NACE MR0103 / ISO 17945:2015
A Comprehensive Guide to Metallic Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments.
Introduction and Purpose
The NACE MR0103/ISO 17945:2015 standard establishes requirements for metallic materials in petroleum refining environments that contain wet hydrogen sulfide (H₂S), also called sour service. It evolved to address limitations in prior standards like MR0175, which was tailored for upstream production. The primary goal is to prevent failures from Sulfide Stress Cracking (SSC) and Hydrogen-Induced Cracking (HIC), ensuring component reliability, personnel safety, and environmental protection by guiding material selection and heat treatment.
Scope and Application
Applies To:
- Refinery equipment exposed to wet H₂S environments.
- Equipment operating at ≤450 °C (842 °F).
- Components like pressure vessels, piping, valves, pumps, compressors, and heat exchangers.
Key Exclusions:
- Upstream exploration and production environments (covered by MR0175/ISO 15156).
- Does not cover fabrication techniques like cladding or weld overlays unless qualified.
Definitions and Terms
- Sulfide Stress Cracking (SSC): Cracking due to the combined effect of tensile stress and a sour environment.
- HIC (Hydrogen-Induced Cracking): Internal cracking caused by hydrogen absorption.
- Sour Environment: Presence of aqueous H₂S sufficient to cause cracking.
- Hardness Requirements: Specified maximum Rockwell (HRC) and Vickers (HV) values depending on alloy type.
Environmental Severity and Risk Assessment
Sour Environment Factors:
- H₂S partial pressure
- pH and chloride concentration
- Presence of cyanides or ammonia
- Wet-dry cycling and galvanic effects
Risk Assessment Should Evaluate:
- Service conditions (temperature, pressure)
- Failure consequences (safety, environmental)
- Inspection and maintenance strategy
Material Selection and Qualification
Carbon & Low-Alloy Steels
- Must meet hardness limits (<22 HRC or 250 HV).
- Weld procedures must maintain base and weld hardness.
Stainless Steels
- Austenitic grades must avoid sensitization.
- Ferritic/martensitic grades require thermal treatment.
- Precipitation-hardened types must be tested.
Nickel & Other Alloys
- Nickel alloys tested via tensile and hardness criteria.
- Copper, titanium, etc., need special evaluation based on field history or lab testing.
Heat Treatment and Hardness Control
Material processing is key to ensure SSC resistance. The primary goal is to refine grain size, reduce residual stresses, and control hardness.
- Carbon Steel Processing: Normalization or Quenching/Tempering is used to refine microstructure.
- Welds and HAZ: Must meet the same hardness and microstructure standards as the base metal.
- Cold Work: Strict limits apply to avoid strain-induced hardening that increases SSC susceptibility.
Testing and Evaluation
Standardized Testing Approaches:
- NACE TM0177: Tensile and four-point bend tests (Methods A, B, or C).
- NACE TM0284: HIC resistance testing.
- Metallographic Evaluation: Checks for delta ferrite, grain size, and phase balance.
Qualification Criteria:
- No cracking in specified exposure time (often 720 hrs).
- Specified maximum hardness (typically <22 HRC).
- Proven welding procedure qualifications.
Documentation & Quality Assurance
The standard mandates comprehensive records to ensure full traceability and compliance:
- Full material traceability reports.
- Welding Procedure Specifications (WPS).
- Procedure Qualification Records (PQR).
- Heat treatment records.
- Laboratory test reports.
- Hardness survey maps and results.
Weldments & Fabrication
Special considerations apply for fabrication to ensure weldments are as resistant as base metals:
- Weld overlays and cladding must be qualified.
- Dissimilar metal welds must be compatible.
- Post-weld heat treatment (PWHT) is often required.
- In-service weld repairs must be evaluated for SSC risk.
Key Points Summary
Material Categories: Specific criteria for carbon steels, stainless steels, and nickel alloys.
Testing Protocols: NACE TM0177 and TM0284 are core methods for evaluation.
Heat Treatment: Required for base metals and welds to control microstructure.
Hardness Control: Maximum hardness (typically 22 HRC) is a central acceptance criterion.
Risk-Based: Selection is based on environment severity and failure consequences.
Documentation: Full traceability, WPS/PQR, and test records are mandatory.