Title of Invention	AN ULTRASONIC MEASURING METHOD IN AN-APPARATUS ADAPTING A SINGLE CRYSTAL 90˚ ANGLE SURFACE WAVE PROBE TO DETECT A SURFACE CRACK INCLUDING DIRECT MEASUREMENT OF THE DEPTH OF THE CRACKS ON ROLLED STRUCTURES
Abstract	The invention relates to an ultrasonic measuring method using a single crystal 90° angle surface wave probe to detect a surface crack including direct measurement of the depth of the cracks on rolled structures made of steel, cast iron or forging, the method comprising the steps of providing an apparatus for ultrasonic detection of cracks, the apparatus deploying a single crystal 90° angle surface wave probe, producing a plurality of calibration blocks of steel or cast iron with several pre measured notches with depth between 0.04 mm to 1.94 mm for calibrating the apparatus, detecting presence or absence of a surface crack by using the apparatus; establishing a relationship between the data representing amplitude of the reflected signals captured in the calibration blocks and that captured in the rolled rolls; and measuring the depth of the crack if detected based on the relationship formed on the amplitude of the reflected flaw-back signals on the calibration block and the apparatus.

Title of Invention

AN ULTRASONIC MEASURING METHOD IN AN-APPARATUS ADAPTING A SINGLE CRYSTAL 90˚ ANGLE SURFACE WAVE PROBE TO DETECT A SURFACE CRACK INCLUDING DIRECT MEASUREMENT OF THE DEPTH OF THE CRACKS ON ROLLED STRUCTURES

Abstract

The invention relates to an ultrasonic measuring method using a single crystal 90° angle surface wave probe to detect a surface crack including direct measurement of the depth of the cracks on rolled structures made of steel, cast iron or forging, the method comprising the steps of providing an apparatus for ultrasonic detection of cracks, the apparatus deploying a single crystal 90° angle surface wave probe, producing a plurality of calibration blocks of steel or cast iron with several pre measured notches with depth between 0.04 mm to 1.94 mm for calibrating the apparatus, detecting presence or absence of a surface crack by using the apparatus; establishing a relationship between the data representing amplitude of the reflected signals captured in the calibration blocks and that captured in the rolled rolls; and measuring the depth of the crack if detected based on the relationship formed on the amplitude of the reflected flaw-back signals on the calibration block and the apparatus.

