quarterly publication rs. 20 january 2020 weld 18 bead 4
TRANSCRIPT
Quarterly Publication Rs. 20
January 2020 Weld 18 Bead 4
AROUND IWS
APAC AWARD FOR IWS
GET-TOGETHER MEETING WITH OTHER PROFESSIONAL
BODIES
WELDFAB TECH AWARD 2019
FREE LECTURE PROGRAMMES
TWO DAY HANDS-ON TRAINING PROGRAMME ON
“ADVANCED TIG AND MIG WELDING PROCESS- EMPHASIS
ON RESEARCH POSSIBILITIES”
“VOCATIONAL TRAINING ON SHIELDED METAL ARC
WELDING (SMAW)” FOR RURAL STUDENTS
“HANDS-ON WELDING DEMONSTRATION TO THE STUDENTS
OF ALVAS INSTITUTE OF ENGG. & TECHNOLOGY (AIET)”
KNOWLEDGE SHARING
EVENING COURSE BY SZ
WAPCON 2019
SYNERGY 2019
ONE DAY HANDS ON WORKSHOP ON “ADVANCED ARC
WELDING PROCESSES”
ONE DAY WORKSHOP ON “DESIGN CHALLENGES IN
WELDING”
WORKSHOP ON “SUSTAINABLE MANUFACTURING USING
AUTOMATION AND ROBOTICS - SMART”
TECHNICAL PAPERS
EFFECT OF CHROMIUM AND NIOBIUM ON
MICROSTRUCTURE AND WEAR RESISTANCE OF HIGH
CARBON HARDFACING ALLOYS
ELECTROMAGNETIC ACOUSTIC TRANSDUCER PHASED
ARRAY FOR INSPECTION OF THIN AND THICK AUSTENITIC
STAINLESS STEEL WELDS
THE JOURNAL OF
Regn. No. 41817 / 2002
QUARTERLY PUBLICATION
JAN 2020 Weld: 18 Bead: 4
PRESIDENT
SHRI R PADMANABHAN
Immediate Past President
SHRI S BISWAS
Vice Presidents
SHRI HIMANSHU I GANDHI SHRI S PRABAKARAN
Dr S ARAVINDAN
Hon. Secretary
SHRI N RAJASEKARAN
Hon. Treasurer
Mrs. A SANTHAKUMARI
Members
Dr K Asokkumar Dr A Chandrasekhar
Shri A Maruthamuthu Dr. T Senthil Kumar
Shri G Rajendran Shri V Ganesh Sinkar
Shri M P Jain Dr Shashikantha Karinka
Shi M Kasinathan Shri Gyan Prakash Bajpai
Shri R Easwaran Dr G Padmanabham
Shri S M Agarwal Shri Muneesh Narain
Shri S M Bhat Dr T Prakash
Shri Amit Agarwal Dr S Shanavas
Dr V Balasubramanian Shri Naresh Malli Reddy
Shri T Baskaran Dr Yadaiah Nirsanametla
Dr N Murugan Shri A K Verma
Dr N Raju Dr P Sivaprakash
Editor in Charge Shri S. CHANDRASEKARAN
ASSOCIATE EDITORS Shri Praveen Kumar Lakavat Shri R. Arivalagan
CO-ORDINATORS Dr. N Raju Shri A K Verma
PUBLISHED BY
On Behalf of IWS by
Shri N RAJASEKARAN Hon. Secretary (IWS)
INDIAN WELDING SOCIETY INSTITUTIONS BUILDING, KAILASAPURAM, TIRUCHIRAPPALLI – 620 014
INDIA Websites: www.iws.org.in www.iwsevents.com
E mail: [email protected]
Page 3 of 32
IWS JOURNAL
WISHES ALL ITS READERS
A
VERY HAPPY & PROSEPROUS
NEW YEAR 2020
&
CHEERFUL
MAKARA SANKRANTI
THAI PONGAL
Haldi Kumkum
Khichdi
Lohri
Magh Bihu
Maghi
Maghi Sankrant
Makara Chaula
Makara Mela
Makara
Sankramana
Poush Sangkranti
Sankranti
Shishur Saenkraat
Suggi Habba
Tila Sakrait
Uttarayan
CITATION
Indian Welding Society is a professional body devoted to welding in India. The
organization is continuing its focus on empowering the youths in the north
eastern part of the country. The Northern Zone of the society, through the
Guwahati Centre, conducted a short-term certificate course in welding
technology. The society has successfully conducted two international events in
the southern and western part of the vast country in 2018 via a 3-day
International Symposium On Joining Of Materials (SOJOM 2018) at Tiruchirappalli
and a 3-day International Welding Symposium (IWS 2k18) at Mumbai. Each event
attracted more than 200 delegates from India and the world.
“Continuing focus on empowering the youth with vital and self-serving skills and
the growth rate equally realistic and achievable”.
- Jeffers Miruka, African Society of Association
Mumbai, India
Page 5 of 32
GET-TOGETHER MEETING WITH OTHER PROFESSIONAL
BODIES
On October 07, 2019, on the day of Ayudha
Pooja Celebrations, a get-together meeting with
other professional bodies, viz. IIM, IIW and CSI
was conducted at the Institutional Building,
Kailasapuram Township, Tiruchy by the Southern
zone.
Mr. S Prabakaran, Chairman (IWS, SZ), Dr. T A Daniel Sahayaraj, Chairman
(IIM Tiruchy chapter), Mr. A.
Maruthamuthu, Imm. Past chairman
(IWS, SZ), Mr. G Uma Shanker, Past
Chairman of IIM Tiruchy Chapter, Mr.
N Rajasekaran, Mrs. A. Santhakumari,
Mr. G Rajendran, Dr. N Raju and host
of office bearers from other professional bodies also participated and graced the occasion.
WELDFAB TECH AWARDS 2019
With an objective to encourage
and reward the welding industry
for their excellence and
innovations, WeldFab Tech
Awards 2019 was organized on
14th September 2019 at Hotel
Sahara Star, Mumbai. IWS has
supported the mega event as knowledge partner.
For the First Time in India, an Awards Night was held exclusively
for the welding fraternity. WeldFab Tech Times, India’s only
welding magazine organized this blissful event, and was successful
in gathering various sectors like welding, fabrication, steel, power,
aerospace, government organizations, railways, etc. under one
roof of WeldFab Tech Awards 2019.
AROUND
Page 7 of 32
The event started with lamp lightening by Dr. P. V. Venkitakrishnan, Outstanding Scientist, Director,
CBPO, ISRO, Guest of Honour Mr. Santosh Kumar Sinha, General
Manager, Indian Ordnance Factory Board, Ambernath and by the
expert jury members which includes Mrs. A Santhakumari, then
NGC Member of IWS. Mr. N Rajasekaran, Hon. Secretary (IWS),
Mr. V K Shirgaokar, Mr. Sanjay Kadam, Mr. Sandeep Ubhaykar, Mr.
