How to choose a flow meter for hydrogen flow measurement

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Hydrogen is a highly valuable and widely measured industrial gas that plays a very important role. Hydrogen has very important applications in the petrochemical industry, food and grain processing, the semiconductor and electronics industry, fuel cell manufacturing, pharmaceutical chemistry, power generation, and more. Since hydrogen is extremely valuable, measurement at the point of trade transfer is a very important aspect of hydrogen flow measurement. Properties of hydrogen: Hydrogen (chemical formula H2) is composed of two hydrogen atoms; it is colorless, tasteless, odorless, non-toxic, and flammable. With a molecular weight of 2 and a specific gravity of 0.0695, hydrogen is considered the lightest gas, being more than 14 times lighter than air (mv=28.8). Hydrogen is highly flammable. At atmospheric pressure, mixtures with a hydrogen content of 4.0% to 74% are flammable. Due to the very low minimum ignition energy of hydrogen (0.02 mJ – one order of magnitude lower than that of hydrocarbons), strict preventive measures are necessary to avoid leaks. Other concerns: Hydrogen embrittlement: Due to its small size, hydrogen molecules can diffuse into the gaps in many metal crystal lattices, which may lead to a decrease in tensile ductility (strength). This effect is known as hydrogen embrittlement, and it primarily affects high-strength steels rather than stainless steels. Austenitic stainless steels, such as 304L and 316L, are actually resistant to hydrogen embrittlement. This is due to the Ni-Cr-Mo structure of the nickel-based alloy C-22. Process connectors: At the same pressure, even if the system is airtight to air or other common gases, hydrogen may still leak from the system. Therefore, the CGA G-5.4-1992 guideline from the Compressed Gas Association of America stipulates that pipe systems and pipe fittings should preferably be welded to prevent leaks and fire hazards. The use of soft solder joints is not allowed. Threaded connectors can be used in hydrogen pipeline systems, but it is necessary to ensure that the possibility of leaks is minimized. Flange joints used in hydrogen pipeline systems should have a metal-to-metal seal or gasket, and the washers should be made of flame-retardant materials. Reliable and accurate flow measurement is key to improving product quality and output. Existing volume measurement technologies such as differential pressure flowmeters, turbine flowmeters, and vortex flowmeters are limited in terms of accuracy; when using these technologies to measure hydrogen, the measured accuracy is typically around ±3~8%. Additionally, the range is also limited. Moreover, the moving parts of turbine flowmeters also compromise reliability. At present, the most widely used and reliable types are still Coriolis mass flow meters and thermal gas mass flow meters. Both of these are flowmeters that measure mass flow rate in a direct manner, and they both have no moving parts as well as a wide range of measurement capabilities. The material used for the fluid contact surfaces is 316L, which enhances durability and safety in field applications. The sensors of Coriolis mass flow meters and thermal gas mass flow meters are fully welded, and since there is no need to correct the flow readings to volumetric flow rates at standard conditions using pressure sensor interfaces and temperature sensors, the number of system piping connections used is minimized. The sensor connection methods include flange connection and flange clamp connection; thermal mass flow meters also offer insertion connection for large pipes. Due to their advanced sensing technologies, Coriolis mass flow meters and thermal gas mass flow meters can achieve accuracy of up to 0.5%, giving them a significant advantage in measurements used for trade settlement. These two types of flowmeters feature advanced measurement technologies, good long-term operational stability, and extremely low on-site maintenance costs, making them very popular measuring instruments. Disadvantages of Coriolis mass flow meters: they have a large diameter and are bulky, making installation difficult; moreover, their purchase cost is extremely high. It is inferior to thermal mass flow meters in terms of low-flow measurement performance. Disadvantages of thermal mass flow meters: they perform poorly in high flow rate ranges compared to Coriolis mass flow meters. To accurately measure hydrogen flow rates, it is necessary to calibrate the flow meter using actual flow calibration, and this requirement means that the products manufactured by most manufacturers do not meet the standards. Currently, there are only a few brands worldwide that possess this capability, such as SIERRA, KURZ, and FCI. There are limits on working pressure, generally below 3.4 MPa; for KURZ, it is no more than 2 MPa. Below are the applications of SIERRA thermal gas mass flow meters in various industries. It should be specifically noted that these flowmeters have been in use for over 8 years.