Effect of Environmental Composition on Fatigue Crack Growth and Hydrogen Permeation in Carbon Pipeline Steel

Abstract

The fatigue crack growth rate diagrams of the carbon pipeline steel were received under the presence of the admixtures of sodium nitrite as the passive component in the basic aqueous hydrogen-containing solution. It has been found that the fatigue crack growth rate \({{\text{d}}a/{\text{d}}N}\) depends ambiguously on the concentration \({C_{{{\text{NaNO}}_{{2}} }} }\) in solution due to the different properties of the passive films formed on the steel surface. The strength of passive films formed under different concentrations \({C_{{{\text{NaNO}}_{{2}} }} }\) was evaluated as a characteristic value of stress intensity factor \(K_{I}^{ * }\), which corresponds to the passive film failure of at the crack tip. For the determination of the parameter \(K_{I}^{ * }\), the special experimental procedure was developed. Received results showed that the dependence \(K_{I}^{ * }\) on the concentration \({C_{{{\text{NaNO}}_{{2}} }} }\) is ambiguous and the maximum exists at some concentration \({C_{{{\text{NaNO}}_{{2}} }} }\) when the value \(K_{I}^{ * }\) is maximal. The study of hydrogen permeation in steel at the presence of the passive film on the metal surface showed on some specific value of \({C_{{{\text{NaNO}}_{{2}} }} }\), at which the formed passive film is the most resistible barrier against electrochemical hydrogen absorption. This value is very close to the above-mentioned value \({C_{{{\text{NaNO}}_{{2}} }} }\), which corresponds to the highest strength of the passive film and also to the maximal deceleration of fatigue crack growth rate. Consequently, it may be concluded that the relationship between passive film strength, its ability to serve as a hydrogen barrier and fatigue crack growth rate exists. Thus, it is possible to decelerate the fatigue crack growth by the targeted variation of environmental composition.