S N Roy and host of members from Western Zone participated in
the event.
During the award night, IWS has been awarded in appreciation of
its outstanding performance and dedication towards the welding
community. Mr. D S Honavar has been honoured with Life Time
Achievement Award for his yeomen services for welding
technology in the
country. Mr. N
Rajasekaran was interviewed by the magazine and it was
published in the special issue of WeldFab Tech times.
The awards night also witnessed a glimpse of panel discussion
on a topic “What can be the initiatives to be taken up to uplift
the technical knowledge and overall development of SME &
MSME’s in Welding,”
FREE LECTURE PROGRAMMES
On 20th September 2019, Mr. N. Rajasekaran, Hon.
Secretary (IWS), delivered a lecture on “Career
Opportunities and Responsibility of Engineers in Social
Growth” at TRP Engineering College, Tiruchirappalli. 1100
students
from various
departments
of the college
attended the lecture and got benefitted. In his talk, he
briefed about ethics for engineers and the role of engineers
in enhancing the quality of life of people. He also
distributed prizes and certificates for the winners of
various competitions.
On 19th December 2019, IWS Coimbatore Centre conducted a free lecture programme on “Laser Metal
Deposition" by Dr Gopal Magadi, Principal Engineer, Cameron International Corporation, Houston, USA
in association with IEI, Coimbatore Local Centre, COEWT, PSGTECH and IIM, Coimbatore Chapter.
TWO DAY HANDS-ON TRAINING PROGRAMME ON “ADVANCED TIG AND MIG
WELDING PROCESS- EMPHASIS ON RESEARCH POSSIBILITIES” BY IWS –
NMAMIT STUDENT FORUM
From 9th April 2019 to 10th April 2019, The IWS - NMAMIT
Student Forum conducted a “Two day Hands-on Training
Programme on Advanced TIG and MIG Welding Process-
Emphasis on Research Possibilities” for students. The two
day free programme was conducted at the NMAMIT -
FRONIUS Center for Welding Technology (CWT).
Mr. S Gopinath, former president (IWS) inaugurated the
programme. Mr. S Singaravelu, Zonal Vice Chairperson of SZ and Dr G Ravichandran former NGC
member of IWS participated in the inauguration and delivered lectures in the programme.
“VOCATIONAL TRAINING ON SHIELDED
METAL ARC WELDING (SMAW)” FOR
RURAL STUDENTS BY IWS – NMAMIT
STUDENT FORUM
The IWS - NMAMIT Student Forum provided a Free
Vocational Training Programme on Shielded Metal Arc
Welding Process from 5th August 2019 to 30th August
2019 at the NMAMIT - FRONIUS Center for Welding
Technology (CWT). Rural students in and around Nitte,
Karnataka got benefitted by this programme.
“HANDS-ON WELDING DEMONSTRATION TO
THE STUDENTS OF ALVAS INSTITUTE OF ENGG.
& TECHNOLOGY (AIET)” BY IWS – NMAMIT
STUDENT FORUM
On 12th September 2019 and 16th September 2019, hands-on
welding demonstration was provided to the students of Alvas
Institute of Engg. & Technology (AIET) by the IWS - NMAMIT
Student Forum at the NMAMIT - FRONIUS Center for Welding
Technology (CWT).
Page 9 of 32
@ CENTRES AND ZONES
EVENING COURSE BY SZ
The Southern Zone of IWS conducted the week long
evening course on “Welding Technology for Fresh
Engineers”. The 55th course was conducted during 25-
11-2019 to 01-12-2019. In the one week course
sessions on Introduction to Welding Process, Shielded
Metal Arc Welding (SMAW), Gas Tungsten Arc
Welding (GTAW), Submerged Arc Welding (SAW),
Gas metal Arc Welding (GMAW), Mechanical Testing,
Basic Metallurgy & Heat Treatment, Welding of Carbon Steels, Welding of Alloy Steels and Stainless
Steels, Residual Stress & Distortion in Weldments, Welding Symbols, Magnetic Particle Inspection and
Ultrasonic Inspection, Liquid Penetrant Inspection and Radiography Inspection, Weld Defects, Causes
and Remedies, Welding Procedures and Welder Qualification as per ASME & AWS D.1 were conducted.
WAPCON 2019 @ COIMBATORE
“Innovation is the need of the hour for transforming
manufacturing sector in India through welding technology
development”, said Dr S Kartikeyan, Former Head Manufacturing
Services, L&T Valves, Coimbatore while inaugurating the National
Welding Conference WAPCON
2019 on 18th October 2019
organised by IWS Coimbatore
centre in associatioin with COEWT, PSGTECH, Coimbatore. He narrated
an example of identifying the low cost automation solution in an
agriculture equipment fabrication. He also released the proceedings of
WAPCON 2019 and Dr K Prakasan, Principal in Charge of PSG College of
Technology, received the first copy, during the inauguration.
The two day welding conference was organised to address the needs of developments in Welding
Processes, Power Source, Automation and Welding Consumables (WAPCON 19). 16 invited speakers
and welding experts from reputed organisations such as BHEL, Fronius India Ltd, Kemppi, DRDO, Messrs
Cutting Systems India Ltd, Centre of excellence in Welding Engg. and Technology, PSG College of
Technology,etc., shared their rich experience.
Dr K Prakasan, Principal in Charge, PSG College of Technology,
spoke about the formation of Centre of Excellence in Welding
about three years ago under financial support of Department of
Heavy Industry, Govt. of India under Make in India to develop
indigenous low cost welding automation, power source and
welding special electrodes during his presidential address.
While welcoming the gathering Mr. Venkat, Chariman, IWS
indicated it was a good start and informed that around 100 participants from all over the country were
participating. Dr. N. Murugan, former chairman of the centre & Convenor of WAPCON 2019 briefed the
background of organising the event to bring the best experts and ensure the dissemination of
knowledge and expertise on welding technology to participants from industry, R&D establishments
and academic Institutions . Dr. K. Asokkumar, NGC member of IWS & Addl. GM of CoEWT proposed the
vote of thanks.
IndiaWelds Synergy 2019 was held on 21st November, 2019 at LE Meridien
Gurgaon Delhi NCR. Indian Welding Society was the Technical Partner to the
event. This was a 1 day event that focussed on various methods of
enhancing the welding sector. This event brought together people from the
fabrication industry, academia, skill development institutions and other
welding solution providers to discuss the many aspects of welding that
needs focus. The theme of the event was “Creating Sustainable Welding
Excellence through Industry- Academia Synergy”.
