FIELD OF THE INVENTION
The present invention relates to a method for non destructive inspection of rolls for hot and
cold rolling of steel strips/coils. More particularly, the present invention is directed to
providing a method of non destructive inspection of surface defects of rolls of Hot Strip Mill
and Cold Rolling Mill in Steel Plant involving portable Ultrasonic and Eddy Current Flaw
Detectors wherein probes are used with selective frequencies for locating flaws and flaw
detectors are duly calibrated on reference block of known defects, setting of the flaw
detector is adjusted so as to filter the defect signal from the noise signal and analyse the
signals to understand the presence or absence of defects with reference to the calibration
data and decide upon the stock removal accordingly, resulting in substantial reduction in roll
consumption and avoiding production delays leading to considerable financial saving.
BACKGROUND OF THE INVENTION
The rolls for hot and cold rolling of steel strips and coils are subjected to complex
mechanical and thermal stresses and severe wear. This leads to generation of fire-cracks
and fatigue cracks on the surface and sub-surface regions of the rolls. These service
induced defects, if not removed completely during intermittent grinding, lead to catastrophic
failures of rolls during the subsequent service campaign resulting in increased roll
consumption and production delays.
Because of the complex stresses present on the surface and sub-surface regions on the roll
body in all the circumferential, tangential and radial directions, the service induced defects
are oriented in all these directions and also in randomly oriented direction. These defects
(fire-cracks and fatigue cracks) are of varying length and width and are present in the form
of continuous and/or non-continuous networks. None of the non destructive methods alone
is capable of detecting all these defects accurately and therefore roll inspection has been
confined to Liquid Penetrant Inspection or Dye Penetrant Inspection (LPI or DPI). Ultrasonic
inspection of rolls too has been confined to detecting manufacturing defects beyond a
certain acceptable sizes as acceptance criteria for the new rolls. However, due to non
reliabilities of test results and also due to being non productive processes, these techniques
are seldom used in roll shops.

With the developments in the area of electronics, more capable ultrasonic and other
electromagnetic generators and sensors have been designed in recent times. Combining the
capabilities of these newly developed electronic devices with more intelligent computing
devices, customized/proprietary automated state-of-the-art roll inspection systems have
been developed that are mainly integrated with the roll grinding machines. Although these
devices allow roll inspection at a much faster pace, they are not getting widely used due to
cost disadvantage.
There has been therefore a need in the related art to develop a cost effective, reliable and
faster method for inspection and detection of the nature of flaws present in the rolls to
rectify defects by machining/grinding prior to a new roll campaign. Since the rolls are one of
the costliest components in hot and cold rolling mills engaged in rolling steel strips and
coils, the prevention of in-service roll failures would not only result in saving towards costly
roll materials but also towards the associated mill delays that adversely affects the mill
productivity.
The present innovation thus provides a method for non destructive inspection of rolls for hot
and cold rolling which is based on taking advantages of the developments in the area of
ultrasonic and eddy current (electromagnetic) testing devices and developing a process that
meets the requirements of detecting the complex nature of defects on rolls.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill in Steel Plant
involving portable Ultrasonic and Eddy Current Flaw Detectors duly calibrated on reference
block of known defects.
A further object of the present invention is directed to a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill which is capable of
determining accurately the location of fire-cracks and fatigue cracks on the surface and sub-
surface regions of the rolls.
A further object of the present invention is directed to a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill wherein the type

and number of probes for flaw detectors and their frequencies are selected to enable
detection of surface defects of varying width and surface depth.
A still further object of the present invention is directed to a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill wherein flaw
detectors are calibrated to precisely detect the defects and analyze the defect signals to
decide upon requirement of the stock removal from rolls.
A still further object of the present invention is directed to a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill wherein
movement of the probe and the rotational speed of the roll are synchronized in a manner so
as to cover the full volume of the roll.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a method of non-destructive
inspection of rolls for hot and/or cold rolling of steel strips/coils comprising:
involving a combination of ultrasonic and eddy current probes
selecting the type and range of ultrasonic and eddy current probes adapted to detect
service induced roll defects;
establishing optimum machine settings adapted to receive signals from defects for
easy and effective detection of defects.
A further aspect of the present invention is directed to said method wherein said eddy
current surface probes having frequencies 10kHz & 100kHz; and transmit-receive ultrasonic
probe having frequencies 2-5 MHz.
A still further aspect of the present invention is directed to said method wherein said
combination of probes are used to detect a continuous or non-continuous networks of both
micro (<0.15mm wide open) and macro (>0.15mm wide open) cracks on the surface and
near surface regions (0-1.0mm radial depth) and sub-surface regions (0-100mm radial

