Corrosion Behavior Of X100 Pipeline Steel In Different Dissolved PH Solutions Under Ocean Dry And Wet Cycling Conditions

At present,the development of marine oil and gas resources has become a key area of energy planning in China.Oil and gas pipeline transportation is one of the important transportation modes for the transportation of marine oil and gas.However,the harsh and complex marine environment is an important factor affecting the corrosion of pipeline steel and restricting the safe operation of pipelines,especially the marine dry-wet cycling zone.X100pipeline steel will occupy an important position in the future construction of marine oil and gas pipelines,due to its corrosion resistance and high strength.Therefore,the study on the corrosion behavior of X100 pipeline steel in the marine dry-wet cycling environment will provide an important theoretical basis for the safe operation and integrity management of oil and gas pipelines.We have took the dry and wet alternating environment of the South China Sea as an example,using the method of weightlessness,potentiodynamic polarization,slow strain rate stretching（SSRT）and scanning electron microscopy.The marine dry and wet environment with different pH values was studied.The effects of electrochemical corrosion and stress corrosion cracking behavior of X100base metal and welded joints,and the changing laws reveal the electrochemical corrosion and stress corrosion cracking mechanism of X100 pipeline steel in different pH environments.The results show that the corrosion rate and corrosion current density of X100pipeline steel base metal and welded joint samples increase gradually with the decrease of pH value in the simulation of the pH value of the dry and wet cycling environment in the South China Sea under the same conditions.In the dry and wet cycling environment,the surface of the X100 pipeline steel forms a relatively stable and dense rust layer.The contact between the substrate and the external environment inhibits the anodize dissolution of the surface of the pipeline steel.When the pH value of the simulated dry and wet environment in the South China Sea is changed in the range of 4⁷,the stress corrosion sensitivities of the X100 pipeline steel base material and the welded joint are as follows according to the pH value:I_?4>I_?5>I_?6>I_?7.The increase of pH value reduces the stress corrosion sensitivity of X100 pipeline steel.The fracture is gradually changed from brittle/ductile fracture to ductile fracture.