Page 11 of 32
The event was graced by Mr. A. K. Tiwari, Principal Executive Director, Railway Board, Ministry of
Railways, who in his keynote address stated the importance of achieving sustainable welding
excellence. There were other members from the Railway
Board, IWS National Governing Council, NRDC who voiced
their opinion on welding excellence during the inaugural
session.
The technical sessions had topics ranging from ‘zero
defects’ in welding, Development of Sound Weld Joints,
Welding with
Responsibility,
Lean in Welding and Industry 4.0. These talks were given
by industry and academic experts giving a fresh perspective
on solutions. Speakers were from IIT Roorkee, RDSO, NTPC,
MECON, TATA Technologies etc.
Prof. Aravindan, Chairman, IWS, Northern Zone, presented
his talk on Advancements in Welding Technologies and also enumerated how IWS is working for
enhancement of welding sector through training programmes.
Mr. M. P. Jain, Former Chairman of IWS NZ and National Governing Council Member chaired a session
on Welding with Responsibility. He also chaired the
Valedictory Session. The day ended with a panel discussion on
Identifying Specific Interventions needed by both Academia
and Industry to boost Synergy between them! This had
panellists from Ministry of Railways, PSU, Academic
Institution, Skill Development Institute dwelling on discussion
on getting the academia industry connect.
With an audience of more than 120 delegates from more than 50 organisations like NTPC, MECON,
Railway Workshops, RDSO, RITES, IIT D, IIT R, DTU, AKG Skill Foundation etc., the sessions saw an active
participation from all quarters.
Besides, there were few displays of Virtual Welding Machines
(Lincoln and Fronius) for training, welding exhaust system
(Kemper), Welding Machines (Panasonic), Welding Robot
(KUKA) and Welding Defect Solution (Spatter Cure
Enterprises). The overall feedback of the event has been a
want of 2 day event next time on same lines which is very
encouraging for the organisers.
ONE DAY HANDS ON WORKSHOP ON “ADVANCED ARC WELDING PROCESSES” @
MANGALURU
A one day hands on workshop on Advanced Arc welding processes was conducted on 15th November
2019 by the IWS - NMAMIT Student Forum. The programme was organised for the 7th semester students
of NMAMIT, Nitte, Mangaluru at the NMAMIT - FRONIUS Center for Welding Technology (CWT). No
delegate fee was levied to the students.
ONE DAY WORKSHOP ON “DESIGN
CHALLENGES IN WELDING” @
MANGALURU
The IWS – NMAMIT Student Forum conducted
a one day workshop on “Design Challenges in
Welding” on 12th December 2019.
Dr G Ravichandran, former GM of WRI and
former NGC member of IWS was the faculty.
The workshop included hands on training at
the CWT.
WORKSHOP ON “SUSTAINABLE MANUFACTURING USING AUTOMATION AND ROBOTICS -
SMART” @ MANGALURU
On 30th December 2019, The IWS – NMAMIT Student Forum conducted a one day workshop on
“SUSTAINABLE MANUFACTURING USING AUTOMATION AND ROBOTICS - SMART” for the benefit of 2nd
PUC students, as a free programme.
SEMINAR ON “ADVANCES IN WELDING TECHNOLOGY” @ COIMBATORE
With the support of IWS Coimbatore Centre, the product launch function by COEWT, PSGTECH was
conducted in a grand manner on 12th December
2019.
Dr. AR Sihag, Secretary, Dept. of Heavy Industry,
Govt. of India inaugurated the product launch
function of the Centre of Excellence in Welding at
PSG College of Technology Coimbatore. In his
inauguraal address he stressed that we should
orient towards Global competitiveness instead of
developing on import substitution. This welding
Page 13 of 32
project is funded by Government of India along with
industrial partners to develop welding automation,
power source and consumables products . The function
was attended by more than 100 industry participants
representing ELGI, LMW, TVS motors, PRICOL, ROOTS
etc., including representatives from CODDISIA, SIEMA,
CII, IWS, ISNT & other professional bodies. The launch function was followed by a seminar where invited
speakers from WRI, MOU partners of CoEW and other experts in welding.
While welcoming the gathering Dr K Prakasan, Principal In-Charge, talked about the important aspects
on welding.
Dr R Rudramoorthy, Director, CARE, spoke on the success
of employability course on one year welding certificate
programme between PSG and BHEL for the past 10 years.
Speaking on initiation of the this project on centre of
excellence in welding project, he said that this project
cover three important areas namely welding
automation,welding power source and welding
consumable under Make in India program.
Mr Arun Renganathan, President, Si’Tarc, spoke on how Coimbatore
has become Manchester of India through textile industries. Major
revenues of Tamilnadu is coming from pump, textile and foundries in
Coimbatore and highlighted the establishment of Si’Tarc test facilities
to cater to the needs of the industries in Coimbatore.
Dr. K. Asokkumar, former Hon. Secretary (IWS) and AGM, COEWTproposed the vote of thanks.
WE APPEAL TO EVERY MEMBER TO ENROLL ONE MORE
LIFE MEMBER TO IWS.
TO DOWNLOAD APPLICATION FORM VISIT TO OUR WEB
SITES
www.iws.org.in www. iwsevents.com
LET US JOIN IN THE MOVEMENT AND STRENGTHEN IWS
EFFECT OF CHROMIUM AND NIOBIUM ON MICROSTRUCTURE AND
WEAR RESISTANCE OF HIGH CARBON HARDFACING ALLOYS
A. Hari Baskar*, Dr. R. Sivasankari**, Dr. J. Krishnamoorthi** & Dr. V. Balusamy**
*CoE- Welding Engineering and Technology, PSG College of Technology, India **Department of Metallurgical Engineering, PSG College of Technology, India
Abstract
Iron based hardfacing alloys are frequently employed in industries due to their good wear resistance
and low cost for extending the service life of components subjected to abrasive or metal to metal
wear conditions. Their exceptional wear resistance is primarily attributed to the formation of high
volume fraction of chromium carbides. In addition to chromium, other carbide forming elements
such as Nb, V, W and Ti were also added to improve the wear resistance. In the present work, an
attempt has been made to develop flux cored alloy steel wire with varying Cr and Nb content for
enhancing wear resistance and mechanical properties. For each hardfacing alloy, chemical
composition was determined and microstructure was studied using both optical and scanning
electron microscopy (SEM) with EDS analysis. Hardness and metal to metal wear test using Pin on
Disc tribometer were carried out for the weld deposits. The SEM and EDS results indicate that the
primary carbides M7C3 and Nb carbides were uniformly distributed in the matrix of austenite which
improves hardness and wear resistance. Hardness and Wear resistance of the hardfacing alloys
increased with addition of Cr and Nb, getting optimized at 25 wt% Cr and 4.6 wt% Nb.