Full Text	TECHNICAL FIELD The present invention relates to an improved method of non- desctructive testing, ultrasonic method for assessing the depth of surface cracks in rolls of rolling mills (hot Strip Mill / Cold Rolling Mill) by using ultrasonic surface wave (90° angle) probe, particularly shallow cracks less than 0.7 mm deep in alloyed steel forged and hardened rolls as well as 0.88 mm deep in cast double poured alloyed cast iron rolls, which are critical for their life as well as the surface quality of the rolled products. BACKGROUND There was no NDT technique which could accurately measure the depth of the tight shallow surface breaking cracks (depth less than 1.0 mm) on the surface of the rolling mill (hot Strip Mill / Cold Rolling Mill) roll. The use of surface wave probes were limited to surface crack detection only. A novel technique using such surface wave probe was developed by the applicant to measure the depth of the surface breaking cracks, within the accuracy of ± 5%. The surface cracks were originated either due to manufacturing fault of the rolls or due to residual, thermal and mechanical stresses developed during their services in the mills. After roll dressing, if these cracks are missed by visual inspection, they will be opened up during operation in the mill and leave marks on the strips it downgrading / rejection. At the same time these cracks may also propagate further either leading to roll spalling or causing the roll unsuitable for use, if it reaches the zone of scrap diameter. To reduce such incidences at cold rolling mill and hot rolling mill of Tata Steel, an ultrasonic technique using single crystal surface wave (90° angle) probe was developed to assess the depth of these surface cracks. OBJECTS OF THE INVENTION US 2003/0183011 discloses an ultrasonic detection apparatus and ultrasonic detection method employing the same. According to the method, while a transmitting transducer (2a) for transmitting an ultrasonic wave and a receiving transducer (2b) for receiving an ultrasonic wave are moved within a predetermined circular region (7) on a surface of a material being measured, ultrasonic waves are transmitted and received 10,000 times. Then, arithmetic averaging is performed every time an ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves that have been received until then. For example, the aforementioned predetermined frequency is given by ((n±(1/2))x(105xv/ΔL)(Hz),where ΔL is a variation in distance between the transmitting transducer and the receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number. Consequently, it is possible to detect, with high accuracy, the thickness of a concrete material having a narrow width and a thick thickness, the thickness of the covering of a reinforcing bar and the diameter thereof, the depth of a crack and the like. An object of the present invention is to provide an ultrasonic method of assessing a very tight cracks, which are invisible to naked eyes being measured for their depths, which is not possible by using A C potential drop method. Another object of the present invention is to measure the depth of the shallow cracks (less than 0.7 mm in forged and hardened alloyed steel rolls and less than 0.88 mm in cast double poured alloyed cast iron rolls) within the accuracy of ± 5%, which is not possible by using Time of flight Diffraction (TOFD) method. The measuring method of depth of cracks according to present invention is insensitive to ascertain width of the cracks since the ultrasonic pulses are reflected from one wall of the crack only. SUMMARY OF THE INVENTION We have invented that using surface wave probe and measuring the amplitude of the reflected ultrasonic echo in terms of % FSH (Full Screen Height) from a surface crack, it is possible to predict the depth of surface crack in rolling mill rolls made of steel or cast iron within accuracy of ± 5%. For this, calibration curves, showing correlation between flaws echo amplutude and notch depths in calibration blocks, made of steel and cast iron, were prepared. A direct correlation was valid upto crack depth equivalent to half of the wavelength of ultrasound in the material of the calibration block. Such calibration curves were used to predict the surface crack depths in the rolling mill rolls of cold rolling mill. There was a good agreement between ultrasonically and actually measured crack depth of surface cracks in these rolls. The present invention provides an improved ultrasonic method for assessing the depth of surface cracks in rolls of rolling mills by using ultrasonic surface wave probe limited to surface crack detection, wherein shallow cracks less than 0.7 mm deep in alloyed steel being forged and hardened rolls, said surface wave probe being developed to measure the depth of surface breaking cracks invisible to necked eyes. DETAILED DESCRIPTION OF THE INVENTION The surface wave of ultrasound travel along the surface of a material at a depth of 1 (one) wavelength from the surface. While traveling, when it interacts a surface cracks, having depth less than one wavelength, they are reflected back to create art ultrasonic signal on the oscilloscope. The amplitude of the reflected signal is a function of area of the reflector (normal plane of the crack). A direct correlation between crack depth and the amplitude of reflected signal has been observed during experimentation with notches (with different depths from 0.04 to 1.94 mm) made on calibration blocks of materials similar to roll material. EXPERIMENTAL WORK The proposed invention will be understood from the following description with reference to the accompanying drawings and tables obtained on experimental results achieved to predict depth of cracks in rolling mill rolls through surface wave probe in which Fig 1 represents schematic diagram of calibration blocks (made of mild steel and cast iron) fabricated to calibrate the instrument for crack depth measurement. Fig 2 represents variation in Echo Amplitude (% FSH) in the calibration blocks (made of mild steel) with varying depths, using 2 MHZ, Surface Wave Probe at 49.5 dB Attenuator setting, measured at 100mm from the notch. Fig 3 represents variation in Echo Amplitude (% FSH) in the calibration blocks (made of cast iron) with varying depths, using 2 MHZ, Surface Wave Probe at 70.5 dB Attenuator setting, measured at 100mm from the notch. Fig. 4 represents a schematic diagram showing measurement of surface crack using an ultrasonic surface wave probe. Fig. 5 represents variation in Echo Amplitude (% FSH) with corresponding crack depth (in mm) for 3% / 4% Cr Forged Steel Rolls. Fig. 6 represents variation in Echo Amplitude (% FSH) with corresponding crack depth, in mm for Doubled Poured Alloy Cast Iron Rolls. Fig. 7 represents correlation between Ultrasonically Measured Surface Crack Depths and their Actual Measured Values in CRM Roll. Fig. 8 represents % Error in Ultrasonically Measured Crack Depths in CRM Roll. Details of the ultrasonic flaw equipment and surface wave probe: Make & Model: Krautkramer Branson USN 52 R Probe: 2 MHZ, 90° angle (Surface Wave), 8x9 mm. The calibration blocks made of steel and cast iron with various notches 0.04. 