Phased array ultrasonic water wedge apparatus

A phased array ultrasonic probe assembly includes, in an exemplary embodiment, a housing and a phased array transducer supported inside the housing. The housing includes a first side wall and an opposing second side wall, and a first end wall and an opposing second end wall. The first and second side walls and the first and second end walls define a housing cavity in which the phased array transducer is positioned. The first and second side walls each have an inside surface that include a plurality of projections.

BACKGROUND OF THE INVENTION

This invention relates generally to ultrasonic inspection of dissimilar metal welds, and more particularly ultrasonic inspection of dissimilar metal welds with phased array transducers.

Pipe welds in, for example, nuclear reactors, have been examined with ultrasonic transducers using 45° and 60° refracted longitudinal waves. These angles have been established as the “norm” based on the weld configurations, ultrasonic theory, and field experience. The pipes are raster scanned in four directions to completely examine the weld volume which is very time consuming. Problems are sometimes experienced with the setup of the manipulator that delivers the ultrasonic transducers to the weld, and more importantly with the contact between the transducers and the specimen being examined. If continuous contact between the transducer and the pipe is not maintained, the scan data collected will be flawed which can result in time consuming rescans or missed defect detections.

Phased array ultrasonic probes have been developed that increase examination efficiency of conventional ultrasonic examination techniques by electronically steering the ultrasonic beam through a given range of angles. One major problem that still exists is the contact between the phased array ultrasonic transducer and the specimen being examined. Complex gimbling mechanisms that apply downward pressure on the transducers have been used to attempt to overcome this problem. However, other issues, for example, improper scanner setup and irregularities in the pipe surface can also effect inspection accuracy.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a phased array ultrasonic probe assembly is provided that includes a housing and a phased array transducer supported inside the housing. The housing includes a first side wall and an opposing second side wall, and a first end wall and an opposing second end wall. The first and second side walls and the first and second end walls define a housing cavity in which the phased array transducer is positioned. The first and second side walls each have an inside surface that include a plurality of projections.

In another aspect, a phased array ultrasonic probe assembly is provided that includes a housing and a phased array transducer pivotably mounted inside the housing. The phased array transducer includes a plurality of elements. The housing includes a first side wall and an opposing second side wall, and a first end wall and an opposing second end wall. The first and second side walls and the first and second end walls define a housing cavity in which the phased array transducer is positioned. The first and second side walls each have an inside surface that include a plurality of projections.

In another aspect, a method of inspecting a portion of a weld in a metal object using a phased array ultrasonic probe assembly is provided. The probe assembly includes a housing and a phased array transducer pivotably mounted inside the housing. The housing includes a first side wall and an opposing second side wall, and a first end wall and an opposing second end wall. The first and second side walls and the first and second end walls define a housing cavity in which the phased array transducer is positioned. The first and second side walls each have an inside surface that includes a plurality of projections. The method includes positioning the phased array ultrasonic probe assembly adjacent an outer surface of the portion of the weld to be inspected, adding a fluid to the housing cavity, and scanning the weld.

DETAILED DESCRIPTION OF THE INVENTION

A phased array ultrasonic probe assembly that includes a housing and a phased array transducer supported inside the housing is described below in detail. The housing includes opposing side walls having a plurality of “saw tooth” projections, and opposing end walls each having a at least one “saw tooth”, or triangle shaped, projection. The housing holds the phased array ultrasonic transducer in a standing column of water. The water fills the volume between the bottom of the transducer and the material that is being examined and permits for the ultrasonic sound waves to travel from the probe directly to the material with no break in contact. Sound exits the transducer at a predetermined angle and travels through the water until it comes in contact with the material where a velocity change is experienced. The change in speed causes the sound to refract as it penetrates that material permitting the weld volume to be inspected using the predetermined angle. To minimize the amount of noise introduced into the system, the walls of the housing are designed to absorb or scatter the near surface reflectors which improves resolution. Both circumferential and axial flaws can be identified. The circumferential flaws are detected when the transducer is perpendicular to the longitudinal axis of the pipe. To detect axial flaws, the transducer is rotated along the longitudinal axis of the pipe.

Referring to the drawings,FIG. 1is a perspective illustration of a phased array ultrasonic probe assembly10in accordance with an exemplary embodiment of the present invention. Probe assembly includes a housing12and a phased array ultrasonic transducer14pivotably mounted in housing12. Housing12is substantially rectangular shaped and includes a first side wall16, an opposing second side wall18, a first end wall20, and an opposing second end wall22. Side walls16and18, and end walls20and22define a cavity24in which transducer14is mounted.

