Development of the NACE “MR-01-75” and NACE “TM-01-77” Standards, Part II: Accelerated Material Qualification Testing in Sour Environments at Near Atmospheric Pressure

Abstract

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.

Simultaneous Enhancement of Strength and Sulfide Stress Cracking Resistance of Hot-Rolled Pressure Vessel Steel Q345 via a Quenching and Tempering Treatment

“…Therefore, Q&T processing could improve SSC resistance by decreasing residual stress. In addition, it is recognized that SSC failure only occurs in steel with a hardness value higher than 22 HRC or 248 HV; otherwise, the peak C H value at high-concentration regions is insufficient to generate SSC failure [41][42][43]. The measured hardness values of the matrix and the carbon-rich banded structures for the initial hot-rolled specimens corresponded to ~190 HV and ~260 HV, respectively, while that of the matrix for the Q&T specimens corresponded to ~220 HV.…”

“…Therefore, Q&T processing could improve SSC resistance by decreasing residual stress. In addition, it is recognized that SSC failure only occurs in steel with a hardness value higher than 22 HRC or 248 HV; otherwise, the peak CH value at high-concentration regions is insufficient to generate SSC failure [41][42][43].…”

Effect of Cooling Rate on Sulfide Stress Cracking Resistance of a Q345 Pressure Vessel Steel Subject to Hydrogen Sulfide

“…In addition, it has been recognized in the applicable codes that the SSC become a problem only when the steel has a hardness higher than 248 HV, which is equivalent to 22 HRC. [5,31] Unless the steel is hard enough, the peak C H at the high-concentration region is insufficient to cause the SSC. Table 3 lists the Vickers hardness of both the ferrite matrix region and the banded structure region in microstructure.…”

“…[3,4] For conventional industrial applications, steels with the hardness of higher than Rockwell hardness (HRC) 22 (equivalent to 550 MPa YS) are thought to have high sulfide stress cracking (SSC) susceptibility. [5] Just from a strength point of view, the SSC cracking of the Q345 pressure vessel steel does not seem to be a concern even when applied in sour oil and gas environments containing H 2 S. Unfortunately, however, practical service experience indicated that the Q345 pressure vessel steel might suffer from SSC failure in wet H 2 S environments. A concern on the SSC failure is valid for this steel as applied in sour oil and gas environments containing H 2 S. The general opinion is that hydrogen ingress can occur under the condition that allows a release of hydrogen.…”