Degradation of a low-carbon steel in long operation in an oil-hydraulic unit

We present an atypical example of corrosion fracture of a low-strength high-plasticity steel from an internal surface formed by a hole in a choke of an oil-hydraulic unit, operated for 35 years. The conclusion that, in terms of the effect on the mechanical behavior of the metal operated for a long time, oil can be considered to be an aggressive medium is made. Its influence is enhanced by the preliminary plastic deformation of subsurface layers of the metal using force drilling of the hole in the choke. We detected fractographically the subcritical growth of a crack from the internal surface of the choke with multiple secondary cracking, which is interpreted as a manifestation of the mechanism of hydrogen embrittlement of the metal degraded during long operation.