Q: I've seen references to a new NACE standard, MR0103. What is it? How does it fit in with NACE MR0175?
A: NACE MR0103 is a new standard entitled "Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments." Think of it as "NACE MR0175 for petroleum refineries." NACE MR0175 was originally created to cover sulfide stress cracking in the oil and gas production industry. Refineries and other industries were outside of MR0175's scope. Even so, refineries sometimes referred to MR0175 because it was the only standard in existence that listed acceptable materials and material conditions for resistance to sulfide stress cracking (SSC). During the recent MR0175 revision process-which expanded the scope of MR0175 to cover chloride stress corrosion cracking (SCC) in addition to sulfide stress cracking, it became apparent that MR0175 would no longer be a suitable document for refinery use. The main issue was the temperature limits that would be imposed on austenitic stainless steels to prevent chloride SCC. Refinery applications are typically low chloride, so chloride SCC is not a primary issue. This precipitated the development of a new standard to directly serve the needs of the refining industry.
In general, MR0103 was created by "borrowing" information from MR0175-2002 and the proposed MR0175 rewrite (before it was approved as MR0175-2003), modifying requirements in some instances to better fit the needs of the refining industry, and adding information that was specific to refining. The resulting standard, MR0103-2003, was released in April 2003, shortly after the release of MR0175-2003. The 2003 revision is still current.
Differences between MR0103 and MR0175
- MR0103 includes different guidelines than MR0175 for determining if an environment is "sour," because the sour environments in refineries differ quite significantly from those in oil and gas production. The standard explicitly states it is the user's responsibility to determine if the environment is sour, based upon the guidelines in the document, on plant experience, or on risk-based analysis, and to specify if equipment must meet the MR0103 material requirements.
- Because MR0103 only covers SSC, it does not include environmental restrictions (i.e., temperature limits, chloride limits, pH, etc.) on materials. Although listed materials display varying degrees of resistance to SSC, no attempt is made to rank the materials.
- Materials and/or material conditions are included in MR0103 that are not listed in previous and/or current versions of MR0175, and vice versa.
- Because welding is prevalent in refinery piping and equipment, extra emphasis is placed upon welding controls in several material groups, most notably the carbon steels.
Some notable material requirements of MR0103
- Welds in P-No. 1 carbon steel materials must be performed per NACE Standard RP0472 "Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments." This recommended practice includes much more rigorous requirements than MR0175. RP0472 includes three different methods for controlling heat-affected zone (HAZ) hardness, and requires production weld deposit hardness testing unless welding is performed using SMAW with E70XX fillers or GTAW with ER70S-X (except -6, -7, or -G) fillers. Deposit hardness testing is even required on minor repairs and welds that have received a PWHT. This can cause a problem when trying to "upgrade" a standard commercial casting to meet MR0103. Most foundries use multiple welding processes (SMAW, GTAW, GMAW, and FCAW) for repairs, and even SMAW and GTAW can be performed with fillers that aren't exempted. It's often difficult or impossible to determine where weld repairs have been performed, so it can't be determined where to perform weld deposit hardness tests. If the locations of the repairs cannot be determined, and it cannot be verified that an exempt process/filler combination has been used, it may be necessary to order a special casting per MR0103 requirements.
- Alloy steels are defined as steels with a chromium content of less than 10%, in essence, steels that contain alloying elements greater than the amounts allowed in carbon steels but not enough chromium to be considered stainless steels. This allows the use of more highly-alloyed materials than MR0175, such as C12 (9% Cr - 1% Mo). Also, there is no 1% nickel restriction as in MR0175, so the 3% Ni, impact-tested steels (such as LC3 castings) can be used.
- MR0103 defines acceptable austenitic stainless-steel grades using a chemical composition range rather than listing each individual alloy, similar to MR0175-2003. MR0103 allows stainless steels with 0.10% maximum carbon to cover the high-temperature grades. Otherwise, requirements are similar to MR0175.
- Wrought S17400 and S15500, and cast CB7Cu-1 and CB7Cu-2 are allowed for general use. When S17400 or S15500 are used for pressure-retaining bolting, only the H1150M condition is allowed, and the hardness is limited to 29 HRC maximum.
- N04400, N04405, M35-1, M35-2, M30C, N05500 (alloy K500) and N07750 (alloy X750) are acceptable with hardness limits matching those in MR0175-2002. These materials were all omitted from MR0175-2003. This is only a brief summary of some of the major features and requirements. Consult MR0103 and RP0472 for detailed information. Obtain MR0103- 2003 and RP0472-2000 from NACE International's website (http://www.nace.org/nacestore) in either electronic (PDF) or paper form.