CNG Cylinder Safety: SSCC Testing by TCR as per ISO 11439
- Rohit Bafna
- Aug 7
- 3 min read
As the use of Compressed Natural Gas (CNG) continues to grow globally in automotive, industrial, and energy sectors, ensuring the integrity and safety of CNG storage cylinders becomes critical. One of the most important tests for evaluating the reliability of these cylinders is the Sulphide Stress Corrosion Cracking (SSCC) Test, conducted as per ISO 11439, Method A.
What is SSCC Testing and Why Is It Important?
SSCC (Sulphide Stress Corrosion Cracking) is a form of hydrogen embrittlement that occurs when high-strength steels are exposed to wet hydrogen sulfide (H₂S) environments under stress. This type of cracking can lead to catastrophic cylinder failure if not properly assessed and mitigated.
Since CNG cylinders are often used in environments where sulfide-containing gases may be present or generated, testing for SSCC is essential to:
Validate material resistance under sustained load and corrosive exposure
Ensure long-term safety during operational and storage conditions
Comply with international safety regulations for pressure vessels
Reduce risk of fracture, leaks, or ruptures in the field
The SSCC test mimics real-world stress and corrosion conditions to ensure that cylinders can withstand the combined mechanical and chemical stresses without failure.
What is ISO 11439 and the Role of Method A?
ISO 11439 is the international standard for high-pressure cylinders used for the storage of natural gas as fuel for automotive vehicles. It provides guidelines for design, manufacture, and testing, ensuring that CNG cylinders meet stringent safety and quality requirements.
Method A under ISO 11439 specifically refers to the tensile-based SSCC test, which is conducted as follows:
Test Duration: 144 hours
Test Temperature: 24 ± 3°C
Stress Applied: Tensile load derived from the specified minimum yield strength (SMYS)
Environment: Typically involves an H₂S-containing solution (as per test specification)
This method simulates worst-case operating scenarios where a CNG cylinder may be under continuous stress in a corrosive atmosphere, providing a highly conservative safety benchmark.
TCR’s Testing Capability and Process
At TCR Engineering Services, we offer ISO 11439 Method A-compliant SSCC testing using calibrated tensile rigs and controlled environmental chambers. The testing is supervised by experienced metallurgists and supported by detailed documentation.
Third-Party Inspection (TPI) Support
Clients requiring witness testing by agencies such as Bureau Veritas (BV) or Lloyd’s Register (LRS) can opt for Third-Party Inspection (TPI) services. Typically, 3–4 visits are necessary for SSCC or HIC (Hydrogen Induced Cracking) test witnessing, and TPI charges are quoted separately.
Information Required Before Sample Submission
To ensure test accuracy and compliance, please provide the following details before submitting your samples:
Type of gas intended for testing
Stress level to be applied (based on SMYS)
Solution composition to simulate operating conditions
Modulus of Elasticity (Young’s modulus) of the material
Test temperature and duration if deviating from standard
Providing this information upfront allows for a precise test setup and minimizes turnaround time.
Conclusion
SSCC testing as per ISO 11439 Method A is not just a regulatory formality—it is a vital safety check for any CNG cylinder expected to operate under high pressure and potentially corrosive conditions. At TCR, we combine international standards with practical field insight to deliver reliable, certified, and actionable test results.
For further assistance or to schedule your SSCC test, connect with our technical team at TCR Engineering Services.
