Method and apparatus for ultrasonic pipeline inspection

Apparatus for determining the wall thickness of a pipe having fluid therein, the pipe having an interior wall and an exterior wall, the fluid having a known acoustic impedance, comprising:

• a housing;
• fluid sealing means associated with said housing to cause said housing to travel through said pipe by the force of fluid flow;
• odometer means providing odometer electrical signals response to the travel of said housing in a pipe;
• a plurality of multi-element transducers attached to said housing that transmit acoustic pulses into said pipe and receive reflected acoustic signals from said interior wall and exterior wall of said pipe;
• circuit means contained within said housing to cause transmission of said acoustic pulses and to provide electrical indicator signals in response to said reflected acoustic signals, which electrical indicator signals have a direct relationship to the distance between said interior wall and said exterior wall of said pipe;
• means to record said electrical indicator signals in relationship to said odometer signals;
• each of said multi-element transducers being comprised of a plurality of discrete piezoelectric elements with a polymer fill between the elements, the piezoelectric elements having sidewalls arranged in adjacent mechanically isolated relationship with each other providing interstices therebetween, each piezoelectric element having a forward face and a rearward face, the interstices being filled with a viscous polymer;
• a first conductive film in electrically continuity with each said piezoelectric element forward face;
• a second conductive film in electrical continuity with each said piezoelectric element rearward face;
• and
• conductors connecting said first and second films to said circuit means.

A method of measuring the wall thickness of a pipe having an interior and exterior wall employing a pig body having a circumferential surface and having fluid sealing means to cause the pig body to travel through the pipe by the force of a fluid flowing in the pipe, the fluid having a known acoustic impedance, comprising:

• (a) mounting on said pig body circumferential surface a plurality of multi-element transducers in spaced apart relationship, each transducer having a plurality of discrete piezoelectric rod-like elements each having sidewalls, a forward face and a rearward face, the plurality of rod-like elements separated by a polymer being arranged so that their sidewalls are in adjacent and mechanically isolated relationship, said rod-like elements presenting said forward faces thereof in a common surface and presenting said rearward faces thereof in a common surface, a first conductive film being secured to said forward faces of said rod-like elements and a second conductive film being secured to said rearward faces of said rod-like elements;
• (b) by means of a circuit carried by said pig body, sequentially transmitting an electrical pulse in the form of a voltage differential between said first and second conductive films of each of said multi-element transducers to cause each said multi-element transducer to initiate an ultrasonic pulse in said fluid flowing in said pipe, ultrasonic pulses being reflected by said pipe interior and exterior walls, the reflected ultrasonic pulses impinging on said multi-element transducers;
• (c) in each multi-element transducer, converting said reflected ultrasonic pulses to electric signals;
• and
• (d) analyzing said electrical signals to provide a measurement of said pipe wall thickness determined by the time lapse between said ultrasonic pulses reflected by said pipe interior and exterior walls.