Underground well storage of Hydrogen gas (H2) under higher pressure than what ambient storage allows is becoming an increasing area of interest. This enables large scale storage of Hydrogen that can be a potential input to various industries and applications on demand similar to natural gas. Currently, there is vast experience in the industry with underground well storage of natural gas. While quite a few aspects of well construction can be common between storage of natural gas and hydrogen; there are significant other challenges with regards to storage of hydrogen gas compared to natural gas. One important aspect is compatibility of metallic materials used for well operations and construction, especially with regards to assessing risk for hydrogen embrittlement. In this work, 41XX type Cr-Mo steels and 13Cr (AISI 420mod) type stainless steels, commonly used for well equipment, both in conventional upstream oil and gas production and in natural gas storage, were assessed for compatibility with high pressure Hydrogen gas at ambient and elevated temperature of 80°C (176°F). Evaluation was mainly performed via Slow Strain Rate Testing (SSRT) per ASTM G142.1 Details of this assessment and post testing evaluation of the specimens will be provided in this paper.
Hydrogen gas (H2) is touted for potential as future fuel as it could be a way to convert excess energy produced when demand is lower. Depending on the source of excess energy used for conversion to Hydrogen this process could have low or no carbon footprint. This Hydrogen gas could then be stored and used for electricity, transportation, chemical processes when the demand arises similar to how natural gas is being used currently. Thus, storage of Hydrogen in vast volumes would be one of the key elements for the success of Hydrogen as a future fuel.2-4
Underground storage wells at sites such as salt caverns, depleted oil/gas reservoirs etc. have been successfully used for storing large volumes of natural gas for many decades now to facilitate use of it in power generation, feedstock for chemical plants on demand.5 Similar approach with Hydrogen could provide a low or no carbon fuel for these applications. While there are similarities on storage of natural gas and Hydrogen gas; underground well storage of Hydrogen can be more complex due to physical, chemical properties differences between Hydrogen gas and natural gas (mainly methane). The Hydrogen molecule is smaller in size and has lower viscosity compared to methane which could be cause for leaking. Chemical reactions between Hydrogen and other substances present in an underground storage system could lead to Hydrogen losses and/or production of other corrosive elements such as H2S, acids etc. A very important concern would be that metallic materials used for well construction at the underground sites could suffer Hydrogen Embrittlement (HE) from exposure to high pressure Hydrogen gas. Since embrittlement leads to sudden, catastrophic failure of equipment understanding the HE susceptibility of various metals that could be used for such applications is very important and would be key for material selection.
