Claims:WE CLAIM

1. A calibration block (100) to determine the Time of Flight Diffraction (ToFD), the calibration block (100) comprising:
five slits (1, 2, 3, 4 & 5) to check the defect height sizing resolution of TOFD probe; and
five notches (6, 7, 8, 9 & 10) to determine the near surface and far surface resolution of the probe.

2. The calibration block (100) as claimed in claim 1, wherein the slits (1, 2, 3, 4 & 5) are made in the middle of the thickness of the block (100) and the notches (6, 7, 8, 9 & 10) are made from the bottom of the block (100) towards the top surface of the plate.

3. The calibration block (100) as claimed in claim 1, wherein the clits (1 – 5) are arranged in decreasing order of height, slit 1 being the tallest and slit 5 being the smallest.
, Description:FIELD OF THE INVENTION
[001] The invention relates to a calibration block that can be used to evaluate time of flight diffraction probe. In particular, the invention relates to calibration block that can be used to determine the resolving power of a time of flight diffraction probe. More particularly the invention relates to a standard block which can be used to assess the damping characteristics of the probe.

BACKGROUND OF THE INVENTION
[002] Time of flight diffraction technique is one of the advanced ultrasonic testing. Ultrasonic testing is one of the volumetric non-destructive testing which is having continuous improvement and are being implemented widely.

[003] Non-destructive material testing for welds is well known in the art and depending on the particular welded materials and welding processes, various testing methods can be employed, including liquid penetrant testing, X-ray analysis, eddy current testing, and ultrasonic testing. While most of the currently known test methods provide reproducible and unambiguous results for many materials, ultrasonic testing (e.g., single-probe, TOFD, phased array, etc.) has proven to be particularly advantageous as the test results are typically immediately available using relatively simple equipment.

[004] Time of flight diffraction technique is one of the advancement of ultrasonic testing technique in which diffraction of ultrasound is used to detect and size the defect. Time-of-flight diffraction (TOFD) method of ultrasonic testing is a sensitive and accurate method for the nondestructive testing of welds for defects.

TOFD Basic Theory
[005] TOFD is usually performed using longitudinal waves as the primary detection method. Ultrasonic sensors are placed on each side of the weld. One sensor sends the ultrasonic beam into the material and the other sensor receives reflected and diffracted ultrasound from anomalies and geometric reflectors. TOFD provides a wide area of coverage with a single beam by exploiting ultrasonic beam spread theory inside the wedge and the inspected material. When the beam comes in contact with the tip of a flaw, or crack, diffracted energy is cast in all directions. Measuring the time of flight of the diffracted beams enables accurate and reliable flaw detection and sizing, even if the crack is off-oriented to the initial beam direction. During typical TOFD inspections, A-scans are collected and used to create B-scan (side view) images of the weld. Analysis is done on the acquisition unit or in post-analysis software, positioning cursors to measure the length and through-wall height of flaws.

[006] TOFD probes differ from conventional UT probes by its highly damped characteristics and small diameter crystal. High damping is made in these probes to have good resolution and to have better accuracy in sizing the defect. Less damped probes will have better penetration but comparatively low resolving power. Resolution of the probe is important characteristics while selecting a probe for inspection. Different probes of same frequency will not have same resolving power. Therefore, to achieve good sizing accuracy some standard blocks and procedure has to be followed and the probes have to be evaluated.

[007] Measuring the amplitude of reflected signal is a relatively unreliable method of sizing defects because the amplitude strongly depends on the orientation of the crack. Instead of amplitude, TOFD uses the time of flight of an ultrasonic pulse to determine the position and size of a reflector.

[008] In a TOFD system, a pair of ultrasonic probes sits on opposite sides of a weld. One of the probes, the transmitter, emits an ultrasonic pulse that is picked up by the probe on the other side, the receiver. In undamaged pipes, the signals picked up by the receiver probe are from two waves: one that travels along the surface and one that reflects off the far wall. When a crack is present, there is a diffraction of the ultrasonic wave from the tip(s) of the crack. Using the measured time of flight of the pulse, the depth of a crack tips can be calculated automatically by simple trigonometry.

