Hydrogen embrittlement static tests

Static tests carried out with non-precracked specimens allow us to characterize, for a given environment, the sensitivity of an alloy to stress corrosion cracking and hydrogen embrittlement. TyfpicaUy, the test specimen subjected to a constant load or a constant strain is exposed to a corrosive environment and one measures the time to failure. The test specimens sometimes contain a notch—not to be confused with precracking—that fixes the location where failure will occur. In constant strain tests, the time to failure corresponds to the appearance of the first cracks. This kind of experiment thus indicates the crack initiation time. In constant load tests, on the other hand, the time to failure is the time leading to fracture of the specimen. It corresponds to the sum of the crack initiation and the crack propagation times. 

In dynamic tests platinum and gold were resistant to attack under all conditions, but niobium corroded at an appreciable rate, about 7 mpy at 15 fps. The corrosion rate of niobium depended on the flow rate of the solution, and at higher flow rates somewhat higher corrosion rates were observed. Static tests showed that tantalum and chromium are corroded only slightly under most conditions. If the solution contained dissolved hydrogen, tantalum was seriously embrittled highly oxygenated uranyl-sulfate solutions at temperatures above 250 C oxidized chromium to the soluble hexavalent state, and under these conditions the rate of attack was several mils per year. 

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