depth) that the rolls under considerations are induced with in a typical mill operation for
rolling of hot and cold steel strips/coils.
A still further aspect of the present invention is directed to said method that comprises the
step of carrying out ultrasonic inspection comprising:
calibrating the flaw detectors on the reference block of known defects;
adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analyse the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;
holding the probe, preferably mounted in a holder or housing, resting on the roll
surface at one end of the roll barrel and moving it along the longitudinal axis of the
roll starting from one end towards the other end while the roll is rotated around its
axis on the lathe or the grinding machine;
ensuring that the speed of movement of the probe and the rotational speed of the
roll are synchronized in a manner so as to cover the full volume of the roll to the
extent possible with the manual operation; and
calibrating the flaw detectors on the reference block of known defects.
A still further aspect of the present invention is directed to sais method wherein said
ultrasonic inspection is carried out involving a combination of TR (Transmit Receive) probe,
normal beam probe, angle beam probes ( 30/45/70°) and/or surface wave probe (90°).
Yet another aspect of the present invention is directed to said method comprising the steps
of:
a) mounting the roll on lathe or grinding machine, as the case may be;

b) removing the skin comprising worn out layer, from the roll surface so as to
make the roll diameter uniform along the entire roll barrel length;
c) selecting suitable surface probe frequencies for eddy current inspection so as to
enable detection of surface defects of varying width and surface depth;
d) calibrating the flaw detectors on the reference block of known defects;
e) adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analyzing the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;
f) holding the probe, preferably mounted in a holder or housing, resting on the roll
surface at one end of the roll barrel and moving it along the longitudinal axis of
the roll starting from one end towards the other end while the roll is rotated
around its axis on the lathe or the grinding machine;
g) ensuring that the speed of movement of the probe and the rotational speed of
the roll are synchronized in a manner so as to cover the full volume of the roll to
the extent possible with the manual operation;
h) calibrating the flaw detectors on the reference block of known defects;
i) adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analysing the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;
j) inspecting the rolls after stock removal once again in the manner stated in order
to ensure the defect free rolls for the subsequent campaign in the mill; and
k) performing the ultrasonic inspection in a manner as described under Step (d)
through Step( h) involving combination of TR (Transmit Receive) probe or normal
beam probe, angle beam probes (30/45/70°) and/or surface wave probe (90°) for
said ultrasonic inspection.

The objects and advantages of the present invention are described hereunder in greater
details with reference to the following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 is the schematic diagram illustrating the roll inspection methodology according to
the present invention showing the probe position with respect to roll surface and the relative
movements of probe in relation to rotation of roll to carry out the inspection/detection of
defects.
Figure 2: is the graphical presentation of frequency distribution of defect depth.
Figure 3: is the bar chart showing the effect of NDT roll inspection on occurrence of roll
spalling.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWING
The present invention is directed to a method of non destructive inspection of surface
defects of rolls of Hot Strip Mill and Cold Rolling Mill in Steel Plant involving portable
Ultrasonic and Eddy Current Flaw Detectors duly calibrated on reference block of known
defects so as to enable accurate detection of surface defects of varying width and surface
depth. The method of non destructive inspection according to the present invention for
detection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill that includes the
selection of type and range of ultrasonic and eddy current probes capable of detecting
service induced roll defects, establishing the machine settings that are most optimum to
receive signals from the defects so as to make the interpretation of test results easy,
sequencing the inspection methodology steps, performing the test to simulate the principles
behind automated state-of-the-art roll inspection systems.
To execute the method of inspection according to the invention, an used roll with defects
/cracks , the roll is first mounted on lathe or grinding machine, as the case may be and the
skin, i.e. worn out layer is removed from the roll surface so as to make the roll diameter
uniform along the entire roll barrel length. Accompanying Figure 1 shows the schematic
diagram illustrating the roll inspection methodology according to the present invention

