FIELD OF THE INVENTION
The present disclosure relates to a field of non-destructive testing of thickness of ductile
iron (DI) pipe. Particularly the disclosure relates to a non-contact probe which enables
thickness profiling along the axial length of different diameters of pipes.
BACKGROUND OF THE INVENTION
Ductile iron pipe is manufactured by centrifugal casting process. Magnesium treated hot
metal is transferred from the ladle to the pouring machine of the centrifugal casting
equipment. The hot metal travels down a trough into a spinning mold of a centrifugal
casting machine. When the hot metal enters the spinning mold, it spreads the hot metal
due to centrifugal force against the mold wall. A suitable cooling system cools the mold
walls in order to solidify the hot metal. After solidification, the extractor pulls out the iron
pipe from the mold. Due to the brittleness of the pipe, it should be annealed in order to
achieve a uniform grain microstructure throughout the length of pipe. The pipe is zinc
coated after annealing for imparting corrosion resistance.
The important issue faced by the pipe manufacturers presently is fine tuning the
parameters of centrifugal casting process in pipe production line in order to produce the
uniform thickness of the ductile iron pipe. The thickness distribution of the pipe depends
on many parameters of centrifugal casting such as pouring speed, pouring temperature,
trough movement etc.
A consequence of non-uniform thickness is extremely lower thickness in some
regions of the cast pipe. This results in rejections on account of failing specified quality
assurance norms. Another consequence is the wastage of hot metal in the regions of pipe
cast with significantly higher thickness than what the specifications demand.
It is therefore essential to have a non-destructive online thickness profiling tool for
quality assurance as well as process optimization purposes.

Online thickness profiling of ductile iron pipes necessitates high speed thickness
measurements along the axial length of the pipes. The speed of testing should be
sufficiently high to keep up with the rate of production of pipes.
US4003244 describes an apparatus for ultrasonic thickness measurement using a
piezoelectric transducer. The transducer is kept in contact with the test object and
coupled with either oil/water/grease. An ultrasonic pulse is transmitted in the test object
which traverses the thickness of the object and reflects back to the transducer. The time-
of-flight is measured and knowing the velocity of sound in the material, thickness of the
object is calculated. This instant invention describes a contact type transducer which will
undergo severe wear if used for scanning on the surface of rough/ peened pipe.
US8600702 B2 describes a mechanism for generating vibration in ductile iron
pipes. The vibration in the form of a Gaussian white noise is generated in the pipe.
Depending on the material and thickness, the pipe wall will vibrate with a corresponding
resonant frequency. This vibration is detected at various locations of the pipe using a
laser vibrometer. The material of pipe being constant, the thickness of the pipe is
measured at various locations. The instant invention measures the thickness by
measuring vibration of pipe using laser vibrometer. Vibration of the production line and
other environments will obstruct the signal making reliable measurements difficult. Also
vibration generated in the pipe will be a resultant of overall geometry of pipe thereby
giving an average thickness of the whole pipe and not localized measurements.
Indian patent application #201631008010 describes a high speed non-contact
focused ultrasonic sensor which can be used for thickness measurements. The
application utilizes a focused ultrasonic probe encased in a water chamber for enabling
non-contact inspection of welds as discussed in the prior art. FIG. 1 depicts the
application of a sensor (104) for thickness measurement of ductile iron (DI) pipe (108).
DI pipes have a peculiar peen pattern on the outer surface (112). Due to this
uneven surface, ultrasonic wave will be scattered from the outer surface (112) of the pipe
when the sensor (104) is traversed along the pipe surface. This unevenness is in the form
of dimples or bumps formed due to a peening pattern utilized in the centrifugal casting
mold.

