Electromagnetic analysis of concrete tensioning wires

A method of detecting discontinuities in tensioning wires of a concrete pipe comprising:

• (i) providing a driving signal to a driver having an axis oriented orthogonal to an axis of a concrete pipe and proximal to an inside surface thereof to generate an induced current in pre-stressing elements extending substantially circumferentially of the pipe;
• (ii) providing a detector for producing an output responsive to a magnetic flux, the detector located in close proximity to an interior wall of a pipe and axially displaced not more than one pipe diameter of a plane orthogonal to the axis of the pipe and common to the driver,
• (iii) moving the detector along the wall of the pipe;
• and
• (iv) recording the output and the location of the detector as it moves.

A method of testing the tensioning wires of a pre-stressed concrete pipe along a length thereof using apparatus including magnetic flux production means spacedly disposed from magnetic flux detector means, said magnetic flux detector means adapted to be disposed proximal to a surface of a pipe, the magnetic flux production means producing a magnetic field in response to a driving signal and the detector means producing a detector signal in response to magnetic flux and locating means to indicate a location along said pipe and control means operatively connected to said locating means, to said magnetic flux production means and to said magnetic flux detector means, the method comprising performing the steps of:

• (i) providing a driving signal of at least one frequency;
• (ii) receiving a detector signal;
• and
• (iii) recording the detector signal in relation to the frequency of the driving signal and the location indication over a range of locations traversed along a length of pipe.

A method of testing tensioning wires of a pre-stressed concrete pipe along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of a pipe to be tested in a spaced relationship to the other and axially disposed within one pipe diameter to the other, the magnetic flux production means producing a magnetic field in response to a driving signal and the detector means producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

• (i) providing a driving signal of at least one frequency;
• (ii) receiving a detector signal;
• (iii) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal;
• and
• (iv) recording the output representative of the detector signal in relation to the fundamental frequency and the location;
• whereby at least one fundamental frequency is recorded over a range of locations traversed along a length of pipe.

An inspection apparatus for detecting discontinuities in tensioning wire of a concrete cylinder, comprising:

• (i) a driver coil adapted to be oriented with an axis orthogonal to an axis of a concrete cylinder to induce a current in a tensioning wire of a concrete cylinder in response to a driving signal;
• (ii) means for producing a driving signal;
• (iii) detector apparatus to produce an output responsive to a magnetic flux, said detector apparatus has an axis orthogonal to the axis of said driver coil and spacedly disposed there from, said detector coil adapted to be oriented proximal to a surface of said concrete cylinder and substantially in a plane orthogonal to an axis of the concrete pipe in common with the driver coil;
• and
• (iv) filter means for producing an output signal representative of differences between the driving signal and the output produced by said detector apparatus.

A method of detecting discontinuities tensioning wires a concrete cylinder comprising:

• (i) providing a driving signal to a driver coil means having an axis oriented orthogonal to an axis of a concrete cylinder to generate induced current in pre-stressing elements extending substantially circumferentially around the cylinder;
• (ii) providing a detector proximal to a surface of the concrete cylinder and spacedly disposed from said driver means along said axis of said driver coil means, the detector to produce an output responsive to a magnetic flux;
• (iii) filtering the output of the detector relative to the driving signal;
• and
• (iv) recording the filtered output and the location of the detector.

A method of testing the tensioning wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each proximal to a surface of a cylinder and in a spaced relationship to each other, the magnetic flux production means to produce a magnetic field in response to a driving signal and the detector means to produce a detector signal in response to magnetic flux and locating means to indicate a location along said cylinder and control means operatively connected to said locating means, to said magnetic flux means and to said detector means, the method comprising performing the steps of:

• (i) providing a driving signal of at least one frequency;
• (ii) receiving a detector signal;
• (iii) filtering the received detector signal relative to the driving signal;
• (iv) receiving a location indication;
• and
• (v) recording the filtered detector signal, the frequency of the driving signal and the location indication over a range of locations traversed along a length of cylinder.

A method of testing the tensioning wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of the cylinder in a spaced relationship to the other and axially disposed not more than one cylinder diameter from the other, the magnetic flux production means for producing a magnetic field in response to a driving signal and the detector means for producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

• (i) providing a driving signal of at least one frequency;
• (ii) receiving a detector signal;
• (iii) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal;
• and
• (iv) recording the output representative of the detector signal in relation to the fundamental frequency, the fundamental frequency and the location;
• whereby at least one fundamental frequency is recorded over a range of locations traversed along a length of cylinder.

A method of testing the tension wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of the cylinder, the magnetic flux production means for producing a magnetic field in response to a driving signal and the detector means for producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

• (i) providing a driving signal of at least one frequency;
• (ii) positioning the detector means in relation to the magnetic flux production means, each said detector means and the magnetic flux production means axially disposed not more than one cylinder diameter to the other;
• (iii) receiving a detector signal;
• (iv) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal;
• and
• (v) recording the location of the detector means and output representative of the detector signal in relation to the fundamental frequency, the fundamental frequency and the location of a deter;
• whereby at least one fundamental frequency is recorded over a range of locations traversed by said detector means along a length of a pre-stressed concrete cylinder.

A method of detecting discontinuities in spirally wound metallic pre-stressing elements of a concrete pipe having such elements which comprises:

• (i) providing a detector coil which has its axis parallel to the axis of the pipe, and which is of a diameter less than one quarter of the diameter of the pipe,
• (ii) placing the detector coil in close proximity to the interior wall of the pipe,
• (iii) generating a periodically varying induced current in the pre-stressing elements,
• (iv) moving the detector coil along the wall of the pipe and
• (v) recording the distance moved or the location of the detector coil, and the induced voltage or current sensed by the detector coil as it moves.