By Brent Sherar, Eric Caldwell, Peter Ellis II, Russell Kane
This paper is Part II of a two-part series intended to narrate the history, some of which has been forgotten over time, leading up to the publication of the first Material Requirement (MR-01-75) standard prepared by NACE and its subsequent auxiliary standards. Previously, Part I described the field observations and discussed the metallurgical factors that were being investigated by the historical NACE T-1B and 1F committees to support the development a of sour service materials standard. In Part II, we focus on the rationale behind the use of accelerated laboratory test procedures designed to differentiate metallurgical behavior in sour environments. The original sulfide stress cracking (SSC) test methodologies would later be codified as a Test Method in NACE TM-01-77 (1977). A review of the historical events culminating in NACE MR-01-75 and NACE TM-01-77 provides a technical basis for the historical use of NACE Solution A (5 wt% NaCl + 0.5 wt% acetic acid) to evaluate metallurgical factors, and the origins of several common SSC NACE Test Methods still used today: Methods A (tensile), B (three-point bent beam), and C (C-ring). The accelerated laboratory test results, in combination with parallel field trials (performed in advance of the first NACE MR-01-75 publication), supported the ≤ 22 Rockwell C (22 HRC) hardness limit for carbon and low alloy steels in sour environments containing ≥ 0.05 psia H<sub>2</sub>S partial pressure. As the oil and gas industry continues to innovate and mature, it is imperative to maintain knowledge of the origins of the NACE MR-01-75 and TM-01-77 standards and their intended purposes.
