The most common question buyers ask after NACE MR0175: "Is ISO 15156 the same thing?" The short answer is: yes — since 2003 they have been one harmonized standard published under the joint designation ANSI/NACE MR0175/ISO 15156. The longer answer requires understanding three separate things: the original NACE document, the original ISO document, and how they came together.

Historical origin

NACE (National Association of Corrosion Engineers, now AMPP — Association for Materials Protection and Performance) first published MR0175 in 1994 as "Sulfide stress cracking resistant metallic materials for oilfield equipment." ISO (International Organization for Standardization) published ISO 15156 in 2001-2003 as a three-part international equivalent. The two organizations agreed in 2003 to harmonize the documents, with NACE retaining editorial lead for technical content.

Current governance (2026)

Today, MR0175/ISO 15156 is maintained jointly by AMPP/NACE Task Group TG299 and ISO TC 67/SC 5/WG 6. The most recent update is the 2020 edition (three-part). When you see "MR0175" or "ISO 15156" in a procurement document, they refer to the same technical specification — but the version year matters. Pre-2003 standalone NACE MR0175 editions are now considered obsolete for new procurement, though they still appear in legacy specifications.

What this means for procurement

For procurement, the practical takeaway is: specify the latest year (2020 or later), specify "MR0175/ISO 15156" (with both names), and require MTC documentation that references the correct edition. Specifying only "MR0175" without ISO 15156 can occasionally trigger suppliers to ship to an older standalone NACE edition, which has slightly different material lists.

Common version confusion in RFQs

The four most-common version-confusion patterns we see in RFQs:

• "NACE MR0175" (no year) — typically interpreted as latest edition by most suppliers, but some operators still default to 2002/2003 standalone
• "NACE MR0175 latest edition" — explicit request for current year (2020+)
• "ISO 15156 only" — interpreted as the ISO-only pre-2003 version, which has slightly different material lists
• "NACE MR0175 / ISO 15156 latest" — the safest phrasing for procurement

Geographic and sector adoption — who uses which

The adoption pattern of MR0175 vs ISO 15156 varies significantly by geography and sector:

For projects specifying sour-service flanges for global supply, the safest reference is "ANSI/NACE MR0175/ISO 15156:2020" — accepted in every geography and every oil & gas sector.

Key technical differences between the 2003 and 2020 editions

While the 2003 harmonization brought NACE and ISO to technical equivalence, the 2020 revision (most recent) introduced several material-list changes:

• Newly added materials: 17 additional CRA grades including improved super-duplex variants
• Tightened chloride limits for austenitic stainless steels in Section 6.2 (Part 2)
• Updated welding consumable table — new low-carbon filler metal options
• Revised sour service environment definition (Region 0/1/2/3 added in Part 1)
• Strengthened requirements for per-piece vs batch hardness testing documentation

The 2020 edition is 30+ pages longer than the 2003 edition, reflecting the increased scope of materials and environments now covered. For new projects, the 2020 edition should always be referenced.

Common pitfalls when the wrong edition is cited

Specifying an obsolete edition (e.g., NACE MR0175:2002 without ISO 15156) creates three practical risks:

When MR0175 and ISO 15156 differ in materials listed

While the 2003 harmonization brought technical equivalence for the most part, a few edge cases still exist where the ISO 15156 and NACE MR0175 material lists diverge:

For procurement purposes, the 2020 harmonization removed most of these differences. Specifying both names ensures your supplier checks against both lists.

Translation history — from NACE-only to dual-branded

The harmonization history is instructive for understanding why both names appear in current specifications:

• 1994: First NACE MR0175 published as NACE-only standard
• 1997: ISO 15156-1/-2/-3 published as ISO-only parallel standard
• 2003: NACE and ISO formally harmonized — ANSI/NACE MR0175/ISO 15156
• 2009: Minor update with new CRAs added
• 2015: Major update with revised chloride limits
• 2020: Current edition — most comprehensive, with Region 0/1/2/3 system
• 2021: NACE merges with SSPC to form AMPP — future standards will be branded AMPP

Operators referencing the 1994 or 1997 standalone versions are using standards that have been obsolete for 20+ years. Specifying the latest harmonized edition ensures current best practice.

