STUDY ON FACRTORS AFFECTING LOW CR ALLOY STEELS IN A CO2 CORROSION SYSTEM

摘要

With better anti-CO_2 corrosion performance than carbon steel, low Cr (1%~5%) alloy steel has potential for use as pipeline steel to transport oil and gas. To understand the anti-corrosion mechanism of steels containing Cr, the formation of protective corrosion products was thoroughly studied. A large number of autoclave experiments simulating the oilfield environment had been carried out in the temperature range of 40-140 °C. Further more, other factors affecting film formation, such as CI~- concentration (ranging from 10g/L to 50g/L), microstructure and Chromium content were studied. The surface morphology and the composition of the corrosion product were analyzed using surface analytical techniques (SEM and EDS) and X-Ray diffraction (XRD), respectively. The result showed that, above 3%Cr addition to steels could remarkably improve the resistance to CO_2 corrosion due to three-dimensional mixed resistant networks within the corrosion products. With the increase of either temperature or Cl~- concentration, maxium corrosion rates of 3Cr steel was observed. Otherwise, with the same chemical composition, the microstructure difference between 3Cr steels resulted in the different anti-CO_2 corrosion performance.