The hydrostatic re-testing of pipelines is one of the general methods of determination of service reliability of pipes in the zones characterized by high risk of stress corrosion. The detailed complex metal-physics studies of structural and stress-strain state of steel, as well as topography of stress-corrosion cracks, hydrogenation in fragments of pipes damaged at various stages of loading during re-testing were carried out due to the idea of “damage” of steel caused by harmful effect of increased pipes deformation. Templates of pipes having fractures and zones with or without stress-corrosion defects were cut out for studies. It has been shown that no deterioration of mechanical and ductility properties occurs in the parts of pipes without stress-corrosion defects. No considerable changes of character and degree of cracking as well as cracks topography have been detected during various stages of re-testing.

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.