showing the probe position with respect to roll surface and the relative movements of probe
in relation to rotation of roll to carry out the inspection/detection of defects-
Portable eddy current flaw detector is engaged with selected probes having selective surface
probe frequencies for eddy current inspection, preferably 2 eddy current probes having
frequencies 10 kHz and 100 kHz are used so as to enable detection of surface defects of
varying width and surface depth. The flaw detector is calibrated on the reference block of
known defects. The setting of the flaw detector is adjusted so as to filter the defect signal
from the noise signal and analyse the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly. To conduct the inspection, the selected probe is held, preferably mounted in a
holder or housing, resting on the roll surface at one end of the roll barrel and is moved
along the longitudinal axis of the roll starting from one end towards the other end while the
roll is rotated around its axis on the lathe or the grinding machine. The speed of movement
of the probe and the rotational speed of the roll are synchronized in a manner so as to cover
the full volume of the roll to the extent possible with the manual operation.
The rolls are inspected after stock removal once again in the stated manner in order to
ensure the defect free rolls for the subsequent campaign in the mill. The ultrasonic
inspection is performed for this using ultrasonic flaw detector in a manner as described
under above steps using combination of TR (Transmit Receive) probe or normal beam
probe, angle beam probes (30/45/70°) and/or surface wave probe (90°) for ultrasonic
inspection. Transmit Receive ultrasonic frequency having frequencies 2-5 MHz.
The method of non destructive inspection of surface defects of rolls of Hot Strip Mill and
Cold Rolling Mill according to the present invention thus comprises the steps of:
Step 1: Mounting the roll on lathe or grinding machine, as per requirement.
Step 2: Removing the skin, i.e. worn out layer, from the roll surface so as to make the roll
diameter uniform along the entire roll barrel length.
Step 3: Selecting the suitable surface probe frequencies for eddy current inspection (based
on the theoretical information and practical experience, it is preferred to use 2 eddy current
probes having frequencies 10 kHz and 100 kHz), so as to enable detection of surface
defects of varying width and surface depth.
Step 4: Calibrating the flaw detectors on the reference block of known defects.

Step 5: Adjusting the settings of the flaw detector so as to filter the defect signal from the
noise signal and analyse the signals to understand the presence or absence of defects with
reference to the calibration data and decide upon the stock removal accordingly.
Step 6: Holding the probe, preferably mounted in a holder or housing, resting on the roll
surface at one end of the roll barrel and move it along the longitudinal axis of the roll
starting from one end towards the other end while the roll is rotated around its axis on the
lathe or the grinding machine.
Step 7: Ensuring that the speed of movement of the probe and the rotational speed of the
roll are synchronized in a manner so as to cover the full volume of the roll to the extent
possible with the manual operation.
Step 8: Calibrating the flaw detectors on the reference block of known defects.
Step 9: Adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analyse the signals to understand the presence or absence of defects with
reference to the calibration data and decide upon the stock removal accordingly.
Step 10: Inspecting the rolls after stock removal once again in the manner stated in order
to ensure the defect free rolls for the subsequent campaign in the mill.
Step 11: Performing the ultrasonic inspection in a manner as described under Step 4
through Step 8, making use of combination of TR (Transmit Receive) probe or normal beam
probe, angle beam probes (30/45/70°) and/or surface wave probe (90°) for ultrasonic
inspection.
The step for skin removal by turning on lathe or grinding machine though is an isolated step
but forms an integral part of the roll inspection methodology under the claim. This provides
nearly equal surface conditions for the ultrasonic and eddy current inspection enabling
comparable and reproducible results in regard to the presence or absence of cracks.
Besides, turning the rolls on lathe or grinding machine provides a mechanism of changing
the orientation of cracks which may be oriented in tangential, radial, circumferential or
randomly oriented directions and would otherwise be left out of the ambit of testing probes
if the rolls are not rotated. It is therefore an integral part of the roll inspection methodology
in order to ensure the detection of cracks in the full roll volume many of which will be left
undetected if the rolls are kept static on a cradle or so while inspecting and this would give
a false indications for absence of cracks on the roll bodies.
In the above method, the optimum machine settings are dynamically determined which
depends on the surface conditions of the roll body before inspection, nature and extent of

defects induced during specific roil service campaigns, type of devices used for roll
inspection.
The frequency distribution of defects as observed upon inspection employing the said
technique has also been plotted as percent of the total observed occurrences of defects.
Accompanying Figure 2 is the graphical presentation of frequency distribution of defect
depth.
As can be seen in figure 2 that though the extent of defects ranges from 0.2 mm deep to
2.5 mm deep, the defects in the range of 0.2 mm to 0.8 mm account for the majority of the
cases (~80%). The data corresponds to about 3000 nos. of tested rolls during one year
period. Further, it is observed that out of these 80% cases, the defects in the range of 0.2
mm to 0.5 mm accounts for 90% of the cases and the rest 10% of the cases represents the
defects in the range of 0.5 mm to 0.8 mm. The occurrence of defects in the ranges
observed justifies the need of using the combination of types and frequency ranges of eddy
current and ultrasonic probes.
Accompanying Figure 3 shows the reduction in incidences of spalling upon roll inspection
with ultrasonic and eddy current techniques indicating the effectiveness of roll inspection
methodology.
It is thus possible by way of the present invention to providing a method of non destructive
inspection of surface defects of rolls of Hot Strip Mill and Cold Rolling Mill in Steel Plant
involving portable Ultrasonic and Eddy Current Flaw Detectors wherein probes are used with
selective frequencies for locating flaws and flaw detectors are duly calibrated on reference
block of known defects, setting of the flaw detector is adjusted so as to filter the defect
signal from the noise signal and analyse the signals to understand the presence or absence
of defects with reference to the calibration data and decide upon the stock removal
accordingly, resulting in substantial reduction in roll consumption and avoiding production
delays leading to considerable financial saving.