0.08, 0.15, 0.25, 0.35,0.46, 0.58, 0.70, 0.78, 0.86, 0.94, 1.06, 1.17, 1.25, 1.35, 1.47, 1.53, 1.66, 1.77, 1.90 and 1.94 mm deep were fabricated, as mentioned in Table 1 and shown in Fig.1, to calibrate the said conventional instrument for crack depth measurement. For 3% / 4% Cr Steel rolls, variation in echo amplitude (% FSH) in the calibration blocks (made of mild steel) with varying depths, using 2 MHZ, Surface Wave Probe at 49.5 dB attenuator setting has been shown in Table 2 and plotted in a graphical form as shown in Fig. 2. For alloy cast iron rolls, variation in echo amplitude (%FSH) in the calibration blocks (made of cast iron) with steps of varying depths, using 2 MHZ, surface wave probe at 49.5 dB attenuator setting has been shown in Table 3 and plotted in a graphical form as shown in Fig.3. Fig. 4 shows a schematic diagram of a surface crack (developed in mill operation), which propagated in transverse direction and was measured using surface wave probe. As obvious from Fig. 2, up to 0.70 mm notch depth of the fabricated calibration block (made of mild steel), there is increase in echo amplitude with increase in the notch depth. Beyond 0.70 mm the relationship is reverse up to 0.86 mm and between 0.86 to 1.94 mm there is no direct correlation. These results show implications in measuring crack depth using surface wave probe if the depth of the crack is more than 0.70 mm. The crack depth can be measured only if it is less than 0.70 mm. Similarly, it is clear from Fig. 3, up to 0.88 mm notch depth fabricated calibration block (made of cast iron), there is increase in echo amplitude with increase in the notch depth. Beyond 0.88 mm the relationship is reverse up to 1.06 mm and between 1.06 to 1.94 mm there is no direct correlation. These results show implications in measuring crack depth using surface wave probe if the depth of the crack is more than 0.88 mm. The crack can be measured only if it is less than 0.88 mm in the case of cast iron. Cracks (in which depth is less or equal to the half wave length of the surface wave probe) can be measured accurately by using surface wave (90° angle) probe for the 3 % / 4% Cr Forged steel and alloy cast iron by using the graphs as shown in the Fig. 5 and Fig. 6 respectively. Fig. 7 shows the correlation between Ultrasonically Measured Surface Crack Depths and their Actual Measured Values in CRM Rolls. Fig. 8 shows the % error in Ultrasonically Measured Surface Crack Depths in CRM Rolls. It is well within ± 5%. After, implementation on the roll shop of cold rolling mill of Tata Steel, it has been observed that using this method, it is possible to predict the depth of surface cracks within an accuracy of ± 5%. We Claim: 1. An ultrasonic measuring method in an apparatus adapting a single crystal 90° angle surface wave probe to detect a surface crack including direct measurement of the depth of the cracks on rolled structures made of steel, cast iron or forging, the method comprising the steps of: - providing an apparatus for ultrasonic detection of cracks, the apparatus deploying a single crystal 90° angle surface wave probe; - producing a plurality of calibration blocks of steel or cast iron with several pre measured notches with depth between 0.04 mm to 1.94 mm for calibrating the apparatus; - detecting presence or absence of a surface crack by using the apparatus; - establishing a relationship between the data representing amplitude of the reflected signals captured in the calibration blocks and that captured in the rolled rolls; and - measuring the depth of the crack if detected based on the relationship formed on the amplititude of the reflected flaw-back signals on the calibration block and the apparatus. 2. The method as claimed in claim 1, wherein, the depth of the crack can be directly measured without additional calculation. 3. The method as claimed in claim 1, wherein the measuring the depth of the crack comprises a depth between 0.70mm and to 0.88 mm respectively in respect of mild steel and cast iron. 4. The ultrasonic measuring method as claimed in claim 1 wherein the calibration blocks made of steel and cast iron are fabricated with various notches for example, 0.04, 0.08, 0.15, 0.25, 0.35, 0.46, 0.58, 0.70, 0.78, 0.86, 0.94, 1.06, 1.17, 1.25, 1.35, 1.47, 1.53, 1.66, 1.77, 1.90 and 1.94 mm depth for calibration of the apparatus for crack depth measurement 5. The ultrasonic measuring method as claimed in claim 1, wherein for 3% /4% Cr steel rolls, variation in echo amplitude (% FSH) in the calibration blocks made of mild steel with varying depths, is measured at 100 mm from the notch. 6. The ultrasonic measuring method as claimed in any of the preceding claims wherein for alloy cast rolls, variation in echo amplitude (% FSH) in the calibration block made of cast iron with varying depths, is measured at 100 mm from the notch. 7. The ultrasonic measuring method as claimed in one of the preceding claims wherein cracks in which notch depth is less or equal to the half wave length of the surface wave probe by using the surface wave (90° angle) probe for 3% / 4% Cr forged steel and alloy cast iron. 8. The ultrasonic measuring method as claimed in one of the preceding claims, wherein correlation between ultrasonically measured surface crack depths and their actual measured values in cold rolling mill rolls of Cr forged steel and alloy cast iron is measurable within ± 5% of accuracy. 9. An ultrasonic measuring method using a single crystal 90° angle surface wave probe to detect a surface crack including direct measurement of the depth of the crack on rolled structures made of steel, cast iron or forging, the method as substantially described and illustrated herein with reference to the accompanying drawings. The invention relates to an ultrasonic measuring method using a single crystal 90° angle surface wave probe to detect a surface crack including direct measurement of the depth of the cracks on rolled structures made of steel, cast iron or forging, the method comprising the steps of providing an apparatus for ultrasonic detection of cracks, the apparatus deploying a single crystal 90° angle surface wave probe, producing a plurality of calibration blocks of steel or cast iron with several pre measured notches with depth between 0.04 mm to 1.94 mm for calibrating the apparatus, detecting presence or absence of a surface crack by using the apparatus; establishing a relationship between the data representing amplitude of the reflected signals captured in the calibration blocks and that captured in the rolled rolls; and measuring the depth of the crack if detected based on the relationship formed on the amplitude of the reflected flaw-back signals on the calibration block and the apparatus.