Keywords: FCAW, M7C3 Carbide, niobium carbide, hardness, wear rate.
1.0 INTRODUCTION
Hard surfacing is the application of a durable surface layer to a base metal to impart properties
like resistance to metal-to-metal sliding with high contact stress, impact wear, abrasion, erosion
or pitting and corrosion or any combination of these factors [1]. The high-carbon high Cr-based
hard facing alloy is well known for its excellent resistance to abrasion, oxidation, and corrosion,
and has been extensively used in aggressive conditions, such as mining and mineral process,
cement production, pulp and paper manufacture industries. Many recent investigations have
revealed that the microstructure of Fe-Cr-C hard-facing alloy consists of Cr–Fe solid solution
phase (α-ferrite) and complex carbides (such as M23C6 and M7 C3), depending on the carbon
content of hard-facing alloy [2].
Fe-based hardfacing electrodes containing different combinations of chromium and carbon are
very commonly used in industries. It has revealed that the formation of microstructures
composed of α-ferrite and complex carbides, such as M3C, M7C3 and M23C6, depending on the
chemical concentration of alloy [3]. The good abrasive wear resistance of the weld depositions of
iron-based hardfacing alloys is predominantly attributed to the formation of hard M7C3 carbides.
However due to coarser, more brittle M7C3 chromium carbides tend to separate from the matrix
during the wear process, the application of these iron-based hardfacing alloys to parts exposed
to heavy external impacts is limited [4].
Page 15 of 32
In Fe-Cr-C hardfacing alloys, large amount of primary M7C3 carbides uniformly distributed in the
[α +M7 C3] eutectic colonies had the best performances (such as hardness and wear resistance)
[5]. In the wear process, the coarse M7C3 carbide plays an important role in the improvement of
the wear resistance of the alloy through the provision of a barrier against micro cutting and micro
ploughing. As the amount of M7C3 carbide increases, the wear resistance of the hardfacing alloy
is improved. The morphology of M7C3 carbides also plays an important role in wear resistance [6].
If the carbides are harder, finer, and more closely spaced than the original M7C3 carbides, and if
they possess a uniform distribution, the abrasives cannot effectively penetrate into the matrix
and the carbides cannot easily separate off from the matrix and in this way the abrasive wear
resistance of iron-based hardfacing alloys under heavy external impacts can be improved.
Therefore, many researchers have added strong carbide-forming elements such as W, V, Nb, and
Ti were added into the alloys to obtain MC-type carbides, which are finer and harder than M7C3
carbides. These efforts have led to limited improvement in the wear-resistance properties of iron-
based hardfacing alloys [7].
Iron-based alloys with niobium (Nb), titanium (Ti), molybdenum (Mo) in combination with boron
(B) and carbon have been selected as hardfacing alloys due to their high hardness and wear
resistance gained by the precipitation of different abrasion resistant hard phases [8]. In the
present investigation, the aim was to study the effect of chromium and niobium on
microstructure and wear properties of hardfacing alloys. So the carbide forming elements were
varied to achieve a hardfacing alloy having high volume percentage of carbides and a tough
matrix which improves hardness and wear properties.
2.0 EXPERIMENTAL DETAILS
FCAW hardfacing alloys were developed by varying chromium and niobium in the ranges HF 1- 20
wt% Cr, HF 2- 25 wt% Cr and HF 3- 25 wt% Cr with 4.5 wt% Nb. Five layers of developed alloys
were deposited on mild steel plate with the dimension of 50 x 50 x 20mm (Refer Figure 1.a). In
order to obtain the homogeneous specimen, welding parameters were maintained constant
(Refer Table 01). The chemical composition of the alloys was analyzed by BRUKER Optical
Emission Spectroscopy (OES). The metallographic and wear testing samples were machined from
hardfacing deposits using wire EDM (Refer Figure 1.b). Metallographic samples were then
grounded successively using belt grinder, emery papers, finally polished with diamond paste and
then etched with 4% Nital for 15 minutes. The microstructures were observed by Optical
microscope and Scanning electron microscope (SEM). The image analysis was carried out using
LAS phase expert for finding the volume percentage of carbides and matrix. EDS analysis was
carried out to confirm the type of primary carbides formed in the hardfacing alloys. Hardness
testing was carried out on the top surface of the alloys by QNESS micro hardness testing machine.
Wear testing was carried out for the developed alloys with a load of 3 kg and at a velocity of 2
m/s using pin-on-disc wear testing machine, and then wear tracks were observed by SEM.
3.0 RESULTS AND DISCUSSIONS
3.1 Chemical Composition Analysis
There was a slight deviation in aimed composition with composition of weld deposit measured
using OES, as result of variation in the recovery rate of the alloys added (Refer Table 2). For
reducing the cost of production of FCAW wire, high carbon ferro-chrome (Fe-Cr, containing 60-70
%wt of Cr), ferro-niobium (Fe-Nb, containing 60 wt% of Nb) were used instead of alloy powders.
The ferro alloys had a low recovery rate of 50-60% when compared with alloy powders. The
recovery rate of powders in the weld deposit also depends on heat input provided during
welding.
3.2 Microstructural Characterization
The optical and SEM micrographs of HF-1 alloy reveals the presence primary carbides in the form
of hexagon was uniformly distributed in the matrix of austenite (Refer Figure 2). These primary
carbides were identified as M7C3 type of carbides, rich in chromium, containing typically 56.56
wt% Cr, as revealed by EDS analysis (Refer figure 6). The volume percentage of primary carbides
present in the matrix of HF-1 alloy was estimated to be 45% by image analysis (Refer figure 5.a).
Optical and SEM micrographs of HF-2 alloy was similar to that of HF-1 alloy (Refer Figure 3), but
the volume percentage of primary carbides M7C3 had increased to 51% with addition of chromium
content because of its strong affinity towards formation of carbides (Refer Figure 5.b). Optical
and SEM micrographs reveals the presence of white regions as niobium carbides in addition to
M7C3 primary carbides in the matrix of HF-3 alloy (Refer Figure 4). Maximum volume percentage
of carbides was obtained for HF-3 alloy with 53%, as a result of formation of M7C3 primary
carbides and niobium carbides in the matrix (Refer Figure 5.c). The primary carbides were
identified as M7C3 type of carbides, containing typical composition of 56.56 wt% Cr and 6.44 wt%
C as inferred from liquidous projections for the Fe-Cr-C ternary system (Refer Figure 6) [2]. SEM-
EDS compositional map of HF-2 alloy reveals the presence of high volume percentage of
chromium being distributed in the primary carbides (Refer Figure 7)
3.3 Hardness Testing
There was a gradual raise in hardness with respect to addition of chromium and niobium as
carbide forming elements (Refer Figure 8). HF-1 alloy had a hardness of 62 HRC was lowest among
the developed hardfacing alloys. There was a slight rise in hardness of HF-2 alloy with 63 HRC, as
result of raise in volume percentage of primary carbides M7C3 due to addition chromium.
