Material Degradation
Atomized gas migration occurs when hydrogen molecules split into single atoms on the surface of a metal sensor component. This process causes diaphragm hydrogen permeation, where the tiny atoms diffuse through the solid metal barrier of a pressure transmitter. Once inside, the atoms recombine into molecular hydrogen, forming gas bubbles within the internal fill fluid of the sensor.
Measurement Drift
The presence of gas bubbles inside the fill fluid alters the mechanical response of the measuring cell. Because the trapped gas is compressible, unlike the incompressible silicone oil fill fluid, the transmitter suffers from severe zero drift and non-linear response curves. Over time, the internal pressure generated by the trapped gas can distort or permanently rupture the isolation diaphragm itself.
Barrier Coating
Specialized metal coatings slow the diffusion rate by blocking the atomic transition sites on the outer surface. Gold plating is a common defense, as gold possesses an extremely low diffusion coefficient for atomic hydrogen. This thin layer is applied via electroplating or physical vapor deposition, providing a robust barrier that extends the sensor lifespan in hydrotreating and chemical processing applications.
Material Selection
Sensing assemblies exposed to high-pressure hydrogen must use materials selected specifically for their atomic structure. Austenitic stainless steels and nickel alloys resist hydrogen embrittlement, but they still require gold barriers when operating at high temperatures where the diffusion rate increases exponentially.
