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Monday, October 18, 2004 - 3:00 PM
FA 2.3

Corrosion Related Failures of Stainless Steels-Case Histories

R. M. Kain, Corrosion Consultant to the Nickel Institute, Wilmington, NC

Over the years, stainless steels have been used successfully in a broad range of applications and environments. From time-to-time, however, corrosion related failures have occurred to the dismay of owners and operators. Corrosion issues related to stainless steel usage in chloride containing aqueous and atmospheric environments are reviewed. The predominant modes of corrosion, and hence corrosion related failures, in these environments are pitting, crevice corrosion and chloride stress corrosion cracking (SCC). The cause of stainless steel corrosion failures is often related to a combination of factors. In general, these can be categorized as metallurgical, environmental and design or fabrication influenced. In some instances, one form of corrosion may lead to another. For example, localized chemistry changes associated with pitting or crevice attack may promote SCC. Conversely, an initiated crack may serve as an effective crevice site for further propagation. A case history involving 300 series stainless steel in a cooling coil application is reviewed. Over a period on several years of service, both pitting and SCC contributed to system leaks. In some cases, SCC was attributed to residual weld fabrication stress. Other contributing factors were mineral deposits, early history chlorination practice and equipment steam cleaning. In another case, pitting corrosion affected a vast amount of stainless steel in an enclosed water treatment facility. On- site testing revealed that the corrosion was not due to a off specification material or to workmanship, as originally postulated by others. Results indicated that even an initial selection of a higher grade stainless would not have alleviated the problem without added consideration to environmental changes. Case examples are also presented to illustrate the influence of intentionally and inadvertently applied coatings on the localized corrosion behavior of a stainless steel tank, fasteners and a heat exchanger.

Summary: The causes of stainless steel corrosion failures in chloride containing aqueous and atmospheric environments are presented. Contributing factors such as material susceptibility, environmental conditions and design elements are reviewed. In some case specially designed tests replicated the service failures.