Abstract
In accordance with Annex A of ANSI(1)/NACE(2)MR0175/ISO(3) 15156-2, low-alloy steel (LAS) components for oil and gas (O&G) are acceptable if they contain less than 1 wt.% Ni. As an alloying element in steels, nickel improves low-temperature toughness and hardenability and does not promote the formation of carbides that could retain hydrogen into the steels. In this work, a set of five steels with different nickel content was specially fabricated to study the effect of that element on the sulfide stress cracking (SSC) resistance. Quenching and tempering (Q&T) heat treatments were customized to each chemical composition to obtain a tempered martensite microstructure with a hardness level below but near the 22 HRC threshold. The effect of nickel content on the anodic and cathodic behavior of those steels was evaluated by electrochemical polarization tests in substituted NACE TM0177 A test solution, where H2S bubbling was replaced by thiosulfate additions (i.e., Tsujikawa Method). Hydrogen permeation tests were conducted in a Devanathan-Stachurski cell, to evaluate the effect of nickel on the hydrogen diffusion. Additionally, slow strain rate tests (SSRTs) were performed at the open circuit potential (OCP) to assess the role of nickel on the SSC resistance.
