FIELD: fault detection.SUBSTANCE: usage for non-destructive testing of large-sized carbon graphite products and blanks. Gist of the invention is that fixation of a carbon product, application of a coordinate grid with vertical and horizontal steps on the side and end surfaces are carried out (H+100) mm and (W+100) mm, where: H – height of the antenna array of an ultrasound tomograph, W – width of the ultrasonic tomograph antenna array, line-by-line survey of a product surface using a low-frequency ultrasonic tomograph with a two-dimensional antenna array of electroacoustic transducers with dry point contact, while the operating frequency of the tomograph is set in the range of 20–100 kHz, marking the grid cell when detecting internal reflectors in this cell, if two or more neighboring cells are labeled, a rectangular area including all adjacent labeled cells is labeled with a half step by dividing the cells of the survey grid in half, line-by-line survey of the area, marked at half-step, is carried out
