Study On Hydrogen Sulphide Corrosion Behavior Of Steel N80

With the development of oil and gas field, the possibility of stress corrosion cracking is enhanced in excavation and transpotion equipment because of the increasing corrosion gas H2S and water content of most oil and gas field in China.The key way to transport oil and gas is oil and casing pipe, so there is an important meaning in studying the corrosion behavior of the steel, then we can take corresponding measures and reduce the lost.N80 is the main material of oil and casing pipe, in this text, the experiment is conducted on stress corrosion tester to study the effect of concentration and temperature H2S on stress corrosion sensitivity about base metal and welding line. Fracture analysis is done to study the mechanism of stress corrosion cracking by SEM. This paper has studied the characteristics of polarization curve in different concentrations of H2S, Cl- and PH value by using electrochemical methods, and analyses the influence of the above factor.By stress corrosion tests, it shows that with the increasing H2S or temperature, fracture time, percentage elongation, section shrinkage rate and fracture absorption energy decreases, the stress corrosion cracking sensitivity increases, and that of the welding line is higher than base metal in the same corrosive condition.By SEM, it finds that there are many dimples on fracture, and characteristics of toughness fraction are showed as the concentration of H2S reduced. On the contrary, cleavage fracture is showed, and there are many secondary bench propagation cracks that show characteristics of brittle fracture when the concentration of H2S increases.By measuring the cathode and anode polarization curve of N80 steel in different concentration of H2S, Cl- and pH value by using electrochemical methods, it shows: in acidic solution, the concentration of H2S, pH value interacted with each other, the high concentration of H2S or low pH value can promote the reaction of anode ,and accelerate the corrosion rate, and H2S can make the anode process increased with augment of acidic solution. Adding Cl- into the solution, Cl-, H2S and pH interacted with each other, polarization curve moves rightward, self-corrosion current increases, corrosion potential negative shifts, and the corrosion rate increases.