We Claim:
1. A method of non-destructive inspection of rolls for hot and/or cold rolling of steel
strips/coils comprising:
involving a combination of ultrasonic and eddy current probes;
selecting the type and range of ultrasonic and eddy current probes adapted to detect
service induced roll defects;
establishing optimum machine settings adapted to receive signals from defects for
easy and effective detection of defects.
2. A method as claimed in claim 1 wherein said eddy current surface probes having
frequencies 10kHz & 100kHz; and transmit-receive ultrasonic probe having
frequencies 2-5 MHz.
3. A method as claimed in anyone of claims 1 or 2 wherein said combination of probes
are used to detect a continuous or non-continuous networks of both micro
(<0.15mm wide open) and macro (>0.15mm wide open) cracks on the surface and
near surface regions (0-1.0mm radial depth) and sub-surface regions (0-100mm
radial depth) that the rolls under considerations are induced with in a typical mill
operation for rolling of hot and cold steel strips/coils.
4. A method as claimed in anyone of claims 1 to 3 comprising step of carrying out
ultrasonic inspection comprising:
calibrating the flaw detectors on the reference block of known defects;
adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analyse the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;

holding the prove, preferably mounted in a holder or housing, resting on the roll
surface at one end of the roll barrel and moving it along the longitudinal axis of the
roll starting from one end towards the other end while the roll is rotated around its
axis on the lathe or the grinding machine;
ensuring that the speed of movement of the probe and the rotational speed of the
roll are synchronized in a manner so as to cover the full volume of the roll to the
extent possible with the manual operation; and
calibrating the flaw detectors on the reference block of known defects.
5. A method as claimed in anyone of claims 1 to 4 wherein said ultrasonic inspection is
carried out involving a combination of TR (Transmit Receiver) probe normal beam
probe, angle beam probes ( 30/45/70°) and /or surface wave probe (90°).
6. A method as claimed in anyone of claims 1 to 5 comprising the steps of:

a) mounting the roll on lathe or grinding machine, as the case may be;
b) removing the skin comprising worn out layer, from the roll surface so as to
make the roll diameter uniform along the entire roll barrel length;
c) selecting suitable surface probe frequencies for eddy current inspection so as to
enable detection of surface defects of varying width and surface depth;
d) calibrating the flaw detectors on the reference block of known defects;
e) adjusting the setting of the flaw detector so as to filter the defect signal from the
noise signal and analyzing the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;
f) holding the prove, preferably mounted in a holder or housing, resting on the roll
surface at one end of the roll barrel and moving it along the longitudinal axis of
the roll starting from one end towards the other end while the roll is rotated
around its axis on the lathe or the grinding machine;

g) ensuring that the speed of movement of the probe and the rotational speed of
the roll are synchronized in a manner so as to cover the full volume of the roll to
the extent possible with the manual operation;
h) calibrating the flaw detectors on the reference block of known defects;
i) adjusting thesetting of the flaw detector so as to filter the defect signal from the
noise signal and analysing the signals to understand the presence or absence of
defects with reference to the calibration data and decide upon the stock removal
accordingly;
j) inspecting the rolls after stock removal once again in the manner stated in order
to ensure the defect free rolls for the subsequent campaign in the mill;and
k) performing the ultrasonic inspection in a manner as described under Step (d)
through Step( h) involving combination of TR (Transmit Receive) probe or normal
beam probe, angle beam probes (30/45/70°) and/or surface wave probe (90°) for
said ultrasonic inspection.

ABSTRACT

The present invention relates to a method of non destructive inspection of surface defects of
rolls of Hot Strip Mill and Cold Rolling Mill in Steel Plant involving portable Ultrasonic and
Eddy Current Flaw Detectors wherein probes of selective type and range are used with
selective frequencies for locating flaws and flaw detectors are duly calibrated on reference
block of known defects, setting of the flaw detector is adjusted so as to filter the defect
signal from the noise signal and analyse the signals to understand the presence or absence
of defects with reference to the calibration data and decide upon the stock removal
accordingly, resulting in substantial reduction in roll consumption and avoiding production
delays leading to considerable financial saving.