units ofDepartment of Atomic Energy (DAE) such as BARC(Bhabha Atomic Research Centre), IGCAR (Indira GandhiCentre for Atomic Research) and in addition regulatoryauthorities, the Atomic Energy Regulatory Board (AERB).The following paragraphs would give insight to the variousmethodologies followed during the process of licenserenewal of SSCs using various NDE techniques.

2. LICENSE RENEWAL – A CHALLENGINGTASK [1]

In late 90’s several nuclear power plants all over the worldhad completed their initial authorized periods of operation.Review of safety performance, operating experience andmaterial condition of majority of these reactors hadestablished that these NPPs could be safely operated forseveral more years. The international nuclear communitygot convinced that these early generation NPPs could beoperated for significant periods beyond their originalauthorized period. In this regard, IAEA has laid downbroad guidelines i.e. Safety Series No. 50-SG-O12 on“Periodic Safety Review of Operational Nuclear PowerPlants”, for assessing the condition of NPPs with the aimto operate them beyond the initial permitted operatingperiod. Meanwhile, Probabilistic Safety Assessment (PSA)has been developed as a tool for risk assessment and

resultant risk-informed safe operation and maintenance ofNPPs. For Critical components inspection methodologieshave been enhanced based on the Operating Experience(OE) feedback received from time to time from overseasBWRS including various agencies such as BWROG (BWROwners Group) and GE in the form of SIL (ServiceInformation Letters) & other technical correspondences.A comprehensive review of SSCs for renewal ofauthorization involves in-depth analysis & review covering(a) Operational Performance of the station till date (b)Ageing Management (c) Design Basis (d) Safety Analysis& (e) Seismic Re-evaluation. Out of these, ageingmanagement is one of the critical issues where-in applicationof NDE is associated with for detection and evaluation ofcomponent’s fitness for service.

3. AGEING MANAGEMENT PROGRAMME(AMP) OF SSCS[2]

3.1 Managing ageing for nuclear power plants meansensuring the availability of required safety functionsthroughout the service life of the plant, with accounttaken of changes that occur with time and use. Thisrequires addressing both physical ageing of structures,systems and components (SSCs), resulting indegradation of their performance characteristics, andobsolescence of SSCs, i.e. their becoming out of datein comparison with current knowledge, standards andregulations, and technology. Effective management ofageing of SSCs is a key element of the safe andreliable operation of nuclear power plants. Effectiveageing management is in practice accomplished bycoordinating existing programmes, includingmaintenance, in-service inspection and surveillance, aswell as operations, technical support programmes(including analysis of any ageing mechanisms) andexternal programmes such as research anddevelopment.

3.2 The purpose of Ageing Management Programme (AMP)is to assess the condition at the component level andput the same in service meeting functional as well asdesign intent. Ageing effects is one of the concerns ofolder generation plants and methodologies are beingadopted to identify various degradation mechanismsand are eliminated either by design modification or byreplacements with better resistant materials. Thisprocess is required to enhance the life of componentsfor continued service.

3.3 In order to address the ageing of SSCs, acomprehensive study was carried out by the stationwith the help of expertise from NPCIL-HQ andidentified the list of the SSCs important to safeoperation that needs to be addressed and evaluated forits integrity either by analysis or by using variousinspections & testing methods. The total plantcomponents were categorized into two, i.e., (a)Components that are replaceable either with new designor by reverse engineering methodology and (b)

Fig. 1 : Tarapur Atomic Power Station 1&2 (2001)

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Components that are not replaceable. Components arefurther divided based on its safety significance onnuclear safety/reliability and plant availability. Thecritical components that can not be replaced are (a)Reactor Pressure Vessels (RPV) (b) ContainmentPressure Vessels (drywell) (c) Containment civilstructures (CC). The components and systems thatcan be replaced are Equipments in conventional systemsincluding both mechanical & electrical components,pressure vessels & heat exchangers, Piping-fittingcomponents, Pumps & Valves and Supportingstructures of these.

4. DEGRADATION MECHANISMS -IDENTIFICATION

4.1 TAPS has engineered many inspection methodologiesto detect various degradation mechanisms such asIGSCC (Inter Granular Stress Corrosion Cracking),TGSCC (Trans Granular Stress Corrosion Cracking),Erosion-Corrosion (EC), Stress Corrosion Cracking(SCC), Mechanical Fatigue and Flow AcceleratedCorrosion (FAC). These degradation mechanisms weretimely detected using various inspection methodologies/techniques developed from time to time. TAPS hasdeveloped a data base with regard to surveillance,inspection and testing of primary system componentsincluding RPVs[5] & its associated components,Primary system piping/components, RecirculationCoolant Pumps (RCPs), Containment Vessels etc.,.The requirements enlisted while formulating theinspection & testing programmes are based on thegeneric issues [5]. The test results from theseinspections have been utilized for enhancing theinspection scope of SSCs, in few cases with advancedNDE techniques.