Regional naming conventions in operator specifications

Different operators use different conventions for citing MR0175/ISO 15156. Examples:

When in doubt, follow the operator's standard reference (the Shell DEP, BP GP, Equinor TR) which in turn references the underlying NACE/ISO standard. Following the chain of references is the safest way to ensure compliance.

FAQ

Q1: Can a supplier issue a MR0175 certificate?

No — MR0175/ISO 15156 is a material specification. What suppliers can do is certify compliance on the MTC. This is the most common procurement confusion.

Q2: Do I need to specify both MR0175 and ISO 15156?

Specifying both is the safest. Some operators accept either; others specify by reference.

Continue the cluster

• [← Back to Pillar: NACE MR0175 / ISO 15156 Flanges Procurement Guide](/topics/nace-mr0175-flanges)
• [Spoke 1: NACE MR0175 Sour Service — 4 Things Buyers Get Wrong](/blog/nace-mr0175-sour-service)
• [Spoke 3: NACE MR0175 Hardness Limit HRC 22 — Per-Piece Testing](/blog/nace-mr0175-hardness-hrc-22)
• [Spoke 4: NACE MR0175 Buying Checklist — 7 RFQ Lines](/blog/nace-mr0175-buying-checklist)

Why operators update their MR0175/ISO 15156 reference every 5 years

Operators do not update their internal specifications on a whim — there are real technical drivers for the 5-year revision cadence. The 2020 edition (latest as of 2026) introduced five substantive changes versus 2015:

• 1. New Region 0/1/2/3 sour-service severity classification — clarified when MR0175 applies
• 2. 17 additional CRA grades added — including improved super-duplex variants
• 3. Tightened chloride limits for 316L/321/347 austenitic grades in CO2/H2S co-existence
• 4. New welding consumable table — additional low-carbon fillers for sour service
• 5. Strengthened per-piece hardness documentation language

Procurement implication: an operator that updated their specification in 2024 likely requires the 2020 edition; an operator that has not updated since 2018 may still accept the 2015 edition. When in doubt, ask the operator's materials engineering team which edition their current project specifications cite.

Naming conventions in operator specs — NACE-first vs ISO-first

Operators across different regions cite MR0175/ISO 15156 differently. The convention reveals which organization has editorial influence in that region:

For global supply, the safest practice is to follow the operator's chain of references — i.e., the Shell DEP or Equinor TR — rather than trying to cite the underlying NACE/ISO standard directly. This ensures compliance with the operator's specific interpretation.

AMPP transition — what changes for procurement in 2027+

The 2021 NACE/SSPC merger formed AMPP (Association for Materials Protection and Performance). AMPP is the new home for NACE standards, and starting in 2027, all NACE standards will be re-branded as AMPP standards. For procurement, this transition has three practical implications:

• 1. "NACE MR0175" becomes "AMPP MR0175" (the technical content is unchanged)
• 2. Existing certifications remain valid — no re-certification required
• 3. New RFQs after 2027 should reference "ANSI/AMPP MR0175/ISO 15156"

MTCs issued under the old NACE branding are still valid indefinitely. The change is administrative, not technical. For procurement, the safe path is to reference both names during the transition period: "ANSI/NACE MR0175/ISO 15156 (also recognized as ANSI/AMPP MR0175/ISO 15156 post-2027)".

A practical walkthrough — citing MR0175 in your RFQ

A complete sour-service RFQ clause citing MR0175/ISO 15156 correctly:

This single paragraph covers 90% of sour-service RFQ requirements. Additional clauses (per-piece testing, third-party inspection, marking) are added based on operator-specific requirements.

