An electromagnetic inspection system for detecting, in-situ, the location and character of flaws in a relatively long, thick-walled small bore tube of a heat exchanger wherein a resultant magnetic field is induced in the wall of the tube of selected direction and magnitude by the vector addition of the...http://www.google.ca/patents/US4649343?utm_source=gb-gplus-sharePatent US4649343 - Electromagnetic flux leakage inspection system for ferromagnetic tubes
