Electrochemical Behavior of Nickel-Containing LAS in Deaerated TM0177 Solution A

Abstract

Low alloy steels (LAS) are extensively used in oil and gas (O&G) production due to their good mechanical properties and low cost. NACE MR0175/ISO15156 specifies a maximum of 1wt% nickel (Ni) in LAS. That is, the NACE/ISO restriction excludes a significant number of high-strength and high-toughness alloys, such as Ni-Chromium (Cr)-Molybdenum (Mo), Ni-Mo and Ni-Cr-Mo-Vanadium (V) grades, for sour service applications. Ni is desirable in LAS because it: a) increases hardenability, strength, and fracture toughness, b) has a low penalty on weldability, and c) lowers the ductile to brittle transition temperature (DBTT) below -100°C. The aim of the current research was to melt eight experimental steels containing 0.2%C + 0.8% Mn and a varying concentration of Ni between 0 and 5%, and test their electrochemical response in deaerated NACE TM0177 solution A. Preliminary experimental results showed that Ni did not have a linear effect on the electrochemical behavior of the experimental steels at the corrosion potential and under cathodic polarization. In the anodic potential range, additions of 1% Ni or higher reduced the anodic dissolution current.