Maximum hardness was achieved for HF-3 alloy with 65 HRC, as result of high volume percentage
of M7C3 primary carbides and niobium carbides in the matrix.
3.4 Wear Testing
The wear testing results were in correlation with the hardness of the alloys, the wear resistance
increased with raise in hardness (Refer Table 3). Maximum wear rate was obtained for HF-1 alloy
with 0.0579 mg/m (Refer Figure 9). There was a slight reduction in wear rate of 0.0496 mg/m for
HF-2, as result of high volume percentage of primary carbides M7C3 when compared to HF-1 alloy.
Page 17 of 32
There was a drastic reduction in wear rate with 0.034 mg/m for HF-3 alloy, as result of high
volume percentage of niobium carbides in addition to M7C3 primary carbides. SEM micrograph of
the wear track reveals that the matrix was strong enough to hold the carbides intact and there
was a mild wear with fine scratches on the surface of the hardfacing alloy (Refer Figure 10).
Therefore, lowest wear rate was obtained for HF-3 alloy having highest volume percentage of
carbides.
CONCLUSION
The optical and SEM micrographs clearly reveals the presence of hexagonal structured
primary carbides M7C3 were uniformly distributed in the matrix of HF-1 and HF-2 alloys.
The white regions were recognized as niobium carbides in addition to M7C3 primary
carbides in HF-3 alloys.
Maximum hardness of 65 HRC was obtained for HF-3 alloy with highest volume percentage
of M7C3 primary carbides and niobium carbides.
Wear resistance was in correlation with hardness, lowest wear rate of 0.03 mg/m was
obtained for HF-3 alloy.
REFERENCES
[1] N. Yuksel, S. Sahin, Wear behavior-hardness-microstructure relation of Fe-Cr-C and Fe-Cr-C based hardfaing
alloys, Materials and Design, Vol.58, pp.491-99, 2014
[2] Chi-Ming Lin, Chia-Ming Chang, The effects of additive elements on the microstructure characteristics and mechanical
properties of Cr–Fe–C hard-facing alloys, Journal of Alloys and Compounds, Vol.498, pp.30-36, 2010.
[3] Xinhong Wang, Fang Han, Xuemei Liu, Microstructure and wear properties of the Fe–Ti–V–Mo–C hardfacing alloy, Wear,
Vol.265, pp. 583-589, 2008.
[4] Dashuang Liu, Renpei Liu, Effects of titanium additive on microstructure and wear performance of iron-based slag-free
self-shielded flux-cored wire, Surface & Coatings Technology, Vol.207, pp.579-586, 2012.
[5] S. Buytoz, Microstructural properties of M7C3 eutectic carbides in a Fe–Cr–C alloy, Mater. Lett. Vol.60, pp.605-608, 2006.
[6] S. R. Wang, L. H. Song, Y. Qiao and M. Wang, Effect of carbide orientation on impact-abrasive wear resistance of high-Cr
iron used in shot blast machine, Tribol. Lett., Vol.50, pp.439-448, 2013.
[7] V.E. Buchanan, D.G.Mccartney, P.H.Shipway, A comparison of the abrasive wear behavior of iron–chromium based
hardfaced coatings deposited by SMAW and electric arc spraying, Wear, Vol.264, pp.542-549, 2008.
[8] Azimi G, Shamanian, Effect of silicon content on the microstructure and properties of Fe–Cr–C hardfacing alloys, Journal
of Materials and Science. Vol.45, pp. 842-849, 2010.
Table 01 Welding parameters
Process parameter Constant value
Welding current, A 270-310
Arc Voltage, V 26-32
Electrode Polarity Positive
Welding speed, m min-1 2.6
Stick out, mm 20-25
Electrode angle to plate surface, ˚ 15
Table 02 Chemical composition of hardfacing alloys measured using OES
Table 03 Wear testing results of hardfacing alloys using Pin on Disk
a) Weld pad deposited by hardfacing alloys b) Machined samples by Wire EDM
Figure 1
Alloy No.
Chemical composition (wt. %)
C Si Mn P S Cr Ni Nb Fe
HF-1 4.05 0.77 0.44 0.06 0.11 21.85 0.14 0.03 Bal
HF-2 4.10 1.09 0.45 0.02 0.02 26.39 0.09 0.02 Bal
HF-3 4.12 1.19 0.43 0.04 0.04 24.32 0.11 4.6 Bal
Sample ID Initial weight
(g) Final weight
(g) Weight loss (g)
Wear rate (mg/m)
Hardness (HRC)
HF-1 21.7528 21.7339 0.0189 0.0579 62.18
HF-2 22.6965 22.6803 0.0162 0.0496 63.3
HF-3 24.6490 24.6379 0.0111 0.034 65.12
Page 19 of 32
M7 C3
MATRIX M7 C3
MATRIX
Figure 2 Optical and SEM micrographs of HF-1 alloys with M7C3 primary carbides
Figure 3 Optical and SEM micrographs of HF-2 alloys with M7C3 primary carbides
Figure 4 Optical and SEM micrographs of HF-3 alloys with M7C3 primary carbides and Nb
carbides
Figure 7 SEM-EDS Composition distribution mapping of HF-2 alloy
Figure 5 Image analysis using Phase expert a) HF-1, b) HF-2 and HF-3
Figure 6 SEM-EDS spot analysis of HF-2 alloy having M7C3 primary carbides
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
002
0
80
160
240
320
400
480
560
640
720
800
Counts
CK
aC
rLl
CrL
a
CrK
a
CrK
b
FeL
lF
eLa
FeK
esc
FeK
a
FeK
b
C K- 6.44 %
Cr K- 56.66 %
Fe K-36.89 %
Page 21 of 32
Figure 9 Wear Vs Time
Figure 10 SEM micrograph of wear scars formed in HF-2 alloy
Figure 8 Hardness results of developed hardfacing alloys
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9
WEA
R-µ
m
TIME-Minutes
WEAR Vs TIME
HF-1 HF-2 HF-3
60
61
62
63
64
65
66H
AR
DN
ESS,
HR
C
SAMPLE ID
HARDNESS TESTING
HF-1 HF-2 HF-3
M7 C3
Worn surface
ELECTROMAGNETIC ACOUSTIC TRANSDUCER PHASED ARRAY FOR
INSPECTION OF THIN AND THICK AUSTENITIC STAINLESS STEEL
WELDS
R. Dhayalan, Anish Kumar & C. K. Mukhopadhyay
Non Destructive Evaluation Division, Indira Gandhi Centre for Atomic Research,
Kalpakkam-603 102, Tamil nadu, Email: [email protected]
ABSTRACT
Non Destructive testing (NDT) of austenitic welds are important for nuclear vessels and components.
