Sulphide Stress Cracking (SSC) Testing: Standards, Methods & Lab Services
Sulphide stress cracking (SSC) is a form of hydrogen embrittlement that occurs in high-strength metals exposed to aqueous environments containing hydrogen sulphide (H₂S)—commonly encountered in oil and gas production, refining, and petrochemical processing. SSC causes sudden, brittle fracture at stress levels well below the material’s yield strength, making it one of the most dangerous corrosion-related failure mechanisms in the energy industry. For companies seeking SSC testing at a US-based testing lab, Infinita Lab provides comprehensive sour service corrosion evaluation through its accredited laboratory network.
How SSC Occurs
H₂S in the production environment dissociates at the metal surface, generating atomic hydrogen that diffuses into the steel lattice. In high-strength steels (typically >22 HRC), this absorbed hydrogen reduces ductility and fracture toughness at the crack tip, enabling brittle crack propagation under applied or residual tensile stress. The combination of susceptible material, hydrogen charging from H₂S, and tensile stress creates the SSC failure triad.
Testing Standards
NACE TM0177 – SSC Testing of Metals
NACE TM0177 is the primary standard for evaluating SSC resistance and defines four test methods: Method A (tensile test in H₂S environment), Method B (bent beam), Method C (C-ring), and Method D (double cantilever beam for fracture toughness). Testing is performed in NACE Solution A (5% NaCl + 0.5% acetic acid saturated with H₂S) at 24°C.
NACE MR0175 / ISO 15156 – Material Requirements
NACE MR0175/ISO 15156 specifies material requirements and hardness limits for equipment used in H₂S-containing (sour) environments. Carbon and low-alloy steels are limited to a maximum of 22 HRC. CRAs require specific qualification testing.
Prevention Strategies
Material selection within NACE MR0175 hardness limits, proper heat treatment to achieve tempered microstructures, use of corrosion-resistant alloys (CRAs) for severe sour service, H₂S scavenging and corrosion inhibition, and stress relief of welds and cold-worked areas prevent SSC failures.
Why Choose Infinita Lab for Corrosion Testing?
At the core of this breadth is our network of 2,000+ accredited labs in the USA, offering access to over 10,000 test types. From advanced metrology (SEM, TEM, RBS, XPS) to mechanical, dielectric, environmental, and standardized ASTM/ISO testing, we give clients unmatched flexibility, specialization, and scale. You are not limited by geography, facility, or methodology—Infinita connects you to the right testing, every time.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote
Frequently Asked Questions (FAQs)
What is sulphide stress cracking? SSC is a hydrogen embrittlement mechanism where H₂S in the environment charges atomic hydrogen into high-strength steel, causing brittle cracking under tensile stress at levels well below the material’s normal strength.
What NACE standards cover SSC testing? NACE TM0177 defines SSC test methods (tensile, bent beam, C-ring, DCB). NACE MR0175/ISO 15156 specifies material requirements for sour service. NACE TM0284 covers hydrogen-induced cracking (HIC) testing.
What hardness limit prevents SSC? NACE MR0175 limits carbon and low-alloy steels to a maximum of 22 HRC (equivalent to approximately 248 HV or 237 HBW) for sour service. This hardness limit ensures that the microstructure is resistant to hydrogen embrittlement.
What is NACE Solution A? NACE Solution A is 5% sodium chloride plus 0.5% glacial acetic acid, saturated with H₂S gas at ambient temperature and pressure. It provides a standardized, aggressive sour environment for SSC qualification testing.
Which industries are most affected by SSC? Oil and gas production (wellhead equipment, tubing, casing), petroleum refining (hydrotreaters, amine units), petrochemical processing, and geothermal energy are the industries most affected by SSC.