Transducer pivot pins26and28extend through end walls18and20respectively to pivotably mount transducer14in housing12. An angle adjustment block30is coupled to one end of transducer14and interfaces with an angle selection member32coupled to housing12. In the exemplary embodiment, angle selection member32includes an arcuate portion34that mates to an arcuate shaped end36of angle adjustment block30. A set screw38in angle selection member locks angle adjustment block30in place thereby setting the desired angle of transducer14.

Housing cavity24is filled with a liquid. In the exemplary embodiment, the liquid is water, and in another embodiment, the liquid is a combination of liquids that facilitate the transmission and reception of ultrasonic sound beams. A fluid inlet40is located in housing12to permit the filling of housing cavity24with fluid. Housing12also includes at least one air release vent42(two shown) to remove any air trapped in cavity24during the filling of cavity24with a fluid.

A first flexible membrane seal44covers the area between transducer14and side walls16and18to hold the fluid inside housing cavity24. A second seal46seals the bottom of housing12with the object that is being inspected. Seal46in one embodiment is a membrane seal having at least one slit or opening to permit the fluid to flow through housing cavity24while maintaining a volume of fluid in housing cavity24that fills the volume of cavity24between the bottom of transducer14and the object that is being examined. In an alternate embodiment, seal46is a resilient material that is located around the bottom edge of housing12to provide a watertight seal so that the liquid cannot drain out of housing cavity24. Housing12also includes at least one tool manipulator attachment member48to couple probe assembly10to a tool manipulator (not shown)

FIG. 2is a sectional illustration of side wall16of phased array ultrasonic probe assembly10, andFIG. 3is a sectional illustration of end wall20. Referring also toFIGS. 2 and 3, side walls16and18include a plurality of projections50extending from inner surfaces52and54respectively. End walls20and22include at least one projection56extending from inner surfaces58and60respectively. In the exemplary embodiment, projections50and56have a triangle or “saw tooth” shape. In alternate embodiments, projections50and56can have other shapes, for example, semi-circular, elliptical, or any other shape that reduces noise produced by the sound waves bouncing off the walls of housing12.

FIG. 4is a schematic illustration of phased array transducer probe assembly10mounted on a pipe61, andFIG. 5is a schematic illustration of phased array ultrasonic transducer12. Referring also toFIGS. 4 and 5, transducer12includes a plurality of elements62that emit ultrasonic beam64. An important aspect of probe assembly10usage is the ability to dynamically synthesize ultrasonic beam64and create a “Virtual Probe” of any angle within the overall beam spread of an individual element62. During operation, beam64is created by sequentially firing each element62to create a wave front66following a desired angle68. Angle68is selected and set up by angle selection member32and angle adjustment block30. This “Virtual Probe” can also be “swept” through a weld70in pipe61by firing groups of elements in a large array. This effect can be used to dynamically focus or “electrically steer” ultrasonic beam64by selecting the probe firing order and pulse delays. This can be changed on a pulse by pulse basis to effectively “sweep” a focal point through weld70. Beam steering and dynamic focusing can be combined to enable resultant beam64to be both focused and angled in predetermined increments. Ultrasonic phased array transducers14are commercially available from Krautkramer Ultrasonic Systems Group of Agfa NDT, Inc., Lewistown, Pa.

Referring toFIG. 5, the basic parameters of transducer14are defined as frequency, aperture A, element size X, element width Y, pitch P, and number of elements62. A suitable frequency is 1.0 to 5.0 MHz for the material type and thickness of weld70in pipe61located in a nuclear reactor. However, other transducer frequencies can be used for pipes and pipe welds manufactured from other materials.

Element pitch P is determined by calculating the acoustic aperture A needed to focus beam64at the required sound path and dividing this value by the total number of elements62and the amount of steering needed to create the desired angles. The size X of elements62is set as the maximum possible pitch. The width Y of elements62is determined by calculating the effective diameter for a near field of fifteen centimeters to give the smallest beam profile in the y-plane. The physical restrictions of the scanning surface must also be considered in determining the basic parameter values of transducer14.

Referring again toFIG. 4, a volume72of beam64that is examined includes weld70and pipe61extending from outer surface74towards inner surface76. Just as transducer14can be oriented in a plurality of angles68, as discussed above, beam64can be oriented or steered in plurality of angles. In one embodiment, beam64can be steered along a substantially axial path across weld70in a linear path in the orientation of weld70. In another embodiment, beam64can be steered along a substantially axial path across weld70in a linear path perpendicular to the orientation of weld70in predetermined increments. In yet another embodiment, beam70can be steered along a substantially circular path across weld70.