51312-01357-The Anti-pitting Mechanism of Low Cr Alloy Steel in CO2 Corrosion Environment

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Product Number: 51312-01357-SG

ISBN: 01357 2012 CP

Author: Lining Xu

Publication Date: 2012

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ABSTRACT: With the better localize corrosion resistance than carbon steel the low Cr(1%-5%) alloy steels are amongst the most promising candidates as pipeline steel to transport oil and gas. An increase in Cr content leads to a lower susceptibility to localize corrosion however the anti-pitting mechanism of low Cr alloy steel has not been clarified. To understand the growth of the protective corrosion film a large number of autoclave experiments simulating the oilfield environment had been carried out at various corrosion time(8-720h). Further more man-made pitts which were prepared beforehand on low Cr alloy steel and carbon steel were used for observing the development of the pitting through the subsequent corrosion.The surface morphology and the composition of the corrosion product were analyzed using surface analytical techniques (SEM and EDS) and Electrochemical impedance spectrum (EIS) respectively. The result showed that the higher Cr/Fe of the scale leads to the better corrosion resistance. The enrichment of Cr in the corrosion product film locally will restrain the potential pitting and the man-made pit to grow. The changes of the EIS clearly reflect the appearance and evolvement of the pitting which is observed by scanning electron microscopy. KEY WORDS: CO2 corrosion low Cr pipeline steel Electrochemical impedance spectrum localize corrosion