FITNESS FOR PURPOSE DESIGN OF A STEEL CYLINDER FOR HYDROGEN- NATURAL GAS BLENDS

The present paper deals with a structural integrity assessment of a seamless steel cylinder for transportation of HCNG blend for a 200 bar pressure application with 30% H2 content. First a fracture mechanics approach with an estimation of expected number of cycles and failure mode is applied to a typical cylinder for CNG transportation designed with a traditional approach. The same approach is then used for an assessment of the same cylinder working in a HCNG environment. Fracture toughness was experimentally measured in HCNG blend according to a stepwise procedure and used as input for cylinder failure mode prediction. Fatigue crack growth rate was estimated based on comparison of two interrupted full scale tests carried out in oil and in the investigated HCNG environment. Acceleration of crack propagation, when using HCNG blend, suggests that a dedicated structural integrity assessment of the cylinder is needed to determine the proper design parameters for a safe product life.