Part 2 of 4 on Qualifying Casing Connections for Underground Hydrogen Storage
Part 2 discusses why a small-scale material test program is required to understand the impact of hydrogen on the casing material performance and to characterize the variability of the material used to fabricate the test specimens.
The combination of cyclic pressure and hydrogen exposure in an underground hydrogen storage well creates an environment where crack formation and growth could be significant concerns for the well casing.
Various small-scale test procedures can be used to assess the resistance to cracking (fracture toughness) of the material and the rate of crack growth under cyclic loading (fatigue crack growth rate). Due to the complexity of the cracking mechanism, there can be significant scatter in the results from these tests, making it necessary to adopt special approaches to testing to minimize this scatter.
Small-scale Testing Process
Small- and full-scale test specimens should be cut from the same mother tube to ensure that the range of material properties across the specimens is minimized. The preparation of small-scale test specimens should be done following ASTM E8/E8M-16 “Standard Test Methods for Tension Testing of Metallic Materials”, or ASTM A370-21 “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”.
For small-scale tests, it is recommended that material tests be conducted under ambient conditions (i.e. in air) to establish baseline material property values. These tests should be repeated with continuous, pressurized hydrogen exposure to simulate field operating conditions. Comparing the material performance in air with performance in hydrogen will help to determine if specific hydrogen environments impact performance of the test specimens more than others.
The results of the small-scale material tests should be used to generate a special pipe body load envelope for hydrogen service to define the safe load paths and end points for the full-scale testing program.
