NACE MR0175/ISO 15156: Material Selection for H₂S Corrosion Safety

Interpretation of NACE MR0175/ISO 15156 Standards: Material Selection and Safety Practices in H₂S Environments

1. Introduction: The Challenge of Hydrogen Sulfide Corrosion in the Oil and Gas Industry

Hydrogen sulfide (H₂S) poses significant corrosion threats to oil and gas equipment, making it one of the primary challenges in pipeline and equipment safety. NACE MR0175/ISO 15156 standards were developed to ensure material reliability and long-term safety in these harsh environments.

2. Scope of Application

These standards apply to equipment used in:

• Oil and gas exploration

• Production and processing facilities

• Pipeline and piping systems

They serve as a critical reference for engineers, manufacturers, and quality inspectors.

3. Core Content of NACE MR0175/ISO 15156 Standards

3.1 Material Selection Requirements

• Carbon Steel: Requires control of sulfur and phosphorus content with specific heat treatment procedures.

• Stainless Steel: Focuses on critical temperature and H₂S partial pressure, especially for austenitic and duplex grades.

• Nickel-Based Alloys: Covers materials like Inconel and Hastelloy for specialized applications.

• Non-Metallic Materials: Includes elastomers and coatings for sour service applications.

3.2 Hardness Control and Testing Methods

• Maximum hardness for carbon steel is generally HRC 22, adjusted for environmental conditions.

• Guidelines for Vickers (HV) to Rockwell (HRC) hardness conversion are provided.

• Requirements for testing welds and heat-affected zones (HAZ) are specified.

3.3 Environmental Parameter Limitations

The standards consider:

• H₂S partial pressure

• Temperature

• pH value

• Chloride ion concentration

Example: For sour service, H₂S partial pressure ≥ 0.3 kPa defines critical conditions.

3.4 Manufacturing and Quality Control

• Traceability: Chemical composition reports and heat treatment records required.

• Non-Destructive Testing (UT/RT/PT): Acceptance criteria strictly defined.

• Sulfide Stress Cracking (SSC) Testing: Must be performed in simulated service environments.

Compliance involves supplier audits, material technical document reviews, and certification requirements.

4. Industry Application Case

An example is provided for carbon steel pipeline material selection in high-H₂S gas fields in the Middle East, demonstrating real-world applications of the standards.

5. Long-Term Value and Future Updates

Future revisions may add rules for CO₂-H₂S coexisting environments.
The latest standard version is ISO 15156:2020, divided into:

• Part 1: General Principles, Carbon, and Low Alloy Steels

• Part 2: Corrosion-Resistant Alloys and Stainless Steels

• Part 3: Crack-Resistant Alloys Requirements

6. Quick Reference Parameters

• Carbon Steel Hardness: ≤ HRC 22, adjustable for H₂S levels and pH.

• Duplex Stainless Steel: Use below critical temperatures (e.g., 250°C).

7. References and Resources

• NACE Technical White Papers: Offer in-depth interpretations.

• SY/T 0599 Standard: Domestic reference from China National Petroleum Corporation, technically aligned with ISO 15156.