Experimental Evaluation of Hydrogen Addition in LNG Peak-Shaving Systems: Thermal and Material Response

The study investigates the effects of hydrogen addition on the thermophysical behavior of liquefied natural gas (LNG) and the performance of 9% nickel steel used in peak-shaving systems. An intermediate-scale experimental program exceeding 800 hours was conducted using a 95-liter cryogenic dewar. Hydrogen sparging produced measurable cooling, with temperature reductions of approximately 3°C at moderate injection rates and up to 11°C at higher rates. Hydrogen concentrations were highest in the vapor space, while vaporized samples withdrawn from the liquid contained less than approximately 0.3% hydrogen. Hydrogen associated with the liquid samples decreased below the measurement limit within approximately 48 hours after sparging ceased. Complementary material testing included a 38-day cryogenic exposure, during which no crack extension was observed. Because the dewar-exposed specimens did not satisfy linear elastic fracture mechanics validity requirements, they were used to assess crack extension rather than valid fracture toughness. Separate room-temperature hydrogen tests showed fracture toughness reductions of approximately 25% at 100 psig and up to 75% at 1,000–3,000 psig. These elevated-pressure tests provide a conservative indication of material susceptibility and are not directly representative of low-pressure cryogenic LNG storage conditions. The results show that hydrogen can lower LNG storage temperatures and may affect 9% nickel steel fracture resistance under certain conditions, supporting further tank-specific and longer-duration evaluations.