Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
NACE MR0175: Super Duplex 2507 for Sour Service
NACE MR0175 (now also published as ISO 15156) sets material requirements for metallic components used in oil and gas production environments containing hydrogen sulphide (H2S). The standard covers carbon steels, low-alloy steels, austenitic stainless steels, duplex and super duplex stainless steels, nickel alloys, and titanium alloys. Super duplex 2507 (UNS S32750) is qualified under Part 3 of the standard, which addresses cracking-resistant CRAs.
TorqBolt supplies super duplex 2507 fasteners, bar, pipe, and forgings to NACE MR0175 / ISO 15156-3 with mill test certificates that record hardness, ferrite content, and heat treatment history.
NACE MR0175 / ISO 15156 Scope
MR0175 / 15156 applies to metallic materials used in equipment for upstream oil and gas production where H2S is present. The standard is structured in three parts. Part 1 covers principles, Part 2 covers carbon and low-alloy steels, and Part 3 covers CRAs (corrosion-resistant alloys). Super duplex 2507 falls under Part 3, Section 7 (duplex stainless steels) and the duplex-specific tables in Annex A.
Hardness Limit: 28 HRC Maximum
Super duplex 2507 must not exceed 28 HRC hardness for sour service per Part 3 of MR0175 / 15156. The limit applies to the bulk material; weld and HAZ regions must also meet 28 HRC. Solution-annealed and water-quenched 2507 typically lands at 22 to 26 HRC, comfortably under the limit. Cold-worked 2507 can exceed the limit and is excluded from sour service unless re-annealed and re-tested.
Ferrite Content Window
Ferrite content for sour service must fall within 35 to 65 percent, measured per ASTM E562. Ferrite outside this window degrades sulphide stress cracking (SSC) resistance. The window is wider than the M-630 parent metal window (35 to 55 percent) because MR0175 accounts for weld metal as well as parent.
H2S, Chloride, and Temperature Limits
MR0175 / 15156-3 publishes environmental limits for super duplex 2507 in tabular form. The qualified envelope depends on the combination of H2S partial pressure, chloride concentration, pH, and temperature. Typical 2507 qualification covers H2S partial pressure up to 100 kPa (about 14.5 psi) at chloride levels up to 120,000 ppm and temperatures up to 232 degrees Celsius. The exact envelope is read from Annex A tables on a project-specific basis.
Heat Treatment for Sour Service
2507 components for sour service must be solution annealed at 1040 to 1100 degrees Celsius and water quenched. The quench must drive the section through the 600 to 1000 degrees Celsius critical band rapidly to suppress sigma-phase precipitation. Cold-worked components must be re-annealed before sour service exposure. Welds must use a qualified WPS that maintains ferrite within the 35 to 65 percent window.
Required Testing for MR0175 Compliance
| Test | Requirement |
|---|---|
| Hardness (bulk) | 28 HRC max, full cross-section traverse |
| Hardness (weld and HAZ) | 28 HRC max |
| Ferrite content | 35 to 65 percent per ASTM E562 |
| Heat treatment | Solution annealed 1040 to 1100 degrees Celsius, water quench |
| Microstructure | No sigma, no chi, no nitride; per ASTM A923 Method A |
| SSC test (if invoked) | NACE TM0177 Method A or B per project spec |
Welding Restrictions
Welds in sour service 2507 must use filler metal and a qualified WPS that produces ferrite within the 35 to 65 percent window in both weld metal and HAZ. Heat input is controlled to avoid sigma-phase precipitation in the HAZ. Post-weld solution annealing is required when WPS qualification cannot demonstrate as-welded compliance. ER 2594 (super duplex filler) is the typical filler for matching strength and corrosion resistance.
Cross-Reference: MR0175 to ISO 15156
MR0175 and ISO 15156 are technically equivalent. Most operators cite both. The ISO designation is preferred internationally; the NACE designation persists in North American specifications. Compliance to one demonstrates compliance to the other. See the dedicated ISO 15156-3 page for the ISO-format requirements.
Related Standards
- ISO 15156-3: ISO equivalent of MR0175 Part 3
- NACE TM0177: SSC laboratory test methods
- NORSOK M-630: Norwegian MDS (D55, D57)
- API 6A: wellhead and Christmas tree material requirements
- API 17D: subsea wellhead material requirements
- ASTM A923: intermetallic detection in duplex / super duplex
NACE MR0175 Frequently Asked Questions
What is the hardness limit for super duplex 2507 in sour service?
28 HRC maximum, in bulk metal, weld metal, and HAZ. Solution annealed and water quenched 2507 typically lands at 22 to 26 HRC. Cold-worked components must be re-annealed before sour service.
What ferrite content window applies to 2507 under MR0175?
35 to 65 percent ferrite by point count per ASTM E562. The window covers parent metal, weld metal, and HAZ. Wider than the NORSOK M-630 parent-only window (35 to 55 percent) because MR0175 explicitly addresses welds.
Is MR0175 the same as ISO 15156?
Technically equivalent. MR0175 is the NACE (North American) designation; ISO 15156 is the international designation. Most operators cite both jointly. Compliance to one demonstrates compliance to the other.
What H2S partial pressure can super duplex 2507 handle?
Up to 100 kPa (about 14.5 psi) within the qualified envelope, at chloride levels up to 120,000 ppm and temperatures up to 232 degrees Celsius. The exact envelope depends on the combination of H2S, chloride, pH, and temperature, read from Annex A tables of MR0175 / 15156-3.
Can cold-worked 2507 fasteners be used in sour service?
Cold-worked 2507 typically exceeds 28 HRC and is not admissible without re-annealing. Hot-headed and solution-annealed fasteners are the standard sour-service supply route. Mill test certificates must record hardness post heat treatment.
What welding filler is used for 2507 in sour service?
ER 2594 super duplex filler is typical, qualified per a WPS that maintains ferrite within 35 to 65 percent in weld and HAZ. Heat input is controlled to avoid sigma-phase precipitation. Post-weld solution annealing is invoked when WPS qualification cannot demonstrate as-welded compliance.
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