The local concentration of hydrogen absorbed from the environment in the section of high strength steels, where the hydrostatic stress is the highest under loading and where the initiation of delayed fracture takes place, was investigated stochastically. For the investigation, the results of statistical analysis of critical hydrogen concentration for delayed fracture obtained by using conventional strain rate tests and the ratio of fracture of exposed high strength bolts were used. The probability distribution of the local hydrogen was successfully evaluated and the correspondent environmental pH was estimated. The pH value simulating the maximum hydrogen entry caused by atmospheric corrosion in Okinawa was slightly lower than 2.
