JNDE

Volume 9

issue 2

September 2010

1

vol 9 issue 3 December 2010

from the Chief Editor

Dr. Krishnan BalasubramaniamProfessor

Centre for Non Destructive EvaluationIITMadras, Chennai

[email protected]: http://www.cnde-iitm.net/balas

The last issue of 2010 brings forth three new sections that will add to the

value of the Journal. The HORIZONS section, coordinated by

Dr. C.V. Krishnamurthy, will bring forth some of the technologies that

shows promise for a paradigm change in the field of NDT. In this edition

of HORIZONS, the focus is of a new concept in X-rays. The BASICS

section, coordinated by Dr. O. Prabhakar, will henceforth discuss the

fundamental concepts relating to a selected NDT technique or concept. In

this issue, he covers the basic concepts of Radiography with excellent

illustrations and thorough coverage of the physics behind the technique. The

PRODUCTS & PATENTS section, coordinated by Dr. M.T. Shyamsunder,

will discuss the new products that have been recently introduced in the

NDT market as well new patents in the field of NDE.

This volume of the Journal has 4 technical articles. The article from BHEL,

Tiruchy on Digital Radiography and Computed Tomography discusses the

application of these advanced NDT technologies for improving the

inspection of weldments. The HOMC Guided Wave technique is a patented

technology that promises the inspection of hidden and difficult to access

regions in pipes, tank floors, etc. and has been covered by the authors. The

inspection of adhesively bonded structures and the application of mode

selection in guided wave based inspection of repair patches have been

covered in the technical paper from Pennsylvania State University.

Finally, the ASTM standards on digital radiography detectors have been

reviewed by the authors from General Electric Company. As we look

forward to the NDE2010 in Kolkatta and we wish ISNT Kokatta Chapter

all the best for a grand and informative NDE2010. The Editorial Board

joins me in congratulating all the ISNT Award Winners for the 2010 and

look forward to a great 2011.

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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. VinzeShri B.B.Mate

Shri G.V.PrabhugaunkarShri B.K.PangareShri M.V.Rajamani

Shri P.V. Sai SuryanarayanaShri Samir K. Choksi

Shri B.K.ShahShri S.V.Subba Rao

Shri Sudipta DasguptaShri N.V.WagleShri R.K.Singh

Shri A.K.Singh (Kota)Shri S. Subramanian

Shri C. AwasthiBrig. 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] S. Kalyana Sundaram, Hon. SecretaryScientist, STDivision,National Aerospace Laboratories,B a n g a l o r e - 5 6 0 0 1 7 . i s n t b l r @ g m a i l . c o m

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 B.S.Chhonkar, Chairman,90A, Pocket-1, Mayur Vihar - 1New Delhi 110 [email protected] Dinesh Gupta, Hon.Secretary,[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]

JamshedpurMr J. C. Pandey, Chairman,Researcher, R&D, TATA Steel,P. O. Burmamines, Jamshedpur - 831 [email protected]. M K Verma, Hon. Secretary,Manager, SNTI, TATA SteelN-Road, Bistupur, Jamshedpur - 831 [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 John Minu Mathew, Chairman,General Manager (Technical),Bharat Petroleum Corporation Ltd. (Kochi Refinery),PO Ambalamugal 682 302. [email protected] K.D.Damien Gracious, Hon. Secretary,CM (Advisory Services),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, Associate 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 N.V. Wagle, Chairman,A-601, CASCADE-3, Kulupwadi,Borivali East, Mumbai 400 066. [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 K.R.V.S.Mehar, ChairmanManager – SGS India Pvt. Ltd.218 Bajaj Nagar, Nagpur-440 [email protected]. D.R.Peshwe, Hon. Secretary,Professor, Dept. of Metall. & Materials Engineering,Visveswaraya National Institute of Technology,Nagpur 440 011. [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 D.K.Sisodia, Chairman,CS, R&D, TMS, NPCIL 3 & 4,Tarapur 401 502. [email protected] D. Mukherjee, Hon.Secretary,Superintendent, QC & NDE, AFFF, BARC,Tarapur-401 502. [email protected]

TiruchirapalliShri V Thyagarajan, ChairmanGeneral Manager (WRI & Labs)BHEL Tiruchirapalli 620014 [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 Ltd.NBCC Plaza,Opp. Utkarsh petrol pump, Kareli Baug,Vadodara-390018. [email protected] S Hemal Mehta, Hon.Secretary,P-MET, Hi Tech Pvt. Ltd.1/5-6, Baroda Indl. Estate, GorwaVadodara-390016. [email protected]

ThiruvananthapuramDr. V.R. Ravindran, ChairmanDivision Head, Rocket Propellant Plant,VSSC, ISRO, Thiruvananthapuram - 695 [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

Volume 9 issue 3 December 2010Journal of Non-DestructiveTesting & Evaluation

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

Co-EditorDr. BPC [email protected]

Managing EditorSri V Parie-mail: [email protected]

Topical EditorsDr D K Bhattacharya,Electromagnetic MethodsDr T Jayakumar,Ultrasonic & Acoustic EmissionMethodsSri P Kalyanasundaram,Advanced NDE MethodsSri K Viswanathan,

Radiation Methods

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 & Evaluationis published quarterly by the Indian Society for Non-Destructive Testing for promoting NDT Science andTechnology. The objective of the Journal is to providea forum for dissemination of knowledge in NDE andrelated fields. Papers will be accepted on the basisof their contribution to the growth of NDE Scienceand Technology.

Published by RJ Pardikar,General Secretary on behalf ofIndian Society forNon 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]

Printed at VRK Printing House3, Potters Street, Saidapet,Chennai 600 [email protected]: 09381004771

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13

17

25

About the cover page:

The cover page shows the Ultrasonic C-Scan Image of a graphite epoxycomposite laminate with a resin starved region shown in red/pink colorand fiber orientations in the background (Courtesy: AdvancedComposites Division, National Aerospace Laboratory, Bangalore, India)

Chapter News

Basics

Horizon

Producs & Patents

Digital radiography and Computed radiography forEnhancing the Quality and Productivity of Weldments inBoiler componentsR.J. Pardikar

ASTM standards on digital detector arrays for industrialdigital radiography – a bird’s eye viewG.K. Padmashree, Debasish Mishra, Clifford Bueno and Joe Portaz

Inspection of Adhesively Bonded Aircraft Repair Patchesusing Ultrasonic Guided WavesPadmakumar Puthillath, Cliff J. Lissenden and Joseph L. Rose

HOMC Guided Wave Ultrasonic Technique – A new paradigmfor corrosion detectionKrishnan Balasubramaniam, K.S. Venkataraman and Issac Anto

5

NDE 2010December 9-11, 2010

@ Science City Convention Centre, Kolkata

www.nde2010.com

31

34

39

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Madras Metallurgical Services (P) LtdMetallurgists & Engineers

Serving Industries &Educational

Institutes for thepast 35 years

24, Lalithapuram street, Royapettah, Chennai 600014Ph: 044-28133093 / 28133903 Email: [email protected]

A-3, Mogappair Indl. Area (East) JJ Nagar,Chennai 600037 Phone 044-26564255, 26563370

Email: [email protected];[email protected] www.kidaolabs.com

KIDAO Laboratories

Scaanray Metallurgical Services(An ISO 9001-2000 Certified Company)

NDE Service ProviderProcess and Power Industry, Engineering andFabrication Industries, Concrete Structures,

Nuclear Industries, Stress Relieving

Transatlantic Systems

Electro-Magfield Controls & Services &LG Inspection Services

Plot 165, SIDCO Industrial Estate, (Kattur)Thirumullaivoil, Vellanur Village, Ambattur Taluk

Chennai 600062 Phone 044-6515 4664 Email: [email protected]

We manafucture : Magnetic Crack Detectors, Demagnetizers, MagneticParticles & Accessories, Dye Penetrant Systems etc

Super Stockist & Distributors: M/s Spectonics Corporation, USA fortheir complete NDT range of productrs, Black Lights, Intensity Meters,

etc.

Betz Engineering &Technology Zone

An ISO 9001 : 2008 Company

Call M. Nakkeeran, Chief Operations,Lab: C-12, Industrial Estate, Mogappair (West), Chennai 600037

Phone 044-2625 0651 Email: [email protected] ;www.scaanray.com

Support for NDT ServicesNDT Equipments, Chemicals and Accessories

Call DN Shankar, Manager14, Kanniah Street, Anna Colony, Saligramam,

Chennai 600093Phone 044-26250651 Email: [email protected]

49, Vellalar Street, near Mount Rail Station, Chennai 600088Mobile 98401 75179, Phone 044 65364123Email: [email protected] / [email protected]

International Training Division21, Dharakeswari Nagar, Tambaram to Velachery Main Road,Sembakkam, Chennai 600073www.betzinternational.com / www.welding-certification.com

NABL Accredited Laboratory carrying out Ultrasonic test,MPL and DP tests, Coating Thickness and Roughness test.

We also do Chemical and Mechnical testsMetallographyStrength of MaterialsNon Destructive TestingFoundry Lab

Shri. K. Ravindran, Level IIIRT, VT, MT, PT, NR, LT, UT, ET, IR, AE

Southern Inspection SerSouthern Inspection SerSouthern Inspection SerSouthern Inspection SerSouthern Inspection ServicesvicesvicesvicesvicesNDT Training & Level III Services in all the

following ten NDT Methods

No.2, 2nd Floor, Govindappa Naicker Complex,Janaki Nagar, Arcot Road,

Valasaravakkam, Chennai-600 087Tamil Nadu, India

Phone : 044-2486 8785, 2486 4481E-mail: [email protected] and

[email protected] Website: www.sisndt.com

OP TECH01J, First Floor, IITM Research Park, Kanagam Road, Taramani,

Chennai 600113 India Phone : +91 44 6646 9880

Dhvani R&D Solutions Pvt. Ltd

Educational CDs -PT, UT, RT, MT, ET, BasicMetallurgy and Mechanical Testing

ASNT Level III Intensive Taining

Call93828 12624

Land044 - 2446 1159

B Ram PrakashA 114, Deccan Enclave,72, T M Maistry Street,Thiruvanmiyur, Chennai 600 041

• Inspection Solutions - CUPS, TAPS, CRISP, TASS• Software Products - SIMUT, SIMDR• Training - Guided Waves, PAUT, TOFD• Services & Consultancy - Advanced NDE, Signal Processing

- C-scans, On-line Monitoring

E-mail: [email protected] www.dhvani-research.com

Classifieds

5


Chennai

Course, Exams & Technical Talk:

UT Level-II (ASNT) course was conducted from20.08.2010 to 29.08.2010. No. of participants were 18and for examination 21. Mr.R.Balakrishnan was thecourse Director and Mr.Sathya Srinivasan was theexaminer 19.09.2010 Dr. VAIDEHI GANESAN, NDED,Metallurgy & Materials Group, Indira Gandhi Centrefor Atomic Research, Dept of Atomic EnergyKalpakkam-603 102 delivered a technical talk on“FAILURE ANALYSIS AND STRUCTURALINTEGRITY ASSESSMENT OF SOMEENGINEERING COMPONENTS USING VARIOUSNDE TECHNIQUES”. 60 members attended themeeting. MT & PT Level-II (ASNT) course wasconducted from 17.09.2010 to 23.09.2010. No. ofparticipants were 7 and exam 8. Mr.M.V.Rajamani wasthe course Director and Mr.P.N.Udayasankar was theexaminer In-house training on MT Level-I & II held from27.09.2010 to 01.10.2010 at M/s.Sundram FastnersLimited, Autolec Division, Chennai. No. of participantsfor Level-I is 11 and Level-II is 8. Mr.M.S.Ramachanranwas the course director and Mr.P.N.Uhayasankar wasthe examiner.

PT Level-II (ISNT) course was conducted from04.10.2010 to 10.10.2010. No. of participants were 7.Mr.R.Sreedharan was the course Director andMr.P.N.Udayasankar was the examiner ; EC Meeting04.08.2010 ; EC Meeting 19.09.2010 ; EC Meeting09.10.2010 One day workshop on “Positive MaterialIdentification Using HandHeld XRF with SpecialReference to API RP 578 and API RP 938” held on11.11.2010. No. of participants attended 90. R TLevel-II (ASNT) course was conducted from 22.10.2010to 31.10.2010. No. of participants were 18 for courseand 20 for examination. Mr.S.Subramanian was thecourse Director and Mr.P.N.Udayasankar was theexaminer UT Level-II (ASNT) course was conducted from12.11.2010 to 21.11.2010. No. of participants were 21for course and 25 for examination. Mr.R.Balakrishnanwas the course Director and Mr.Sathya Srinivasan wasthe examiner One day workshop on “Helium Leak Testing”was held on 30.11.2010. No. of Participants attendedwere 60 MT & PT Level-II (ASNT) course wasconducted from 26.11.2010 to 05.12.2010. No. of

CHAPTER NEWS participants were 10. Mr.M.V.Rajamani was the courseDirector and Mr.Sathya Srinivasan was the examiner

ASNT LEVEL-III HELDFROM 02.10.2010 TO 29.10.2010

Method Date No of Methodparticipants Director

Visual 02.10.10 – 4 Mr.R.Ramakrishnan04.10.10

Basic 05.10.10 – 20 Dr.O.Prabhakar08.10.10

Penetrant 09.10.10 – 10 Mr.G.Jothinathan11.10.10

Magnetic 12.10.10 – 17 Mr.R.RamakrishnanParticle 14.10.10Ultrasonic 18.10.10 – 20 Dr.O.Prabhakar

21.10.10Basic 22.10.10 – 24 Mr.G.Jothinathan

25.10.10Radiographic 26.10.10 – 25 Mr.R.Subburathinam

29.10.10Eddy Current 01.10.10 – 0

04.10.10

Total 120

Kalpakkam

Course & Exams: Kalpakkam Chapter has been quiteactive under the able guidance of Shri Y.C.ManjunathaChairman ISNT Kalpakkam, Shri P.Kalyanasundaram,Past Chairman and the support and patronage of DrBaldev Raj, Distinguished Scientist and Director IGCARand Shri Prabhat Kumar Project Director, BHAVINI.The Executive committee meetings were held and thechapter had also organised about four technical talks.More than 25 members were enrolled during the lastone year. The thrust of Kalpakkam Chapter has been infostering NDE Science and Technology in Educationand Research. As part of this objective, the Chapter hadactively collaborated with educational institutions inorganising the following events at Kalpakkam andChennai.

1. Orientation program for Engineers, St. JosephsCollege of Engineering, April 2010. About 50students and faculty in the field of mechanicalengineering participated in this event.