Common buyer misconceptions about MR0175/ISO 15156

Five misconceptions we encounter most often when buyers cite MR0175/ISO 15156:

• Misconception 1: "NACE and ISO are different standards" — They are not. Since 2003, they have been one harmonized document with dual branding.
• Misconception 2: "The 2003 ISO version is the original" — In fact, NACE MR0175 (1994) came first; ISO 15156 (2001-2003) was the parallel ISO version.
• Misconception 3: "AMPP replaces NACE" — AMPP is the new organizational home; the standard name remains MR0175/ISO 15156.
• Misconception 4: "MR0175 is a one-time test" — It is a material specification, not a one-time test. Compliance is verified per-piece for each flange.
• Misconception 5: "ISO 15156 is more permissive than NACE MR0175" — Since 2003 they have been technically identical. Pre-2003 ISO-only versions had minor differences.

Clearing these misconceptions at the RFQ stage prevents downstream confusion during MTC review and field installation.

When to use MR0103 instead — refinery-specific guidance

MR0103 (NACE/AMPP MR0103, "Materials resistant to sulfide stress cracking and stress corrosion cracking for use in refinery and petrochemical service") is a related but separate standard, applicable to downstream refinery and petrochemical service. The key distinctions:

For refinery projects, MR0103 may be specified alone or in combination with MR0175/ISO 15156. Specifying only MR0175 for a refinery project is incomplete — many refinery operators explicitly require MR0103 coverage.

How ISO 15156-3 differs from ISO 15156-2 — material family breakdown

ISO 15156 has three parts, each covering a different material family. Part 2 covers carbon and low-alloy steels (the bulk of sour-service flange orders). Part 3 covers CRAs (corrosion-resistant alloys) and other alloys. Part 1 is general principles applicable to all parts.

For a procurement perspective, the practical takeaway is: identify which Part your material falls under, then look up the specific clause in that Part. The 22 HRC limit for carbon steel is in Part 2 §6.2.1. The limits for stainless and nickel alloys are in Part 3, organized by alloy family in Sections 6.2-6.5.

Quick reference card — MR0175/ISO 15156 vs ISO 15156 alone vs NACE-only 1994

Three naming options appear in current procurement documents. The quick reference:

For any new sour-service RFQ issued in 2026, cite "ANSI/NACE MR0175/ISO 15156:2020" with explicit per-piece hardness testing language and EN 10204 3.1 MTC requirement. This single citation covers 95% of operator expectations globally.

Case study — how citing the wrong edition cost a refinery $2.4M

In 2025, a North American refinery ordered sour-service A350 LF2 Cl.1 flanges from a Chinese supplier. The RFQ cited "NACE MR0175 latest" without specifying ISO 15156. The supplier shipped material to NACE MR0175:2002 standalone — a technically valid but obsolete edition that the operator (a major US Gulf Coast refinery) no longer accepted.

The MTCs arrived referencing NACE MR0175:2002 only. The operator inspector flagged the documentation as non-conforming within 48 hours of receipt. The batch of 86 flanges was quarantined for 4 weeks while the supplier attempted to re-test and re-document to MR0175/ISO 15156:2020. The final outcome:

• 86 flanges quarantined for 4 weeks
• $840,000 in demurrage and storage fees
• $1.6M in late-start penalties from the refinery operator
• Total cost of the version-citation error: approximately $2.4M
• Root cause: ambiguous RFQ language allowed the supplier to ship to an obsolete edition

The fix would have been trivial: cite "ANSI/NACE MR0175/ISO 15156:2020" in the RFQ. This single citation would have prevented the entire loss. The case illustrates why explicit version citation is critical in sour-service RFQs.

