Understanding NACE MR0175 / ISO 15156 (Sour Service Material Standard)
NACE MR0175 / ISO 15156 is an international standard that defines material requirements for metallic components used in hydrogen sulfide (H₂S) environments in oil and gas production. It ensures resistance to sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and other forms of corrosion damage.
What is NACE MR0175 / ISO 15156?
NACE MR0175 (now aligned with ISO 15156) is a globally recognized standard developed to:
- Prevent material failure in sour (H₂S-containing) environments
- Specify acceptable materials for oil & gas systems
- Define testing, hardness, and chemical limits.
Scope and Structure
The standard is structured into three parts, covering the entire production chain from the wellhead to surface facilities:
Part 1: General principles and requirements for resistance to SSC.
Part 2: Application requirements for Corrosion Resistant Alloys (CRAs).
Part 3: Requirements for carbon and low-alloy steels in wet H₂S environments (incorporating the former NACE MR0103).
Widely used in:
- Oil & gas production
- Offshore platforms
- Refineries
- Gas processing plants
What is Sour Service?
Sour service refers to environments containing hydrogen sulfide (H₂S).
H₂S can cause serious material failures such as:
- Sulfide Stress Cracking (SSC)
- Hydrogen-Induced Cracking (HIC)
- Stress Corrosion Cracking (SCC)
These failures can occur even under low stress conditions
Key Requirements of NACE MR0175
1. Material Selection
Only approved materials may be used, including:
- Carbon steel
- Low alloy steel
- Stainless steel
- Nickel alloys
2. Hardness Limitation of NACE MR 0175
For carbon steel:
- Maximum hardness: 22 HRC (~187 HBW)
This limit reduces susceptibility to SSC.
| Steel Type | Grades Included | Comments |
| Ferritic | 405, 430, 409, 434, 436, 442, 444, 445, 446, 447, 448 | Hardness up to 22 HRC |
| Martensitic | 410, 420 | Hardness up to 22 HRC |
| Martensitic | F6NM | Hardness up to 23 HRC |
| Martensitic | S41425 | Hardness up to 28 HRC |
| Austenitic | 201, 202, 302, 304, 304L, 305, 309, 310, 316, 316L, 317, 321, 347, S31254(254SMO), N08904(904L), N08926(1925hMo) | Solution annealed, hardness up to 22 HRC |
| Austenitic | S20910 | Hardness up to 35 HRC |
| Duplex | S31803, S32520 (UR 52N+), S32750 (2507), S32760 (Zeron 100), S32550 (Ferralium 255) | PREN ≥30, ferrite 35–65% |
| Precipitation Hardening | 17-4 PH | 33 HRC Age hardening at 620°C |
| Precipitation Hardening | S45000 | 31 HRC Age hardening at 620°C |
| Precipitation Hardening | S66286 | 35 HRC |
3. Chemical Composition Control
- Low sulfur (S) and phosphorus (P)
- Controlled alloy elements
Chemical composition for carbon and low alloy steel
Per Clause A.2.1.2 – Carbon & low-alloy steel are acceptable at 22 HRC max. hardness provided they contain less than 1% mass fraction Nickel.
Per Clause 8 – Max. acceptable level for flat-rolled produce is 0.003% mass fraction of sulfur
Max. acceptable level for seamless product is 0.01% mass fraction of sulfur
Conventional forgings with sulfur levels less than 0.025% mass fraction and castings are not considered sensitive to HIC and SOHIC
4. Environmental Conditions
Material selection depends on:
- H₂S partial pressure
- Temperature
- Chloride content
- pH level
Not all NACE materials are suitable for all conditions
Types of Corrosion Covered
| Failure Type | Description |
|---|---|
| SSC | Cracking under stress in H₂S |
| HIC | Internal cracking due to hydrogen |
| SCC | Cracking due to corrosion + stress |
NACE MR0175 vs ISO 15156
- NACE MR0175 = original standard (USA)
- ISO 15156 = international version
Today, they are technically aligned and used together
NACE MR0175 vs NACE MR0103
| Standard | Application |
|---|---|
| MR0175 / ISO 15156 | Oil & gas production |
| MR0103 | Refineries |
MR0103 is generally more restrictive for carbon steel
Typical Materials for Sour Service
- ASTM A105 (controlled hardness)
- ASTM A350 LF2
- AISI 316L stainless steel
- Duplex / Super Duplex steels
- Nickel alloys (Inconel, Monel)
Testing Requirements
To ensure compliance, materials may undergo:
- Hardness testing
- Chemical analysis
- HIC testing (NACE TM0284)
- SSC testing
- Ultrasonic and NDT inspection
Applications of NACE MR0175 Materials
Used in:
- Oil & gas production systems
- Offshore platforms
- Pipelines transporting sour crude
- Gas processing units
- Pressure vessels
Quick Summary of NACE MR0175
- Standard: NACE MR0175 / ISO 15156
- Purpose: Prevent failure in H₂S environments
- Key limit: Hardness control/Low sulfur (S) and phosphorus (P)
- Risks: SSC, HIC, SCC
- Industry: Oil & gas
FAQ: NACE MR0175 / ISO 15156
Q1: What is NACE MR0175 used for?
It defines material requirements for sour service environments in oil and gas.
Q2: What does sour service mean?
It refers to environments containing hydrogen sulfide (H₂S).
Q3: Why is hardness important?
Higher hardness increases risk of sulfide stress cracking.
Q4: Is ISO 15156 the same as NACE MR0175?
Yes, ISO 15156 is the international equivalent of NACE MR0175.
Download detail standard of NACE MR0175