PRIOR ARTS
[009] US8746069 discloses an ultrasound time-of-flight diffraction reference block which has a plurality of notches that extend into the block to simulate cracks, wherein the notches have a normal and transverse orientation with respect to a test path formed on the block. It further claims a device that can be used to set the equipment sensitivity for Time of Flight Diffraction inspection. This block consists of EDM notches that represent reheat cracks and they are used to set and confirm the detectability of defect using TOFD technique.

[0010] CN 203595688U discloses a T-shaped welded joint TOFD (Time of Flight Diffraction) detection comparison test block which is suitable for the check of an instrument during T-shaped welding seam TOFD detection. The comparison test block is formed by cutting a steel board according to the practical welding angle dimension line of a checked welding seam, the thickness of the steel board is greater than the width of a TOFD probe wedge, three through holes being Phi 2 mm in diameter are located in a simulated T-shaped joint region of the comparison test block from top to bottom, which are used for identifying the covering of a TOFD detection acoustic beam, and meanwhile used for regulating the detection sensitivity. The comparison test block is easy to process, convenient to carry, and can fully satisfy the T-shaped welding seam TOFD detection demand.

[0011] This invention is about Time of flight diffraction technique which is one of the advanced ultrasonic testing method. Conventional ultrasonic testing uses reflection of sound wave to detect the defect present in materials. Whereas Time of flight diffraction technique uses the principle of diffraction of sound waves. ToFD technique uses two probes placed in the opposite sides of welds to be inspected where one probe act as transmitter and the other act as a receiver. In a defect free component only lateral wave and back wall will be present in the A scan Display (Time vs Amplitude display) as shown in figure 1. When a defect is present, sound beam gets diffracted from the top tip and bottom tip of the defect. In a defective welds, in addition to the lateral wave (Lw) and back wall echo (Bw), diffracted echo from top tip (Tt) and bottom tip (Bt) of the defect will also be present as shown in figure 2. The diffracted wave that reaches the receiver will be represented in different location because of transit difference between them. The depth and height of the defects are determined by using this time of flight difference. If the defect is high enough to have separate top tip and bottom tip of the defect then the height of the defect can be determined accurately. The resolving capability depends on the probe characteristics like central frequency and pulse width. Bandwidth of the ToFD probe is important variable which has to be selected properly based on the resolution required for inspection.

OBJECTS OF THE INVENTION
[0012] It is therefore an object of the invention to propose a calibration block which can be used to assess the resolution of TOFD probe.

[0013] Another object of the invention is to propose a standard block that supports the operator in selecting the probe with high accuracy, suitable for TOFD inspection.

[0014] Another object of the invention is to propose a block that can be used to determine the smallest defect height that can be resolved by the probe.

[0015] A still another object of the invention is to propose a block which can be used to measure near surface resolution.

[0016] A still further object of the invention is to propose a block which can be used to measure far surface resolution capability of the probe.