The bottom orifice of the water chamber has to be small to form the water column
essential for ultrasonic testing. Thus, the reflected ultrasonic wave can be detected by the
sensor only when the wave interacts at near normal incidence with tangent to the outer
surface of pipe. This condition may not be satisfied at most instances thereby disallowing
direct use of this sensor for DI pipe thickness profiling.
Challenges involved in the utilization of this ultrasonic probe for thickness
measurement of DI pipes with uneven surface are depicted in FIG. 1. As the wave is
being focused on a small area on the surface of the pipe, the ultrasonic wave has high
possibility of reflecting in random directions. As the aperture of water chamber of the
probe is very small (so as to form the water jet), the possibility of detection of reflected
ultrasound by the piezoelectric probe is highly probabilistic. This will make the thickness
profiling along the length of pipe extremely sporadic.
The peen pattern on the surface of the DI pipes is inherent due to centrifugal
casting process. The mold utilized for centrifugal casting is peened on the inner surface
so as to prevent slippage of liquid metal within the mold during casting. This peen pattern
results in an uneven surface which particularly poses specific challenges for non-contact
ultrasonic thickness measurements using the state of the art.
OBJECTS OF THE INVENTION
In view of the foregoing limitations inherent in the prior-art, it is an object of the
disclosure to measure the thickness profile of ductile iron pipes along its length
automatically in a non-contact manner.
Another object of the disclosure is to measure the thickness of DI pipe online.
SUMMARY OF THE INVENTION
In one non-limiting an embodiment of the present disclosure an arrangement for
measuring thickness at a point on DI pipe and subsequently thickness of the entire DI
pipe is disclosed. The arrangement comprises an ultrasonic probe positioned above a
subject DI pipe having a peened surface, the focus of the ultrasonic probe being greater
than the distance between two consecutive crests or troughs of the peened surface, a

constant thin liquid film maintained between the subject DI pipe and the ultrasonic probe,
the ultrasonic waves being decomposed into perpendicular and non-perpendicular
components after impinge over the peened surface through the liquid film, the
perpendicular and non-perpendicular components being reflected back to the ultrasonic
probe from thickness end of the subject pipe, the perpendicular and non-perpendicular
components being considered for thickness measurement and the ultrasonic probe being
coupled to a computable device for processing the ultrasonic data for thickness
calculation.
In another embodiment of the present disclosure, a frame arrangement for
measuring thickness of DI pipe at a point is disclosed. The frame arrangement comprises
a standing frame comprising two standing verticals and a horizontal bar coupling the two
standing verticals, an adjustable frame placed below the standing frame comprising
atleast two arc shaped platform for placing a subject DI pipe, an ultrasonic probe
positioned and movable over the horizontal bar via a profiler above the subject DI pipe
having a peened surface, the focus of the ultrasonic probe being greater than the
distance between two consecutive crests or troughs of the peened surface, a constant
liquid film maintained between the peened surface and the ultrasonic probe, the ultrasonic
probe being configured to transmit and receive the ultrasonic waves, the ultrasonic waves
being decomposed into perpendicular and non-perpendicular components after impinge
over the peened surface through the liquid film, the perpendicular and non-perpendicular
components being reflected back to the ultrasonic probe from thickness end of the subject
pipe, the perpendicular and non-perpendicular components being considered for
thickness measurement and the ultrasonic probe being coupled to a computable device
for processing the ultrasonic data for thickness calculation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates prior art over peened surface of DI pipes.
FIG. 2 illustrates an arrangement for measuring thickness at a point on DI pipe in
accordance with an embodiment of the disclosure.

Fig. 3 illustrates an automation system for measuring thickness of DI pipe at a point in
accordance with an embodiment of the disclosure.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the disclosure provide an arrangement for measuring
thickness at a point on DI pipe, the arrangement comprising an ultrasonic probe
positioned above a subject DI pipe having a peened surface, the focus of the ultrasonic
probe being greater than the distance between two consecutive crests or troughs of the
peened surface, a constant thin liquid film maintained between the subject DI pipe and
the ultrasonic probe, the ultrasonic probe being configured to transmit and receive the
ultrasonic waves data signal, the ultrasonic waves being decomposed into perpendicular
and non-perpendicular components after impinge over the peened surface through the
liquid film, the perpendicular and non-perpendicular components being reflected back to
the ultrasonic probe from thickness end of the subject pipe, the perpendicular and non-
perpendicular components being considered for thickness measurement and the
ultrasonic probe being coupled to a computable device for processing the ultrasonic data
for thickness calculation.
In other embodiments of the disclosure provide a frame arrangement for
measuring thickness of DI pipe at a point, the frame arrangement comprising a standing
frame comprising two standing verticals and a horizontal bar coupling the two standing
verticals, an adjustable frame placed below the standing frame comprising atleast two arc
shaped platform for placing a subject DI pipe, an ultrasonic probe positioned and movable
over the horizontal bar via a profiler above the subject DI pipe having a peened surface,
the focus of the ultrasonic probe being greater than the distance between two consecutive
crests or troughs of the peened surface, a constant liquid film maintained between the
peened surface and the ultrasonic probe, the ultrasonic probe being configured to
transmit and receive the ultrasonic waves, the ultrasonic waves being decomposed into
perpendicular and non-perpendicular components after impinge over the peened surface
through the liquid film, the perpendicular and non-perpendicular components being
reflected back to the ultrasonic probe from thickness end of the subject pipe, the
perpendicular and non-perpendicular components being considered for thickness

measurement and the ultrasonic probe being coupled to a computable device for
processing the ultrasonic data for thickness calculation.
Shown in FIG. 2 is an arrangement (200) depicting the concept for measuring
thickness at a point on a subject DI pipe (204). The DI pipe (204) comprises a peened
surface (208) all over. The arrangement (200) comprises an ultrasonic probe (212) is
positioned above the DI pipe (204) to measure the thickness at one single point. The
ultrasonic probe (212) is mounted on a wide plate (216) and is configured to transmit and
receive the ultrasonic waves. The probe (212) is further coupled to a computable device
(not shown) which computes the ultrasonic data into thickness of the DI pipe.
The focus (f) of the ultrasonic probe (212) is greater than the distance between two
consecutive crests or troughs (d) of the peened surface (208), i.e. f>d.
A constant thin liquid film (220) is maintained between the ultrasonic probe (212)
and the peened surface (208). An angular projections (224) are provided in the wide plate
(216). The angular projections (224) are connected to the liquid supply. The angular
projections (224) aid in channeling liquid in the space between the plate (216) and the
peened surface (208).
In some embodiments the liquid can be water, oil etc.
In the present embodiment 4 (four) numbers of such angular projections are made
around the ultrasonic probe (212) with spacing of 90O. In an embodiment the numbers of
such projections can be varied as per the requirement. liquid is pumped in at a sufficiently
high flow rate to maintain a constant liquid film (220) of few millimeters thick. This
constant thin liquid film (220) provides the necessary acoustic coupling between the
ultrasonic probe and the peened surface.
Shown in FIG. 2 is the ultrasonic wave travelling path from the liquid film (220) and
the peened surface (208). Due of varying angle of incidence of the waves at the particular
points (i.e. liquid-peened surface intersection and peened surface-air intersection) causes
refraction of ultrasonic waves. Therefore the ultrasonic wave at such intersections gets

decomposed into perpendicular (P) and non-perpendicular (N-P) components. The
perpendicular (P) and non-perpendicular (N-P) components reflected from the thickness
end to the probe gives the understanding of the thickness of the DI pipe, which are
considered for measuring thickness of the DI pipe.
Also, due to the large focal spot of the ultrasonic probe (212), all these
perpendicular and non-perpendicular components can be detected by the probe, enabling
reliable thickness measurements.
To further compliment the reliable thickness measurement, the height of the liquid
film (220) can be maintained as less as possible (in few mm), so that the probe (212)
placed above the liquid film (220) captures all the reflected and refracted signals.
Once the thickness measurement of one single point over the DI pipe is taken,
subsequently more such numbers of thickness measurements is done to understand the
thickness of the entire DI pipe.
AUTOMATION SYSTEM FOR INTEGRATING THE PROBE IN PRODUCTION LINE
Shown in FIG. 3 is a frame arrangement (300) for online thickness measurement of
the subject DI pipe (304). The frame arrangement (300) includes a standing frame (328)
having two standing verticals (336) and a horizontal bar (348) coupling the two standing
verticals (336).
The frame arrangement (300) further includes an adjustable frame (352) placed
below the standing frame (328). The adjustable frame (352) is configured to adjust the
height and orientation of the subject DI pipe (304) to fall just below the ultrasonic probe.
The adjustable frame (352) is configured to bow down, receive and position the DI pipes
(304) for each round of thickness measurement below the frame arrangement (300). The
adjustable frame (352) (352) comprises atleast two arc shaped platform (356) to hold the
DI pipes (304) for thickness measurement.

In the present embodiment 2 (two) arc shaped platforms have been employed
whereas in some other embodiments there may more than two arc shaped platform to
support the subject DI pipe firmly.
The ultrasonic probe is coupled to the horizontal bar (348) by means of a profiler
(360). The profiler (360) is configured to travel along the horizontal bar so that the probe
(312) captures as many data along the length of the DI pipe (304), thereby calculating
reliable thickness of DI pipe.
The pipe (304) may also be rotated about its axis at any desired angle with a
cylindrical rollers (368) for a second set of measurements in the pipe.
As already discussed, minimal height (in mm) between the probe and the peened
surface (308) is to be maintained for reliable thickness measurement.
The constant liquid film is maintained by means of a liquid pipe (not shown in the
FIG). The liquid is constantly charged through the angular projections (344) at such a
pressure so as to maintain the constant thickness level. The liquid at the time of thickness
measurement spills out of the DI pipe.
THE OPERATION:
The DI pipe rolling into the measurement system from a previous station will be stopped
and arrested in the arc shaped platform. Once the pipe has been arrested, the adjustable
frame lifts the pipe up in the vertical direction. The pipe is then moved in the axial
direction to align one end of the pipe with the ultrasonic probe in its starting position. The
probe then traverses along the horizontal guide making ultrasonic thickness
measurements along the entire length of the DI pipe. The pipe may then be rotated about
its axis at any desired angle with the cylindrical rollers for a second set of measurements
in the pipe. Once the scan is completed, the probe is retracted to its starting position and
the pipe is retracted back. An ejector mechanism (364) is then put in action to release the
pipe back in the production line for further processing. The ejector mechanism (364) is a

wedge shaped bar pushed up against the pipes such that the pipe rolls down onto the
production line under gravity.
ADVANTAGES
It is an advantage of the disclosure to measure the thickness profile of ductile iron
pipes along its length automatically in a non-contact manner. Further, it also measures
the thickness of DI pipe online in speedy manner.

WE CLAIMS
1. An arrangement (200) for measuring thickness at a point on DI pipe, the
arrangement (200) comprising:
an ultrasonic probe (212) positioned above a subject DI pipe (204) having a peened
surface (208), the focus of the ultrasonic probe (212) being greater than the distance
between two consecutive crests or troughs of the peened surface (208);
a constant thin liquid film (220) maintained between the subject DI pipe (204) and the
ultrasonic probe (212), the ultrasonic probe (212) being configured to transmit and receive
the ultrasonic waves data signal;
the ultrasonic waves being decomposed into perpendicular and non-perpendicular
components after impinge over the peened surface (208) through the liquid film (220), the
perpendicular and non-perpendicular components being reflected back to the ultrasonic
probe (212) from thickness end (210) of the subject pipe (204), the perpendicular and
non-perpendicular components being considered for thickness measurement; and
the ultrasonic probe (212) being coupled to a computable device for processing the
ultrasonic data for thickness calculation.
2. A frame arrangement (300) for measuring thickness of DI pipe at a point, the frame
arrangement (300) comprising:
a standing frame (328) comprising two standing verticals (336) and a horizontal bar
(348) coupling the two standing verticals (336);
an adjustable frame (352) placed below the standing frame (328) comprising
atleast two arc shaped platform (356) for placing a subject DI pipe (304);
an ultrasonic probe (312) positioned and movable over the horizontal bar (348) via
a profiler (360) above the subject DI pipe (304) having a peened surface (308), the

focus of the ultrasonic probe (312) being greater than the distance between two
consecutive crests or troughs of the peened surface (308);
a constant liquid film (320) maintained between the peened surface and the
ultrasonic probe, the ultrasonic probe being configured to transmit and receive the
ultrasonic waves;
the ultrasonic waves being decomposed into perpendicular and non-perpendicular
components after impinge over the peened surface through the liquid film, the
perpendicular and non-perpendicular components being reflected back to the
ultrasonic probe from thickness end (210) of the subject pipe (304), the
perpendicular and non-perpendicular components being considered for thickness
measurement; and
the ultrasonic probe being coupled to a computable device for processing the
ultrasonic data for thickness calculation.