The paper presents an approach of non-destructive testing of plastic deformation of metals and alloys by measuring the differential thermoelectric power. Using the developed measuring device for this purpose, measurements of thermoelectric power were performed on several types of steels that are used in the manufacture of product pipelines. Incisions were made on the surface of the testes objects, for the purpose of experimental detection of the place of plastic deformation. In the process of stretching, thermoelectric power was measured at and near the place of the proposed plastic deformation. During the process of stretching the sample, the decrease in thermoelectric power measurement occurs almost linearly. The maximum change in the thermoelectric power measurement of the tested object was observe before the rapture discontinuity.