Abstract: 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 magnetic fields produced by two magnetic field generators, at least one of which is carried by a scanner for traversing the tube and having an array of sensors mounted in close proximity to the wall of the tube generating a unique signal as the scanner passes a flaw in the tube.