The results of expert studies of large diameter pipes damaged due to external stress corrosion cracking are presented in the report. These data obtained in the 1993–1995 are typical for various regions of Russia. The results of laboratory studies of the stress-corrosion mechanism for pipe steels in suspensions of soils from the places where the operating failure had occurred are given in the report also. The mechanism of hydrogen-induced stress-corrosion cracking (HISCC) realizing through local hydrogenation of steel during plastic deformation has been determined by means of the technique of slow strain rate test (SSRT) of samples in the soil under cathodic, anodic and free corrosion potentials in combination with hydrogenation and hydrogen distribution analyses along length of a sample. No hydrogenation of volumes of pipes non-subjected to cracking was observed but hydrogenation took place in the zones subjected to stress corrosion.