Hydrogen diffusion through vessel walls

Four appendixes are included. Appendix A contains standard materials selection used by many refiners and contractors in petroleum processing equipment. Appendix B contains a rules of thumb overview of refinery materials of construction. Appendix C contains background information on hydrogen diffusion through vessel walls, and Appendix D contains a standard specification for steel line pipe. 

In another case, acidic water was used to clean the inside of the water Jacket that surrounded a glass-lined vessel. Some hydrogen diffused through the wall of the vessel and developed sufficient pressure to crack the glass lining. 

The probe comprises a small electrochemical cell with one electrode, a thin inert metal foU, usually palladium, in direct contact with the pipe wall. As the hydrogen diffuses through the vessel or pipe wall and the metal foil, it is electrochemically oxidized on the inner face of the foil that is in contact with the cell electrolyte. The current flowing in the cell is directly proportional to the rate of hydrogen permeation through the wall of the equipment and provides a direct measure of hydrogen activity. 

The amount of hydrogen (substance A is hydrogen) which diffuses through the vessel wall is equal to the reduction in the amount stored ... 

Fig. 14.2. Double-capsule technique designed to hold an experimental system at a fixed, known oxidation state. This arrangement is held in a pressure vessel containing a fluid at high temperature and pressure. The pressure is transmitted to the experimental system by the flexible walls of the gold and platinum tubes, and at the experimental temperature hydrogen, but not other components, is able to diffuse through the metals.

Consider a steel reservoir containing an acidic electrolyte and the outside of the reservoir is exposed to the atmosphere. Hydrogen will be evolved inside the walls of the vessel because of corrosion. A part of the atomic hydrogen will diffuse through... 

The aqueous-phase CN ions sensitize the steel walls of the vessel to permit atomic hydrogen to diffuse through the metal lattice structure ... 

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. 

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