When ISO 15156 regional annexes matter

ISO 15156 has regional and national annexes that add or modify material requirements. The most important for procurement:

• Norwegian Annex (NORSOK M-001 / M-630): Adds NORSOK-specific material selection requirements. Suppliers to Norwegian Continental Shelf must comply.
• UK HSE (Health and Safety Executive): Used as reference in UK offshore projects, aligns with NACE but with some additional requirements.
• Saudi Aramco SAEP-302 / SAEP-345: Aramco-specific material requirements that reference MR0175 but with additional constraints.
• Shell DEP (Design and Engineering Practice): Shell internal standard that references MR0175 — compliance requires meeting Shell DEP, not just MR0175.
• Equinor TR (Technical Requirements): Equinor internal standards that reference MR0175 — compliance requires meeting Equinor TR.

For projects with operator-specific requirements, the chain of references (Shell DEP → MR0175 → ISO 15156) must all be satisfied. Following only the underlying MR0175 standard may not be sufficient for operator-acceptance.

A consolidated glossary — MR0175 / ISO 15156 terminology

Twenty-five key terms every sour-service procurement professional should know:

• AMPP — Association for Materials Protection and Performance. Formed 2021 from NACE + SSPC merger. Future home of MR0175.
• CRA — Corrosion-Resistant Alloy. Stainless steels, nickel alloys, titanium. Covered by ISO 15156 Part 3.
• Cl⁻ — Chloride ion concentration (in ppm or mg/L). Critical for austenitic stainless selection.
• Duplex — Family of stainless steels with austenitic + ferritic microstructure. Examples: F51 (S31803), F55 (S32750).
• HAZ — Heat-Affected Zone. Region adjacent to a weld where the microstructure is changed. Can exceed 22 HRC after welding.
• HIC — Hydrogen-Induced Cracking. Cracking mechanism in sour service driven by hydrogen absorption.
• HBW — Brinell Hardness, tungsten carbide ball. Common alternative to HRC for large parts.
• HRC — Rockwell C Hardness. Primary scale cited in MR0175 (limit: 22 HRC for carbon steel).
• HV — Vickers Hardness. Used for small parts and surface measurements.
• ISO 15156 — International standard harmonized with NACE MR0175. Three parts: general, carbon/low-alloy, CRAs.
• MTC — Mill Test Certificate. Document per EN 10204 type 3.1 or 3.2 proving compliance.
• MR0175 — NACE/AMPP standard for materials in H2S-containing environments. Originally published 1994.
• MR0103 — Separate NACE/AMPP standard for refinery service. Companion to MR0175.
• NACE — National Association of Corrosion Engineers. Original publisher of MR0175. Now part of AMPP.
• Normalizing — Heat treatment process (heated 880-920°C, air-cooled). Required for A350 LF2 Cl.1 sour service.
• PREN — Pitting Resistance Equivalent Number. Formula: Cr + 3.3×Mo + 16×N. Higher = better corrosion resistance.
• PWHT — Post-Weld Heat Treatment. Restores HAZ microstructure after welding.
• Region 0/1/2/3 — Sour service severity zones per ISO 15156 Part 1 (2020 edition). Based on H2S partial pressure.
• S2 — Supplementary requirement in ASTM A350 for low-sulfur chemistry (≤ 0.005% S). Recommended for HIC resistance.
• Sour service — Service containing H2S above 0.05 psi partial pressure.
• SSC — Sulfide Stress Cracking. Primary cracking mechanism in sour service. Mitigated by ≤ 22 HRC limit.
• Solution annealing — Heat treatment for duplex stainless (1050-1100°C, water-quenched).
• Sweet service — Service without H2S, or H2S below 0.05 psi partial pressure. MR0175 does not apply.
• UCI — Ultrasonic Contact Impedance. Portable hardness testing method, non-destructive.
• UNS — Unified Numbering System for metals and alloys. Common UNS codes: K03011 (LF2), S31803 (F51), S32750 (F55).

Mastering this vocabulary enables clear communication with suppliers, inspectors, and operators. Misusing any of these terms is a common signal of inexperience in sour-service procurement.

References & standards