PSL 1 and PSL 2
25% Wall Coverage Solution
WALL THICKNESS INSPECTION
The following drawings depict the difference between conventional ultrasonic probes and the curved composites used in the current invention, both from a practicality standpoint and the associated cost benefits.
Figure 1 above depicts the problems associated with using a long conventional transducer element for taking ultrasonic wall thickness measurements. It can be seen that the sound emitted from the center of the transducer strikes the tube perpendicular (90 degrees) to the surface, which is a requirement for compression wave wall thickness readings, while the beam from the outer edges strikes the pipe surface at an incident angle of 69 degrees to the tangent of the circle, which would result in no return of signal for wall measurement, as shear waves would be induced in the part at the outer edges of the probe.
Figure 2 above shows how to overcome the restrictions of using a large flat element for wall thickness measurements by using multiple individual elements, or arrays, arranged in a curved case equidistant from the curved surface. This is commonly done with conventional, composite, and newer phased array systems, though it is apparent to anyone versed in the art that the cost associated not only with the individual elements but to a larger degree, the individual ultrasonic channels required to pulse the multiple elements, that this method pales in comparison to the potential to use a single element, though as we have shown, standard flat transducers will not work for this application.
It is important to realize that the use of the proposed curved composite probe methodology for wall thickness measurement is on it's own merits a viable and valuable invention and product. The measurement of wall thickness with ultrasound is commonly accepted as the most accurate measurement system currently in use. A unique property of ultrasonic wall thickness measurement is that to a large degree, increasing the distance from the transducer face to the surface of the part being inspected does not detract from the accuracy of the measurements taken.
As demonstrated below in Figure 3, the use of the curved composite probes contemplated in the present invention not only lend themselves to the testing of multiple diameter tubulars, but in fact when the curvature is designed for 100% coverage of the larger diameter range, and the selected transducer radius is slightly larger than the largest diameter to be inspected for wall thickness, the increase of the water path or delay line also insures 100% + coverage on subsequent smaller diameters passed through the fixed circular array without the necessity of changing the probes or their position relative to the center of the circle. This is possible because the incident angle for wall thickness inspection is perpendicular to the tubular being tested and the relative movement closer or further from the test specimen does not alter this angle of incidence. The ability to inspect for wall thickness in this manner reduces changeover time for varying diameters of tubes and guarantees full coverage over a range of diameters. This is of particular importance given upcoming changes to API specifications (already in draft form) in the area of Product Specification Levels (PSL's) that may require 100% wall coverage on tubulars historically inspected with the gamma wall source found on electromagnetic (EMI) tube inspection units. This feature makes the wall inspection component of the patent viable as a replacement for current gamma wall measurement systems, in use worldwide, well know to those familiar with the currently available technology.
As depicted below in Figure 3 showing a circular array of curve probes, with the various diameters of pipe (in this case 9.625” – 7.00” – 5.5” pipe sizes, it can be seen that insert a smaller diameter of tube inside the circular array of probe maintains the desired coverage while only increasing the water path to the pipe surface. Wipers and Seals only need be changed for a change-over there are no moving parts nor consumables contacting the pipe surface.
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