4.2 Examples of degradation mechanisms that haveoccurred in LWR components are (a) Intergranularstress corrosion cracking (IGSCC) in boiling waterreactor (BWR) piping (b) Stress corrosion cracking(SCC), pitting, wastage, and other degradation in steamgenerator tubes (c) Thermal fatigue cracking in reactorpiping components (d) Flow-accelerated corrosion (e)Irradiation-assisted SCC of reactor internal components(f) Boric acid corrosion of low alloy and carbon steelsand (g) SCC in Alloy 600 and weld Alloy 182/82dissimilar metal welds.

4.3 The cause of components degradation has beenidentified and mitigated either by replacements withsuitable technical advancements in material selectionor by strengthening the surveillance. Some of thegeneric issues pertaining to BWRs primary piping havealso been addressed as part of Plant ageing managementprogramme and feedback from overseas reactorsexperience coupled with in-house practical experienceon various inspection observations/results, a systematicmethodology-cum-guidelines were established fordeveloping surveillance programme of monitoring.

4.4 The inspection programmes has been revised basedon the feedback obtained from In-Service Inspectionresults and ageing management related comprehensiveinspection & testing. In addition to this, TAPS hasdeveloped and established many of the inspectiontechniques/procedures to assess the component’sintegrity using various non-destructive testing methods.

5. INSPECTION METHODOLOGIES -SURVEILLANCE, INSPECTION &TESTING CRITERIA

5.1 Managing the effects of Systems StructuresComponents (SSCs) ageing requires effectiveimplementation of ageing management programme.This includes timely detection and mitigation ofdegradation mechanisms of SSCs so that their integrityand capability is ensured throughout the plant life. Theaim of ageing management programme of SSCs is toidentify the components affected by various degradationmechanisms and assess their condition vis-à-vis itsintegrity for continued service life. Thereforesurveillance programmes of critical system componentswere devised based on OE and implemented effectivelyto identify the degradation mechanisms.

5.2 Methodology for assessing ISI effectiveness including(a)Determination of inspection effectiveness (b)Typeof NDE being implemented in the ISI program and itsassociated Probability Of Detection (POD) for reliablydetecting the expected degradation mechanism (c)determining degradation that may remain undetectedafter inspection and (d) Frequency of inspectionscoupled to growth rates for the targeted degradationmechanism(s).

5.3 Over the years, TAPS has accumulated four decadesof experience in identifying various degradationmechanisms with various non-destructive testingmethods; mitigation of the degradation by either repairor replacement with suitable material; monitoring thecondition of SSCs with appropriate NDE techniquesfor continued service. A systematic methodology hasbeen evolved for timely identification of degradationmechanisms, making appropriate modificationsmaterials, procedures and environmental conditionsvulnerable to degradation. TAPS has referred many ofthe documents with respect to inspection requirementsincluding IAEA-TECDOCs [2,3,4] and AERB SafetyGuides etc.,

5.4 A comprehensive inspection programme has beenprepared and followed while assessing the integrity &condition of critical components such as primarysystem piping, reactor pressure vessels, Vessels otherthan reactor pressure vessels etc., Even though mostof the components are being inspected as per the plantin-service inspection programme in a specifiedinspection interval as indicated above, additionalexaminations have been planned covering the effectsof ageing also. The components were examined using

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various non-destructive testing techniques; specialexamination techniques were also developed in somecases based on the operating experience feed backreceived from time to time from overseas BWRs.

5.5 In addition to the feedback from overseas BWRs oninspection & testing requirements, TAPS followedASME Boiler & Pressure Vessels Code, Section-XI,1998 edition in formulating the surveillance programmeof class-1,2&3 system components. As per this code,a comprehensive inspection & testing programme wasprepared and followed scrupulously for the 3rd & 4th

inspection interval. Some of the generic issues werealso identified and addressed along with the routineinspection requirements.

6. EXAMINATION OF CRITICALCOMPONENTS- HEALTH ASSESSMENTUSING NDE TECHNIQUES:

Following paragraphs indicates some of the criticalcomponents which were assessed for their integrity usingvarious NDE methods for license renewal of TAPS unitsin the year 2006. A comprehensive inspection andindependent assessment was done by various agencies ofDAE and confirming the codal requirements based on theexamination &test results.

