Effect Of Temperature On Corrosion Behavior Of X70 Pipeline Steel In Dry And Wet Cycling Environment

The marine environment is one of the most cruel natural corrosive environments.The complex and variable environmental factors in the marine dry-wet cycle environment pose a huge hidden danger to the safe operation of marine oil and gas pipelines.Temperature factor is one of the important factors affecting the corrosion of pipeline steel.X70 high-strength pipeline steel has high strength and toughness,good resistance to hydrogen induced cracking and resistance to sulfide stress corrosion cracking.It can effectively adapt to the marine environment and reduce transportation costs.It has been widely used in marine oil and gas engineering.Therefore,in the cycling environment of ocean dry and wet,the study of the influence of different temperature environments on the corrosion behavior of X70 pipeline steel is of great significance to the corrosion protection and safe operation of marine oil and gas pipelines.Taking the X70 pipeline steel base metal and weld as the research object,the weight loss test,electrochemical test and slow strain rate tensile test in the corrosion test chamber were simulated by simulating the marine environment periodic infiltration,and the metallographic microscope,SEM,EDS and other characterization methods were used.The effects of simulated ambient temperature of the wet and dry environment in the range of 10~40 °C on the corrosion behavior of X70 pipeline steel samples were studied,and the variation of temperature on the corrosion mechanism was revealed.The results show that with the increase of test environment temperature,the corrosion rate of X70 pipeline steel base metal and weld seam shows a trend of rapid rise and then tends to be gentle,and under the same conditions,the weld corrosion rate is higher than that of the base metal.rate.The higher ambient temperature increases the rate of material flow between the pipeline steel matrix and the external environment,which in turn increases the corrosion rate of the X70 pipeline steel.When the ambient temperature reaches 40 °C,the enrichment of chlorine in the rust layer of X70 pipeline steel occurs,acidifying the local environment in the rust layer,forming a mechanism for the combination of anodic dissolution and de-cathodic polarization on the corrosion process.Under the condition,the number and area of corrosion pits on the surface of X70 pipeline steel increased significantly,and the maximum diameter of corrosion pit exceeded 50 ?m.In addition,the higher ambient temperature increases the stress corrosion sensitivity of X70 pipeline steel base metal and weld.With the increase of temperature,the SEM morphology of the fracture of the specimen gradually transforms from ductile fracture to brittle fracture.