Full Text

TECHNICAL FIELD
The present invention relates to an improved method of non-
desctructive testing, ultrasonic method for assessing the depth of surface
cracks in rolls of rolling mills (hot Strip Mill / Cold Rolling Mill) by using
ultrasonic surface wave (90° angle) probe, particularly shallow cracks
less than 0.7 mm deep in alloyed steel forged and hardened rolls as well as
0.88 mm deep in cast double poured alloyed cast iron rolls, which are
critical for their life as well as the surface quality of the rolled products.
BACKGROUND
There was no NDT technique which could accurately measure the
depth of the tight shallow surface breaking cracks (depth less than 1.0 mm)
on the surface of the rolling mill (hot Strip Mill / Cold Rolling Mill) roll.
The use of surface wave probes were limited to surface crack detection
only. A novel technique using such surface wave probe was developed by
the applicant to measure the depth of the surface breaking cracks, within
the accuracy of ± 5%.
The surface cracks were originated either due to manufacturing fault
of the rolls or due to residual, thermal and mechanical stresses developed
during their services in the mills. After roll dressing, if these cracks are

missed by visual inspection, they will be opened up during operation in the mill
and leave marks on the strips it downgrading / rejection. At the same time these
cracks may also propagate further either leading to roll spalling or causing the
roll unsuitable for use, if it reaches the zone of scrap diameter. To reduce such
incidences at cold rolling mill and hot rolling mill of Tata Steel, an ultrasonic
technique using single crystal surface wave (90° angle) probe was developed to
assess the depth of these surface cracks.
OBJECTS OF THE INVENTION
US 2003/0183011 discloses an ultrasonic detection apparatus and ultrasonic
detection method employing the same. According to the method, while a
transmitting transducer (2a) for transmitting an ultrasonic wave and a receiving
transducer (2b) for receiving an ultrasonic wave are moved within a
predetermined circular region (7) on a surface of a material being measured,
ultrasonic waves are transmitted and received 10,000 times. Then, arithmetic
averaging is performed every time an ultrasonic wave is received, on the
ultrasonic wave and ultrasonic waves that have been received until then. For
example, the aforementioned predetermined frequency is given by
((n±(1/2))x(105xv/ΔL)(Hz),where ΔL is a variation in distance between the
transmitting transducer and the receiving transducer, v is a transmission velocity
of an ultrasonic wave transmitting in a material being detected, and n is a
natural number. Consequently, it is possible to detect, with high accuracy, the
thickness of a concrete material having a narrow width and a thick thickness, the
thickness of the covering of a reinforcing bar and the diameter thereof, the
depth of a crack and the like.