6.1 Reactor Pressure Vessels (RPVs) & itsassociated components

One of the degradation mechanism associated with RPVis Irradiation/neutron Embitterment of vessel materialincluding weld/HAZ. Tarapur reactor pressure vessels aredesigned for integrated neutron (energy > 1 Mev) exposureover Lifetime is 2.3x1018nvt. The specified designed lifeof vessels is 40 Effective Full Power Years (EFPY) andso far both the reactors have completed nearly 24 EFPYs.The health assessment of RPV includes Nozzles & itswelds, safe end welds, RPV head welds, RPV welds andinternal core support structures. In-Service Inspectionenhances confidence in component performance. Periodicin-service inspection provides vital information in the formof flaw characterization for assessment of structuralintegrity of reactor pressure vessels. The intent of ISI isto detect any discontinuities or flaws in the areas of interest,which affects the functional requirement of the componentsfor continued service. Calibration blocks were developedas per ASME Section XI. RPV is having corrosion resistantinternal clad in as-deposited condition and hence, calibrationblocks have been developed simulating the actual fieldcondition. RPV head consists of 3 nozzles and entire headsurface is accessible for both surface & volumetricexamination. Based on the generic issue, high cycle thermalfatigue [6] with regard to Primary Feed water Nozzles, adetailed examination was carried out and subsequentlymonitored for its condition. The condition is found to behealthy and no degradation was noticed in any of the feedwater nozzles. Similarly, some of the safe ends connectedwith the nozzles of Reactor core spray and reactor clean-

up system were found to have IGSCC type of indications.Hence, these safe ends were subsequently replaced withcorrosion resistant nuclear grade material with modifiedwelding procedures. Thus cause of SCC has beeneliminated. The examinations as indicated above werecompleted during the four 10-year inspection interval havebeen completed and the condition of the Pressure vesselwelds and associated components is satisfactory.

Examination did not show any relevant indications eitherin LPT as well as in Ultrasonic testing. In order to assessthe condition of internal clad of RPV head, a representativeclad surface area has been identified “Surveillance area”which was also subjected to surface examination, did notshow any abnormality.

6.2 RPV-Internal Core Support Structure

The core support structures & its welded attachmentswhich provide lateral support to the fuel is vulnerable toIGSCC as well as IASCC type of degradation mechanisms.Some of the overseas BWRs detected these mechanismsduring their in-service inspection programmes. Based onthe OE, TAPS also had also conducted a comprehensiveinspection using IVVI (In-Vessel Visual Inspection) systemsespecially developed using radiation resistant under watercamera system coupled with remote handling manipulators.These manipulators were designed and developed jointlyby NPCIL-HQ, DRHR/BARC and TAPS-site personnel.

Fig. 2 : Reactor Pressure Vessel (RPV)

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The examinations were independently verified by QAD &IGCAR inspection personnel. Special VT qualifications wereconducted for inspection personnel to meet the codalrequirements.

All the required examinations (VT-3) as per ASME Section-XI did not show any deficiency; hence the condition ofreactor core support structures is healthy.

6.3 RPV closure studs

The closure studs of RPV at the main closure flange aresusceptible to fatigue and Stress Corrosion Cracking (SCC)as well. The reactor pressure vessel closure studs aresubject to high tensile stress during bolt-up, hydrostatictest and normal operation. The bolt-up is the most severecondition because the temperature and, therefore thefracture toughness are lower and the applied tensile loadsare higher. The lower potion of the closure studs may beexposed to oxygenated BWR coolant water during boltup. Also the threaded holes in the RPV shell flanges withoutbushings are subjected to wear because the flange materialis considerably softer than the studs. These studs aresubjected to volumetric examination with enhanced UTtechnique.

6.4 BWR pressure vessel nozzle and attachmentwelds

These welds are susceptible to IGSCC. High residual andapplied stress, use of Alloy 182 weld material, and BWRcoolant with high electrochemical potential can causeIGSCC. In addition to this, stainless steel cladding withvery low ferrite can also cause Inter-Dendritic StressCorrosion Cracking (IDSCC). GE-BWR reactor pressurevessel safe ends are fabricated from low alloy steel, carbonsteel, stainless steel, or Ni-Cr-Fe alloy. IGSCC has beenobserved in many stainless steel and Alloy-600 safe ends[7]. IGSCC in stainless steel safe ends was caused bysensitization from welding or furnace post weld heattreatment. In view of this all the nozzle-safe ends werebeing examined by both surface (LPT) and Volumetricexamination. In addition to this integrity of thesecomponents is checked during each system leakage tests

as well as system hydrostatic tests as per the ASMEsection-XI requirements.

