Stress corrosion cracking failure

In addition, a surprisingly large number of stress-corrosion cracking failures have resulted from the welding of small attachments to vessels and piping after stress-relief heat treatment has been carried out. 

Serious stress-corrosion-cracking failures have occurred when chloride-containing hydrotest water was not promptly removed from stainless-steel systems. Use of potable-quality water and complete draining after test comprise the most reliaole solution to this problem. Use of chloride-free water is also helpful, especially when prompt drainage is not feasible. 

TABLE 4.47 Stress Corrosion Cracking Failures of Different Alloys ... 

Stress corrosion cracking (SCC) is caused by the combined action of a static tensile stress and corrosion. The stress may originate from external loading or be the result of a thermal or mechanical treatment that generates residual stresses in the material. Stress corrosion cracking failures usually occur with some delay and they are limited to particular alloy-environment combinations, temperature ranges and stress levels. 

Some indicators that generally indicate a log-normal distribution are (a) data values that physically cannot be negative, (b) nonnal standard deviations that are proportional to arithmetic means, (c) arithmetic means that are consistently greater than median values, and (d) dependent parameters whose logarithms are proportional to the values of independent parameters. Some t5fpes of corrosion data that are likely to be log-normally distributed are (a) mass loss, (b) thickness loss, (c) time to initial stress corrosion cracks, (d) time to stress-corrosion cracking failures, and (e) polarization currents in the Tafel slope range. 

The depths of deepest pits on specimens, the times to first leaks in pipe lengths, times to initial stress-corrosion cracking failures, and the number of cycles to first corrosion-fatigue failures are, by definition, extreme values. The depth of the deepest pit on a specimen is the upper tail of the distribution of depths of all pits on that specimen. 

Parkins, R.N. Predictive approaches to stress-corrosion cracking failure. Br. Corros. J. 14, 15 (1979)... 

Tlius, a great deal of experience and the results of many specific investigations indicate stress-corrosion cracking of austenitic stainless alloys is not a problem in uranyl sulfate solution environments free of chloride. However, contrariwise, it also seems clear that stress-corrosion cracking failures will be a problem if these solutions become contaminated with chloride. 

Slurry systems. Substantially less experience with aqueous slurries than with uranyl sulfate solutions has been accumulated in austenitic stainless steel equipment. However, it appears that stress-corrosion cracking failures manifest themselves about as one might expect from high-temperature water results. Thus the presence or absence and the concentration of chloride in the slurry are major factors in stress-cracking incidence. 

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