The strong material anisotropy and coarse grain size in the weld zone make these welds very difficult
to inspect using conventional ultrasonic techniques (UT) employed with piezoelectric transducers. It is
well known that the shear horizontal (SH) wave is very well suited for this inspection, and
electromagnetic acoustic transducers (EMAT) are the best for generating this wave mode. In order to
overcome the low efficiency sound generation due to low conductivity and strong attenuation in the
weld zone, an 8-channel EMAT phased array (PA) sensor has been used in a tandem mode to enhance
the power level and to improve the signal to noise ratio. It generates SH waves with almost uniform
amplitude for beam angles from 0 to 90˚ and can cover the entire volume of the weld including the heat
affected zone by scanning from one probe position. The large active apertures allow the use of highly
focused beams for good defect detection and high resolution imaging of weld defects. In this paper, the
EMAT PA probe has been used for detection of defects in thin and thick austenitic stainless steel
weldments at 600 kHz. It has been successfully demonstrated that the EMAT PA probe can detect 3 mm
deep notch and a side drilled hole in 28 mm and 30 mm thick weld pads. It is also used to generate SH
plate wave mode on a 3 mm thick plate and provided enough sensitivity to detect 10% deep notch from
both sides of the weld. Though the exciting frequency of the EMAT PA probe is very low, it offers good
defect sensitivity in thick and thin austenitic stainless steel weldments.
Keywords: Electromagnetic acoustic transducer, Shear horizontal wave, Phased array, Plate wave,
Austenitic stainless steel weld
1.0 INTRODUCTION
Electromagnetic acoustic transducers (EMATs) are now being widely investigated for non-contact
non destructive testing (NDT) of solid materials. This type of transducer can generate or detect
ultrasound in electrically conductive or magnetic materials through the Lorentz force principle or
magneto-elastic effects [1-4]. The main advantage of EMAT over conventional piezoelectric
transducer (PZT) is that it does not need any couplant and can eliminate the inconsistency arising
from the couplant use during the inspection. It permits making acoustic and ultrasonic
measurements at elevated temperatures, in corrosive and other hostile environments [5-7]. This
type of transducer can easily fabricate and quite compatible than the other transducers. The two
primary components of an EMAT are a coil that is fed by a very large alternating current pulse,
and a magnet designed to induce a strong static magnetic flux within the skin depth of the test
specimen directly below the EMAT. The pulsed alternating current fed to the coil induces eddy
currents (je) within the skin depth of the test piece. In the presence of a large bias magnetic flux
(BS); these eddy currents lead to body forces (FL) at the surface layer of the specimen,
Page 23 of 32
L e sF = j × B
(1)
The Lorentz forces (FL) on the eddy currents are transmitted to the solid by collisions with the
lattice. These forces on the solid are alternating at the frequency on the driving current and act
as a source of ultrasonic waves [8]. So, the generation of ultrasonic wave is provided by coupling
between the electromagnetic field and the elastic field in the surface skin. Figure 1 shows the
schematic of a single coil and magnet leading to the generation of Lorentz force for EMAT. The
type of wave mode generation depends upon the coil geometry, the operating frequency and the
applied magnetic field. It can generate any specific ultrasonic mode including normal beam and
angle-beam shear waves, Rayleigh waves, and plate waves [9-11].
Austenitic stainless steel is widely used in the nuclear industry due to its superior resistance to
corrosion. There are many types of austenitic stainless steel weld joints in the nuclear structures
and the most common are stainless to stainless steel, dissimilar metal weld between stainless to
regular and 300 series stainless to Inconel. Conventional ultrasonic testing (UT) of austenitic
welds is very difficult because of the metallurgy of the material; grains are elongated and large
compared to those found in ferritic steel, resulting a large degree of acoustic anisotropy, beam
distortion, and scattering [12, 13]. Moreover, these elongated grains are often organized in
columnar structure near welds, which can result in the elastic waves being skewed in an
unexpected direction. Shear vertical (SV) wave commonly used in UT suffers most from the skew
effect due to anisotropy of austenitic crystal structures. Longitudinal (L) waves skew significantly
less than SV on austenitic weld, but still, experience strong mode conversion at structural and
weld boundaries and require access to both sides of the weld. Early research in 1980’s showed
that the shear horizontal (SH) wave doesn’t present mode conversion at structure boundaries
and has a much smaller skew effect compared to L and SV waves. Figure 2(a) shows the amount
of beam skew expected for L, SV and SH waves and Figure 2(b) shows an austenitic weld model
with different ultrasonic beam pattern [14-16]. As a result, the SH wave has been recognized as
potentially the best solution for the inspection of these welds.
Notwithstanding this, shear energy does not propagate through liquid couplants and the
horizontal polarization cannot be easily excited through mode conversion with a wedge, so it is
very difficult to generate with PZT and it is impractical in field use. EMAT on the other hand is an
effective alternative to generate SH waves in ultrasonic testing. Although EMAT excitation of SH
waves can be very efficient in many engineering materials such as steel, aluminum and copper,
whereas in austenitic stainless steel remains challenging. Because, it has very low conductivity
and low or no magnetism which affect the ability to generate eddy currents, hence sound, with
EMAT. Compared to other non-ferromagnetic materials, austenitic stainless steel is 10-15 times
more resistive with proportional effects on signal-to-noise (SNR).
In the past, a number of different weld inspection schemes using SH wave EMATs have been
proposed [17-19]. In the majority of cases, such schemes relied upon the periodic-permanent-
magnet (PPM) EMAT configuration and other transducer configurations have also been proposed
[20, 21]. The main disadvantages of these types of SH wave EMATs are low transduction
efficiencies, narrow beam angle for single frequency and poor SNR. In order to overcome these
complexities, an 8-channel EMAT phased array (PA) sensor with a high power tones bust
generator and signal amplifiers have been used to enhance the power level for improving the
signal strength and SNR. Since the EMAT PA sensor has been designed in tandem mode and
radiates SH wave with almost equal amplitude from 0 to 90˚. So it can able to cover the entire
volume of the weld including heat affected zone (HAZ) by scanning from one sensor position. In
this paper, the PA EMAT sensor has been utilized for detection of defects in 3 different thick
austenitic stainless steel weldments at 600 kHz. In addition, the PA sensor has also been used to
generate the fundamental SH0 plate wave mode for detection of defects in a 3 mm thick
austenitic stainless steel weld sample. Further, it provides enough sensitivity to detect 10% deep
defects irrespective of the thickness of the weld sample.
