Influence of sodium nitrite concentration in aqueous corrosion solution on fatigue crack growth in carbon pipeline steel

Abstract Fatigue crack growth rate in carbon pipeline steel was studied in aqueous corrosion solution when the passive film formation occurs on the metal surface due to the presence of sodium nitrite admixtures of different concentration. The passive film strength was evaluated as the characteristic value of stress intensity factor K I * , which corresponds to the passive film failure of in the crack tip. For determination of parameter K I * the special experimental procedure was developed and verified. It was found that dependence of K I * on the concentration of passivation component in the environment is ambiguous and some maximum value of K I * is observed. The fatigue tests and hydrogen permeation study showed that under these conditions the formed passive film is the most resistible against electrochemical hydrogen absorption that provides the maximal deceleration of fatigue crack growth rate.