Does hydrogen present any special issues related to service hardware compared to other gases?
Hydrogen certainly presents challenges to hardware design and construction. Some of these are unique to hydrogen while others are exacerbated by hydrogen. These include:
H2 is highly flammable. This makes fire safety a primary concern for valve design, construction and maintenance.
H2 is a small molecule which makes controlling internal tightness and fugitive emissions more challenging.
Hydrogen can deteriorate some material properties resulting in reduction of damage tolerance for some components.
Liquid hydrogen service involves extremely low temperatures.
Are there different challenges depending upon whether we are dealing with a gaseous or liquid hydrogen service?
Yes, there are different factors to consider. For gaseous hydrogen service control of fugitive emissions will be very important to minimize the potential for fire hazard. Proper selection of packing and seals is important. It is also known that molecular hydrogen, under certain conditions of temperature and pressure, can dissociate on metallic surfaces and enter the lattice of the material as atomic hydrogen. There the hydrogen can reduce the damage tolerance of the material via several possible mechanisms commonly referred to as hydrogen embrittlement. This needs to be considered in selection of materials for service hardware. Additionally, non-metallic materials can experience dimensional changes upon rapid decompression within gaseous service lines. Due to the ease with which Hydrogen can diffuse into these materials, this is generally expected to be more relevant in hydrogen services.
Liquid hydrogen service demands very low temperatures (boiling point is -253oC at 1 atmosphere). Although damage caused by hydrogen embrittlement is not frequently observed, there are some other challenges that liquid hydrogen can present. At these low temperatures some non-metallic as well as metallic materials can become very brittle. In addition, dimensional changes that occur in changing temperature from ambient to the service condition can impact internal tightness as well as external sealing points.
From a materials standpoint, what should we look for to optimize safety?
Valmet is highly focused on becoming a knowledge-based supplier of valves that are safe and effective for hydrogen services. Safety training has been a key component of getting our people sensitive to the special needs of hydrogen service components. All persons involved with specifying, designing, building and servicing hydrogen valves can have access to Valmet internal training on hydrogen safety and material compatibility for hydrogen service.
The Valmet materials team has expertise in designing and selecting standard and non-standard test method to generate data on metallic and non-metallic material response to hydrogen environment. Those data are extremely valuable to aid Valmet design engineering to perform engineering-level calculation to qualify material H2 compatibility. In some special cases, when there is a need to go beyond Valmet’s traditional material offerings, the material team can help specify special material compositions, tempers or formats to optimize material compatibility to the extreme service conditions.