Study Of Corrosion Fatigue Crack Growth Characteristic For 07MnNiCrMoVDR Steel In H₂S Solution

Pressure vessels are equipment which endured high pressure for specific production and transportation with explosion danger. Especially for these vessels used in corrosion solution environment, when serious defects were founded in them explosion must occur as soon as defects and corrosion solution reacted each other. If proper measures were not taken in time, serious disaster must happen.The object of the present paper was to study the relationship between corrosion fatigue crack growth rate da/dN and stress intensity factor amplitude ΔK of 07MnNiCrMoVDR steel by corrosion fatigue crack growth rate experiment in H2S solution. This steel is the typical material used in chemistry and oil chemistry equipment in our country. Corrosion fatigue safety assessment method of pressure vessels with defects in service could be explored and investigated.In the present paper, corrosion fatigue crack growth rate and reliability of remainder life of 07MnNiCrMoVDR steel in H2S solution were mainly researched. The research contents and results were as follows.(1)Experiments of corrosion fatigue crack growth rate of 07MnNiCrMoVDR steel in H2S solution were conducted. The results indicated that corrosion fatigue crack growth rate of 07MnNiCrMoVDR steel increased with an increase in H2S solution concentration, stress rate and a decrease in loading frequency.(2)Importance of influence factors was discussed in the process of corrosion fatigue crack growth of 07MnNiCrMoVDR steel in H2S solution. Main influence factors were solution concentration, loading frequency and stress rate. The importance of stress rate was largest among these influence factors. The loading frequency was second important influence factor, while solution concentration was the last one.(3) Neural network technology and Monte-Carlo method were used to predict corrosion fatigue crack growth rate and remainder life. Coefficients C and n of corrosion fatigue crack growth rate of 07MnNiCrMoVDR steel in H2S solution under different conditions (solution concentration, loading frequency and stress rate) were predicted by BP neural network, and then remainder life and its reliability of corrosion fatigue were calculated by combining neural network with Monte-Carlo method.(4)Formula of corrosion fatigue crack growth rate of 07MnNiCrMoVDR steel in H2S solution was proposed. Using neural network, the expression of Cenv could be obtained, and then the formula was regressed with statistical toolbox in Matlab, which could be easily used in engineering.(5)The corrosion fatigue assessment program was compiled by use of Visual Basic. The corrosion fatigue assessment, remainder life prediction and reliability calculation of 07MnNiCrMoVDR steel in H2S solution were realized by the program. Therefore it made the corrosion fatigue assessment engineering method more simple and faster.