2. Training Course on Non-Destructive Testing forAeronautical Engineers in Collaboration withAeronautical Society of India (Chennai), July 1-3,2010. About 80 students belonging to AeronauticalEngineering from the various colleges in Chennaiparticipated.

3. Course on Interpretation of Radiographs, SatyabamaUniversity, NCB and Scanray, Oct. 28-30, 2010. 24candidates from all over India participated.

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4. One Day workshop on NDT organised by TIFAC –Core Hindustan Institute of Technology and Science,Dec. 03, 2010. About 100 students, researchers andfaculty will be participating in this event.

Apart from the above, members of Kalpakkam chapteractively participated as faculty in the ASNT refreshercourses at Chennai and have been contributing for theactivities at a national level. A matter of pride for ISNTKalpakkam chapter is that the Standard on ThermalImaging in Electrical Installations has been accepted bythe International Standard Organisation (ISO) forpublication during the ISO SC 135 meeting in Moscow.This is the first standard from India in NDT to beconsidered and accepted by ISO. Members fromKalpakkam Chapter have also actively contributed tonational and international journals. During this year morethan 15 international journal publications have resulted.Many of the members have also been honoured by othernational and international bodies.

Mumbai

Course & Exams:

Welding Inspector examination on 13.12.09

Interpretation of weld Radiogrpah examination on20.12.09

UT Level II For ONGC 15.02.10-20.02.10

RT level II for ONGC from 22-02-10 to 27.02.10.

General Orientation on NDT for Naval Officers from08-03-10 to 12.03.10

PT Level I for Naval Officers from 13-03.10 to 16.03.10

MT Level I for Naval Officers from 17.03.10 to 20.03.10

PT Level II for ISNT, Tarapur Chapter on 24- 07- 2010at Tarapur,

RT Level I for Ammunition Factory Khadki on 24- 07-2010 at Pune

Welding Inspector at ITT, Mahim on 15.08.10

Technical Lecture:On 13.01.10 by Dr.Garri Passi on Advanced Instruments& Technologies in UTMr. Mr Greg Pupchek and Mr. Silvano Succetti, U.S.A,on Computer Radiography & Digital Imaging on 18-08-2010

Ultrasonic Testing Practices in the Nuclear PowerIndustry by Mr. Peter Schmitt, Germany on 07- 09-2010Conducted One day Workshop on Positive MaterialIdentification using Handheld XRF with specialReference to API RP 578 and API RP 938 on 9th Nov.2010 at Hotel Atithi, Mumbai

Activities:EC meeting on 15.01.2010ASNT Level III Course Directors & Coordinators meeton 16th Feb 2010EC meeting on 26th Feb 2010EC meeting on 7th April 2010EC meeting on 25th June 2010EC meeting was held on 11thAugust, 2010NCB and NGC Meeting held on 29thAugustAGM was held on 25th Sept. 2010 Participants werearound 175 members.APCNDT 2013 committee Meeting was held on 2ndOctober 2010EC Meeting was held on 19thOctober 2010APCNDT 2013 Meeting was held on 15th November2010

PuneNational “ International Certification and CareerOpportunities in NDE and Inspection

1. API Certification - by Shri:D.D. Joshi

2. NDE Certification - by Shri.J.R. Hiremath(ASNT, EN etc.)

3. Welding and Painting

An industrial /field Visit to facilities of industrialX-Ray and allied Radiographers and UT QualityIndia

9th Executive Committee meeting, Technofour, PuneDt. 05/09/2010

Annual General Meeting, Hotel Ambassador, ModelColony, Shivajinagar, Pune, Dt. 20/10/2010

10th Executive Committee meeting, Technofour,Pune, Dt. 27/10/2010

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Industrial RadiographyDr. O. Prabhakar, OP-TECH, Chennai

BASICS

INTRODUCTION

From the time Roentgen discovered X-rays and used itto radiograph his rifle, X-rays are being used in theindustry to reveal internal flaws in manufacturedcomponents. In many industries like thermal and nuclearpower generation, aircraft, chemical industries etc., thismethod plays a key role.

THE METHOD

The industrial radiographic method is based on theprinciple of “Differential Absorption” of Electromagneticradiation in matter.

In addition gamma radiography is extremely portableand does not need electrical power for its operation.

LIMITATIONS

Compared to other methods the initial costs are high.Large spaces are needed particularly if one is employingpowerful isotopes like Cobalt 60. Inspection times arehigh. It is difficult to reveal cracks particularly tightcracks. Radiation safety and protection are major issues.

ELECTROMAGNETIC RADIATION (EM)

All the radiant energies like radio waves, heat radiation,visible or light rays, X-rays, gamma rays and cosmic

X- or gamma rays are passed through a component andthe transmitted rays are recorded on a photographic film,fluoroscopic screen or a detector. The basic arrangementto take a radiograph is shown in figure 1. The mostcommon recording medium employed is the photographicfilm. The exposed film is further developed, fixed andwashed just like an ordinary photo film in a dark room.The developed film called “Radiograph” is viewed underproper lighting arrangement for interpretation andevaluation.

ADVANTAGES

A direct view of the internal discontinuities is obtainedmaking it relatively easier to interpret the radiographs.Discontinuities that are volume based like porosity,shrinkage etc. are easily detected. The method is readilyaccepted by various manufacturers because of the easyinterpretation and extensive codes and standardsavailable.

rays belong to the same spectrum. The EM spectrum isshown in Fig. 2. They all can travel in vacuum andpossess the same velocity in vacuum. They differ intheir wavelength or energy values. One single ray isalso known as “Photon” and does not possess any electriccharge or magnetic moment. The straight line propagationof these waves is utilized in Industrial radiography (RT).These rays can also diffract but this is not of interest inRT but used in metallurgy.

IONIZING ABILITY

X- or gamma rays are not seen by the human eye directly.Fortunately these rays ionize matter, that is it splits theminto positive ions and negative charge. There are fourmajor ionization types of interest to RT and they are:

1. Photographic effect

2. Fluorescence effect

3. Electrical conductivity

4. Biological effect

Fig. 2 : Electromagnetic (em) spectrumFig. 1 : Basic arrangement for radiographic inspection

8


1. Thickness of the sample.

2. Kilovoltage to be employed.

3. Tube current

4. Time of exposure

These four variables are plotted in a graph calledexposure charts that are used by radiographers to takean acceptable quality radiograph. These charts aredependent on the film to focus distance, film type used,material being radiographed and the darkness of the filmdesired. Equations are available for taking into accountall these factors and arrive at the final exposureconditions.

One should try to employ the lowest kilovoltage for anygiven job that gives adequate transmitted X-rays for asatisfactory radiograph. Increasing the kilovoltage wouldincrease the penetrating power of the X-rays but theradiograph will be of poor contrast.

GAMMA RAY PRODUCTION

The type of element in the periodic table is determinedby the number of electrons or protons in the nucleus. Ifthe number of neutrons in the nucleus is altered theelement type is not altered and is known as “isotope”.Some of these isotopes decay giving out radiation andparticles and such isotopes are known as “Radioactiveisotopes”. These radioactive isotopes may occurnaturally or may be produced artificially in a nuclearreactor. Some of these radioactive isotopes give outelectromagnetic waves that can be used to takeradiograph of components. Just to distinguish the sourceemployed to produce the EM waves, the term “GammaRays” is used to denote the EM rays given out byradioactive isotopes.

The most commonly used radioactive isotopes areIridium – 192 and Cobalt – 60. How the unstable Co-60 decays producing gamma rays is described in Fig. 4.

Of these four, the first two are used to take radiographand the third is used to detect and quantify radiationlevels. In RT one has to take safety precautions againstthe biological effects.

A doubt one may have is whether the componentbecomes radioactive after being exposed to X- or gammarays. Under the conditions RT used in the industry thisdanger does not exist as most of the interactions betweenthe X- and gamma rays and the matter involve shellelectrons and not the nucleus. However care must betaken while exposing the modern digital detector panelsto X- or gamma rays. Above a certain kilovoltage theymay damage the detector panels.

X-RAY GENERATION

If an electrical source is used to generate theelectromagnetic waves of the required wavelength, then

Fig. 3 : Scheme of x-ray generation with an x-ray tube

Fig. 4 : Disintegration of cobalt -60.

it is known as X-rays. A basic X-ray tube is shown inFig. 3. The tube is essentially a vacuum tube (diode)with an anode and cathode. Electrons are emitted by aheated filament and they are further accelerated byemploying a very high electrical voltage between thecathode and the anode. The accelerated electrons aremade to strike a target like tungsten and suddenlydecelerated. The kinetic energy of the electrons isconverted into heat and X-rays.

So the production of X-Rays consists of three steps:

1. Thermionic emission of electrons from a heated filament.

2. Accelerating the electrons by employing a high voltage ofthe order of 50 to 400 keV.

3. Suddenly decelerating these accelerated electrons by strikingthem against a target made of high melting point metal.

The variables that one needs to consider while taking aradiograph are:

B A S I C S

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The characteristic curve, sometimes referred to as the Hand D curve (after Hurter and Driffield), expresses therelationship between the exposure applied to aphotographic material and the resultingphotographic density. The characteristic curves of afast and slow film are shown in Figure 6. Thecharacteristic curve can be used to solvequantitative problems arising in radiography and in thepreparation of technique charts. The simple logic weuse is that “Pairs of exposures having thesame ratio will be separated by the same interval on thelog relative exposure scale, no matter what their absolutevalue may be.” (Ref: RT in Modern Industry-Kodak)

RADIOGRAPHIC CONTRAST

Radiographic contrast between two areas of a radiographis the difference between the photographic densities ofthose areas. It depends on both subject contrast and filmcontrast.

Subject contrast is the ratio of x-ray or gamma-rayintensities transmitted by two selected portions of aspecimen. Subject contrast depends on the nature of thespecimen, the energy of the radiation used, and thescattered radiation, but is independent of time,milliamperage or source strength, and distance, and ofthe film characteristics or film processing.

Film contrast refers to the slope (steepness) of thecharacteristic curve of the film. It depends on the typeof film, the film processing, and the density and isindependent of subject contrast.

GEOMETRIC UNSHARPNESS

The area over which the electrons strike the anodedetermines the size of the focal spot. In order to obtaina good radiograph one would prefer to have as small afocus size as possible. However as the focal spot size

The parameters that one needs to consider while selectinga source are:

1. Energy of the gamma rays

2. Half life of the isotope

3. Size of the isotope

4. Cost of the isotope

Figure 5 shows a typical manually operated gamma raysource container.

Exposure charts for gamma radiography are differentfrom that of X-rays. In this case we need to consider thesource strength instead of kilovoltage and tube current.

The gamma rays from cobalt 60 have relatively goodpenetrating ability as the wavelength is smaller. Co 60can be used to radiograph sections of steel 9 inchesthick, or the equivalent. Radiations from iridium 192have lower energy. Ir-192 emits radiations equivalent tothe x-rays emitted by a conventional x-ray tube operatingat about 600 kV. The intensity of gamma radiationdepends on the strength of the particular source usedspecifically, on the number of radioactive atoms in thesource that disintegrate in one second. This is measuredas curies (1 Ci = 3.7 x 10 s-1).

PHOTOGRAPHIC DENSITY

Photographic density is the measure of blackness of thefully developed and fixed radiograph. This determinesthe viewing facility one needs to interpret and evaluateradiographs.

FILM RADIOGRAPHY

In film radiography one employs a film to record theinformation carried by the transmitted X- or gamma rays.

Films used in RT consist of a flexible and transparentbase coated with a radiation sensitive silver compound.The coating is applied on both sides of the base.

Fig. 5 : Gamma ray source container Fig. 6 : Characteristics of industrial radiographic film

B A S I C S

10


decreases the intensity of the EM radiation obtained isalso less. The focal spot should be as small as conditionspermit, in order to secure the sharpest possible definitionin the radiographic image.

The degree of sharpness of any shadow depends on thesize of the source of X-rays and on the position of theobject between the X-ray source and the film—whethernearer to or farther from one or the other. When thesource of X-rays is not a point but a small area, theshadows cast are not perfectly sharp (in Figure 7)because each point in the source of X-rays casts itsown shadow of the object, and each of these overlappingshadows is slightly displaced from the others, producingan ill-defined image.

From simple geometry one can derive an expression forthe geometric unsharpness as:

Ug = F (b/a)

INHERENT UNSHARPNESS

Even without any geometric unsharpness blurring ofthe sharp edge may occur due to movement of electrons

Fig. 7 : Geometric unsharpness

Fig. 8 : Penetrameters Fig. 9 : A typical illuminator to view radiograph

in the film. This is termed as ‘inherent unsharpness’.This depends on the energy of the photon striking thefilm.

PENETRAMETERS

Penetrameters are used while taking every radiograph tocheck whether the radiograph is satisfactory or not. Thetest piece is commonly referred to as a penetrameter inNorth America and an Image Quality Indicator (IQl) inEurope. Examples are shown in Figure 8. It containssome small features (holes, wires, etc.), the dimensionsof which bear some numerical relation to the thicknessof the part being tested. The image of the penetrameteron the radiograph is permanent evidence that theradiographic examination was conducted under properconditions. A penetrameter is used to indicate the qualityof the radiographic technique and not to measure thesize of cavity that can be shown. (Ref: RT in ModernIndustry-Kodak)

DISCONTINUTIES

In castings shrinkage, pipes, gas porosity, lack of fusionof the chills, hot tears and core shift are revealed.However thin cracks are difficult to be revealed. Welddefects like gas porosity, lack of penetration, slaginclusions and tungsten inclusions can be revealed.However, laminations in the base plate can not berevealed by RT.

When dealing with castings, it may be better to usepenetrameters based on finished rather on rough-wallthickness and this way penetrameter sensitivity is notcompromised. Individual casting that are more prone tonon-systematic flaws (random) require more radiography.

Contrary to common misconception, there is nosuch thing as 100 % radiographic coverage for allcastings. To make sure that no coverage problem occursbetween the foundryman and the user, it is essential tofollow proper and early planning of the radiography.

B A S I C S

11


CODES & STANDARDS

The American Society for Testing and Materials hascommittee on Non-Destructive Tests. This committeehas prepared reference materials concerningrecommended practices for radiographic testing, andradiographic references for various industrial processesand materials. For example, it has comparisonradiographs for steel castings, aluminium and magnesiumcastings, steel welds and castings for aerospaceapplications. All the alloys are not represented. Hence amutually acceptable document between the foundrymanand the user may be adopted. As an example, titaniumalloy castings can be judged by aluminium and steelreference radiographs.