SUMMARY OF THE INVENTION

[0017] The proposed calibration block (100) can be used to determine whether TOFD probe has enough resolving power required for accurately sizing the defects. The block consists of five slits (1, 2, 3, 4 and 5) in the middle of the block thickness and five notches (6, 7, 8, 9 and 10) having their tips close to the top surface of the block. The tips of the slits are sharp to have a diffracted echo from the top tip and bottom tip of the slots. The height of the slits is arranged in increasing order from 1, 2, 3, 4 and 5 mm respectively. The slits are being made using Electrical discharge machining (EDM) process and can be done from the side of the block only. Therefore, every EDM slits are made in separate blocks of same thickness and then joined by coinciding the axis of the block. The notches are machined from one side of the plate to approach close to the other side of the plate along through thickness direction. The depth of the notches is such that they form a remaining material thickness of 1, 2, 3, 4 and 5 mm respectively for the notches (6, 7, 8, 9, and 10).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0018] Figure 1 ToFD basic setup in defect free weld
[0019] Figure 2 ToFD setup and signal in defective weld
[0020] Figure 3 A scan signal with good resolution
[0021] Figure 4 A scan signal with poor resolution
[0022] Figure 5 Shows the top view of the calibration block
[0023] Figure 6 shows the front view of the calibration block
[0024] Figure 7 shows the bottom view of the calibration block
[0025] Figure 8 Shows cross section view of the slit number 1.
[0026] Figure 9 Shows cross section view of the slit number 3.
[0027] Figure 10 Shows cross section view of the slit number 5.
[0028] Figure 11 shows the EDM notch 6 which is positioned close to the surface to check the surface resolution
[0029] Figure 12 shows the EDM notch 8 which is positioned close to the surface to check the surface resolution
[0030] Figure 13 shows the EDM notch 10 which is positioned close to the surface to check the surface resolution
[0031] Figure 14 Shows the inspection set up determine the resolution of the probe to measure the through height of defect present in mid wall.
[0032] Figure 15 Shows the inspection set up determine the resolution of the probe to measure the near surface defect.
[0033] Figure 16 Shows the inspection set up determine the resolution of the probe to measure the far surface defect.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0034] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

[0035] In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0036] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the present disclosure to the particular forms disclosed, but on the contrary, the present disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the present disclosure.
[0037] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

[0038] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

[0039] The present invention will be described in detail below with reference to an embodiment as shown in the drawing.

[0040] The calibration block (100) consists of five slits (1, 2, 3, 4 & 5) to check the defect height sizing resolution of TOFD probe and five notches (6, 7, 8, 9 & 10) to determine the near surface and far surface resolution of the probe.

[0041] Figure 1 shows the complete details of the invention. Figure 2 shows the side view of the block where the slits are seen in the middle of the block thickness and notches are made from the bottom of the block towards the top surface of the plate.

[0042] Figure 4 shows the cross section of the slit number 1 which is the maximum height of the defect that can be checked for resolution.

[0043] Figure 5 and 6 shows the slits like the slit 1 but with dimensions less than slit 1. Slit 2 shown in Figure 5 is smaller than slit 1 and slit 5 shown in Figure 6 is smallest of all the slits present in the block. This slit is made of height 1 mm to check whether the probes resolving capability is equal to 1 mm or poor.
[0044] The slits 1 to 5 are arranged in decreasing order of heights. These slits are made in five separate blocks on their sides and then finally welded to form a single block with all five slits.

[0045] A solid block is selected according to the width of final calibration block requirement and vertical slit is made from the side of the block. Totally 5 blocks are made with different slit height in decreasing order say 5mm, 4mm, 3mm, 2mm and 1mm.

[0046] Figure 7, 8 and 9 shows the notch with V shaped top tip to have better diffraction of wave. The depth of the notch varies for reflector number 6 to 10 such the remaining material thickness (as given in figure 12) is from 1 to 5 mm. When these notches are scanned using TOFD probes, the lateral wave and the top tip indication of the notch can be checked for their resolving capability.

[0047] The remaining material thickness of the notch for which the lateral wave and top tip of the notch is resolved clearly, will be the near surface resolution of the TOFD probe. The same notches can be scanned by placing the probes on the bottom side of the block to determine the far surface resolution of the probe. By scanning the block from bottom side of the block, the back wall of the block and notch tip can be ensured for its far surface resolution capacity.

Advantages:
[0048] The calibration block (100) can be used to evaluate the resolving power quantitatively as a measure of damping characteristic.

[0049] The calibration block (100) can be used to determine and select ToFD probe of same frequency but different resolving power.

[0050] The calibration block (100) can be used to evaluate the capability of probe to precisely size the height of the defect.

[0051] The calibration block (100) can be used to determine near surface resolution (i.e. Lateral wave resolution) capability of a ToFD probe

[0052] The calibration block (100) can be used to determine Far surface resolution (i.e. Back wall resolution) capability of a ToFD probe

[0053] The calibration block (100) can be used to determine the minimum height that can be resolved by a probe.

[0054] The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the specification, the reference numerals are merely for convenience, and are not to be in any way limiting, the invention may be practiced otherwise than is specifically described.