Permanent contact to hydrogen may lead to so-called hydrogen embrittlement. The hydrogen can penetrate the material structures leading to a deterioration of the mechanical properties and eventually mechanical failure. To avoid this effect, appropriate materials in direct contact with hydrogen have to be chosen. As a standard austenitic steels like 316L or 316Ti are preferred. But also specific alloys like Hastelloy C276, Inconel 718 or 2.4711 (Elgiloy®) are well-suited for hydrogen applications.
WIKA materials used in hydrogen applications: Mechanical pressure gauges, mechanical switches: Pressure port: 316L; Probe element/movement: 316L
Hydrogen is the simplest element in the periodic table and its atoms are the smallest after helium. When touching metal surfaces only relatively small energy is required to dissociate the hydrogen molecule into single atoms, and eventually into H+ ions. These ions can penetrate metal and resistance structures, which can lead to a signal drift of the sensor element over time. The higher the introduced energy, e.g. through higher process temperatures and higher pressures, the bigger this effect will be. To avoid the permeation of hydrogen through metal structure and with this the signal drift of the sensor a gold plating can be used. It serves as a barrier to hydrogen with a significantly lower permeation rate than for example pure 316L.
WIKA offers gold plating on flush sensor solutions like models E-11, IS-3 (flush version) or diaphragm seals.
Hydrogen in connection with air will create an explosive atmosphere already starting at a content of 4 mole % of hydrogen in the air. An excessive leakage must therefore be avoided. In general, a big focus is put on ventilation. For this reason metal seals often are the preferred solution in hydrogen applications. Also inside the measuring instrument the leakage rate must be avoided or at least reduced to a minimum.
WIKA is providing pressure measuring instruments in a fully welded design, avoiding internal polymeric sealing. Additionally products for hydrogen applications undergo helium-leakage testing during production.
Depending on the physical state in which hydrogen is stored different extremes in handling the media have to be tackled. Hydrogen is stored in gaseous form at a pressure of up to 700 bar. Due to temperature effects and safety factors, pressure sensors need to be capable of measuring up to 1,050 bar in, for example, hydrogen fuelling stations. In liquid form the hydrogen has a temperature of -253 °C or below. Temperature measurement solutions have to be designed in such a way that they can also measure this temperature at a high accuracy while keeping the good insulation of the hydrogen tank.
WIKA offers electrical temperature measuring instruments in a special CryoTemp version that can measure temperatures down to -258 °C, reliably and with repeatable accuracy.