AWS D1.1/D1.1M:2004 code contains the requirementsfor fabricating and erecting welded steel structures. Inthis code, section 6 on inspection section contains criteriafor the qualifications and responsibilities of inspectors,acceptance criteria for production welds, and standardprocedures for performing visual inspection and NDT(Nondestructive testing) including RT.

Fig. 10 : A typical radiograph (schematic).

RADIOGRAPHS

Figure 9 shows a typical illuminator to view a radiograph.

A typical radiograph of a weld showing Porosity is shownin Figure 10.

Weld bead is thicker than the base metal. So it appearswhite. Defects like porosity are of low density materialand hence appear as dark spots in the radiograph asshown in Fig. 10.

B A S I C S

“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 Technical Committee on Acoustic Emission of ChSNDT (TCAE).

Conference Date August 24 to 26, 2011

Venue Beijing International Convention Center and Beijing Continental Grand HotelNo.8 Beichen Dong Road, Chaoyang District, Beijing 100101, P.R. China

Room Reservations: Tel: ++86-10-84980105 ; Fax: ++86-10-84970106E-mail: [email protected] Website: www.bcghotel.com ; www.bicc.com.cn

Call for Papers The papers are sought in all areas related to acoustic emission such as follows:

AE signal detection and processing AE behavior of materials AE in pressure equipment AE in structures AE in civil engineering and geology AE in transportation engineering AE in condition monitoring and diagnosis for mechanics AE in medical science AE

standardization AE instrument and new developments AE and applications in other fields

Key Dates Abstract submission April 30, 2011Notification of acceptance May 15, 2011Submission of full papers June 30, 2011Registrationf and payment of registration fee July 15, 2011

Registration Fees (including: Welcome Party, Welcome Dinner and three Lunches)General: 450 US$ ; Student: 300 US$

Contact Conference-secretariat and Mailing Address

Mr. Zhanwen Wu, WCAE-2011 SecretariatChina Special Equipment Inspection and Research InstituteBuilding 2, Xiyuan, Hepingjie, Chaoyang District,Beijing 100013, ChinaEmail:[email protected]: +86-10-59068313 ; Fax: +86-10-59068666

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HORIZONHORIZONHORIZONHORIZONHORIZON

Can x-rays berefracted, focused and collimated?

C.V. KrishnamurthyDepartment of PhysicsIndian Institute of Technology, MadrasChennai 600036, Tamilnadu, Indiae-mail: [email protected]

monochromatic and naturally narrow as from lasers, thefocal spot sizes cannot reduce beyond a diameter of theorder of the wavelength.

The beam spot quality at the focal plane depends on (a)how parallel the incident beam is, (b) how well the lensis shaped, and (c) how absorptive is the lens material.When the incident beam is diverging, it is possible tocollimate the beam to be parallel by using the samerefraction and phase shifting processes of a lens in a‘reverse’ manner. Imperfections, such as surfaceroughness and curvature errors, arise during lensfabrication. When the corresponding phase errors areless than π/4, the degradation due to imperfections wouldbe negligible. Noting that different parts of the incidentbeam travel different path lengths, any attenuation dueto absorption would lead to unequal amplitudes addingup to form a poor beam at the focal plane. It is thusdesirable either to have a material with insignificantabsorption or to work with a very thin lens.

The creation of refractive lenses and prisms, which aredirect and immediate analogs of devices working in thevisible range, had long been thought of as beingimpossible because of the extremely small deviation ofthe refractive index from unity, for the X-ray range - thesmall deviation of the refractive index from unity(δ=1–n≈10–5–10–6), and a relatively high radiationabsorption. Only a relatively small set of materialswherein refraction prevails over absorption (chemicalelements, inorganic and organic compounds withZ

eff << 12–14) are suited for the implementation of

refractive optical elements. When use is made of thesematerials, owing to the extremely low magnitude of therefractive index decrement it is required to formrefractive profiles with radii of curvature of the order ofseveral micrometers. We note that the refractive indexcan be wavelength dependent or, in other words, energydependent.

Let’s consider the refractive profile shape required tofocus rays on a point lying on the central ray (optical

The (surprising?) answer to all the three characteristicsis yes! But then, it should not be surprising, for X-raysare electromagnetic waves just like visible light are andthey must exhibit such wave-like characteristics.

We are very familiar with “optical elements” such aslenses that produce focused beams or collimated beamsof light. We also know that focused beams improve signalto noise ratio, and enhance image resolution.

Let’s take a closer look at how it happens in optics. Therefractive index of the materials (n), such as glass, usedto make lenses for visible light (wavelength is about530 nm for green) is about 1.5 typically. The refractiveindex of a medium, we recall, scales the path length ofa plane wave in that medium by a factor n. The changedpath length within the medium changes the phase of theplane wave. The change is with respect to vacuum or airand so proportional to n – 1. The material is shaped inthe form of a “lens” to produce refracted rays withcorresponding phase delays such that an incident parallelbeam is changed to a transmitted beam converging at afocal plane. The refraction and focusing phenomenon isdescribed with the help of rays by invoking Snell’s lawat the curved interfaces using local tangents and localnormals at various points on the curved interface.

We are aware that in the focal plane, there is a finitebeam spot size arising out of wavefronts not all addingup with the same phase at every point of the focal plane.In fact, the wave nature prevents the spot width to bereduced beyond a fundamental limit that is based on thewavelength. Even when the incident beam is highly

13


axis). The condition to be satisfied by such a profile isthat equal optical paths result for points equidistant fromthe optical axis. The change of wave-vector directionsin individual portions of the transmitted wave is assumedto be negligible owing to the smallness of the refractiveindex decrement. Then, the refractive profile is equivalentto a thin lens. When a plane wave is incident on theinput plane of a focusing element, according to theHuygens - Fresnel principle the secondary sourcesexcited by the incident wave are located on the curvedprofile. It turns out that the perfect shape of refractivesurfaces for X-ray lenses is close to the parabolic one inthe approximation of paraxial optics.

A focal distance of 10cm < F < 1m is attainable for aradius of curvature of a single refractive profile equal to1 μm < R < 10 μm for typical values of the refractiveindex decrement δ given above.

Fabricating such refractive profiles of X-ray lenses callsfor the development of an adequate technology. Errorsin the profile due to fabrication must be such that theassociated phase errors are within π/4.

The precision of lens formation is determined by thequantity λ/π(n-1) which lies in the range between severalmicrometers to tenths of a micrometer in the visiblelight optics. For a glass lens with for n = 1.5 forλ = 0.5 μm, for instance, an accuracy of 0.3 μm may beconsidered sufficient. In the X-ray band, the admissibledepartures of the refractive profile under fabrication fromthe ideal one are substantially greater. In particular,typical values of the phase-shifting path for materialswhich may be employed in the fabrication of X-ray lensesamount to 10–100 μm. Therefore, the requirements onthe accuracy of refractive profile fabrication are, in viewof the possible departures ranging into the fractions ofa micrometer, attainable for present-day technologies.

To form single lenses with a radius of curvatureR < 1μm, use is presently made primarily of silicon andpolymer materials, which is due to the possibility ofresorting to a wide range of technologies exploited in

microelectronics. Silicon refractive elements arepractically void of intrinsic imperfections and, hence,do not give rise to their associated intensity losses. Singleand compound planar lenses have been fabricated andtested extensively. Compound lenses were found tofollow the additivity property for the lens power.

A property of the parabolic profiles (Figure a) is thatthe optical path of a ray and, accordingly, the total phaseshift in traversing several lenses remain constant. Theretention of the focal distance is ensured for all lensrows, which is confirmed by direct experimentalmeasurements (Figure b). The increase in the number oflenses in a row for a constant aperture is compensatedfor by a corresponding change in the radius of curvature.Accordingly, the lens power of a row is the superpositionof the successive action of single lenses and is the samefor all rows. The lens-power additivity of the refractiveprofiles follows directly from summation of the phaseshifts produced by single lenses in the total phase shiftacquired by the ray in transit through the set of profiles.The additivity of the lens power of a set manifests itselfonly for refractive lenses and is not inherent in othertypes of X-ray focusers such as Fresnel zone plates.

Kinoform lenses have also been fabricated and testedusing beam lines from the European Synchrotron

Refractive profile for an X-ray lens. Optical paths to the focal point

are and OP = y + F, with n = 1 – δ + iβ, andRe n = 1– δ < 1.

Planar parabolic lenses: (a)SEM image; (b) photograph of the focalspots, obtained on the BM05 beamline at an energy of 17 keV. FromV V Aristov, L G Shabel’nikov, Physics - Uspekhi 51 (1) 57 - 77(2008)

Cross-sectional schematic of the kinoform lens. The Brookhavenkinoform single lens made of Silicon shown below has the followingparameters: Energy at 13 keV; focal length = 15 cm; aperure was100 μm (V) x 10 μm (H); focal size achieved ~ 1 μm FWHM(theoretical limit was 0.2 μm FWHM). From: Ken Evans-Lutterodtet al.: “Single-element elliptical hard x-ray micro-optics”, OpticsExpress (2003) 11, 919-926.

HORIZON

x = λ/δ

14


Many other compound element configurations, such asthe prism-array lenses shown below, have beenconceived, fabricated successfully and tested.

The classic manifestation of the wave nature of theelectromagnetic radiation is the interference effect. Herewe see a demonstration of the interference effect withX-rays!

Top panel: Schematic and the SEM image. Bottom panel: Intensity in focal plane measured with knife-edge scan. E = 13.4 keV, F =55 cm,intensity gain = 39, FWHM = 1.4 mm, the fraction of power in the central peak is 41%. Björn Cederström et al.:”Generalized prism-arraylenses forhard X-rays”, J. Synchrotron Rad. (2005). 12, 340–344

Radiation Facility (ESRF). By removing the redundant2π phase-shifting from the refractive counterpart (topleft in the Figure), one arrives at the kinoform (bottomleft in the Figure). This is the analog to the Fresnellenses used in lighthouses. The removal of theunnecessary material greatly reduces losses and increasesthe focusing efficiency.

(a) Schematic view of the x-ray bilens interferometer. (b) Scanning electron microscope micrograph of a single silicon bilens consisting of6 individual parabolic lenses. (c) General view with five bilens systems fabricated on the same substrate. A. Snigirev et al., Phys Rev Lett.,103, 064801 (2009)

HORIZON

15


The planar parabolic bilenses were manufactured usinga process involving electron beam lithography and deepetching into silicon. The length and aperture of eachsingle, double concave individual lens are 102 and 50 μm,respectively. Structures are 70 μm deep. The radius ofthe parabola apex is R=6.25 μm, and the minimumthickness between the parabola apexes is 2 μm. Thesplit distance between lenses is d = 60 μm. The Si bilenssystem was mounted at a distance z

0 = 54.16 m from the

source. Interference patterns were recorded by means ofthe high resolution x-ray CCD camera with a spatialresolution about 1.3 μm (0.645 μm pixel size). Theexperimental tests of the bilenses were carried out at theESRF beam line ID06 for an x-ray energy in the range10–20 keV.

The advent of compound refractive lenses, whichattracted considerable attention of researchers throughoutthe world, significantly broadened both the possibilitiesfor making X-ray optical devices and the spectral range

of their applications. In recent years, refractive opticshas turned into a branch of X-ray optics in its own right,which has seen the realization of novel and uncommonapproaches to lens development, pertaining to bothdesign solutions and fabrication technologies. Newapproaches have been formulated and their elaborationwould allow bringing the spatial resolution to magnitudescharacteristic of modern techniques of scanningmicroscopy.

ADDITIONAL REFERENCES FOR FURTHERREADING:

1. A. Snigirev, V. Kohn, I. Snigireva, B. Leneler, A compoundrefractive lens for focusing high-energy X-ray, Nature, v.384,n.7, p.49-51 (1996).

2. H. Bradaczek, G. Hildebrandt, Real X-Ray Optics - A ChallengeFor Crystal Growers, Journal of Optoelectronics and AdvancedMaterials Vol. 1, No. 2, p. 3 – 8 (1999)

3. V. G. Kohn, On the Theory of X-ray Refractive Optics: ExactSolution for a Parabolic Medium, JETP Letters, v.76, n.10,pp. 600-603 (2002).

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Phone: (044) 2250 0412

HORIZON

16


A new feature in the Journal of NDE

NDENDENDENDENDEP A T E N T S

Starting from this issue, we are introducing a new section, which will discussdifferent aspects of Intellectual property in the area of Inspection and NondestructiveEvaluation and would list some of the recently granted patents in this area. To startwith we are covering United States Patents and Trademark Office (USPTO) andhope to add the others including the Indian, European, Japanese and the WorldPatent organizations in the coming issues. We hope you will find this sectionuseful and interesting. Please send your feedback, comments and suggestions onthis section to [email protected]

and other relevant details of interest to the buddinginventors

http://www.patentoffice.nic.in/

http://patinfo.nic.in/

http://www.uspto.gov/

http://ep.espacenet.com/

http://www.epo.org

http://www.jpo.go.jp/

http://www.wipo.int

In the forthcoming issue of the Journal of NDE, we willdwell in detail on some of the essential aspects of patents,the philosophy behind it, and the patenting process andthe challenges thereof.

Listed below are a few selected patents in the area ofeddy current testing which were issued in 2010. If anyof the patents are of interest to you, a complete copy ofthe patent including claims and drawings may beaccessed at some of the websites mentioned earlier.

UNITED STATES PATENT 7,830,140

Eddy current system and method for estimating materialproperties of parts

Inventors: Tralshawala; Nilesh , Plotnikov; YuriAlexeyevich

Assignee: General Electric Company (Niskayuna,NY)

Abstract : A method of inspecting a test part is provided.The method includes positioning an eddy current probeon a surface of the test part and scanning the test partusing the eddy current probe to generate a first signalcorresponding to a no lift-off condition of the test part.The method further includes positioning the eddy currentprobe at a pre-determined distance from the surface ofthe test part and scanning the test part using the eddycurrent probe positioned at the pre-determined distancefrom the test part to generate a second signalcorresponding to a lift-off condition of the test part. Themethod also includes processing the first and second

In today’s growing and competitive world, anyprogressive and growth oriented individual ororganization cannot undermine the role of IntellectualProperty (IP). Intellectual Property takes a number ofdifferent forms such as, Patents, Trademarks, Copyrights,Trade Secrets, etc. Patents form one of the critical formsof IP from a perspective of a researcher, scientist,engineer or technologist working for academia, R&Dorganizations, product manufacturer, service provider andothers.

