NACE Standard MR-01-75 is being revised to include material requirements for all oil field equipment used in sour environments. The need for such a revision and its effect on drilling technology will be reviewed.


The sudden, brittle failure of oil field equipment exposed to sour environments first attracted attention in the early 1950's. The failure mechanism has been identified as sulfide stress cracking (SSC), a form of internal hydrogen embrittlement that occurs in many metals when they are stressed in the presence of water and hydrogen sulfide (H2S).

The prevention and control of SSC has been the subject of many investigations, and the National Association of Corrosion Engineers (NACE) has published or sponsored many articles, committee published or sponsored many articles, committee studies, reports, and symposia concerning SSC. The outgrowth of this activity was the development of documents such as NACE Publications 1B163 - "Recommendation of Materials for Sour Service", and 1F166 - "Sulfide Cracking Production and Pipeline Service". In 1975, these publications were superseded by NACE Standard MR-01-75 "Materials for Valves for Resistance to Sulfide Stress Cracking in Production and Pipeline Service". Production and Pipeline Service". NEED FOR REVISION OF MR-01-75

Even prior to its publication, the need for revision of MR-01-75 was recognized:

  1. Since MR-01-75 is the only document directly addressing the question of material requirements for service in environments containing H2S, it is being applied to situations involving components and environmental conditions quite different than those for which it was written. Several API and federal publications are referencing MR-01-75 for components other than valves.

  2. Many components used in sour environments require hardnesses (strength levels) greater than those permitted by MR-01-75.

  3. New materials and processing methods are constantly being proposed for use in sour environments.

Therefore, NACE, even before the publication of MR-01-75, established a Task Group (T1F-16) to develop a standard for materials for oil field equipment used in sour environments.

The need for revision became more urgent in early 1976, when the Texas Railroad Commission amended Rule 36 - Oil, Gas, or Geothermal Resource Operations in H2S Areas. Section 6.C. requires that materials and equipment used in drilling and workover operations comply with the requirements of MR-01-75. The current issue of MR-01-75 restricts the hardness of carbon and low alloy steels used in sour environments to 22 HRC maximum, which is equivalent to a tensile strength of approximately 110–115 Ksi and a yield strength of approximately 60–80 Ksi. Since most drilling and workover tools require higher strengths, strict adherence to Rule 36 would effectively prohibit drilling and workover operations in sour environments.


The task of revising MR-01-75 has not been easy. During the past two years approximately 100 persons representing a wide range of interests, have participated in discussions or contributed data for the revision. The result has been a proposed standard that has grown from seven to proposed standard that has grown from seven to 55 pages, has gone through eleven drafts, and is still not completed.

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