Method & Apparatus for Detecting Flaws in the Threaded End of an Elongate Member Using Electromagnetic Excitation and Automated Scanning Sensor

Apparatus for detecting flaws in the threaded end of a ferromagnetic pipe is disclosed. The apparatus comprises means for applying a magnetic force to produce a field generally axially through the threaded end of the pipe, first and second means adjacent successive crests of a thread for sensing a generally radial magnetic field and generating a first and second signal corresponding to the sensed magnetic fields, and means for differentially connecting the signals generated by said first and second sensing means, whereby a differential output signal is produced in response to a flaw between the crests of the thread being inspected. The apparatus also comprises means for helically rotating said sensing means to follow a path corresponding to the threads of the pipe, whereby the first and second signals vary with time. A method for detecting flaws in the threaded end of a ferromagnetic pipe is also disclosed. The method comprises the steps of applying a magnetic force to produce a field generally axially through the threaded end of the pipe, sensing the radial magnetic field adjacent successive crests of a thread of the pipe, generating first and second signals corresponding to the sensed magnetic fields, and differentially connecting the first and second signals.