Technically, a patent is “a set of exclusive rights grantedby a state or national government to an inventor or theirassignee for a limited period of time in exchange for apublic disclosure of an invention.” Some form of thepatent exists in most countries but the laws vary greatly.The USPTO defines a patent as “an intellectual propertyright granted by the Government of the United States ofAmerica to an inventor “to exclude others from making,using, offering for sale, or selling the inventionthroughout the United States or importing the inventioninto the United States” for a limited time in exchangefor public disclosure of the invention when the patent isgranted”.

Some of the principal objectives of patenting one’sinventions include; Revenue from licenses or sale, Keepothers out of the market, Restrict competitors, etc.Patenting can be a lifeline for a company; not only canit be used to keep competitors at a safe distance, it canalso provide a firm with a competitive advantage thatcan lead to expansion and increased profits. There aredifferent perspectives of patenting; one of them statesthe social objectives of patenting as primary and thecommercial objectives as secondary.

Of course with the process of patenting comes issuessuch as costs, liability, infringements, etc and they haveto be dealt with suitably.

Given below are links to a few websites from differentcountries, which will provide you with a lot ofinformation on the patent process, database, statistics

Compiled byDr. M.T. ShyamsunderGeneral Electric, Bangalore

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includes a plurality of coils wound at a predeterminedinclined angle. The plurality of coils is inserted into theinside of a metal tube. Alternating current is applied tothe coils to measure a change in impedance of the coilsdue to a change in an eddy current generated in themetal tube, thus detecting a surface defect of the metaltube.


Method of aligning probe for eddy current inspection

Inventors: Suh; Ui W, Knepfle; Richard C.

Assignee: General Electric Company(Schenectady, NY)

Abstract : A system and method using a touch probedevice for eddy current inspection. The touch probeprovides a simple approach for coming within closecontact of the specimen while maintaining a normal angleand pressure at the right positions. The use of the touchprobe further reduces the total time for the eddy currentinspection. The touch probe aligns the probe to aspecimen to be inspected, for the purpose of reducingmeasurement errors and increasing productivity.


Eddy current testing method, eddy current testingdifferential coil and eddy current testing probe forinternal finned pipe or tube

Inventors: Sawawatari; Naoki

Assignee: Sumitomo Metal Industries, Ltd. (Osaka, JP)

Abstract : The invention provides an eddy currenttesting method for an internal finned pipe or tube whichcan securely detect a micro defect generated in a troughportion in an inner surface of the pipe or tube, even inthe case that an inner surface shape of the internal finnedpipe or tube is non uniform in a circumferential directionof the pipe or tube. The eddy current testing method inaccordance with the invention detects a defect existingin a trough portion of the pipe or tube (P) by arranginga differential coil (2) constructed by a pair of coils (21,22) having such a dimension as to be arranged withinthe trough portion of the pipe or tube (P) and comingaway from each other in an axial direction (X) of thecoil, within the trough portion of the pipe or tube (P)along a direction in which the trough portion of the pipeor tube (P) extends, and relatively moving the differentialcoil (2) in the direction in which the trough portion ofthe pipe or tube (P) extends.


Method and apparatus for eddy current detection ofmaterial discontinuities

Inventors: Lefebvre; J. H. Vivier, Mandache; Catalin V.

Assignee: Her Majesty the Queen in right of Canada,as represented by the Minister of National Defence ofHer Majesty’s Canadian Government National ResearchCouncil of Canada

signals to estimate an electrical conductivity of the testpart.


Material condition assessment with eddy current sensors

Inventors: Goldfine; Neil J, Washabaugh; Andrew P.,Sheiretov; Yanko K, Schlicker; Darrell E., Lyons; RobertJ, Windoloski; Mark D, Craven; Christopher A,Tsukernik; Vladimir B, Grundy; David C.

Assignee: JENTEK Sensors, Inc. (Waltham, MA)

Abstract : Eddy current sensors and sensor arrays areused for process quality and material conditionassessment of conducting materials. In an embodiment,changes in spatially registered high resolution imagestaken before and after cold work processing reflect thequality of the process, such as intensity and coverage.These images also permit the suppression or removal oflocal outlier variations. Anisotropy in a material property,such as magnetic permeability or electrical conductivity,can be intentionally introduced and used to assessmaterial condition resulting from an operation, such asa cold work or heat treatment. The anisotropy isdetermined by sensors that provide directional propertymeasurements. The sensor directionality arises fromconstructs that use a linear conducting drive segment toimpose the magnetic field in a test material. Maintainingthe orientation of this drive segment, and associatedsense elements, relative to a material edge providesenhanced sensitivity for crack detection at edges.


Device for non-destructive eddy current inspection of ahole formed in a conductive part

Inventors: Cabanis; Patrick, Cheynet; Sandra CaroleAngele, Gaisnon; Patrick, Le Corre; Christian.

Assignee: SNECMA (Paris, FR)

Abstract : Using eddy currents to inspect a hole that ispossibly not rectilinear and/or of section that is notcircular. The inspection device comprises a stick shapedand dimensioned to be capable of being engaged in saidhole, at least one arm hinged to a support fastened toone end of the stick, an eddy current sensor beingembedded in said arm, and resilient means for urgingthe arm outwards against the inside surface of the hole.


Sensor for detecting surface defects of metal tube usingeddy current method

Inventors: Kim; Young Joo, Ahn; Bong Young,Lee; Seung Seok, Kim; Young Gil, Yoon; Dong Jin.

Assignee: Korea Research Institute of Standards andScience (Daejeon, KR)

Abstract : A sensor for detecting surface defects of ametal tube solves a problem of a conventional eddycurrent probe in that it is difficult to detect a crack inthe circumferential direction of a metal tube. The sensor

Products & Patents

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UNITED STATES PATENT 7,683,611Pipeline inspection using variable-diameter remote-fieldeddy current technologyInventors: Burkhardt; Gary Lane, Crouch; AlfredEugene, Parvin, Jr.; Albert Joseph, Peterson; RonaldHerbert, Goyen; Todd Hegert , Tennis; Richard FranklinAssignee: Southwest Research Institute (San Antonio,TX)Abstract : The present disclosure relates to a device andmethod for pipeline inspection, The inspection devicemay include an exciter coil capable of providing analternating current magnetic field and producing eddycurrents. A plurality of sensors may then be providedwhich are capable of sensing a magnetic field producedby the eddy currents and the sensors may be engagedwith a sensor shoe. The sensors may then be capable ofbeing positioned at a first distance D1 with respect toan inner pipe wall surface and capable of providingcoupling to the magnetic field produced by the eddycurrents. The sensor shoe may also be capable ofretracting to a second distance D2, wherein D1<D2.The sensor shoe may be connected to a sensor supportarm wherein the support arm may be pivotably attachedto a fixed hub and to a control arm which control armmay then be pivotably attached to a driven hub.

Abstract : A method of eddy current testing without theneed for lift-off compensation. Signal response featuressimilar to those used in pulsed eddy current techniquesare applied to conventional (harmonic) eddy currentmethods. The described method provides advantages interms of data storage, since only two responseparameters, the amplitude and phase, are sufficient toreconstruct any sinusoidal signal, therefore allowing forscanning of large surfaces.


Eddy current data interpolation/extrapolation

Inventors: Junker; Warren R, Nenno; Thomas W,Yaklich; Daniel J, Pocratsky; Ronald J.

Assignee: Westinghouse Electric Co LLC (CranberryTownship, PA)

Abstract: A method of synthesizing nondestructiveexamination data of a component that combines datasets acquired at least two different frequencies. At leastone of the data sets is interpolated or extrapolated to theequivalent of data acquired at one of the otherfrequencies employing a third, reference set of eddycurrent inspection data that is acquired at each of theinspection frequencies being combined.

Products & Patents

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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]

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25Technical Paper

Vol. 9, Issue 3 December 2010 Journal of Non destructive Testing & Evaluation

Digital radiography and Computed radiography forEnhancing the Quality and Productivity of Weldments

in Boiler components

R.J. PardikarAGM / NDT, BHEL, Tiruchirappalli,Tamilnadu-620014.

E-mail:[email protected]

ABSTRACT:

This paper presents a detailed performance analysis and comparison of Conventional film radiography, Real Time Radioscopywith Digital Radiography (DR) using Digital Detector Array and Computed Radiography (CR) using Flexible Phosphor ImagingPlates, in the case of Quality evaluation of weldments in Boiler Components. Conventional Film Radiography is a slow, expensiveand hazardous method, particularly for mass production. Eventhough Real Time Radioscopy (RTR) with Image Intensifiers isan alternative to film radiography, conventional RTR systems are compared unfavorably with film radiography in two aspectsviz.low contrast sensitivity and limited resolution.

The new digital detector arrays have the potential to substitute the X-Ray films as they have considerably higher image qualitythan the conventional Image Intensifiers. They allow fast acquisition of radiography images with high dynamic range, and highsignal to noise ratio.

Computed Radiography is one of the Digital Radiographic Techniques used in lieu of conventional film radiography. The PhosphorImaging plates (IP) are used as digital detectors in place of photographic X-Ray films.

The experimental results revealed that DR can successfully replace Real Time Radioscopy with X-Rays and Image Intensifier,for Tubular Steel welds up to Single wall thickness 12mm. Using the Digital Detector Arrays with 200 microns pixel pitch, itwas possible to achieve more than 3 line pairs / mm, at an MTF of over 20%. On the other hand CR has been found to besuitable for Radiography of thick wall welds (Steel thickness up to 140 mm) in Boiler components using Gamma Ray IsotopicSources like Ir-192, Co-60 and X-Ray sources including Linear Accelerators (up to 6 MeV) with high spatial resolution, meetingthe 2 % Radiographic sensitivity requirements as per ASME code.

Key words: Real Time Radioscopy (RTR), Digital Radiography (DR), Computed Radiography (CR), Weldments in BoilerComponents, Quality evaluation

1. INTRODUCTION

Radiography is very well established as an NDT technique,using both film and electronic X-Ray detection systems.However there are still many inspection problems, whereexisting Radiographic inspection techniques are inadequatein determining the presence of critical defects in steelweldments.

How ever, Film Radiography is a slow and expensive andhazardous method, particularly for mass production wherethousands of weld joints are to be inspected everyday.Real Time Radioscopy (RTR) with Image Intensifiers isan alternative to film radiography with considerable savingin running cost and processing time. However conventionalRTR systems are compared unfavorably with film basedsystems of radiography in two aspects viz.low contrastsensitivity and limited resolution. Focal spot size and limitedspatial resolution in the Image Intensifiers will cause noisyimage compared with film radiography. In order to meetthe sensitivity requirements as per code it is necessary tointerface the RTR system with an image processing systemfor suitably enhancing the images.

The new digital detector arrays have the potential tosubstitute the X-Ray films. Digital Detector Arrays are

imaging plates, are claimed to provide Radiographicinspection with considerably higher image quality than theconventional Image Intensifiers. They allow fast acquisitionof radiography images with high dynamic ranges. Thesedetectors should enable new computer-based applicationswith new intelligent computer based methods.

However, the overall performance of radiographic systemswith digital imaging plates mainly depends upon the qualityof these imaging devices, which converts the radiationprofile into electronic images. The parameters to the imagequality like Linearity, Signal to Noise ratio, Dynamic Range,homogeneity of the images etc, can be influenced by theproducer and user of the system.

2. REAL TIME RADIOSCOPY (RTR) OFWELDS IN TUBULAR PRODUCTS [1]

Real time Radioscopy inspection systems using 320-kVX-Ray system and Image Intensifier (in lieu of Film) asthe Imaging device has been installed at BHEL Trichy foronline inspection of Straight Tube circumferential buttwelds in boiler components. The feedback regarding thequality of the weld is given to the welder immediately, andthe welding parameters are adjusted accordingly to controlthe process. The joints are made by MIG welding between

26 Technical Paper

Journal of Non destructive Testing & Evaluation Vol. 9, Issue 3 December 2010

tubes having outside diameter ranging from 38 to 76 mmand thickness ranging from 4 to 12mm . The major defects,which occur during this welding process, are Porosity,Gas Hole, Crack, Lack of fusion, Incomplete Penetration,Excess penetration, Burn through etc.

To meet the sensitivity requirements it is required thatplanar flaws such as crack, lack of fusion, lack ofpenetration in welds, etc, the criteria of satisfactory imagequality should be more than a conventional IQI sensitivityvalue. An additional measure of image quality is required.This can be provided by the image of a duplex wire IQI,such as the type III A in BS 3971: 1985.

The major limitations of Image Intensifiers are LimitedResolution, Poor Signal –Noise Ratio, Low Contrast, Nonlinearity, Limited Dynamic Range, etc. However using imageprocessing techniques ,image quality is considerablyimproved and brought in par with the film radiography.But due to the degradation of Image Intensifiers over aperiod of time the image quality, even after image processingdoes not meet the sensitivity requirements as per code.Hence the image intensifiers have limited useful life andneed to be replaced once in 3 to 4 years.

3. NEED FOR DIGITAL RADIOGRAPHY

Therefore to meet the quality requirement consistently asper the code, BHEL decided to replace the ImageIntensifiers with new generation Imaging devices such asDigital Detector Arrays .The radiographic process usingdigital detectors is termed as “Digital Radiography”[2]. Itoffers several advantages such as defect recognitionsoftware, advance analysis tools, shorter exposure times,and good response at lower energies. Since these panelsare directly connected to a PC for power and control, thisenables the system to be used in Real time mode.

4. DIGITAL RADIOGRAPHY WITH DIGITALDETECTOR ARRAY[3]

Digital Radiography is the State of art technology basedon Digital Detector Array systems in which the X-rayimage is displayed directly on a computer withoutintermediate imaging optics or mechanical scanning. Theincident X-Rays are converted in to electric charge andthen to digital image through a large area panel sensor.Compared to other imaging devices Digital Detector Arraysprovides high quality digital images even better than filmradiography with better signal to noise ratio and dynamicrange of 12 to 16 bit [4], which provides high sensitivityfor radiographic application. Two distinct technologies areavailable for Digital Detector Array: “indirect conversion”and “direct conversion “. The first design is based on aphoto diode matrix, which is read out by thin filmtransistors (TFT). These components are manufacturedof Amorphous Silicon and they are resistant against high-energy radiation. Incoming X-rays first strike a CesiumIodide scintilator that converts the X-Rays into light. The

photo diodes are charged by this light photons. The primarybenefit of Cesium Iodide technology is the excellent DQE[5]. The light then passes through a photodiode matrix ofamorphous silicon, which is converted into electricalsignals, which are amplified and digitized. The light isdirected onto the silicon without lateral diffusion, whichensures image sharpness. The digital data is then processedinto images via a corresponding gray value table, and isdisplayed, printed or sent to computer as required. Thesystem offers the additional advantages of image post-processing and archiving.

