Preface to the First Edition
The earliest reports of environment-induced cracking or embrittlement of materials include that of “season cracking” of brass, first observed more than 80 years ago (Ref 1), and the suggestion by W.H. Johnson in 1873 that hydrogen was a major cause of embrittlement in iron and steels (Ref 2). The incident of season cracking was discovered to result from the practice of storing cartridge cases in horse barns, where contact with ammonia vapors occurred. Hydrogen embrittlement was probably suspected by users of iron and steel products long before Johnson presented important details of this phenomenon. Many more cases of stress-corrosion or environment-induced cracking have been observed since these early studies.
Unfortunately, discovery of a particular stress-corrosion mechanism has often occurred because of a component failure that resulted in physical hazard or great economic cost. Early examples include the intergranular failure of a ferritic steel boiler (Ref 3), which was explained as hydrogen embrittlement (Ref 4), the explosion of a boiler by caustic “embrittlement” (Ref 5), and the failure of a steel hook (Ref 6) that caused the side of a building to fall on the street below. More recent examples include stress corrosion of steam turbine blading and rotors, nuclear piping, aircraft structures, and gas pipelines.
Stress-corrosion cracking (SCC) undoubtedly occurred prior to the earliest explanations cited above; however, the incidence of SCC has clearly increased since the beginning of the 20th century. This can be attributed to the use of more corrosion-resistant materials (which leads to increased susceptibility to localized corrosion), the use of higher stresses, and the complications caused by welding and complex forming operations. Our phenomenological understanding of SCC has also increased substantially since the beginning of the 20th century, as witnessed by the comprehensive nature of this book. Much is understood about the environmental, microstructural, microchemical, and mechanistic aspects that control stress corrosion, and it is often possible to avoid SCC failure of a particular component if these parameters are sufficiently well known. Unfortunately, relatively small alterations in environment or composition can easily place a material within the “susceptible zone,” resulting in failure rather than extended life. Boundaries between susceptibility and resistance tend to be very distinct, so the exclusive use of phenomenological data to avoid SCC is often insufficient.
A mechanistic understanding of SCC can be used in conjunction with phenomenological data to identify whether environmental or material changes will increase the probability of failure. However, the present level of mechanistic understanding, while greatly increased over the last several decades, is still inadequate for prediction of component life. To underscore this point, the mechanisms for ammonia-induced stress corrosion of brass and hydrogen-induced crack growth of iron and steel, two of the earliest observations of environment-induced cracking, continue to be debated. Recent work by Pugh and his coworkers (Ref 7–9) and by Newman and Sieradzki (Ref 10, 11) has done much to settle the issue for transgranular SCC of brasses. The number of advances made in our mechanistic understanding of hydrogen- induced cracking is far too extensive to list, but includes models that describe atomistics, energetics, surface adsorption/mobility, fracture mechanics, dislocation, and cohesive energy concepts. For some aspects, modeling of hydrogen-induced cracking is sufficiently quantitative that crack growth rate predictions are possible. Yet discussion continues as to whether hydrogen-induced crack growth occurs by a cleavage or a slip mechanism.
This book thoroughly covers the phenomenological aspects of stress-corrosion cracking for a wide range of materials. An overview of SCC mechanisms is presented in Chapter 1, followed by chapters describing SCC of ferritic and austenitic steels and of nickel, copper, aluminum, magnesium, titanium, zirconium, and uranium alloys. Also included are chapters on irradiation-assisted stress corrosion, SCC of glasses, ceramics, and weldments, detection and sizing of cracks in boiling water reactors, evaluation of SCC, and failure analysis methods.
Battelle Pacific Northwest Laboratories
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