Report on Non-destructive techniques, consists of basically two techniques, Remote Field testing and Internal Rotary Inspection System.

1. Presentation Report
On
Tubular Non Destructive Techniques
Amity School of Engineering & Technology
Submitted by: Submitted to:
Abhishek Thakur Dr Ravi Prakash
Akshay Mistri HOI, ASET
Sarthak Anand

2. CONTENTS
Acknowledgement………………………………………………………………...01
Abstract……………………………………………………………………………02
Introduction
 Remote field testing (RFT).………………………………..03
 Internal rotary inspection system (IRIS)…………………...03
Theory of Operation & Principle
 RFT………………………………………………………....04-06
 Signal Interpretation (RFT)………………………………...06-07
 IRIS………………………………………………………...07-08
 Result Interpretation (IRIS)………………………………...08-09
Benefits and Limitations
 RFT…………………………………………………………10
 IRIS…………………………………………………………10
References………………………………………………………………………….11

3. ACKNOWLEDGEMENT
I wish to express my sincere gratitude to Amity University and Amity School of Engineering
and Technology for giving me this great opportunity of learning. I truly admire this opportunity
to get in depth knowledge of the Non-Destructive Techniques subject. It helped me a lot. I truly
thank Dr Ravi Prakash, my faculty guide, who was more than a teacher. He provided his
valuable guidance and support. He is a great help and support throughout and a constant
guidance. He provided great guidance and knowledge and corrected my mistakes every time I
made one. Finally I would like to thank my friends for their understanding and support. Without
the help of the above mentioned people, I would have faced many difficulties.
Abhishek Thakur
Akshay Mistri
Sarthak Anand

4. ABSTRACT
Someone has rightly said that practical experience is far better and closer to the real world than
mere theoretical exposure. The practical experience helps the student to view the real world
closely, which in turn widely influences his/her perceptions and understanding of the real
situation.
Tubular Non Destructive Techniques, as the name suggests, is used to test tubes/pipes without
any kind of destruction. In this report, there are two tubular NDT techniques are discussed.
These two are Remote Field Testing (RFT) and Internal Rotary Inspection System (IRIS).
Remote Field Testing uses Electromagnetic induction to detect cracks in pipes/tubes. This
technique is limited to ferromagnetic materials.
The Internal Rotary Inspection system uses ultrasonic waves for detection of pitting, corrosion
and wall thickness in pipes. The advantage of this system is that it can be used for both
ferromagnetic as well as non-ferromagnetic materials.
Operation principle, equipments, theory of operation, result interpretation of both the
techniques is discussed in detail in this report.

5. Introduction
𝐑𝐞𝐦𝐨𝐭𝐞 𝐅𝐢𝐞𝐥𝐝 𝐓𝐞𝐬𝐭𝐢𝐧𝐠[𝟏]
: It is an electromagnetic method used to detect defects in steel
pipes and tubes. A probe pushed in the tube to be tested, can detect inner and outer defects with
equal sensitivity. Basically the probe consists of an exciter coil which generates magnetic field
and a receiving coil which generates current due electromagnetic induction. As the probe is
moved, the changing magnetic field generates current in pipe/tube. Also, since the receiver coil
is moving with the probe it cuts the magnetic field lines generated by the current in the pipe
wall. The receiving/detector coil is placed two to three pipe diameters away from the exciter
coil. At places where there is metal loss, the field arrives at the detector with less travel time
(greater phase) and with greater amplitude due to reduced path through the pipe wall.
Fig.1 A RFT probe inserted in a tube.
𝐈𝐧𝐭𝐞𝐫𝐧𝐚𝐥 𝐑𝐨𝐭𝐚𝐫𝐲 𝐈𝐧𝐬𝐩𝐞𝐜𝐭𝐢𝐨𝐧 𝐒𝐲𝐬𝐭𝐞𝐦[𝟐]
: It is an ultrasonic method for non-destructive
testing of pipes and tubes. The IRIS probe is inserted into the tube flooded with water and is
slowly pulled out. As it is being pulled data is recorded and displayed on the user interface. It
is normally not used for crack detection and is insensitive to cracks that are parallel to the
longitudinal axis of the tube. It is used for detection of pitting, corrosion and wall thickness.
Fig 2. An IRIS probe inside a tube flooded with water