6.5 Class-1, 2&3 system pressure boundarycomponents

The primary system pressure piping of Tarapur BWRs ismainly austenitic stainless steel either TP-304/TP-316 gradeand is susceptible for IGSCC, which is identified as genericphenomenon of BWRs piping welds. Therefore, acomprehensive review was carried out and the vulnerablepiping has been replaced with corrosion resistant/ nucleargrade piping (TP-316LN/L) and welding procedures weremodified to eliminate IGSCC. Based on the experienceTAPS had developed various interim repair methodologiesand effectively implemented for limited period of operation.Subsequently all the temporary repairs were removed andre-installed with corrosion resistant material.

6.6 Metallic Containment pressure vessels &Concrete containment (CC) structures

As part of plant ageing management programme acomprehensive inspection programme was prepared whichincludes visual inspection of all piping components forany signs of corrosion, ultrasonic thickness gauging ofpressure vessels and containment penetrations sealing areaspneumatic testing as integrity checks were also carriedout. By adopting these systematic inspection methodologies

Fig. 3 : Visual Inspection, Grappler Operated (GOM) Manipulator, Weld cleaning manipulator, Weld/HAZ UT manipulator for fillet weldsand butt welds

Fig. 4 : Tarapur Atomic Power Station (2006)

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overseas nuclear power plants in secondary cycle pipinghave alarmed Indian NPPs. In order to effectivelyimplement the detection methodologies a full-scale mock-up blocks were engineered and examination procedure forultrasonic thickness measurement (UTG) were established.Other than UTG, various alternate NDE methods werealso developed and engineered to detect FAC relateddegradation mechanisms more effectively.

7. CONCLUSION

The examination and test results observed so far did notreveal any abnormality in any of Class-1, 2&3 systemcomponents as well as the critical components as explainedabove. The present inspection methodology & examinationtechniques are sufficient to identify the componentdegradations very effectively. During the plant ageingmanagement programme (AMP) all the safety related

health assessment and integrity of the metallic containmentstructures and CC structures were ensured. In addition allthe CC structures were assessed by using ultrasonic testingtechniques (Velocity measurement) to ascertain the conditionof civil structures.

6.7 Heat Exchangers, Pumps, Valves and otherequipments (Nuclear & Conventional)

Special procedures were developed to assess thecondition of all the critical heat exchangers, including maincondensers, shut down cooling water Hx., reactor clean-up system Hx, plant cooling water system Hxs. In caseof conventional systems, all the feed water heaters werereplaced with modified designs to mitigate degradationsmechanisms associated with heaters. These are (a) Inlet-end erosion, (b) Fretting (c) Shell erosion due to FAC (d)Nozzle erosion due to impingement attack. Vibration analysisof the rotating equipments is one of the NDE techniqueimplemented effectively and high vibration relateddeficiencies were diagnosed and corrective actions wereimplemented to eliminate fatigue related degradationmechanism. As per the plant ISI document all the safetyrelated motor Operated valves (MOVs) were subjected tointernal examination to ascertain the condition of trimmaterial for integrity. In addition to this MOV-signatureanalysis of critical safety related systems was alsoconducted to check the integrity and base line data wasdocumented for reference after maintenance. All theequipment supports and piping supports were verified forits set points and hydraulic snubbers were examined (VT)in detail during the maintenance.

6.8 Piping components vulnerable to FlowAccelerated Corrosion (FAC) (Nuclear &Conventional systems):

Of late it has been identified that Flow AcceleratedCorrosion/Flow Assisted Corrosion (FAC) is one of thedegradation mechanisms with High Energy system pipingcomponents. Wall thinning in steel piping due to flow-accelerated corrosion FAC has resulted in pipe ruptures inhigh-energy (Enthalpy) systems, resulting in forced unitoutages and posing great concern for personnel andequipment safety. The recent pipe rupture incidents in

Fig. 5 : Rehabilitation of feed water heaters with design Modifications

Fig. 6 : Performance Demonstration Assessment (PDA) on Full-Scale mock-up at NDE facility.

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structures, systems and components (SSCs) were assessedwith respect to their condition and integrity. Measureswere also taken to protect the structures and componentsagainst their degradation mechanisms. The availability ofsafety related/critical equipments has been improved to agreater extent. With the various design relatedmodifications, the performance of station has been improvedin terms of plant safety reliability as well as availability.Unit no.2 of Tarapur Atomic Power Station is runningsuccessfully and continuously for the past 478 days. Thisis an indication of systematic efforts that were put-induring the plant re-licensing programme and themethodologies followed meticulously by the plantmanagement. It can be further concluded that thedegradation mechanisms could be effectively detected &identified in time using various NDE techniques. Thesetechniques were developed and implemented with in-houseNDE facility and corrective measures were taken hasenhanced plant safety, reliability and availability with whichthe units can run continuously for Long Term Operation(LTO) beyond its initial design life.

