Hydrogen Permeation Through Metals, Alloys and Oxides at Elevated Temperatures

Permeation rates of hydrogen through AISI Type 446 stainless steel and an iron-chromium-aluminum alloy (20 percent Cr, 5 percent Al, balance Fe) were determined to 2150 F under various conditions of surface oxidation. The presence of a continuous oxide film resulted in a thousand fold reduction in permeation rate over that through the unoxidized metal at elevated temperatures. Under conditions in which the oxide could not be replenished, its barrier effect was largely destroyed through reduction of the oxide by the emerging hydrogen. 3.5.6