The second type of Digital Detector Arrays is based on aphoto conductor like Amorphous Selenium or Cd-Te on amulti-micro electrode plate, which is read out by TFTsagain. This type provides the highest sharpness and hasthe potential for high-resolution systems, which couldcompete with NDT-film. Here the photons when impactover the photo conductor like amorphous Selenium, theyare directly converted to electronic signals which areamplified and digitized. As there is no scintillator (orPhosphor), lateral spread of light is absent here. This is animportant difference between direct and indirectconstruction. A-Se has higher work function and henceless number of charge pairs are produced for a givenenergy; but it directly receives x-rays and hence overallconversion efficiency is better than indirect type. Thiscompensates to an extent for lesser charge pairs [6]. Inthe case of Real Time radioscopy examination of welds itis essential to have a continuous series of images (30frames per second), to enable online inspection withAutomatic Defect Recognition. [7]

5. PERFORMANCE COMPARISON OFIMAGE INTENSIFIER WITH DIGITALDETECTOR ARRAY EXPERIMENTALRESULTS

In order to make the decision with regard to the replacementof Image Intensifier with Digital Detector Array for RTRof tubular welds, a series of experiments were carried outto assess the performance characteristics of the DigitalDetector Array and Image Intensifier and their comparison.A scrupulous account of all the tests done on both ImageIntensifier and Digital Detector Arrays is given in thefollowing sections.

A variety of detailed performance characterizationmeasurements have been performed under a set of typicalIndustrial Radiography conditions. These include spatialresolution (MTF), Contrast Sensitivity, Linearity, andSignal–Noise Ratio. Based on these the performance ofthe detectors can be compared.

5.1 Resolution

The Modulation Transfer Function (MTF) test results ofDigital Detector Arrays are compared with that of ImageIntensifiers. The test results reveal that the Nyquist

27Technical Paper


frequency of the Image Intensifier is 3.5 lp/mm, and forimaging small features at 3.5 lp /mm, the MTF is 20%.For the Flat Panels, the Nyquist frequency is 5.0 lp /mm.The resulting MTF indicates excellent resolution for imagingof small features, with significant MTF(over 20%) at 5.0lp /mm, which makes the spatial resolution superior toImage Intensifier.

5.2 Linearity

Linearity [3. of detector response is a key factor inproducing high-quality digital radiographic images. In orderfor the normalization procedure to work over a wide rangeof exposure conditions, the detector’s basic response needsto be extremely linear over the detector’s useful dynamicrange. Linearity is characterized by illuminating the detectorwith an industrial X-ray source. A series of images areacquired at each dose level, and the mean signal (whichis characterized by the mean Gray level of the image) iscalculated over a small region in the center of the detector.The images are collected at a source-detector distance of70 cm, using a 320kV X-Ray system. The operating voltageis maintained at 45 kV. The variation of the signal valuewith increasing the dosage value is plotted.

By using the results of the linearity test conducted onIndividual detectors, the comparison is obtained here. Thetest results show that, the flat panels show linear behaviorover a wide range of exposure conditions, where as ImageIntensifier is nonlinear.

Fig. 1 : MTF comparison between Digital Detector A rray(left),with 200micron pixel pitch and ImageIntensifiers(right)

Fig. 2 : Linearity Comparison between Digital Detector Array andImage Intensifier

Fig. 3 : Contrast Sensitivity Comparison between Image Intensifiersand Digital Detector Arrays

28 Technical Paper


5.3 Contrast Sensitivity

The measurement of contrast sensitivity (CS)of the DigitalDetector Array and Image Intensifier is carried out byusing three step wedges, which are having thickness 5mm,10mm and 20mm respectively. In the experimentconducted, in order to have better accuracy of the testresults, the CS value for each step in comparison withbase thickness was taken and the mean value was takenas the Contrast Sensitivity of the particular Step wedge.The procedure is repeated for each step wedge at dosagevalues (mA minutes) 2,2.5,3 and 3.5 respectively. Thevalues of contrast sensitivity obtained as a result of thesecalculations are given below. The given below comparisonshows that in the case of Digital Detector Arrays theContrast Sensitivity is better.

5.4 Signal to Noise Ratio (SNR)

The SNR experiments were conducted in the case ofDigital Detector Array and Image Intensifier by using thecontrast sensitivity gauges and exposing, at differentX-Ray dosage level conditions. The images of the stepwedge were captured at different mA minute values of theX-Ray equipment keeping the voltage fixed. Three stepwedges (thickness 5mm, 10mm and 20 mm respectively)were used for conducting the test. Each of these wasexposed to X-Ray radiation at dose values 2, 2.5,3 and3.5 mA min conditions. The signal gray value was measuredfrom each of these images. Also the standard deviation inthese images, which is the measure of noise were noted.For comparison of detectors in terms of signal to noisevariation, we use a parameter called normalized SNR or

SNR norm , which is given by Where ,BSR is

Basic Spatial Resolution of the Detector.

6. COMPUTED RADIOGRAPHY (CR) [8]

Computed Radiography is one of the Digital RadiographicTechniques used in lieu of conventional film radiography.The Phosphor Imaging plates (IP) are used as digitaldetectors in place of photographic X-Ray films. Thesedetectors enable new computer based applications withintelligent computer based methods. They can substitutefilm applications with several advantages like ImageEnhancement, Automated Defect Recognition, shorterexposure times (70% of film), greater Linearity and Range,sharing information, Digital Archiving and Reporting. TheCR also provides considerable saving in cost ofconsumables (Film) and totally eliminates hazardouschemical processing of films. The High Definition ComputedRadiography systems (HD-CR) can produce high imagequality, meeting the Radiographic sensitivity requirementsas per international codes.

The Imaging Plate is a Flexible Polymer support coatedwith sensitive layer (BaFBr doped with Eu2+), used inmuch the same way as X-Ray film and wrapped aroundthe job for exposure to ionizing radiation (X-Ray / GammaRay) during Radiographic Testing. The latent invisible imageis created by Photo Stimulated Luminescence process,when the IP is exposed to ionizing radiation .The conversionof latent image to digital image is obtained by scanning ofIP by LASER, during which the release of electrons emitenergy in the form of blue light that is detected by a Photomultiplier tube and then converted to a digital image. Theamount of blue light is linear measure of RadiographicDensity at this point. The typical pixel pitch of suchscanner is 50 to 150 micrometer. A LASER beam withextremely fine resolution of 12.5-micrometer spot size,together with highly efficient light bunching system canattain 20 lp/mm of resolution, revealing extremely smalldefects.

6.1 Computed Radiography of thick wall Boilercomponents

In order to meet the code of construction (ASME,section I), and the Indian Boiler regulations at present100% radiography is carried out on butt welds of Boilerpressure parts such as Headers, Pipes, Drums etc. SinceRadiography is time consuming, hazardous and expensive,BHEL has decided to go in for Computed Radiography ofthese welds. Initially it is proposed to use the computedradiography system for evaluation of welds of thicknessranging from 10-70 mm using X-Ray source up to 400 kVand Ir-192 source. However the feasibility study forassessing the performance of Computed Radiography hasbeen carried out up to 140mm using the isotopic sourceslike Co-60 and Linear Accelerator. The experimental studywas carried out to evaluate the quality of radiographsachieved with imaging plates (GE IT Imaging plates, IPC-II-High speed, and IPS-III High Contrast) and Laserprocessing using scanner GE IT-CR 100, and comparisonwas made with the performance of Agfa D7 and D4Fig. 4 : SNR comparison between Digital Detector Array and Image

Intensifier.

29Technical Paper


films. Both ASTM strip hole IQI and wire type IQI wereused for assessing the contrast sensitivity and duplex wireIQI as per EN 462 for the spatial resolution. The selectionof IQI was done based on the thickness of the job. Thethickness of the Image Intensifying screens and theexposure time to achieve the required optical density andsensitivity for the specific Phosphor imaging plates, werearrived on trial and error basis as there are no exposurecharts available for Imaging plates.

6.2 Experimental results

Comparative Penetrameter sensitivity achieved withPhosphor Imaging plates and X-Ray films for weldmentsin Steel thickness ranging from 30mm to 160mm,usingvarious radiation sources.

Table 1 : Hole type IQI Sensitivity with Ir-192

Steel weld thickness, mm High High Agfa AgfaRelative exposure speed contrast D 7 D 4

w.r.t Agfa D7 IP IP(0.25)

30 30-1T 30-1T 30-1T 30-1T

40 35-2T 35-1T 35-2T 35-1T

50 35-2T 35-1T 35-4T 35-2T

Table 2 : Hole type IQI sensitivity with Co-60

Steel weld thickness,mm High Agfa AgfaRelative exposure contrast D 7 D 4

w.r.t Agfa D7 IP

40 35-1T 35-2T 35-1T

60 40-2T - 40-2T

80 50-2T 50-2T 50-2T

90 50-2T 50-2T 50-1T

110 - 50-2T 50-1T

Table 3 : Wire type IQI Sensitivity with Co-60

Steel weld thickness, Required High Agfa Agfam m wire contrast D 7 D 4

Relative exposure dia in IPw.r.t Agfa D7 m m

80 1.27 - 0.63 0.6

90 1.27 0.8 1.25 0.8

110 1.6 1.25 1.25 1.25

Table 4 : Hole type IQI Sensitivity with 4 MeV Linac

Steel weld thickness,mm High Agfa AgfaRelative exposure contrast D 7 D 4

w.r.t Agfa D7 IP

80 50-2T 50-2T 50-1T

90 50-2T 50-1T 50-1T

110 50-2T 50-2T 50-1T

160 80-2T 80-1T 80-1T

Table 5 : Wire type IQI Sensitivity with 4 MeV Linac

Steel weld thickness, mm Required High Agfa AgfaRelative exposure wire contrast D 7 D 4

w.r.t Agfa D7 dia in IPm m

80 1.27 - 0.8 0.5

90 1.27 1.25 - 0.4

110 1.6 1.25 - 1.25

160 2.5 - 2.5 1.25

Table 6 : Hole type IQI Sensitivity with X-Rays

Steel weld thickness,mm High HighRelative exposure w.r.t speed IP contrast IP

Agfa D7 (0.25) (1.0)

30 30-2T 30-1T

40 35-2T 35-1T

50 35-2T 35-1T

Table 7 : Wire type IQI Sensitivity with X-Rays

Steel weld thickness,mm Required High HighRelative exposure w.r.t wire dia Speed Contrast

Agfa D7 in mm IP IP

30 0.6 0.5 0.5

40 0.8 0.6 0.5

50 0.8 0.6 0.6

Table 8 : Duplex Wire sensitivity achieved with varioussources

(As per EN 14784-2, Class ClassDuplex wire Separation (EN 472-5)) A B

Ir-192 Required 6 7.00

Achieved 8 8.00

Co-60 Required 6 6.00

Achieved 7 6.00

4 MeV Linac Required 6 7.00

Achieved 7 7.00

NOTE:The relative exposure values for CR with IPs wereapproximately 70% as that of D7 films.

From the test results shown in the above tables, thefollowing conclusions can be drawn. In the case of Ir-192 source, for 50mm Steel thickness, the High Speed IPgives a hole type IQI sensitivity of ASTM 35,2-2T(1.75 %) which is better than, the corresposing value(ASTM 35, 2-4T) achieved by Agfa D7 film (High Speedfilm). Similarly, the High contrast IP gives a sensitivity ofASTM 35,2-1T, which is superior to the correspondingvalue (ASTM 35,2-2T) given by a fine grain film AgfaD4.In the case of the Co-60 source even at 90 mmthickness, a High Contrast IP gives sensitivity on par withFilm. Table (2) shows the performance results with Holetype IQI, which shows the sensitivity ASTM 50, 2-2T,achieved by both IP and Film, Where as the Table (3)shows the same test conducted with Wire type IQI, which

30 Technical Paper


clearly tells that IP has achieved a sensitivity of 1.25 %on par with Films. Table 4 and Table 5 show the Sensitivityvalues achieved, when 4 MeV Linac is used, with Holetype IQI and Wire IQIs respectively .The sensitivity is onpar with Agfa D7 film. In the case of X-Rays upto 300kV,both the High Speed IP and High Contrast IP are able toachieve better than 2 % sensitivity. Table 8 shows thatspatial resolution achieved by IPs, with duplex wire IQIin the case of various Radiation sources are better thanthe required values, as per standards.

7. CONCLUSION

The feasibility study and the experimental results clearlyrevealed that the transition from Film Radiography to Digital/Computed Radiography of the welded components ispracticable and can meet the National and InternationalRadiography Code requirements. Digital Radiography cansuccessfully replace Real Time Radioscopy with X-Raysand Image Intensifier, for Tubular Steel welds up to Singlewall thickness 12mm. Using Digital Detector Arrays with200 microns pixel pitch, it was possible to achieve morethan 3 line pairs / mm,at an MTF of over 20%.Theimplementation of DR will facilitate the Automatic DefectRecognition during online inspection of welded joints,avoiding the subjectivity in humane evaluation .On theother hand Computed Radiography using High ContrastPhosphor Imaging Plates has been found to be suitable forRadiography of thick wall welds (Steel thickness up to160 mm) in Boiler components such as Headers, Pipes,Drums etc using Gamma Ray Isotopic Sources like Ir-192, Co-60 and X-Ray sources including LinearAccelerators (up to 4 MeV) with high spatial resolution,meeting the 2 % Radiographic sensitivity requirements asper ASME code.CR will considerably reduce the exposuretime and also completely eliminate the chemical hazards

associated with Film processing ,thereby increasing thespeed and efficiency of Radiographic Testing. Othersignificant advantages of CR include the electronic archivingof Radiographic images and online transmission of imagesfor away center evaluation.

REFERENCES

1. R.J.Pardikar, ‘Real Time Radioscopy and Digital Image ProcessingTechniques for on-line Inspection of Welds in boiler Tubes’Journal of Non-Destructive Evaluation, 20(3) (2000) 68-72

2. Bruce Blakeley, ‘Digital Radiography- is it for you?’ Insight,46(7) (2004) 403-407

3. G.A.Mohr and C.Beuno, GE A-Si Digital Detector Array detectorin industrial digital radiography’, BINDT Insight, 44(10) (2002).

4. V.R.Ravindran, ‘Digital Radiography Using Digital Flat Panel forNon-Destructive Evaluation of Space Vehicle Components’,Journal of Non-Destructive Testing & Evaluation , Vol.4, Issue2, September 2005.