An object of the present invention is to provide an ultrasonic method of
assessing a very tight cracks, which are invisible to naked eyes being measured
for their depths, which is not possible by using A C potential drop method.
Another object of the present invention is to measure the depth of the shallow
cracks (less than 0.7 mm in forged and hardened alloyed steel rolls and less than
0.88 mm in cast double poured alloyed cast iron rolls) within the accuracy of ±
5%, which is not possible by using Time of flight Diffraction (TOFD) method.
The measuring method of depth of cracks according to present invention is
insensitive to ascertain width of the cracks since the ultrasonic pulses are
reflected from one wall of the crack only.

SUMMARY OF THE INVENTION
We have invented that using surface wave probe and measuring the
amplitude of the reflected ultrasonic echo in terms of % FSH (Full
Screen Height) from a surface crack, it is possible to predict the depth of
surface crack in rolling mill rolls made of steel or cast iron within accuracy
of ± 5%. For this, calibration curves, showing correlation between flaws
echo amplutude and notch depths in calibration blocks, made of steel and
cast iron, were prepared. A direct correlation was valid upto crack depth
equivalent to half of the wavelength of ultrasound in the material of the
calibration block. Such calibration curves were used to predict the surface
crack depths in the rolling mill rolls of cold rolling mill. There was a good
agreement between ultrasonically and actually measured crack depth of
surface cracks in these rolls.
The present invention provides an improved ultrasonic method for
assessing the depth of surface cracks in rolls of rolling mills by using
ultrasonic surface wave probe limited to surface crack detection, wherein
shallow cracks less than 0.7 mm deep in alloyed steel being forged and
hardened rolls, said surface wave probe being developed to measure the
depth of surface breaking cracks invisible to necked eyes.

DETAILED DESCRIPTION OF THE INVENTION
The surface wave of ultrasound travel along the surface of a material at a depth
of 1 (one) wavelength from the surface. While traveling, when it interacts a
surface cracks, having depth less than one wavelength, they are reflected back
to create art ultrasonic signal on the oscilloscope. The amplitude of the reflected
signal is a function of area of the reflector (normal plane of the crack).
A direct correlation between crack depth and the amplitude of reflected signal
has been observed during experimentation with notches (with different depths
from 0.04 to 1.94 mm) made on calibration blocks of materials similar to roll
material.
EXPERIMENTAL WORK
The proposed invention will be understood from the following description with
reference to the accompanying drawings and tables obtained on experimental
results achieved to predict depth of cracks in rolling mill rolls through surface
wave probe in which
Fig 1 represents schematic diagram of calibration blocks (made of mild steel and
cast iron) fabricated to calibrate the instrument for crack depth measurement.
Fig 2 represents variation in Echo Amplitude (% FSH) in the calibration blocks
(made of mild steel) with varying depths, using 2 MHZ, Surface Wave Probe at
49.5 dB Attenuator setting, measured at 100mm from the notch.
Fig 3 represents variation in Echo Amplitude (% FSH) in the calibration blocks
(made of cast iron) with varying depths, using 2 MHZ, Surface Wave Probe at
70.5 dB Attenuator setting, measured at 100mm from the notch.

