NACE MR0103 "Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments"1 was developed by Task Group 231 to provide a standard set of requirements for materials used in sour petroleum refinery equipment. In the past, NACE MR01752, "Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment", was frequently referenced for this equipment, even though refinery applications were outside the scope of MR0175. The process used to develop MR0103 is described, followed by a review of the requirements in the standard accompanied by highlights of the differences between MR0103 and the previous and current versions of MR0175.
INTRODUCTION AND DOCUMENT HISTORY
In 1975, NACE issued standard MR0175, "Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment", to cover requirements for materials resistant to sulfide stress cracking (SSC) in sour oilfield environments. Although the scope of MR0175 includes only oilfield equipment and associated facilities (including gas production and treatment), the lack of similar standards for other industries has compelled many users in those industries to reference MR0175 for materials destined for sour applications. Although the process conditions that constitute the non-oilfield sour environments are often quite different from those defined in MR0175, the material and material condition requirements have proven to be fundamentally on target.
In the late 1990?s, the NACE T-1F-1 task group, now called Task Group (TG) 081, began working on a complete rewrite of MR0175 that included a number of fundamental changes. One of the most significant proposed changes was the expansion of the scope of the document to include chloride stress corrosion cracking (SCC), based upon the fact that most oil and gas production streams contain chlorides in sufficient levels to cause SCC in susceptible alloys. As such, the proposed rewrite included maximum temperature limits for all materials that are susceptible to chloride SCC. For example, the rewrite proposed that the temperature limit for S31600 (type 316 stainless steel) be set at 60°C (140°F) maximum. The proposed changes would mean that MR0175 would be less suitable for use in many applications, including those in petroleum refineries, where chloride ion concentrations tend to be low enough that chloride SCC isn?t a common concern.
Initial discussion regarding the proposed changes to MR0175 and the potential development of a refinery-specific standard covering materials for sour environments occurred during the 1997 Fall Committee Week T-8 Information Exchange session. Further discussions, including review of drafts of proposed document sections, were held at subsequent T-8 Information Exchange sessions and at several Task Group (TG)T-8-25 ("Environmental Cracking") meetings. At Corrosion/2000, it was decided that a T-8-25 Work Group (T-8-25a) would be formed to develop a sulfide stress cracking document. This Work Group was eventually formed in June 2000 as TG (Task Group) 231 under the current NACE technical committee structure. TG 231 is administered by STG (Specific Technology Group) 34 "Petroleum Refining and Gas Processing" and sponsored by STG 60 "Corrosion Mechanisms".
The task group's writing approach was to borrow pertinent concepts and requirements from the current and proposed versions of MR0175, and modify them as needed to create a new standard that would meet the needs of the oil refining industry. For example, the resulting document utilized the alloy grouping philosophy that is used in what is now MR0175-20033, but did not implement environmental limits such as H2S partial pressures,