5. Giakos, G.C.; Suryanarayanan, S.; Guntupalli, R.; Odogba, J.;Shah, N.; Vedantham, S.; Chowdhury, S.; Mehta, K.; Sumrain,S.; Patnekar, N.; Moholkar, A.; Kumar, V.; Endorf, R.E.,‘Detective quantum efficiency [DQE(0). of CZT semiconductordetectors for digital radiography’, Instrumentation andMeasurement, IEEE Transactions, 53(6) (2004) P 1479 – 1484

6. P.R.Vaidya, “Digital Flat Panel Detectors in IndustrialRadiography”, International Workshop on Imaging NDE- 2007,April 25-28, 2007, Kalpakkam, Chennai, India.

7. Rajashekar Venkatachalam , Manoharan V , Raghu C , VenumadhavVedula , Debasish Mishra , 12 th A-PCNDT 2006 – Asia-PacificConference on NDT, 5th – 10 th Nov 2006, Auckland, NewZealand

8. P.R.Vaidya andA.V.S.S.Narayana Rao, “Performance Evaluationof the Imaging Plates for Industrial Radiography Application”,Journal of Non-Destructive Evaluation, 20(3) (2000) 53-56.

31Technical Paper


ASTM standards on digital detector arrays forindustrial digital radiography – a bird’s eye view

Padmashree G K1, Debasish Mishra1, Clifford Bueno2 and Joe Portaz3

1 GE Global Research Bangalore, India2 GE Global Research Niskayuna, USA

3 GE Aviation, Cincinnati, USA

ABSTRACT

Digital detector array technology is becoming increasingly important, as industrial radiography is transitioning from film to digital.Standards for industrial digital radiography are vital to the introduction and widespread use of this technology for inspection,sustenance of digital conversion and accelerated digital-to-shop floor transition. In this paper, we highlight the importance ofstandards and present an overview of the recently published ASTM standards on digital detector arrays for industrial digitalradiography.

1. INTRODUCTION

Digital radiography, in recent times, is gaining momentumin industrial inspection as it stands to offer a multitude ofadvantages over conventional film radiography. The cruxof this technology lies in employing a digital detector arrayfor x-ray imaging of industrial components, as opposed tousing a silver-halide film as the x-ray recording medium.This therefore gives industrial radiography the advantagesof high-throughput inspection together with significantlyreduced cost of repetitive inspections. It also eliminateschemical processing involved in film radiography, allowsfor data archival and improves defect detection.

Alongside these advantages, rapid advances in digitaltechnology have made industrial digital radiographyfascinating from a technology standpoint. Such advancescater to current challenges in the application-space, whilenewer applications propel further advancement of thistechnology. Such interplay between technology andapplications has resulted in a wide variety of digital x-raysystems coming into existence and making their way tothe marketplace. The plethora of applications makes italmost impossible to have a single standard digitalradiography system to address all applications, the designof a digital x-ray detection device being a majorconsideration in its own right. As a result, there are almostas many choices of detectors as there are ways toconfigure the overall test system, leaving the useroverwhelmed. In the absence of any standardization, thechoice of detectors becomes difficult. This warrants thedevelopment of guidelines on ‘minimum requirements anddeployment of digital x-ray detectors for industrialinspection’. Needless to say, absence of such guidelineswill result in a slow standardization process that couldhamper the application of this technology.

Introduction of industrial digital radiography into themarketplace will be slow without effective standards, asmanufacturers of digital detectors find resistance to the

introduction of this new technology while end-users seekthese standards for guidelines on usage. Therefore,standards in digital radiography are vital to the introductionof this technology for industrial inspection.

To this end, several joint committees have worked towardsthe development of standards for industrial digitalradiography in the last decade. These standards includeguidelines on the measurement of instrumental parameters,as well as minimum requirements for instruments, practiceand evaluation. Standards like the ISO standards andEuropean standards have come into existence with mutualrecognition, and they serve to bring about an internationalharmonization of rules across the globe for non-destructiveevaluation (NDT) in general and industrial radiography inparticular. ASTM (American Society for Testing andMaterials) standards have also been under development inthis time frame. The emerging standards from theseorganizations provide guidance in evaluating different x-ray digital systems, methods of calibrating systems, andpractices for use and implementation of radiography forindustrial applications. An overview of the ASTM standardson digital detector arrays (DDA) is presented here.

2. ASTM STANDARDS FOR DIGITALDETECTOR ARRAYS

ASTM has developed and recently published four standardsfor DDAs targeting industrial applications. Each of thefour standards addresses an aspect of DDA manufactureand use, while they collectively address all the aspectspertaining to DDAs in general. Thereby, these standardsserve as a complete and comprehensive source ofinformation to the manufacturers and users by assistingthem in standardization of measurements, reporting DDAproperties that help users make informed decisions onDDA purchase, guidelines on introduction of DDAtechnology into operations for almost any inspectionapplication, providing tests and guidelines on methods to

32 Technical Paper


establish and track baseline performance of DDAs overtime. The four ASTM Standards for DDAs are:

· ASTM E2597: Standard Practice for ManufacturingCharacterization of Digital Detector Arrays.

· ASTM E2698: Standard Practice for RadiologicalExamination Using Digital Detector Arrays.

· ASTM E2737: Standard Practice for Digital DetectorArray Performance Evaluation and Long-Term Stability.

· ASTM E2736: Standard Guide for Digital DetectorArray Radiology.

A chart with all the four ASTM DDA standards and theirhighlights is shown in Fig. 1.

3. OVERVIEW OF THE ASTM STANDARDSFOR DIGITAL DETECTOR ARRAYS

This section gives an overview of the scope andsignificance of the four ASTM standard for DDAs. Thereader is encouraged to refer to the original standards fora detailed and extensive read.

3.1 ASTM E2597 Standard Practice forManufacturing Characterization of DigitalDetector Arrays

ASTM E2597 serves as a starting point for the end userto select a DDA for a specific application, based on theDDA system performance data provided by the DDAmanufacturers and suppliers. This standard describes theevaluation of a DDA in terms of a common standard forquantitative comparison of DDAs, based on a set oftechnical measurements. DDA manufacturers andintegrators are the intended users of this standard. It servesto assist them in providing the end user with quantitativeresults of DDA characteristics and metrics, which wouldin turn help the user to select an appropriate application-

specific DDA to meet the NDT requirements. The metrics,for which each DDA will be evaluated, are listed here.

(a) Basic Spatial Resolution (SRb) is the smallestgeometrical detail that can be resolved using the DDA.

(b) Efficiency of the DDA is the signal-to-noise rationormalized for basic spatial resolution (detectornormalized signal-to-noise ratio dSNRn) at 1 mGy, fordifferent energies and beam qualities.

(c) Achievable Contrast Sensitivity (CSa) is the optimumcontrast sensitivity obtainable using a standard phantom,with an x-ray technique that has minimal contributionfrom scatter.

(d) Specific Material Thickness Range (SMTR) is thematerial thickness range within which a given imagequality is achieved.

(e) Image lag is the residual signal in the DDA that occursshortly after the exposure is completed.

(f) Burn-in is the change in scintillator gain that persistsbeyond the exposure.

(g) Bad pixel is a pixel whose performance is outside thespecification range for a DDA pixel.

(h) Internal scatter radiation (ISR) is the scatter radiationwithin the detector.

An explanation for all the metrics and a detailed procedureto carry out tests for quantifying each of these metrics isdescribed in this standard [1]. Quantitative results for thesemetrics may be presented in the form of a diagram, whichdescribes the DDA performance comprehensively andserves as a user-guidance for appropriate choice of DDA.

3.2 ASTM E2698 Standard Practice for RadiologicalExamination Using Digital Detector Arrays:

ASTM E2698 standard serves to assist the end users inestablishing the minimum requirements for radiological

Fig. 1 : Chart showing the various DDA Standards developed by ASTM.

33Technical Paper


inspection using the purchased DDA, and is intended tocontrol the quality of x-ray images. It establishes the basicparameters for the application, for various components ofthe x-ray inspection chain, namely, system configuration,data acquisition software, DDA, image display station,image quality indicators, and radiation sources. Theprocedure for qualification exposure with image qualityindicators (IQI) includes details on x-ray tube potentials,tube current, integration time, source-to-detector distance(SDD), object-to-detector distance (ODD), collimators andfilters, DDA settings.

The aspects related to geometrical considerations forestablishing image quality, geometric magnification,evaluating IQI visibility using contrast-to-noise ratio (CNR),window-level and image zoom settings are documented inthis standard. It helps the user to get the required signal-to-noise ratio (SNR) to set up the required magnificationand provides guidance for viewing and storage ofradiographs. It also assists the user with marking andidentification of parts during radiological examinations. Theequipment monitoring requirements, proceduralrequirements and examination details are provided in detailin this document [2].

3.3 ASTM E2737 Standard Practice for DigitalDetector Array Performance Evaluation andLong-term Stability

ASTM E2737 is intended to help the end user in confirmingthat the DDA system performs as required, and is stablein its performance over its lifetime. This practice describesthe evaluation of DDA systems for industrial radiology. Itserves to ensure that the evaluation of image quality meetsthe needs of the users and their customers, and enablesprocess control and long-term stability of the DDA system.DDA system performance tests specified in this practiceneed to be completed upon purchase of the detector froma manufacturer, and at intervals specified, so as to monitorits long term stability. Although many of the details listedin this standard have similar metrics to those listed inASTM E2597, data collection methods are not identical.This document establishes standard techniques for assuringrepeatability throughout the lifecycle testing of the DDA.

The general testing procedure includes phantomspecifications, calibration method and bad pixelstandardization for DDAs. Core image quality tests forspatial resolution, contrast sensitivity, signal-to-noise ratio,signal levels and bad pixel distribution, material thicknessrange image lag and burn-in, offset value, are described.A detailed description of the test procedures is documentedin this standard [3].

3.4 ASTM E2736 Standard Guide for DigitalDetector Array Radiology

ASTM E2736 standard is a generic guide on DDAs, whichserves as a tutorial for selection and use of various DDAsystems. It assists the user to understand the definitions

and performance parameters of DDAs, while additionallyserving as an in-detail reference and guide for StandardsE2597, E2698 and E2737. It guides the user to make aninformed decision on the purchase and use of a DDA fora given target application. It is an extensive documentdesigned to assist the end user to set up the DDA withminimum requirements for radiological examinations.

It also describes DDA architecture, various digitizationmethods, and the overall signal chain in a DDA system.Other topics include DDA properties, factors that influencethe image quality in DDAs, various calibration andcorrection procedures, potential sources of radiationdamage to a DDA, general guidelines for DDA selection,imaging considerations with a given DDA, display storageand retrieval methods [4].

3.5 ASTM E2699

In addition to the four Standards summarized above, ASTME2699 Standard on Practice for Digital Imaging andCommunication in Nondestructive Evaluation (DICONDE)for Digital Radiographic Test Methods facilitates uniformityacross operators and digital radiography equipment, byspecifying image data transfer and archival methods incommonly accepted terms. This standard has beendeveloped to overcome the issues that could come upwhile analyzing and archiving data captured with DDAs.This standard defines a method where all the digital x-raytechnique parameters and test results are stored andcommunicated in a standard manner, regardless of changesin digital technology [5].

4. CONCLUSION

Digital radiography for industrial inspection is a technologythat offers a huge advantage in terms of throughput andcost. Standards play a vital role in the introduction of thistechnology to the marketplace. ASTM has developedstandards for digital detectors arrays targeting industrialapplications. All of these four Standards are now published.They are consistent, cross-referenced, and would certainlyexpedite film-to-digital transition and digital sustenance.

REFERENCES

1. ASTM E2597 Standard Practice for ManufacturingCharacterization of Digital Detector Arrays.

2. ASTM E2698 Standard Practice for Radiological ExaminationUsing Digital Detector Arrays.

3. ASTM E2737 Standard Practice for Digital Detector ArrayPerformance Evaluation and Long-Term Stability.

4. ASTM E2736 Standard Guide for Digital Detector ArrayRadiology.

5. ASTM E2699 Standard on Practice for Digital Imaging andCommunication in Nondestructive Evaluation (DICONDE) forDigital Radiographic Test Methods.

34 Technical Paper


Inspection of Adhesively Bonded Aircraft RepairPatches using Ultrasonic Guided Waves

Padmakumar Puthillath, Cliff J. Lissenden and Joseph L. RoseEngineering Science and Mechanics Department

212, EES Bldg., Pennsylvania State University, PA 16802, U.S.A

Email: [email protected]

ABSTRACT

Aircraft structures subject to service loads and chemical environments develop structural weaknesses like cracks, corrosion etc.In order to mitigate the resulting reduction in the useful service life of aircrafts, repairs are done in the form of adhesive bondingof plates such as a titanium plate to aluminum fuselage. Typical of adhesive joints, these bonded repair patches also haveinterfacial (adhesive) or bulk (cohesive) weaknesses in the joint. Nondestructive inspection of these structures is required to ensurethe quality of the repair patches. Conventional inspection approaches using normal or oblique incidence of ultrasonic waves haslimited capability in detecting both the adhesive and the cohesive weaknesses present in the adhesive joints. A systematic approachfor the inspection of adhesive repair patches using ultrasonic guided waves is demonstrated in this work. Among the multiplemodes and frequency combinations possible in a structure, defect sensitive guided wave modes were selected from theoreticalstudies. The selected mode-frequency combination is ensured to work over a range of bondline thicknesses that can occur inreal joints. An angle beam wedge arrangement to generate defect sensitive modes was used to successfully inspect epoxy bondedtitanium - aluminum samples prepared with simulated adhesive and cohesive weaknesses.

Keywords: Adhesively Bonded Repair Patch, Ultrasonic Guided Waves, Dispersion, Adhesive and Cohesive Weakness

1. INTRODUCTION

Aircraft structures are subject to in-service loading likefatigue, thermal and chemical environments that can initiatepoints of weakness within the structure, such as fatiguecracks, corrosion, and delamination, thus leading to areduction in their service life. In the military, aging inducedstructural weaknesses in aircrafts are mitigated usingappropriate repairs because replacement is prohibitive interms of time and cost [Pyles 2003]. Repairs can beperformed using mechanically fastened or adhesivelybonded patches. In comparison to mechanical fastenedrepairs, a bonded repair produces minimal alteration to theaerodynamic contours, results in weight savings in additionto avoiding the stress raisers associated with bolt/rivetholes. Adhesively bonding metal or composite patches tothe damaged surface of aircraft, after appropriate surfacetreatment, can improve the stiffness of the weakened part[Pyles 2003]. The adhesive bonding used is susceptible tointerfacial (or adhesive) and bulk (or cohesive) defects,making nondestructive inspection essential in order toascertain the quality of repairs. Practical cases of adhesiverepairs can be found in the literature [Baker 2009, t’Hartand Boogers 2002].

