Abstract: The apparatus of the invention is a segmented pig body having an electrical instrumentation subassembly mounted thereto. The subassembly consists of a plurality sensors for electromagnetically coupling to the inner surface of the pipeline, each of which generates a signal that varies as the localized relative permeability of the pipeline metal; an odometer assembly for generating correlating data; and an instrument for recording the signal and data for later analysis. The method of the invention comprises passing the pig through the pipeline while it is electromagnetically coupled by the sensors to the inner surface of the pipeline. During the pass, signals varying with the localized magnetic permeability of the pipeline wall and correlative data are generated and recorded. After the pass, the correlative data is used to correlate the signals to wall locations to locate stress occurrences.