Study On Corrosion Behavior Of L360 Pipeline Steel And Weld Joint In CO₂/H₂S Solutions

With the development of oil and gas industry, strong corrosive medium containing CO2 and H2S has brought serious challenges. In this work, the behavior and main influence factors on L360 pipeline steel and L360 weld joints in CO2-H2S saturated solution were systematically studied using weight loss method, electrochemical measurement techniques and surface analytical technology in simulated water from Oilfield environment containing CO2-H2S.In this dissertation, state and distribution of metallographic microstructure, hardness and micro-area eleatrochemical performance of L360 weld joint were investigated in their thermal history zones. The results showed that the structure and characteristics of micro structures of L360 weld joint were different. Corrosion potential and corrosion current density at different zones were dissimilar in the simulation corrosion solution. A complex multiple electrode system occurred between these zones. The heat-affected zone suffered preferred corrosion dissolution. The H2S corrosion was the dominant factor. Corrosion inhibitor could retard the corrosion of weld joint effectively.Factors influencing corrosion rate of oil tube steels, such as effects of temperature, corrosion time, pH value and gas-liquid on corrosion rate in CO2-H2S saturated solution environment were studied by using weight-lossmethod, EDS, SEM and XRD. The results indicated that the temperature remarkably affected the characterization of corrosion rate, and the corrosion rate of L360 steel rose along with the increasing of temperature up to 50℃,then reduced dramatically due to the formation of a protective layer on the surface of steel. Corrosion product was proved to be FeS1-x in higher temperature. Corrosion was aggravated by reducing pH value and increasing the Cl- concentrations. The gas phase corrosion products were loose and a little corrosion pitting appeared on the surface.There was no corrosion pitting on the liquid corrosion product surface.