6. Theory of Operation and Principle
Remote Field Testing: A probe as already explained is pulled through the tube. The exciter
coil is provided with a low frequency AC current. This produces a changing magnetic field
which produces magnetic field axially and radially. Due to this an eddy current is produced in
the tube surface which extends axially in the tube. This eddy current produces a secondary
magnetic field of its own which is less powerful than the field of exciter coil (primary field)
but is more spread out than the primary field. The receiving coil is placed at a distance where
the eddy current field becomes more powerful than the primary field. This can be seen from
the figure below.
Fig 3. Primary and Secondary magnetic fields
As the magnetic field due to eddy current is also changing, a voltage (EMF) is generated in
the receiving coil due to electromagnetic induction. By monitoring this induced voltage we
can detect changes in the specimen. As can be seen from the figure below, the magnetic
intensity at a point of defect seems to increase.
Fig 4. Magnetic field lines at a point of defect
Exciter coil

7. As can be seen above this method works on the principle of electromagnetic induction.
According to different magnetic field intensities area near the probe are divided into different
zones which are explained below[𝟑]
.
Fig 5. Field zones near a RFT probe
o Direct coupling zone: It is the zone where the alternating magnetic field from
exciter coil produces eddy currents in the tube wall. Due to high varying fields
this zone is of very less importance in the test.
o Transition zone: This zone lies just outside the direct coupling zone. Here
occurs a great interaction between the magnetic fields of the exciter coil and of
the eddy currents. The overall field intensity is drawn by green coloured line in
the graph. It can be seen that the field is strongest at the inner diameter of tube
and changes abruptly in the transition zone marked in the tube.
Fig 6. Field strength and Phase at various tube diameters

8. Also, by blue coloured line, where it abruptly changes in the transition zone
shows the region where the field from the eddy currents dominate over the field
of the exciter coil.
o Remote field zone: It is the zone where the direct coupling/interaction between
the exciter coil and the receiving coil is negligible. Coupling takes place
indirectly through the field generated by the eddy currents. This region is
generally two tube diameters away from the exciter coil. The amplitude of field
strength on outer diameter exceeds the strength at inner diameter at 1.65 tube
diameters approximately. Therefore, RFT is sensitive to inner defects as well as
outer defects.
Signal interpretation
The output of the probe i.e. the output voltage of receiving coil is given to an amplifier which
amplifies the output to a readable value because it comes out in microvolt range.
When all conditions are proper (no defect) then the phase of receiving coil’s voltage w.r.t phase
of exciter coil voltage is directly proportional to the sum of wall thickness at that location[𝟒]
.
Thus any change in wall thickness will result in phase and amplitude changes which can be
detected. This change can indicate corrosion, pitting or changes in wall thickness.
Fig 7. Resultant image when defect is wear scar

9. Fig 8. Resultant Image when defect is a hole
Internal Rotary Inspection System: As already discussed, it is an ultrasonic immersion pulse
echo technique to detect pitting and wall thinning in tubes. The probe of IRIS contains an
ultrasonic transducer which converts electronic energy into mechanical energy (in form of
sound waves). The frequency of the sonic waves generated by the transducer ranges from 100
kHz to 50 MHz depending upon the type of test needed[𝟓]
. This sound beam is directed by the
transducer towards a mirror inclined at 45° with the tube axis. Due to this the waves strike
perpendicularly on the tube’s inner surface. Part of this beam is reflected back by inner surface
and part is transmitted through tube wall and reflected by the outer diameter of the tube.
Fig 9. IRIS probe inside a tube under test
Ultrasonic
Transducer
Probe (Body)
Mirror
Water