Fig. 4 represents a schematic diagram showing measurement of surface crack
using an ultrasonic surface wave probe.
Fig. 5 represents variation in Echo Amplitude (% FSH) with corresponding crack
depth (in mm) for 3% / 4% Cr Forged Steel Rolls.
Fig. 6 represents variation in Echo Amplitude (% FSH) with corresponding crack
depth, in mm for Doubled Poured Alloy Cast Iron Rolls.
Fig. 7 represents correlation between Ultrasonically Measured Surface Crack
Depths and their Actual Measured Values in CRM Roll.
Fig. 8 represents % Error in Ultrasonically Measured Crack Depths in CRM Roll.
Details of the ultrasonic flaw equipment and surface wave probe: Make & Model:
Krautkramer Branson USN 52 R Probe:
2 MHZ, 90° angle (Surface Wave), 8x9 mm.
The calibration blocks made of steel and cast iron with various notches 0.04.
0.08, 0.15, 0.25, 0.35,0.46, 0.58, 0.70, 0.78, 0.86, 0.94, 1.06, 1.17, 1.25, 1.35,
1.47, 1.53, 1.66, 1.77, 1.90 and 1.94 mm deep were fabricated, as mentioned in
Table 1 and shown in Fig.1, to calibrate the said conventional instrument for
crack depth measurement.

For 3% / 4% Cr Steel rolls, variation in echo amplitude (% FSH) in the
calibration blocks (made of mild steel) with varying depths, using 2 MHZ, Surface
Wave Probe at 49.5 dB attenuator setting has been shown in Table 2 and plotted

in a graphical form as shown in Fig. 2.

For alloy cast iron rolls, variation in echo amplitude (%FSH) in the calibration
blocks (made of cast iron) with steps of varying depths, using 2 MHZ, surface
wave probe at 49.5 dB attenuator setting has been shown in Table 3 and plotted
in a graphical form as shown in Fig.3.

Fig. 4 shows a schematic diagram of a surface crack (developed in mill
operation), which propagated in transverse direction and was measured using
surface wave probe.

As obvious from Fig. 2, up to 0.70 mm notch depth of the fabricated calibration
block (made of mild steel), there is increase in echo amplitude with increase in
the notch depth. Beyond 0.70 mm the relationship is reverse up to 0.86 mm and
between 0.86 to 1.94 mm there is no direct correlation. These results show
implications in measuring crack depth using surface wave probe if the depth of
the crack is more than 0.70 mm. The crack depth can be measured only if it is
less than 0.70 mm.
Similarly, it is clear from Fig. 3, up to 0.88 mm notch depth fabricated calibration
block (made of cast iron), there is increase in echo amplitude with increase in
the notch depth. Beyond 0.88 mm the relationship is reverse up to 1.06 mm and
between 1.06 to 1.94 mm there is no direct correlation. These results show
implications in measuring crack depth using surface wave probe if the depth of
the crack is more than 0.88 mm. The crack can be measured only if it is less
than 0.88 mm in the case of cast iron.
Cracks (in which depth is less or equal to the half wave length of the surface
wave probe) can be measured accurately by using surface wave (90° angle)
probe for the 3 % / 4% Cr Forged steel and alloy cast iron by using the graphs
as shown in the Fig. 5 and Fig. 6 respectively.
Fig. 7 shows the correlation between Ultrasonically Measured Surface Crack
Depths and their Actual Measured Values in CRM Rolls.
Fig. 8 shows the % error in Ultrasonically Measured Surface Crack Depths in CRM
Rolls. It is well within ± 5%.
After, implementation on the roll shop of cold rolling mill of Tata Steel, it has
been observed that using this method, it is possible to predict the depth of
surface cracks within an accuracy of ± 5%.

We Claim:
1. An ultrasonic measuring method in an apparatus adapting a single crystal
90° angle surface wave probe to detect a surface crack including direct
measurement of the depth of the cracks on rolled structures made of
steel, cast iron or forging, the method comprising the steps of:
- providing an apparatus for ultrasonic detection of cracks, the
apparatus deploying a single crystal 90° angle surface wave probe;
- producing a plurality of calibration blocks of steel or cast iron with
several pre measured notches with depth between 0.04 mm to
1.94 mm for calibrating the apparatus;
- detecting presence or absence of a surface crack by using the
apparatus;
- establishing a relationship between the data representing amplitude
of the reflected signals captured in the calibration blocks and that
captured in the rolled rolls; and
- measuring the depth of the crack if detected based on the
relationship formed on the amplititude of the reflected flaw-back
signals on the calibration block and the apparatus.

