Hydrogen Probes and Patch Monitors

Hydrogen is the product of corrosion reactions in many systems, but most signiflcantly where the process streams contain water and HjS, HCN, or HR 

The combination of hydrogen atoms to form hydrogen gas at the corroding metal surface is retarded by certain anions, the most common being sulfide, cyanide, and fluoride. These anions thereby promote the diffusion of atomic hydrogen into the steel substrate. 

Equipment for measuring the rate of diffusion of atomic hydrogen into structural materials is available in two forms, either as thin-waUed tubular probes inserted directly into the process stream through standard 5.08 cm (2 inch) high pressure access fittings, or as patch detectors clamped or welded to the outer pipe or vessel wall. 

The rate of pressure build-up can be related to the potential for hydrogen damage occnrring in the vessel or piping materials. A period of stabilization is reqnired to enable the tnbnlar element to saturate with atomic hydrogen before meaningfnl data can be accnmnlated. 

There are two types of non-intrnsive hydrogen patch probes. The first comprises a carbon steel patch contoured to fit the outside of the vessel or pipe, and welded to it. 

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