ACKNOWLEDGEMENTS

The author is thankful to TAPS-1&2/NPCIL managementin giving me the opportunity to publish the study carriedout on the above issue. Various NDE techniques weredeveloped with in-house NDE facilities of QA section atTAPS-1&2/NPCIL is possible with the managementsupport. Also we are also thankful to Technical Committeeof NDE -2010 in accepting the above technical paper in“National seminar & Exhibition on Non-DestructiveEvaluation-NDE 2010”.

REFERENCES

1. License renewal of boiling water reactors - experience at TarapurAtomic Power Station -1&2 Published in “Nu-Power” Magazine;Volume 20 (2006) & Volume 21(2007), N.N.Pisharody, A.Ramuand B.L.Sharma.

2. IAEA safety Standards, safety Guide. NS-G-2.12 “Ageingmanagement for Nuclear Power Plants”, (2009).

3. Assessment and management of ageing of major power plantcomponents important to safety: BWR pressure vessels, IAEA-TECDOC-1430.

4. Assessment and management of ageing of major power plantcomponents important to safety: BWR pressure vessel internals,IAEA-TECDOC-1431.

5. Assessment and management of ageing of major power plantcomponents important to safety: Metal components of BWRcontainment systems, IAEA-TECDOC-1181.

6. Generic Ageing Lessons Learned (GALL) Report, NUREG-1801,Volume 1, USNRC.

7. IAEA-TECDOC-1470 “Assessment and management of ageingof major nuclear power plant components important to safety:BWR pressure vessels”, (2005).

8. Instruction manual Tarapur Reactor Vessel, CombustionEngineering, Inc. GE, C.E.Book No. 5363, September 1966.

9. ASME Boiler & Pressure Vessel code, Section-XI, In-serviceInspection of Nuclear Plant Components.

10. AERB Safety Code. AERB/NPP/SC/QA (Rev.01), “QualityAssurance in Nuclear Power Plants” January 2009

11. AERB Safety guide no.AERB/NPP/SG/O-2" In-Service Inspectionof Nuclear Power plants”March 2004.

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PROBE

PPPPPrrrrrobeobeobeobeobeThe world was recently a mute witness to an unforeseen natural calamity in Japan. Earthquakeresulting in Tsunami of horrendous magnitude resulting in unprecedented devastation as well asravaging a Nuclear power plant culminating evacuation of thousands of people from their land,creating a big question mark on their future. Several TV Channels relayed again and again theagony of the people and the waves progressing at great speed sweeping (moving) cars and houses asif they were just toys. The safety of Nuclear Power Plants have become a question mark. Severalarguments are put forth for and against Nuclear energy as safety has become a main concern. Whatis the guarantee that an earthquake greater than 9 on Reichter Scale cannot occur (Circle ofinfluence)?

Earthquake happens due to movement of the tectonic plates of the earth. Tsunami is energy.Movement causes not only devastation. It is the basis of generating energy. The difference betweenuseful energy and devastation is the magnitude.

Move : To go or cause to go from one place to another. (Dictionary meaning).The molten core of the earth is constantly moving, Earth exhibits magnetism producing magneticflux lines. The electron flows and hence electricity is generated.Change : To alter.

When a movement takes place things are altered. So we can construe that change representsmovement. The earth is moving. The universe is expanding. If the movements are stoppedabruptly everything will collapse. Hence the oft repeated phrase “Change is permanent”. Hence wecan deduce that change is the basis of life (energy flow). Life is built upon the fundamentalprinciple of change and so we cannot resist it but adapt to it.

Meditation helps the adaptation to the change. Meditation is the art of going into silence andobserving the change (become a witness). By going into meditative silence we develop the “Art ofAllowing it to Happen”. The Art of Allowing it to Happen can be divide into 7 areas. They are1. Patience, 2. Possibility thinking, 3. Perception, 4. Peace with self, 5.Process, 6.Pondering overthe past success, and 7. perseverance.

Each area plays an important role in the Art of Allowing it to Happen. As more and more areasmerge with each other the holistic picture develops. This state can be attained only throughPractice, Patience and Perseverance and a wantonness to arouse the our souls and arise higher in theechelons of evolution. Please allow me to express each one in the coming issues..

Ram.

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