2.0 SH WAVE EMAT PA PROBE
In recent years, systems with PA technology have been widely used for inspection of welds to
achieve better sensitivity and resolution. These systems typically employ PA probes in the
frequency range from 1 to 5 MHz and utilize 16 or more elements (piezoelectric crystals) to steer
beam within the base material for weld inspection. In most of the conventional PA probes, L or
SV wave modes have been used for inspection of ferritic steel welds. For the reasons explained
in the previous section, these types of high frequency conventional PA has inherent limitations
for austenitic stainless steel weld inspection. To overcome the metallurgical issues, the operating
frequency of the probe needs to be lowered (less than 1 MHz) to reduce scatter and attenuation,
and by using SH waves the beam skewing can be reduced significantly. Given the advantages
associated with SH waves, the concept of PA functionality is replicated with EMATs for SH wave
EMAT PA probe. In this probe, a series of coils and a set of magnets are arranged like an array in
analogous form to the small piezoelectric crystals that are arranged together in a conventional
PA probe. An 8-channel SH wave EMAT PA probe (M/s. Innerspec Technologies, Spain) is used for
this work which is developed by using flexible meander RF coils and permanent magnet arrays.
Figures 3(a) and 3(b) show the photograph and the pitch-catch tandem arrangement of the 8
channel SH wave EMAT PA probe. Figure 3(c) shows the schematic of the principle of SH wave
EMAT transmitter with meander coil and permanent magnet array. The flexible coils and magnet
arrays permit complying from flat to any curved specimen surfaces.
In this EMAT PA probe, the transmitters and receivers are arranged in a pitch-catch tandem mode
in the same housing. The eight transmitters are excited with independent time delays so the
wavefronts constructively interfere with each other around the focal spot to achieve a wave field
of strong intensity. The reflected signals from the focal region arrive at each element at a different
time, and it is delayed according to focal laws so the signal from the focal region sums up in phase.
As a result, the SH wave can be steered across a predefined range. Without the effect of mode
conversion, SH waves can be focused at any range of angle and can be used for both zero degree,
Page 25 of 32
and angle beam steering. The magnet array determines the wavelength (channel pitch) which is
about 3.2 mm. Figure 3 (d) shows the frequency response of the EMAT PA probe in which the
peak or optimum frequency is 600 kHz and it is recommended to operate within 500 to 700 kHz.
The active area or footprint of the probe is about 58 mm length and 45 mm width. The larger
aperture can also provide improved sensitivity and focused inspection of thick components.
3.0 EXPERIMENTAL DETAILS
In order to excite the 8-channel SH wave EMAT PA probe, an eight channel high power tone burst
system temate® Power Box-8 (M/s. Innerspec Technologies, Spain) was used along with signal
conditioning box to compensate the impedance mismatch between the system and PA probe. It
can provide power level up to 20 kW or 2000 Vpp of peak power per channel at 1% duty cycle for
frequency from 100 kHz to 7 MHz. Figures 4(a) and 4(b) show the photograph and schematic of
the experimental set-up used for inspection of thin and thick welds. The SH wave EMAT PA probe
was connected to the high power system through high power cables. This system was controlled
through an external PC over an Ethernet connection. The input parameters were fed through the
computer for the pulsing signal including tone-burst frequency of 600 kHz. After receiving the
input, a low-voltage pulse train was generated and subsequently amplified to high-voltage that
was fed through the signal conditioning box to the transmitter. With the high-voltage excitation,
SH wave with wide beam profile was generated into the material. The reflected waves were
received and converted into electrical signals by the receiver. These signals were amplified and
filtered by the signal conditioning box and sent to the system for further amplification and
treatment. Finally, the signals were digitized and sent to the PC for further processing if needed
for display and storage.
The EMAT PA system is mainly used for the inspection of weld joints in main and safety vessels
of fast breeder reactor (FBR). Due to the complex structure of the vessels, there are different
types of weld geometries developed by various techniques, materials and welding parameters.
Based on the weld geometry, the scan plan for inspection was configured with the EMAT PA
system. The input parameters like the selection of probe frequency, gain setting, and scanning
pattern were configured in the system. The PA probe was excited with 3 cycles square modulated
sine wave tone burst signals at 600 kHz. With proper selection of material thickness, SH wave
velocity, and probe delay the calculation of focal law depth, sound path, surface distance were
completed automatically. The sector scan representation of angle from 0 to 90˚ was selected with
1˚ angle increment. On the receiver side, a 32 dB gain was used to amplify the received signals.
The generated SH waves were allowed to make 3 full skips (more than 3 legs/zoom) so that to
cover the entire volume of the weld including the heat affected zones (HAZ) on both sides of the
weld. The inspection procedure was validated by using three sets of the mock-up weld samples
as shown in Figures 5 (a) - 5(c). All the three mock-up samples were made by using austenitic
stainless steel type 316 LN. For the first mock-up sample shown in Figure 5(a), three plates were
joined together by double V weld configuration and the size of the plate sample was 500 x500x
28 mm. In this weld plate, 12 thermal fatigue type defects (artificial notches) of the same length
(25 mm), width (25 mm) and varying depths were made parallel and perpendicular to the weld
orientations. The depth of the notches as a percentage of thickness was 10%, 20%, and 30%
respectively. For the second mock-up sample shown in Figure 5 (b), a 30 mm plate was welded
with 25 mm plate with K- type weld configuration in which 6 artificial notches of the same length
(25 mm), width (25 mm) and varying depths were made parallel and perpendicular to the weld
orientations. The depth of the notches as a percentage of thickness (25 mm) was 10%, 20%, and
30% respectively. A side drilled hole (SDH) of 2.5 mm diameter and 25 mm length was made on
the side of the weld plate at 20 mm depth. The notches were made on both the weld and HAZ.
For the last mock-up sample shown in Figure 5(c), two thin plates of 3 mm thickness were welded
and two notches of ~20% (0.5 mm) and ~30% (1 mm) plate thickness (WT) were made on both
sides of the HAZ. For all the mock-up samples, the inspection procedure was to scan the PA probe
along the weld path, pausing at regular intervals for data acquisition.
