Stress-corrosion cracking Environment-sensitive

A.J. Forty and P. Humble, Surface Films and Stress-Corrosion Cracking, Environment-Sensitive Mechanical Behavior, A.R.C. Westwood andN.S. Stoloff, Ed., Gordon and Breach, New York,... 

S. Ahmad, M.L. Mehta, S.K. Saraf, and I. Saraswat, Stress Corrosion Cracking of Sensitized 304 Austenitic Stainless Steel in Petroleum Refinery Environment, Corrosion, Vol 38, 1982, p 347-353... 

In addition to the form of attack described above, sensitized welds are prone to pitting, stress-corrosion cracking in certain environments (see Chap. 9), and crevice corrosion (see Chap. 2). 

The addition of chromium forms a family of Ni-Cr-Mo alloys such as Hastelloy alloys C-276, C-22, and C-2000. These alloys contain 16 to 22 percent chromium and 13 to 16 percent molybdenum and are very resistant to a wide variety of chemical environments. They are considered resistant to stress-corrosion cracking and very resistant to localized corrosion in chloride-containing environments. These alloys are resistant to strong oxidizing solutions, such as wet chlorine and hypochlorite solutions. They are among only a few alloys that are completely resistant to seawater. The carbon contents are low enough that weld sensitization is not a problem during fabrication. These alloys are also more difficult to machine than stainless steel, but fabrication is essentially the same. 

From studies of service behavior and from extensive laboratory investigations, the well-established terms stress-corrosion cracking (SCC) and corrosion fatigue have been shown to relate to a continuum of failure modes classified as environment-sensitive fracture. In many environments, the addition of stress, with associated strains, introduces a variable that can result in brittle failure in the sense of very limited plastic flow in otherwise ductile materials such as the stainless steels. Environment-sensitive fractures propagate at an advancing crack tip at which, simultaneously, the local stresses can influence the corrosion processes, and the corrosion can influence the crack-opening processes. Since these processes proceed by kinetic mechanisms, they are time and stress dependent with the result that the crack propagation rate can become very sensitive to the stress application rates. Conventional SCC usually has been associated with static stress, but this is seldom realized... 

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. 

Austenitic stainless steels are sensitive to stress corrosion cracking in chloride-containing environments, above a temperature threshold that depends on the chloride-... 

The copper nickel alloys (Cu-Ni) generally resist well in neutral chloride environments. They are much less sensitive to stress corrosion cracking than brass. 

Lisagor, W. B., Influence of Precracked Specimen Configuration ind Starting Stress Intensity on the Stress Corrosion Cracking of 4340 Steel, Environment Sensitive Fracture Evaluation and Comparison of Test Methods, ASTM STP 821, S. W. Dean, E. N. Pugh, and G. M. UgiEmslQf, Eds., ASTM International, West Conshohocken, PA, 1984, pp. 80-97. 

Some of the original studies with the use of smooth bar specimens found It lacks correlation with service conditions. Interpretation of results is difficult. It often indicates stress corrosion cracking in alloy-environment combinations that do not cause failures in service. It does not address notch sensitivity [42],... 

Observations on Stress Corrosion Cracking Initiation Sites in Carbon Steel Conference Corrosion 94, Paper No. 234 NACE, Houston, TX, USA, 1994, 13 S. [4 Van der Sluys, W. A. DeMiglio, D. S. Use of a Constant Delta Test Method in the Investigation of Fatigue Crack Growth in 288 deg C Water Environments. Conference Environment-Sensitive Fracture Evaluation and Comparison Test Methods, Gaithersburg, Maryland, USA, 26-28 Apr. 1982... 

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