10. The time difference between the two reflected beams is used to measure the wall thickness. For
measurement of complete inner surface of the tube, the mirror is mounted on a water turbine
that rotates at a speed of 2000 RPM[𝟔]
. As the probe is slowly pulled out (2.5 to 4 cm/sec)
measurements of full tube length can be made. Since the beam makes a spiral movement, for
complete coverage the probe has to be pulled slowly. On an average there are 150 reading per
revolution and 2400 revolutions per minute. Each pulse is marked on a horizontal scan line on
the user interface screen as shown in Fig 9.
Result Interpretation
With the help of modern interfaces, we can see the real time images of the tubes and the
flaws can be pointed out in real time. There are 3 different views of the tube obtained on the
user screen. These views are usually called as:
 B Scan
 C Scan
 D Scan
are shown below.
Fig 10. 3 different views at desired section of tube

11. The C scan shows the plan view of the tube when it is being rolled out flat. Colour coding is
used to display the wall thickness at different locations of the tube. Different softwares use
different colour coding which can be better understood from the Fig 11 given below. The red
color spot shows metal loss at that point.
Fig 11. An IRIS viewer with colour coding
The B scan provides the 2D transverse view of the tube at any location along the tube length.
While the D scan provides the 2D longitudinal view of the tube length at any desired
circumferential location on tube.

12. Benefits and Limitations
Remote field testing
Benefits:
o Most suitable for ferromagnetic tubes used in boilers and heat
exchangers.
o Equally sensitive to internal and external flaws.
o Can inspect tube with 75 mm outer diameter and 5 mm thickness.
o Relatively insensitive to probe lift-off and wobble.
o Fast probe pulling speeds ranging between 6 to 12 inches/sec.
o The size of probe w.r.t the inner diameter is not so critical (fill factor).
Limitations:
o Not good in detecting gradual metal loss.
o Pits smaller than 6% of tube cross section cannot be detected.
o Examination of tubes with big diameters cannot be done.
o Examination of finned tubes has lot limitations.
Internal Rotary Inspection System
Benefits:
o Both ferromagnetic as well as non-ferromagnetic tubes can be tested.
o Provides very accurate readings of wall thickness. With 15 MHz
transducer frequency, accuracy of 0.1mm can be obtained.
o Can detect and size corrosion, pitting and gradual metal loss.
o It provides a 3D image of defect, providing its profile and depth.
o As image is provided, result interpretation is much easier in this
method.
Limitations:
o It is a slow technique, since the probe is pulled slowly. Only 80 to 90
tubes can be checked in a 12 hour shift.
o For successful test, the tube needs to be cleaned properly as compared
to other techniques.

13. o The tube is required to be filled with water for testing. This is not
possible in all cases.
o The probe must be centralized in the tube for accurate results.
References
1. Wikipedia, (2013) Remote field testing
http://en.wikipedia.org/wiki/Remote_field_testing [accessed 03/08/2014]
2. Wikipedia, (2013) Internal rotary inspection system
http://en.wikipedia.org/wiki/Internal_rotary_inspection_system [accessed 03/08/2014]
3. Anastos, J (2001) RFT Theory of operation
https://www.nde-
ed.org/EducationResources/CommunityCollege/Other%20Methods/RFT/RFT_Theor
y.htm [accessed 05/08/2014]
4. Anastos, J (2001) RFT Signal Interpretation
https://www.nde-
ed.org/EducationResources/CommunityCollege/Other%20Methods/RFT/RFT_Signal
s.htm [accessed 05/08/2014]
5. Olympus NDT, (2006) Design Characteristics of Transducers
https://www.olympus-ims.com/data/File/panametrics/UT-technotes.en.pdf [accessed
14/08/2014]
6. Innospection Ltd., (2008) Internal Rotary Inspection systems (IRIS)
http://www.innospection.com/pdfs/IRIS.pdf [accessed 15/08/2014]