4.0 RESULTS AND DISCUSSION
As mentioned earlier, the EMAT PA probe generates SH wave with uniform amplitude for a wide
beam angle from 0 to 90˚. In order to verify the radiation pattern of the SH waves, a semicircular
solid block of 120 mm length with 100 mm diameter was used. It was made by the same material
on which the EMAT PA probe was kept exactly at the center of the flat surface and by facing to
the curvature as shown in Figure 6(a). It was determined to generate the waves directly towards
the curvature of the block and reflect back to the EMAT PA probe. Figure 6(b) shows the sector
scan image of SH waves reflected from the curvature of the solid block. From the sector scan, it
was observed that the reflected energy or amplitude of the SH wave was almost same at all the
angles. The A-scan signal shown on the left side of the sector scan was corresponding to the wave
at zero degree and the initial random signals were the EM noise within the EMAT probe. From
Figure 6, it was confirmed that the EMAT PA probe generates SH waves at all angles, and it can
cover the entire volume of the weld including HAZ. Also, it is possible to identify the location of
the defects from the sector scans images.
For all the mock-up weld samples, the scanning was performed on both surfaces by using the
EMAT PA probe. Figure 7 shows the schematic diagram of the test set-up and the typical sector
scan images obtained from the weld sample shown in Figure 5(a). In the schematic diagram, the
defects are shown on the same axis but in actual all of them were well separated about 50 mm
laterally. The reflected energies for all the defects are highlighted as red color dotted circles and
the corresponding angle represent the locations of the defects (notches and SDH). The reflected
signals at 0˚ represent the multiple reflections from the base material (HAZ). The reflected signals
at ~20˚, ~60˚ and 90˚are corresponding to the bottom notch (10% WT), SDH at the middle of the
sample and the surface notch (20% WT) respectively. It was interfered that the intensity of the
reflected wave for the larger defect shows maximum amplitude or intensity as compared to the
other defects. It has also been seen that the reflected signal from the SDH was slightly scattered
compared to other defects. Figure 8 shows the schematic diagram and the test results obtained
Page 27 of 32
with the second weld sample shown in Figure 5(b). Though mockup sample was made with more
number of notches with different sizes and orientations, the sector scan images of selective
notches are shown in Figure 8. Since the sample was made with two different thick plates and
the probe was kept at the tapered portion, the multiple reflections from the base material were
slightly inclined with respect the normal. The reflected energies from all the defects were
highlighted and the corresponding locations were predicted from the beam angles. It has been
observed that the intensity of the reflected wave for the larger defect shows maximum intensity
similar to the first sample. The reflected energy from the surface notch was very less since it was
made perpendicular to the weld path. The reflected signal for the SDH was highly scattered when
compared to the previous sample because it was accessed about 20 mm height from the top
surface. Therefore, the reflection amplitude was also affected by the location and orientation of
the defect.
In general, the SH wave EMAT generates plate (guided) wave mode efficiently in thin plates
having the thickness of the order of wavelength [22]. This type of EMAT generates the
fundamental SH0 mode in thin austenitic stainless steel plate at low frequency. Since the SH0
wave is non-dispersive, it is an effective wave mode for inspection of welds in thin plate like
structures [23]. Figures 9(a) and 9(b) show the phase and group velocity dispersion curves for 3
mm thick austenitic stainless steel plate. It has been observed that the velocity of SH0 mode
remains constant (non-dispersive) irrespective of the exciting frequency. This mode was excited
with linear excitation by the EMAT PA probe on the thin mock-up weld plate sample shown in
Figure 5(c). The scanning of the weld was performed manually as shown in Figure 10(a) and the
C-scan image of the weld sample is shown in Figure 10 (b). The indications of thermal fatigue type
notches are highlighted as red color dotted circles. Since the 30% WT defect was on the opposite
side of the HAZ, the reflected signal traveled a longer distance. In order to check the detection
capability of the SH0 mode, the scanning was performed from the bottom surface of the plate
and obtained the same results as shown in Figure 10(b).
From all the test results, it was inferred that the amplitude of the defect signal varies due to the
defect geometry and orientation, but all the defects could be reproduced with measurable
indications on both sides of the welds. Inspection from one side of the weld is highly desirable
when access to the other side is difficult or impossible. In such cases, multiple angle inspection
accompanied with probe scan perpendicular to the weld shall be sufficient for the entire volume
of the weld including HAZ. Although the exciting frequency of the EMAT PA probe is very low, it
provides enough sensitivity to detect defects down to 10% WT from both sides of the weld.
CONCLUSIONS
This paper has reported on test results of thick and thin austenitic stainless steel weld inspection
using an eight channel SH wave EMAT PA probe. The pitch-catch tandem arrangement of the
EMAT PA probe provides enhanced power levels with superior SNR compared to conventional
ultrasonic transducers. It has been verified that the EMAT PA probe radiates SH wave with almost
equal amplitude from 0 to 90˚and it provides the entire volume coverage of the weld including
HAZ from one probe position. It has also been observed that the EMAT probe generates SH wave
with maximum amplitude at 600 kHz. At this optimum frequency, it has been utilized for
detection of artificial defects in thick and thin weld mock-up samples and confirmed that the
probe is capable of detecting defects as small as 10% WT of thick weld joints. It has also been
shown that the EMAT PA probe generates SH plate waves very efficiently in thin plates and
demonstrated for defect detection in thin weld. The capability of detecting defects from one side
of the weld confirms the possibility of using this probe in situations where there is only one side
accessibility.
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Figure 1 Lorentz Force Mechanism
Figure 2 (a) Relationship between skew angle and incident angle with respect to columnar direction
(b), (c) and (d) modeling of different ultrasonic beam profiles in an austenitic weld
Figure 3 (a) 8-channel SH wave EMAT PA probe (b) pitch-catch arrangement for beam focusing
(c) Schematic of SH wave EMAT with meander coil and magnet array and d) Frequency response of SH wave EMAT PA probe
Figure 4 (a) Photograph (b) schematic of the experimental set-up
Figure 5 Mock-up weld plate samples with artificial defects for EMAT PA inspection.
Page 31 of 32
Figure 6 (a) Photograph of the semi-circular block with EMAT PA probe arrangement and (b) sector scan image of SH waves obtained with the same set-up.
Figure 7 Schematic diagram of the test set-up and sector scan images obtained on first mock-up sample with defects on both sides of the weld.
Figure 8 Schematic diagram of the test set-up and sector scan images obtained on second mock-up sample with defects on both sides of the weld.
(a) Phase velocity (b) group velocity
Figure 9 SH wave dispersion curves for 3 mm thick stainless steel plate
Figure 10 (a) Photograph of the test plate showing the scanning direction and defects, and (b) C-scan image
obtained with the test plate
Mumbai, India