Corrosion Studies in High Temperature Water By a Hydrogen Effusion Method

Steel Corrosion Mechanisms

“…In a discussion of the mechanism of general corrosion in these alkaline systems (6), it was pointed out by two of the present authors that the explanation of the effect of increased alkalinity in increasing the corrosion rate might be due to one of two alternative processes, depending on w h e t h e r the films w e r e sufficiently porous to allow access of the solution to the metallic surface or not. In the case w h e r e they are sufficiently porous, we would expect a gradual filling of the pores with magnetite as a result of an anodic reaction such as 3Fe + 4 O H -~ Fe304 + 4H + 4 e - [2] w h e r e the O H -would be rate-controlling. In the case w h e r e they are not sufficiently porous to allow access of the solution to the metallic surface, the corrosion would have to proceed by diffusion of ionic or atomic species through the film, and the controlling effect of O H -would have to be attributed either to its control of the diffusion of o x y g e n -b e a r i n g species from the solution to the metallic surface as postulated by Potter and Mann, if diffusion w e r e rate-controlling, or to its effect on a surface reaction at the o x i d e -w a t e r interface such as 3Fe + + + 6 O H -~ Fe304 + H2 -t-2H20 [3] if the surface reaction w e r e rate-controlling.…”

“…Perhaps the t w o -l a y e r e d scale is related to the fact that hydrogen is generated on all sides of the block specimens and any generated at the m e t a loxide interface by such a reaction as Eq. [2] would have to penetrate the growing oxide scale to escape. Interference with crystal growth under these conditions may produce the finely divided "inner layer" which has been observed.…”

“…Techniques for removing thin uniform layers from metals have been used extensively in studying the range of energetic ions in solids (1,2) and also in investigating the effects of short range diffusion (3). For range measurements, the most reliable and sensitive technique has been the two-step process of anodic oxidation at constant voltage, followed by subsequent dissolution of the oxide.…”

“…The effect of alkali on the corrosion rate of steel in high-temperature water, originally studied by Berl and Van Taack (1) in 1930, has recently been the subject of a number of investigations (2)(3)(4)(5)(6)(7)(8). Berl and Van Taack, who heated small samples of steel powder in a static autoclave for 7.5 hr at 310~ obtained data indicating a minimum in the corrosion rate at a concentration of 0.7 g/1 which corresponds to a pH of 12.24.…”

Tritium Handling Problem in Controlled Thermonuclear Reactors.

“…It has been shown that the corrosion rate by steam inside of a steel boiler tube can be measured quantitatively by determining the rate of hydrogen effusion from the outside of the boiler tube. 19 Data presented in Eef. 12 indicate that, for a system having a boiler tube matrix of the proportions considered here, the back diffusion of normal hydrogen through plain stainless steel tubes would amount to 1.5 kg/yr at a steam temperature of 600°P.…”