2. The method as claimed in claim 1, wherein, the depth of the crack can be
directly measured without additional calculation.
3. The method as claimed in claim 1, wherein the measuring the depth of
the crack comprises a depth between 0.70mm and to 0.88 mm
respectively in respect of mild steel and cast iron.
4. The ultrasonic measuring method as claimed in claim 1 wherein the
calibration blocks made of steel and cast iron are fabricated with various
notches for example, 0.04, 0.08, 0.15, 0.25, 0.35, 0.46, 0.58, 0.70, 0.78,
0.86, 0.94, 1.06, 1.17, 1.25, 1.35, 1.47, 1.53, 1.66, 1.77, 1.90 and 1.94
mm depth for calibration of the apparatus for crack depth measurement
5. The ultrasonic measuring method as claimed in claim 1, wherein for 3%
/4% Cr steel rolls, variation in echo amplitude (% FSH) in the calibration
blocks made of mild steel with varying depths, is measured at 100 mm
from the notch.
6. The ultrasonic measuring method as claimed in any of the preceding
claims wherein for alloy cast rolls, variation in echo amplitude (% FSH) in
the calibration block made of cast iron with varying depths, is measured at
100 mm from the notch.

7. The ultrasonic measuring method as claimed in one of the preceding
claims wherein cracks in which notch depth is less or equal to the half
wave length of the surface wave probe by using the surface wave (90°
angle) probe for 3% / 4% Cr forged steel and alloy cast iron.
8. The ultrasonic measuring method as claimed in one of the preceding
claims, wherein correlation between ultrasonically measured surface crack
depths and their actual measured values in cold rolling mill rolls of Cr
forged steel and alloy cast iron is measurable within ± 5% of accuracy.
9. An ultrasonic measuring method using a single crystal 90° angle surface
wave probe to detect a surface crack including direct measurement of the
depth of the crack on rolled structures made of steel, cast iron or forging,
the method as substantially described and illustrated herein with reference
to the accompanying drawings.

The invention relates to an ultrasonic measuring method using a single crystal
90° angle surface wave probe to detect a surface crack including direct
measurement of the depth of the cracks on rolled structures made of steel,
cast iron or forging, the method comprising the steps of providing an
apparatus for ultrasonic detection of cracks, the apparatus deploying a single
crystal 90° angle surface wave probe, producing a plurality of calibration
blocks of steel or cast iron with several pre measured notches with depth
between 0.04 mm to 1.94 mm for calibrating the apparatus, detecting
presence or absence of a surface crack by using the apparatus; establishing a
relationship between the data representing amplitude of the reflected signals
captured in the calibration blocks and that captured in the rolled rolls; and
measuring the depth of the crack if detected based on the relationship
formed on the amplitude of the reflected flaw-back signals on the calibration
block and the apparatus.

Documents:

104-kol-2004-granted-abstract.pdf

104-kol-2004-granted-claims.pdf

104-kol-2004-granted-correspondence.pdf

104-kol-2004-granted-description (complete).pdf

104-kol-2004-granted-drawings.pdf

104-kol-2004-granted-examination report.pdf

104-kol-2004-granted-form 1.pdf

104-kol-2004-granted-form 13.pdf

104-kol-2004-granted-form 18.pdf

104-kol-2004-granted-form 2.pdf

104-kol-2004-granted-form 3.pdf

104-kol-2004-granted-form 5.pdf

104-kol-2004-granted-gpa.pdf

104-kol-2004-granted-reply to examination report.pdf

104-kol-2004-granted-specification.pdf

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Patent Number

227265

Indian Patent Application Number

104/KOL/2004

PG Journal Number

02/2009

Publication Date

09-Jan-2009

Grant Date

05-Jan-2009

Date of Filing

11-Mar-2004

Name of Patentee

TATA TEEL LIMITED.

Applicant Address

JAMSHEDPUR

Inventors:

#	Inventor's Name	Inventor's Address
1	RAJ MANISH	TATA STEEL LIMITED., JAMSHEDPUR-831 001
2	PANDEY J. C.	TATA STEEL LIMITED., JAMSHEDPUR-831 001

PCT International Classification Number

G01N 29/34

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA