FIELD OF INVENTION:
The present invention relates to an NDT forassessment of mash seam welds in cold rolled steel sheets. More particularly, it relates to a high speed automated ultrasonic based NDT system for online assessment of mash seam welds in cold rolled steel sheets in a continuous galvanizing line of a cold rolling mill.
BACKGROUND OF THE INVENTION:
A continuous galvanizing line processes cold rolled steel sheets into galvanized steel. This is a continuous process in which the steel strip is first annealed and then dipped into a pot containing molten zinc. These processes are carried out successively in a continuous manner for achieving a high production rate. Cold rolled steel, which is the input raw material for a galvanizing line is stored in coil form. Since these coils are of finite length, the coils are weldedend to end at the start of a continuous galvanizing line to form a continuous strip of sheet which is fed into the line. The welded sections are cut at the end of the processing line and re-coiled. It is essential that the welds sustain the tension induced in the strip during processing in the mill.Any defects in the weld may result in breakage of the weld in the line under the processing conditions. Failure of welds in the line during processing results into mill stoppages which eventually lead tohuge production downtime.Thus, a system to access the integrity of the weld online by non-destructive testing (NDT) techniques can aid in averting such outages by alerting operators of any defective welds. It must also be kept in mind that due to continuous processing of sheet in the line, the inspection of the weld must be done at a very fast speed. The typical opportunity time available to assess a 1.2 meter long weld is about 1 minute.

Prior Art:
Non-destructive assessment of mash seam welds of cold rolled sheets is a significant challenge particularly due to the requirement of high scanning speed and capability to detect very small sub-surface defects simultaneously. Assessment of welded joints has been addressed in previous works; details of which are given below.
U.S. Patent No. 5537876 claims an electro-magnetic acoustic transducer (EMAT) based technique using horizontal shear ultrasonic waves for assessment of butt welded sheets. The apparatus moves in tandem with the flash trimmer knife which removes the flash after welding. The EMAT probes are mounted on a cart with wheels enabling them to be driven along the weld line for scanning. A pneumatic lifter is used to lower the cart in a proper position to start the scan. Since the EMAT probes are sensitive to “liftoff” or the spacing between the sheet and probe, the contact face of the probe is lined with wear resistant titanium layer. The shear horizontal ultrasonic waves are generated in the sheet and guided in the direction of the weld. Any discontinuity in the weld will cause a reflection of ultrasonic wave.
U.S. Patent No. 5777229 claims an automated sensor transport system for a combination flash butt welder based on the sensor as per U.S. Patent No. 5537876. A computer control unit which co-ordinates the testing system with the main welding equipment and edge detection apparatus for positioning the sensor are claimed.
U.S. Patent No. 6298727 B1 describes an apparatus for acoustic inspection of a work piece in arbitrary orientations. An acoustic transducer housed in a multi-piece assembly having flexible material at the contact face is claimed. The inner portion of the housing provides a chamber for couplant to be continuously supplied to the transducer. The second portion is used to create a vacuum to suck any couplant that is leaked from the inner chamber. The flexible bristles at the contact face aid in adjusting the device on an uneven surface.

U.S. Patent No. 3921442 claims a hydrophilic polymer based coupling membrane with acoustical properties which can be used with any conventional ultrasonic transducer. The coupling membrane claims to eliminate the need for using any additional coupling fluid for contact testing.
The Patent JP55001541 claims an arrangement which creates a water tight chamber around the pipe weld to be inspected. Water is pumped into this chamber and ultrasonic probe is used to scan the area. The ultrasonic scan is displayed using a flaw detector.
U.S Patent No. 7412890 claims a ultrasonic based device for detecting cracks in welds of a nuclear reactor pressure vessel. An ultrasonic phased array probe mounted in a housing containing a liquid for coupling is described. The housing has to be configured at a predetermined location on the weld. The phased array probe then generates an electronically steered ultrasonic beam to scan the weld region covered within the housing.
U.S Patent No. 6948369 B2 claims an ultrasonic inspection method for spot and seam resistance welds in metallic sheets. A method which enables the weld to be inspected ultrasonically without the requirement of immersing the welded material in water or other liquid is described. A focused ultrasonic transducer is housed in a “hub” which is filled with coupling liquid (water). Water is continually pumped into the hub to replenish any spillage. The tip of the hub is kept in contact with the weld and the probe is scanned either manually or by using any other mechanism. The scan results are represented in the form of A-scan, B-scan or C-scan as desired. The hub is interchangeable such that it can be replaced after the tip has worn out.
All the above patents are intended for assessment of welds. However these inventions are not suitable for high speed online inspection of welds in a production line. The main reason for being, all above inventions require the sensor to be in contact with the weld or parent metal. It must be noted that steel strips in a steel

mill have certain amount of waviness, both along the length and width. Although clamping can minimize the waviness to a great extent, slight waviness will always exist. Inventions described in US5537876 and US5777229 use EMAT sensors for which the “liftoff” or spacing between sensor and test object needs to be very accurately controlled. These inventions will fail for online conditions due to this waviness of strip along the width as the waviness will cause the liftoff to fluctuate.
In addition to the strip waviness, the weld surface itself is usually very rough. The use of sensors that need to be in contact to the weld surface for inspection will undergo constant wear. For high speed scanning the wear will be even higher. Continual wear of sensor head will cause a great inconvenience to the mill operators as they will need to be replaced frequently. Inventions described in US6298727B1, US3921442 and US6948369B2 fail due to this aspect.
Inventions described in JP55001541 and US7412890 describe the creation of a temporary water chamber in the inspection region using water tight seals at the contact surface. Although, this method overcomes the problem of wear of sensor head, elaborate mechanisms will be required for creation of temporary water chamber around the weld in a production line. This will demand considerable space requirements which may not always be available in existing production lines.
The seam weld needs to be assessed online immediately after welding. As described earlier, the galvanizing mill is a continuous line and the assessment of weld condition should be completed within a time frame of 45seconds so that production is not affected.As the weld is to be inspected immediately after welding; the temperature of the weld zone is approximately 200OC. In addition to this, the surface of the weld is rough.These conditions make it impractical to use contact ultrasonic sensor systems (US6298727B1, US3921442 and US6948369B2) as they would be subject to severe wear requiring frequent replacement of sensor heads. It is therefore ideal to have a non-contact type sensor.

Ultrasonic C-scan is a well-established technique used for carrying out pulse-echo ultrasonic testing over a surface without the ultrasonic sensor directly touching the sample.This technique requires the sample to be submerged in water while maintaining a constant water column between the surface of the sample and the ultrasonic probe. The probe then scans the area of interest generating A-scans at each point and stitching all the resulting A-scans to form a C-scan. This principle can be effectively applied to the problem at hand. However, it is not practical to introduce a tank of water (JP55001541 and US7412890) within the galvanizing line as this would significantly increase the inspection time and additionally require elaborate modifications to the line.
An extremely effective workaround to this problem is described in US6298727B1, US3921442 and US6948369B2. Since it is only required that a constant water column be maintained between the ultrasonic sensor and the surface of the sample, a water chamber with an open bottom is constructed around the ultrasonic probe. The walls of the chamber rest on the sample and the open bottom allows water to be in direct contact with the sample. This methodology works very efficiently for smooth surface as it makes it easy to maintain a constant water column. But, the rough surface will not allow the side walls of the chamber to be water tight, making it extremely difficult to maintain the water column. In addition due to direct contact of the sensor tip, it will be subject to constant wear, necessitating frequent replacement of contact tip.
OBJECTS OF THE INVENTION:
In view of the foregoing limitations inherent in the prior-art, it is an object of the invention to develop a non-destructive testing technique for the assessment of mash seam welds.

Another object of the invention is to develop a high speed online assessment of the mash seam welds in a continuous galvanizing line of a cold rolling mill.
Still another object of the invention is to develop NDT with high defect sensitivity.
SUMMARY OF THE INVENTION
In one aspect, the invention providesa non-destructive arrangement for assessment of mash seam weldcomprising an ultrasonic transducer, the ultrasonic transducerbeing sealed and housed within a chamber to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld, an inlet port and an outlet port at the chamber being configured to pump in and pump out an acoustic coupling fluid from the chamber thereby maintaining constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld andthe ultrasonic transducer being coupled to an ultrasonic pulser receiver which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates a non-destructive arrangement with focused ultrasonic transducer in accordance with an embodiment of the invention.
FIG. 2 illustratesan array of non-destructive arrangement in accordance with an embodiment of the invention.
FIG. 3illustrates a mill setup for high speed assessmentof mash seam weldin accordance with an embodiment of the invention.

FIG. 4shows2 mm thick sheet with artificial weld defects (EDM notches) as an experimentalanalysis in accordance with an embodiment of the invention.
FIG. 5shows ultrasonic B-Scan of 2 mm thick sheet with artificial weld defects using the prototype systemas an experimentalanalysis in accordance with an embodiment of the invention.
FIG. 6shows ultrasonic C-Scan of 2 mm thick sheet with artificial weld defects using the prototype systemas an experimental analysis in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION:
Various embodiments of the invention providea non-destructive arrangement for assessment of mash seam weld, the non-destructive arrangement comprising: an ultrasonic transducer, the ultrasonic transducer being sealed and housed within a chamber, the ultrasonic transducer being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld; an inlet port and an outlet port at the chamber, the inlet port and the outlet port being configured to pump in and pump out an acoustic coupling fluid from the chamber thereby maintaining constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld; and the ultrasonic transducer being coupled to an ultrasonic pulser receiver which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver.

Another embodiment of the invention provides an array of non-destructive arrangement for high speed assessment of mash seam weld, the arrangement comprising a plurality of non-destructive arrangements coupled to each other, each ofthe non-destructive arrangement comprising, an ultrasonic transducer, the ultrasonic transducer being sealed and housed within a chamber, the ultrasonic transducer being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld, an inlet port and an outlet port at the chamber, the inlet port and outlet port being configured to pump in and pump out an acoustic coupling fluid in the chamber thereby maintaining constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld; and the ultrasonic transducer being coupled to an ultrasonic pulser receiver which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver.
Still another embodiment of the invention provides a mill setup for high speed assessment of mash seam weld, the mill setup comprising a table configured to receive a steel sheet with a mash seam weld; an overhead beam erected over the table; a clamp configured to flatten and hold the steel sheet; a video camera coupled with a laser pointer configured at the overhead beam, the video camera being configured to give the view of the weld sheet to an operator and the laser pointer being configured to point the length of the mash seam weld for scanning and positioning an array of non-destructive arrangement at a height to the mash seam weld, the arrangement comprising a plurality of non-destructive arrangements coupled to each other, each ofthe non-destructive arrangement comprising; an ultrasonic transducer, the ultrasonic transducer being housed and sealed within a chamber, the ultrasonic transducer being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld; an

inlet port and an outlet port at the chamber, the inlet port and outlet port being configured to pump in and pump out an acoustic coupling fluid in the chamber; the chamber being configured to supply the acoustic coupling fluid so as to maintain constant acoustic coupling contact between the ultrasonic transducer and the mash seam weld; and the ultrasonic transducer being coupled to an ultrasonic pulser receiver which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver.
FIG. 1 shows a non-destructive arrangement (100) for assessment of mash seam weld over a steel sheet (101). The non-destructive arrangement (100) comprises an ultrasonic transducer (104) being sealedand housed within a chamber (108). The ultrasonic transducer (104) is configured to transmit and receive ultrasonic waves to and from the mash seam weld through constant acoustic coupling contact between the transducer (104) and the mash seam weld. In case there is discontinuation of contact, signal from the transducer willbe uncertain.
To maintain constant acoustic coupling contact, a constant flow of an acoustic coupling fluid (112) is maintained between the mash seam weld and the transducer.The pumping in of the acoustic coupling fluid (112) is done by an inlet port (116) at the chamber (108). Subsequently pumping out of the acoustic coupling fluid (112) is done by an outlet port (120) at the chamber (108).
In an embodiment water can be used as the acoustic coupling fluid. The pressure of the acoustic coupling fluid (112) into the chamber (108) is maintained to be greater than the pressure at the outlet port (120). Due to thisfluid will flow out of the outlet port (120) in the form of a jet (124)and continuous acoustic fluid column between the mash seam weldand the ultrasonic probe (104) is created.

The ultrasonic transducer (104) is coupled to an ultrasonic pulser receiver (120). The receiver (120) is further coupled to a data acquisition system (not shown). Data signal received from the mash seam weld to the ultrasonic transducer (104) is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver (120). The data acquisition system generates c-scan image from the data signal of the weld.
The entire arrangement (100) is fixed at a constant height above the mash seam weld thereby maintaining a constant height of liquid column. This height is chosen based on the focal length of the ultrasonic probe (104) used.In an embodimentfrequency of the ultrasonic transducer is 20MHz for 0.1 mm depth resolution of mash seam weld.
Since the focused ultrasonic transducer (104) is used, the ultrasound is focused onto a small spot of about 1 mm on the weld surface. The width of mash seam weld is usually much larger than the focal spot diameter of the probe. If the arrangement (100) using single transducer is used, a raster scan will have to be done to cover the entire weld zone. This will require the sensor head to move back and forth along the weld line multiple times to complete the raster scan. This process will increase the scan time significantly.
Thusan array of non-destructive arrangement (200) with similar arrangements (100)coupled to each other with transducersfor high speed assessment of mash seam weldis designed and is shown in FIG. 2. Also shown isits top view and front view.
It is designed such a manner that the focal spots of transducers of adjacent arrangement (100) are separated apart by minimal distanceso as to provide a higherscan resolution across the width of the weld seam. The arrangements (100) are placed in two rows to enable this since the diameter of each arrangement (100)

is larger than the minimum spacing between adjacent focal spots. The numbers of rows can be decreased or increased as per the required scan resolution.
The number of transducers in the array can be chosen based on the width of the weld zone to be scanned. Care must be taken that the array covers the entire weld zone and in addition also covers some part of the parent metal. This is particularly useful in simplifying the algorithm for construction of the c-scan image.
FIG. 3shows front view of amill setup (300) for high speed assessmentof mash seam weld. A table (304)is sufficiently large enough to support the full width and around 1 m length of the steel sheet (101)with the mash seam weld can be utilized to install the mill setup (300). The steel sheet on the table (304) is received from the mill. The movement of the steel sheet (101)is in z-axis. An overhead beam (312)iserected over the table (304)houses various electrical cabling, water/coupling fluid pipes for the transducer and mechanical arrangements.
A clamp (316) is used for flattening and holding the steel sheet (101) in place during scanning. The clamp (316)can be operated using either hydraulic/pneumatic actuators (320). The array of non-destructive arrangement (200) comprising transducers as described earlier is supported and traversed using a lead screw and stepper motor assembly (328). Thenon-destructive arrangement (200) is coupled with a wheel driven limit switch (332)for maintaining a constant spacing between the transducer (104) and the steel sheet (101). The coupling fluid is stored in a sump (336)and circulated to the non-destructive arrangement (100) of the arrangement (200)using a pump (340). The table (304)contains provisions for drainage of spill overthe acoustic coupling fluid (112). The drained coupling fluid is channelled back through a gantry (340) to the sump (336)for recirculation. A video camera (344) coupled with a laser pointeris mounted on the overhead beam (312) for viewing the weld sheet by an operator. The laser pointer points the length of the mash seam weld and position the arrangement (200) at certain height over the

mash seam weld. The laser pointer is configured to point the length of the mash seam weld for scanning.
Once the sheet has been welded, the operator can move and position the system (200) accurately over the weld seam using a joystick control. The laser pointer indicates the exact position on the arrangement (200) prior to start of scan. Motion control, data acquisition, A/D conversion, data representation and report generation for the measurement system is computer controlled.
Once the scanning is completed, the arrangement (200) moves up and the next slot of steel sheet is brought forward to the table (304).
Weld samples with artificial defects were used for testing in accordance with an embodiment of the invention. A scanning speed of 20 m/min, ultrasonic frequency of 20 MHz and pulse repetition frequency (PRF) of 2 kHz were used for the test. A 2 mm thick sheet with artificial weld defects (EDM notches) of 200 μm, 400 μm and 800 μm as shown in FIG. 4 was used for the test. The ultrasonic B-Scan for this sample was obtained as shown in FIG. 5, the corresponding ultrasonic C-Scan is shown in FIG. 6. The shift in back wall echoes indicates the presence of defects in the B-Scan. White patches indicate the corresponding defects in the C-Scan.
Advantages
The developed technique for the assessment of mash seam welds is non-destructive with high defect sensitivity.
The developed technique has a featured high speed online assessment of the mash seam welds in a continuous galvanizing line of a cold rolling mill.

We claim:
1. A non-destructive arrangement (100) for assessmentof mash seam weld,
thenon-destructive arrangement (100) comprising:
an ultrasonic transducer (104), the ultrasonic transducer (104)being sealed and housed within a chamber (108), the ultrasonic transducer (104) being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld;
an inlet port (116) and an outlet port (120) at the chamber (108), the inlet port (116) and the outlet port (120) being configured to pump in and pump out an acoustic coupling fluid (112) from the chamber (108) thereby maintaining constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld; and
the ultrasonic transducer (104) being coupled to an ultrasonic pulser receiver (120) which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer (104) is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver (120).
2. The non-destructive arrangement (100) as claimed in claim 1, wherein the acoustic coupling fluid is water.
3. The non-destructive arrangement (100) as claimed in claim 1, wherein frequency of the ultrasonic transducer (104) is 20MHz for 0.1 mm depth resolution of mash seam weld.

4. An array of non-destructive arrangement (200) for high speed assessment of
mash seam weld, the arrangement (200) comprising:
a plurality of non-destructive arrangements (100) coupled to each other, each ofthe non-destructive arrangement (100) comprising;
an ultrasonic transducer (104), the ultrasonic transducer (104) being sealed and housed within a chamber (108), the ultrasonic transducer (104) being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld;
an inlet port (116) and an outlet port (120) at the chamber (108), the inlet port (116) and outlet port (120) being configured to pump in and pump out an acoustic coupling fluid (118) in the chamber (108) thereby maintaining constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld; and
the ultrasonic transducer (104) being coupled to an ultrasonic pulser receiver (120) which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer (104) is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver (120).
5. The array of non-destructive arrangement (200) as claimed in claim 4, wherein the acoustic coupling fluid is water.
6. The array of non-destructive arrangement (200) as claimed in claim 4, wherein frequency of the ultrasonic transducer (104) is 20MHz for 0.1 mm depth resolution.

7. A mill setup (300) for high speed assessmentof mash seam weld, the mill setup (300) comprising:
a table (304) configured to receive a steel sheet (101) with a mash seam weld;
an overhead beam (312) erected over the table (304);
a clamp (316) configured to flatten and hold the steel sheet (101);
a video camera (344) coupled with a laser pointer configured at the overhead beam (312), the video camera (344) being configured to give the view of the weld sheet (101) to an operator and the laser pointer being configured to point the length of the mash seam weld for scanning and positioning an array of non-destructive arrangement (200) at a height to the mash seam weld, the arrangement (200) comprising
a plurality of non-destructive arrangements coupled to each other, each ofthe non-destructive arrangement (100) comprising;
an ultrasonic transducer (104), the ultrasonic transducer (104) being housed and sealed within a chamber (108), the ultrasonic transducer (104) being configured to transmit and receive ultrasonic waves to and from a mash seam weld through a constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld;
aninlet port (112) and an outlet port (116) at the chamber (108), the inlet port (112) and outlet port (116) being configured to pump in and pump out an acoustic coupling fluid (118) in the chamber (108);

the chamber (108) being configured to supply the acoustic coupling fluid so as to maintain constant acoustic coupling contact between the ultrasonic transducer (104) and the mash seam weld; and
the ultrasonic transducer (104) being coupled to an ultrasonic pulser receiver (120) which is being further coupled to a data acquisition system, the data signal received from the mash seam weld to the ultrasonic transducer (104) is further transmitted to the data acquisition systemvia the ultrasonic pulser receiver (120).
the acoustic coupling fluid (112) being stored in a sump (336) and pumped to the inlet port by a pump (340); and
a gantry (340) being connected between the table and the sump (336) to channel back the drained coupling fluid to the sump (336).
8. The mill setup as claimed in claim 7, wherein the clamp (316) is operated by hydraulic/pneumatic actuator(s).
9. Themill setup as claimed in claim 7, wherein the height of the array of non¬destructive arrangement (200) is maintained bya limit switch (332).
lO.The mill setup as claimed in claim 9, wherein thelimit switch(332) is wheel driven.