Recently, researchers have demonstrated a method forhealth monitoring of repairs using strain gages bonded tothe aircraft skin and repair patch [Baker 2009]. The ratioof strains was used to detect debonding between the skinand the repair patch. This is a good approach for localinspection, but requires either an extensive coverage ofthe repair patch using strain gages or optical fibers toobtain a global inspection. The use of commercial bond

testing equipment like Bondascope [Baker 2009] and theFokker Bondtester [t’Hart and Boogers 2002] insuccessfully detecting cohesive defects is also shown inthe literature. This is again a local inspection approach,and similar to an ultrasonic C-scan, is not successful indetecting adhesive weakness in bonding.

Ultrasonic wave propagation through structures isdependent on the material elastic properties. Ultrasoundprovides a nondestructive means of adhesive bond qualityassessment. Pilarski and Rose [1988] have shown theimportance of generating shear at the interface betweenthe adhesive and adherend. This was an improvement ofthe bulk wave approach that needed very high frequencies(> 10 MHz).

Ultrasonic guided waves are special kinds of wavespropagating primarily under the influence of the geometryand boundary conditions of a waveguide. They arecharacterized by dispersion which is captured in the formof phase and group velocity variation with frequency [Roseand Pilarski 1988]. Rose and co-workers [1996] havesuccessfully demonstrated mode selection principles byemploying modes from the overlap between dispersioncurves of the individual plate that form the adhesive bond.

This study comprehends the progress made in modeselection for inspection of defects in an adhesive joint -titanium patch bonded to aluminum aircraft skin usingepoxy. In this paper, a theoretical study is carried outwhere the guided wave phase velocity dispersion curvesare used in conjunction with wave structures to determineoptimal conditions for inspection of adhesive and cohesive

35Technical Paper


weakness in continuous waveguides. Epoxy bondedaluminum - titanium repair patches were prepared withinterfacial weakness conditions simulated by using tefloninserts and other surface variation techniques. Theinspection technique presented here is applicable to theinspection of bonded repair patches under the conditionthat both the transmitter and the receiving transducersrest on the bonded joint. The optimal guided wave modewas generated in the bonded sample using an ultrasonictransducer mounted on an acrylic angle beam wedge. Thedifference in transmission in terms of the signal contentwas successfully analyzed and used to discriminate betweenthe defective and non-defective regions in the structure.This work has been recently reported by Puthillath andRose [2010].

2. GUIDED WAVE MODE SELECTION

Ultrasonic guided wave dispersion curves provide thetheoretically possible phase velocity and frequencycombinations that can exist in a structure having free

boundaries. Each point on a dispersion curve has a uniquewavestructure and it holds the potential to solve differentinspection problems. In the literature there have beeninstances [Rose and Pilarski 1992] where the guided wavemode selection has been carried out to address differentdefect detection scenarios.

The Lamb wave phase velocity dispersion curves for atypical adhesive repair patch - epoxy (0.66 mm thick)bonded titanium (1.6 mm), aluminum (3.175 mm) joint –is shown in Fig. 1. Since the repair patch geometry understudy is not mid-plane symmetric, the modes are referredby numbers rather than the conventional Antisymmetric(A) or Symmetric (S) notation.

In this work, both the adhesive and the cohesive weaknessin the epoxy layer are studied. The adhesive weakness isassumed to be located between the aluminum and theepoxy layer. This assumption comes from the fact thatrepairs are performed on field and hence the possibilitythat the surface of aluminum does not meet the cleanlinesscondition required for bonding is high.

Fig. 1 : Lamb wave dispersion curves for aluminum-epoxy-titanium adhesive repair patch and two wave structures or cross-sectionaldisplacement profiles (at locations 1 and 2 on the dispersion curves). The dotted lines demarcate the aluminum, epoxy and thetitanium regions, with aluminum being at the bottom. A larger in-plane displacement (ux) at the aluminum-epoxy interface canbe noticed at location 2.

36 Technical Paper


In order to inspect the interfacial weaknesses at thealuminum-epoxy interface in the bonded repair patch, thein-plane displacement at that interface was used as thecriterion. The normalized displacement wavestructures fortwo neighboring modes (modes 17 and 18) on thedispersion curves at the same phase velocity value (14.37km/s) and frequency 2.5 MHz is also shown in Fig. 1.The interfacial in-plane displacement profile across thefrequency-phase velocity space of choice is shownsuperimposed on the guided wave modes on Fig. 2 as aneasy reference tool.

In addition to the interfacial in-plane displacement feature,in order to simplify the interpretation of the experimentallymeasurements waveform, it is mostly preferred to haveminimum number of modes excited within the structure.The guided wave mode selected should also have a smallerwavelength to improve sensitivity to smaller defects. Themode 18 (from Fig. 1), identified with an arrow in Fig. 2,at a higher phase velocity range (14-16 km/s) was thusselected for inspection of the bonded joint.

A big challenge in practical adhesive bond inspectionproblems is the change in the bond-line thickness. Despiteattempts made to control the thickness of the bond linenamely the use of cured epoxy strips, glass beads, shim-stocks etc., local variation in adhesive thickness is possible.In the guided wave based inspection scenario, a change inbond line thickness implies a change in the thickness ofjust one layer of the layered waveguide – implying a newproblem to be solved. The effect of 100 % variation in thethickness of the bond-line on the Lamb wave phase velocitydispersion curves was studied by varying the thicknessfrom 0.4318 mm to 0.8636 mm. Though not shown here,it was noted that the selection of ~15 km/s and 2.5 MHzwas found to result in a high interfacial in-planedisplacement throughout the range of the thicknessconsidered.

3. PREPARATION OF SAMPLES WITHSIMULATED DEFECTS

In order to verify the theoretical work, small repair patchsamples – i.e. epoxy bonded titanium-aluminum joint werecreated. Aerospace grade sheet epoxy – EA9696 was usedas the adhesive. Defects were introduced at controlleddepths in order to study the wave propagation acrosscohesive and adhesive weaknesses. aluminum (3.175 mm)and titanium (1.6 mm) plate samples were degreased usinga solvent, polished using abrasive disc pads, cleaned withacetone followed by coating with sol-gel and water basedprimer. The use of the sol-gel is to improve the adhesionfor bonding metals. The primer provides better mechanicalproperties and corrosion resistance.

For each repair patch, two epoxy layers were stackedbetween the prepared faces of the aluminum and titaniumplates and cured under vacuum conditions with theapplication of appropriate pressure and temperature insidean autoclave. Square defects with 0.5" sides wereintroduced at the aluminum-epoxy interface for creatingadhesive weakness and between the layers of epoxy tocreate cohesive weakness. A folded strip of teflon wasalso suitably placed for creating both adhesive and cohesiveweaknesses in the repair patch. A bubble wrap was usedto create another instance of adhesive weakness.

The repair patches prepared were cut to form samples fortesting shear strength using ASTM 3165. From the testresults, it was observed that the good bond region in therepair patch sample was stronger than any simulatedweaknesses. The results from the ASTM 3165 tests thuspoint to the reliability of the fabrication procedureimplemented and also provide support to the methods ofsimulating weaknesses in the bonding.

4. EXPERIMENTAL WORK AND RESULTS

There are various techniques for exciting guided waves instructures for experimental work viz. acrylic wedge,oblique incidence in a water immersion mode, or a combtransducer with or without time delays. A variable angleacrylic wedge arrangement was adopted due to its ease ofimplementation and flexibility to generate guided wavemodes at different phase velocities.

The mode identified in Fig. 2 (mode 18) was generatedusing a variable angle beam acrylic wedge set to anincidence angle of 10°. Experiments were performed byarranging the wedge mounted transducers (2.25 MHz,and 12.7 mm in diameter) in pitch-catch configurationand varying the excitation frequency from 1 MHz to 3 MHzin steps of 50 kHz. The RF signals collected were squaredand summed to obtain an energy quantity for each excitationsignal in the range of frequencies 1 MHz and 3 MHz at50 kHz intervals. A comparison of the variation in thetransmitted energy quantity obtained from the frequencysweep experiments is shown in Fig. 3.

Fig. 2 : Normalized in-plane displacement value is shownsuperimposed over the dispersion curves for titanium-epoxy-aluminum joint. The arrow on top of the figureindicates the mode 18 – that has one of the highest in-plane displacements at the aluminum-epoxy interface.

37Technical Paper


It can be observed from the Fig. 3 that the range ofexcitation frequencies - 2 to 2.5 MHz, with incidence andreception angles of 10°, is sensitive to the adhesive andcohesive defects simulated in the bonded repair patchsamples. The transmission is maximum in the case of agood bond and minimum in the case of a cohesively weakbond. The energy transmission in the adhesive weaknesscases lies between the two extremes. The variable anglewedges were replaced by small fixed angle wedges havingthe same incidence angle (10°), thus reducing the numberof contacting interfaces between each of the transducersand the bonded plate by one from the initial count ofthree.

The signals collected in pitch-catch mode across thesimulated defects using a pair of 2.25 MHz, 6.7 mmdiameter commercial transducers mounted on fixed anglewedges is shown in Fig. 4. The pulse input to thetransmitter was a tone burst cosine pulse at 2.5 MHz. TheRF signals from Fig. 4 clearly show that the guided wavemode selected from the theoretical study was able todistinguish between the different cases of interfaceconditions simulated and a good joint among the repairpatch samples fabricated.

It is interesting to note that the mode selected specificallyfor sensitivity to adhesive weakness is also sensitive to thecohesive weakness because the displacement at the middleof the epoxy layer is still significantly high.

CONCLUSIONS

In this work, a theoretically driven systematic approach toselection of guided wave modes for the inspection ofadhesive and cohesive weaknesses in an adhesively bondedrepair patch, comprised of epoxy bonded aluminum andtitanium repair patch, is presented.

One of the guided wave modes with large in-planedisplacement at the aluminum-epoxy interface in a titanium-epoxy-aluminum bonded joint was selected for theinspection. Several repair patch samples - epoxy bondedaluminum-titanium plates - were fabricated in the lab withsimulated interfacial weakness conditions. Acrylic anglebeam wedges set to an angle of 10°, with 2.25 MHztransducer mounted on top was found to be able to generateinterface sensitive mode in the bonded repair patch. Usinga matching receiver, it was possible to distinguish betweenthe good and bad repairs. The applicability of the selectedexperimental parameters over a very large range of adhesivethickness was ensured in order to keep the selection validfor a real repair patch sample where the bondline thicknesscan vary.

Though the solution presented in this paper is specificallytailored to detection of adhesive weakness at the aluminum-epoxy interface in a repair patch sample, the generalapproach laid here can be applied to the problem of detectingdefects in any layered anisotropic media. In such a case,modes can be selected for sensitivity to the differentinterfaces present there.

REFERENCES

1. Raymond Pyles. Aging Aircraft: USAF workload and materialconsumption life cycle patterns, RAND Pittsburgh, U.S.A. 2003.

2. Alan Baker, Nik Rajic and Claire Davis. Towards a practicalstructural health monitoring technology for patched cracks inaircraft structure, Composites: Part A, 40 (2009) 1340-1352.

3. W. G. J. t’Hart and J. A. M. Boogers, Patch repair of cracks inthe upper longeron of an F-16 aircraft of the Royal NetherlandsAir Force. Structures and Materials Division, National AerospaceLaboratory NLR-TP-2002-294. (2002).

Fig. 3 : Energy transmission from frequency sweep experimentsusing variable angle acrylic wedges adjusted to 10° incidenceand reception angle in pitch-catch mode. Commerciallyavailable 2.25 MHz transducers were used as transmitterand receiver and tone burst input was supplied to thetransmitter.

Fig. 4 : The RF signals collected by placing fixed angle wedges(10°) with 2.25 MHz transducers mounted on top, acrossthe defective and non-defective repair patches in a pitch-catch mode. A tone burst excitation source was used topulse the transmitter.

38 Technical Paper


4. J.L. Rose, Ultrasonic wave in solid media, Cambridge UniversityPress, Cambridge, (1999).

5. A. Pilarski and J.L. Rose. A transverse wave ultrasonic oblique-incidence technique for interfacial weakness detection in adhesivejoints, Journal of Applied Physics, 63 (1988) 300-307.

6. J.L. Rose, K.M. Rajana and J.N. Barshinger, “Guided waves forcomposite patch repair of aging aircraft,” in Review of Progressin QNDE, 15B, eds. D.O. Thompson and D.E. Chimenti, PlenumPress, New York (1996) 1291-1298.

7. A. Pilarski and J.L. Rose. Lamb wave mode selection conceptsfor interfacial weakness analysis, Journal of NondestructiveEvaluation, 11(34) (1992) 237-249.

8. P. Puthillath and J.L. Rose. Ultrasonic guided wave inspectionof a titanium repair patch bonded to an aluminum aircraft skin.International Journal of Adhesion and Adhesives, 30 (2010) 566-573.

39Technical Paper


HOMC Guided Wave Ultrasonic Technique– A new paradigm for corrosion detection

Krishnan Balasubramaniam1, K.S. Venkataraman2 and Issac Anto2

1 Centre for Nondestructive Evaluation, Indian Institute of Technology Madras, Chennai-600036, India2 ESCON Technologies, SINGAPORE

3 Dhvani Research and Development Solutions Pvt. Ltd, Taramani, Chennai INDIA 600113

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

ABSTRACT

The paper describes the application of Higher Order Modes Clusters (HOMC), a new guided ultrasonic waves based technique.HOMC uses relatively very high frequency guided ultrasonic waves, when compared to the long range guided wave techniques,and travel in a relatively non-dispersive manner. However, the range of inspection for HOMC is relatively short, up to 2 m.The HOMC technique can be implemented in several modes, particularly Axial HOMC and Circumferential HOMC techniques.The range of applications includes corrosion detection in hidden pipe support regions, tank floor annular plate in the storagetank floor, hidden regions under flanges in off-shore structures, etc.

1. INTRODUCTION

In-service degradation due to mechanisms such ascorrosion at pipe supports is one of the leading causes ofprocess piping failure. The support regions in pipes arevery vulnerable to accelerated corrosion as these are sitesfor water logging, stress and contamination. While thelong range guided waves, using the fundamental guidedwave modes operating in the low frequency regimes, canbe employed for the corrosion damage in pipes, thepresence of sacrificial weld pads, the co-located flanges,pipe bends, etc., limit the long range techniques. In addition,it is the beam supports and the saddle clamps that havehistorically caused the majority of the problems.[1].

