Hydrogen Pressure Sensors

The US government and European Union continue to fund development of alternative fuels to reduce dependency on oil and improve the environment. This has resulted in a continuous improvement and increased activity in the usage of hydrogen. Hydrogen has a large potential to be the fuel of the future since it is environmentally friendly. However, the generation and storage of hydrogen poses problems that has to be addressed by ensuring correct material compatibility for safety and performance.

Hydrogen is the simplest and smallest atom element and is found in water, acids, bases and organic compounds. Hydrogen atoms are not considered corrosive, however, if the atoms split into hydrogen ions (two H+ atoms), it can penetrate through thin metal diaphragms. It is important to ensure material compatibility when selecting components for hydrogen application since it will dictate the two major forms of corrosion: hydrogen permeation and embrittlement.

Pressure sensors employing thin isolation diaphragms with fluid fill are prone to hydrogen permeation. Hydrogen ions will penetrate the diaphragm and will be trapped in the fill fluid, producing hydrogen bubbles. These bubbles will cause the zero and span readings to change, degrading the performance of the pressure sensor. Over time the build up of hydrogen will cause outward expansion of the isolation diaphragm, leading to cracks and sensor failure through loss of fill fluid. Hydrogen permeability occurs in both pure and non-pure hydrogen applications involving high pressure-temperature in pure hydrogen applications, galvanic reaction such as seawater and steam at high temperatures. To reduce or eliminate hydrogen permeation in thin diaphragms, sensor manufacturers employ expensive plating process involving gold or platinum.

Another form of corrosion involving hydrogen is hydrogen embrittlement that results in reduction of mechanical properties of the metal, leading to failure of the pressure sensor. Material selection is very important and emphasis on material compatibility and hazardous analysis must be considered prior to hydrogen service. Factors for hydrogen embrittlement are environmental, internal absorption and chemical reaction in the presence of hydrogen ions. Susceptibility of embrittlement increases with increase in tensile stress and ultimate strength of the metal as a function of hydrogen purity levels. To reduce or eliminate embrittlement, material selection together with thickness, surface finish, weld free joints and conservative design stresses must be considered. Avoiding metals such as 410 stainless steel, 1040 steel, 17-4 / 17-7 stainless steels, and Inconel 718 since these are extremely embrittled in hydrogen. Metals such as 310 and 316 stainless steel offer negligible embrittlement.

AST2000H2 Hydrogen Pressure Sensor - Click the image for more details

To overcome hydrogen permeability and embrittlement, AST/HKST offers a complete line of pressure sensors for hydrogen service that employ one-piece thick diaphragm 316L diaphragms, free on internal O-rings, welds or fill fluids. Using Krystal Bond™ Technology, AST/HKST pressure sensors are constructed with the most advanced MEMS process in the pressure sensor industry.

AST/HKST products are available with a number of approvals including TUV material compatibility, UL EMC requirements, and Detroit Testing Labs environmental tests. The AST2000H2 covers pressures ranges up to 15,000PSI (1000Bar). Along with all 316L wetted parts, many options on pressure ports and electrical outputs are available. Below is a cross section of a typical AST/HKST pressure transducer for hydrogen service, highlighting the one-piece sensor design.

For a copy of any testing data or how AST/HKST can assist with your application, please contact us about your application.