The ultrasonic guided waves, unlike longitudinal andtransverse bulk wave modes, are a manifestation ofgeometrical confinement of acoustical waves betweenboundaries [2, 3]. In many instances, these waves travellong distances, depending on the frequency and modecharacteristics of the wave, and follow the contour of thestructure in which they are propagating. Usually, thesewaves not only propagate along the length of the structurebut also cover the entire thickness and circumference (inthe case of cylinders and rods). The use of guided wavemodes is potentially a very attractive solution to the problemof inspecting the embedded portions of structures becausethey can be excited at one point on the structure,propagated over considerable distances, and received at aremote point on the structure. Applications to problemslike corrosion monitoring, pipeline wall thinning inspection,weld defect detection and such industrial problems arewell known [4,5].

A new concept for the improved inspection of corrosionat the support region of pipelines using a short-rangeultrasonic guided wave technique that uses a collection of

Higher Order Modes Clusters, called here as HOMC hasbeen developed. Ultrasonic guided waves (circumferentialor axial modes), once generated will be reflected fromcorrosion and other features on the pipe. Inspection canbe carried out from the accessible portion of the pipe[6-10].

Circumferential HOMC guided wave modes are used formost pipe sizes, however, in larger diameter pipe wherethe support pad welded extends over nearly one half ofthe circumference, the Axial HOMC guided wave modewill be more advantageous to deploy.

2. THE HOMC METHOD

To identify the relevant guided waves for specificapplications, their dispersion characteristics and excitationmodes need to be examined. Three standard ways ofrepresenting the steady state solution for guided wavesare shown in Fig. 1. This solution is for a mild steel platewith the wave incident through Plexiglas. Fig. 1a showsthe phase velocity curves for various modes as a functionof frequency-thickness (MHz-mm) product. While the non-dispersive regions are indicated by flat portions, the highlydispersive regions of the modes are indicated by steepslopes. Fig. 1(b) shows the group velocity curves forthese modes. Figure.1(c) provides a convenientrepresentation in terms of angles of excitation for each ofthese modes. The plot in Fig. 1c represents the incidenceangle in degrees through Perspex. For instance, to generateS0 mode at 1.5 MHz-mm product Fig. 1c indicates thata 300 angled Perspex wedge needs to be used for excitation.

Dispersive modes are complex to work with as it involvessophisticated signal processing techniques to handle them.Non-dispersive modes are very useful in many practicalNDE applications. Fig. 1b shows the group velocity curves

40 Technical Paper


for these modes. When phase velocities are difficult tomeasure in dispersive regimes, group velocities aremeasured.

Fundamental modes like A0 and S0 shown in Fig. 1c asregion 1, are relatively easy to generate and work with inpractice as these modes are well separated in time owingto their vast difference in velocity.

The region marked 2, in Fig. 1c belongs to the higherorder mode guided waves (HOM-GW) regime at a higherfrequency-thickness (MHz-mm) product (3 MHz-mm to10 MHz-mm). HOM-GW was recently exploited to lookinto application involving pipe support corrosion detection

work [7,8] as these modes have higher spatial and temporalresolution characteristics than the fundamental modes.However working with HOM-GW involves dealing withcomplex multimodal and dispersive signals requiringsophisticated techniques for interpretation.

The region marked 3, in Fig. 1c, lying between 15 MHz-mm product to 35 MHz-mm product is the higher ordermodes cluster of guided wave (HOMC- GW) regime andforms the subject of the present investigation. Modes inthis regime are found to have small differences betweentheir group velocities and small differences in the associatedangles of excitation. Table 1, constructed specifically at16 MHz-mm product presents the various modes andassociated angles of excitation through Perspex. Owing tothe small differences in group velocities and nearness inangles of excitation between the adjacent modes, excitationat any given frequency – thickness (MHz-mm) productwithin this regime is seen to lead to a formation of a multimodal cluster. As the various modes that take part in thecluster move with nearly the same group velocity, withthe cluster appearing to move as a distinct non-dispersiveenvelope. It is worth noting from Table 1 that althoughthe group velocities of the fundamental modes A0 and S0are close to the higher order modes, their angles ofexcitation are distinctively different from the higher ordermodes resulting in their negligible contribution to theHOMC-GW.

3. ADVANTAGES AND LIMITATIONS

The HOMC techniques have the following characteristicsthat favor its selection for corrosion detection:

1. The use of high frequencies that allows for improvedsensitivity to smaller defects and improved resolutionin imaging corrosion defects including pitting type.

2. The minimal displacement at the pipe surfaces leadingto insensitivity to surface conditions. This allows forthe inspection on loaded and coated structures andinsensitivity to surface welds such as tack welds.

3. Non-dispersive nature of the wave mode cluster thatis insensitive to subtle changes in geometry of thestructures.

The key limitation of the technique is the careful choiceof the wedge angle and the distance of inspection beinglimited to approximately 2 meters.

4. RESULTS AND DISCUSSION

There are three different techniques in HOMC that will beexplained with relevance to specific applications as below.

4.1 Corrosion under pipe support (CUPS)

Pipelines in process industries such as refineries andchemical plants are supported at intermediate distances bypipe supports. Corrosion is more prone to occur at these

Fig 1 : Disperse plot for a Mild steel plate with Plexiglas incidence.(a) Phase velocity plot, (b) Group velocity plot, (c) Angleof incidence through Plexiglas. (1) Conventional guidedwave regime. (2) Higher order modes guided wave regime.(3) Higher order modes cluster guided wave regime.

41Technical Paper


support regions of pipelines due to the presence of all thekey ingredients needed to accelerate corrosion like water,minerals, and the stress concentration in the presence ofa crack. The common types of corrosion at the supportsinclude corrosion spread along the circumferential orlongitudinal direction of the pipe. In most cases thecorrosion defect at the support locations is localized innature with smaller pitting corrosion.

In order to mitigate the corrosion to pipes at these locations,the industry often resorts to providing a sacrificial plate(often called sacrificial welded pad) that is placed inbetween the pipe and the support. The plate is tack weldedaround the boundaries of the plate. However, it has beenobserved that while this sacrificial pad reduces corrosion,it does not completely prevent it. The inspection of thepipe in this region with the welded pad is more difficultin comparison to the scenario without the pad.

Among the various techniques used for the detection ofcorrosion like defect in pipelines, ultrasonic NDE plays a

major role. To perform a conventional ultrasonic inspectionin such inaccessible region (i.e. at support locations), thepipes have to be lifted out of the supports, which involvescomplete shutdown of the flow lines and the risk ofstressing a pipe that would have been already weakenedby corrosion.

Circumferential guided wave modes are used for mostpipe sizes, however, in larger diameter pipe where thesupport pad welded extends over nearly one half of thecircumference, the axial guided wave mode will be moreadvantageous to deploy.

Experimental data obtained from the calibration samplewith programmed defects and on field tests show that thesize and location of the defects correlates well with thetime-of flight and amplitude ratio of the reflected signalsfrom the defects. A and B-scan images were used tovisualise and classify the defect size and location.

A Semi-Automated Scanning system called CUPS(Corrosion Under Pipe-support Scanner) has beendeveloped and tested to ensure high speeds of inspectionin line with industry requirements.

4.2 Critical Region Inspection Scanner for Pipes(CRISP)

Pipelines systems in the industries have various criticalregions where the susceptibility of corrosion is very highand the possibility of inspecting them very low.

Fig. 2 : (a) The schematic of the C-HOMC technique for corrosiondetection under pipe supports using HOMC guided wavetechnique and (b) a photograph of the pipe support witha sacrificial weld pad.

Fig. 3 : Typical C-HOMC imaging Results for corrosion in pipesupport locations.

42 Technical Paper


These Critical Regions include, but not limited to cases asbelow:

Under clamps

- Riser Pipes

- Plant piping (U bolt clamp corrosion)

Soil to Air Interface

- Road Crossing Pipes

- Partially buried piping including Lamp Posts

Protective wrapping covered region

- Temporary Repair Locations with clamps orcoating.

Inspection of Girth Welds especially at Heat AffectedZone (HAZ).

Few of such applications are shown in Fig. 4.

Conventional NDT techniques do not help in reliableinspection of these regions and very often requires, clampremoval followed by visual inspection. Techniques thatprovide some information do not have the sensitivity tofind small defects such as localized pitting corrosion

Fig. 4 : Typical applications for the CRISP based HOMCtechnique.

Ultrasonic guided waves (axial modes), once generatedwill be reflected from corrosion and other features (welds,etc.) on the pipe. Inspection can be carried out all aroundthe pipe by moving the probe around the pipecircumference. Inspection can be carried out with thescanner at distances up to 2 m, along the length of thepipe, from the region of interest. An example result andthe CRISP scanner used for obtaining this result is shownin Fig. 5.

Experimental data obtained from the calibration samplewith programmed defects and on field tests show that thesize and location of the defects correlates well with thetime-of flight and amplitude ratio of the reflected signalsfrom the defects. A and B-scan images were used tovisualise and classify the defect size and location.

The A-HOMC technique is capable of detecting small pinhole type defects, such as caused by pitting corrosion, aswell as large area corrosion damage. Other types of defectssuch as cracks, weld defects, gouging damage, etc. arealso imaged using the method. The presence of surfacecoatings such as insulation does not affect the wave.

A Semi-Automated Scanning system called CRISP (CriticalRegion Inspection Scanner for Pipes) has been developedand tested to ensure high speeds of inspection in situationswhere hidden regions must be inspected for corrosiondetection.

Fig. 5 : A typical A-HOMC scanner along is shown for a tacwelded region in a pipe and (b) shows the A-HOMCresult showing the detection of corrosion in the pipeabove the weld pad region.

43Technical Paper


4.3 Tank Annular Plate Scanner (TAPS)

Corrosion detection in the annular plate region of above-ground storage tanks is a critical need for tank farmoperators in the oil and gas industry. In the case of storagetanks, since the region of the annular plate near the shell-to-bottom fillet weld (both on the top and bottom side) issubjected to metallurgical change due to the irregularheating and cooling arising from the welding process, itmakes the region more vulnerable to corrosion whencompared to other regions. It is also observed that themaximum stress in a tank bottom exists at the toe of theinside shell-to-bottom fillet weld at the annular plate. Thesemay result in stress corrosion cracks and/or pittingcorrosion on the liquid side of the annular plate andsubsequently cause leakage. The schematic of the annularplate corrosion is shown along with a typical plate withcorrosion is illustrated in Fig. 7.

The critical zone between the tank shell wall and the firstfew inches of the annular plate is difficult to inspect withconventional floor scanning methods due to the presenceof coatings, uneven surfaces and a lack of access due tothe presence of the weld toe.

This region, however, is prone to accelerated corrosiondue to the additional stresses caused by the weight of thetank wall and the increased possibility of water entrapmentunder the annular plate. Repairs in this region demandreplacement of the entire annular plate and this leads tolong shutdown of the tank, and often failures occur withoutany warning.

Fig. 6 : (a) Schematic of application of HOMC technique forTAPS and (b) a typical tank floor annular plate withthinning in the critical region close to the wall.

Fig. 7 : (a) A typical result using TAPS showing corrosion nearwall and (b) robotic scanner with probe holder for scanningthe storage tanks.

Standard inspection techniques often involves the emptyingthe tanks for internal inspections, which implies largeperiods of operational unavailability, with expensive, timeconsuming and hazardous cleaning processes, involvingsafety issues to workers. For safety and environmentalreasons, the Magnetic Flux Leakage (MFL) technique isone of the commonly used methods for carrying out thisinspection. Alternatively, Acoustic Emission (AE) has alsobeen shown to indicate regions of corrosion activity. .Accessibility to this zone of the annular plate (very closeto and/or under the retainer wall) is highly restricted andhence poses difficulties when using the currently availableMFL and similar floor scanning NDE methods.

A Robotic Scanner called TAPS (Tank Annular PlateScanner) has been developed and tested to ensure highspeeds of inspection in line with industry requirements.Typical result for imaging the detection of corrosion nearthe wall location in the annular plate is shown in Fig. 7.

6. CONCLUDING REMARKS

HOMC-GW appears to have several attractive features forNDE applications. These are (i) tighter envelope thatimproves the temporal resolution (ii) shorter wavelengththat improves the spatial resolution, (iii) The vanishingsurface displacements of the out-of-plane component thatis insensitive to surface loading, and (iv) sub-surface defectdetectability.

Using the new HOMC technique new applications for hiddenand inaccessible regions can now be made inspectable.

44 Technical Paper


6. Wei Luo, Xiaoliang Zhao, and J.L Rose., A Guided Wave PlateExperiment for a Pipe, Journal of Pressure Vessel Technology2005 by ASME AUGUST 2005, Vol. 127 / 345.

7. K. Shivaraj, K .Balasubramaniam, C.V. Krishnamurthy and R.Wadhwan, ASME Trans. J. Pressure Vessel Technology (2007).

8. L. Satyarnarayan, J. Chandrasekaran, Bruce Maxfield, KrishnanBalasubramaniam, “Circumferential higher order guided wavemodes for the detection and sizing of cracks and pinholes in pipesupport regions”, NDT&E International 41 (2008) 32–43.

9. C. Jayaraman, C. V. Krishnamurthy, and K. Balasubramaniam ,Higher Order Modes Cluster (HOMC) Guided Waves – A NewTechnique for NDT Inspection AIP Conference Proceedings,Rev. of Prog. QNDE (Ed. D. Thompson and D.E. Chimenti) Vol.28 1096, 121 (2009)

10. Chandrasekaran. J, I. Anto, K. Balasubramaniam and K.S.Venkatraman, Higher order modes cluster (HOMC) guided wavesfor online defect detection in annular plate region of aboveground storage tanks, INSIGHT, 51(11) (2009).

REFERENCES

1. Jim Britton, “Corrosion at pipe support, Causes and solutions”,2003

2. Meeker T.R and A.H. Meitzler, “Guided Wave propagationElongated Cylinders and Plates,” Physical acoustics, Vol. 1 PartA, 1964, pp. 111-167.

3. Zemmanek J.JR. , “An Experimental and Theoretical Investigationof Elastic Wave Propagation in a Cylinder,” The JASA, Vol. 52,No. 1 (part 2), 1972, pp. 265-283

4. W. D. Wang, “Applications of guided wave technique in thepetrochemical industry” in Review of Progress in QNDE, 18A,op. cit. (1998), pp. 277-284.

5. USNRC, “An Approach for Plant Specific, Risk- InformedDecision Making. In- service Inspection of Piping”, U.S. NuclearRegulatory Commission, Draft Regulatory Guide DG-1063(1997).

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