Perricone, Matthew J. and Keith E. Wagner, Material Failures: The Importance of Validating First Impressions, Corrosion Solutions Conference, Lake Louise, Alberta, Canada, September 25-30, 2011.
Effective maintenance of complex systems relies on the understanding of how parts will wear out and eventually fail so that such events can be anticipated and avoided. Recently, the Nuclear Regulatory Commission placed particular emphasis on the stewardship of buried piping in the nuclear energy industry. Whether the system is a nuclear reactor or a gas pipeline, several types of material degradation are generally known and can be monitored in various ways. When an unanticipated failure does occur, root cause failure analysis is essential to avoid similar problems in the future and to demonstrate to regulators that the system is under control despite the failure. While in some cases a presumptive decision about the cause of failure is made on a cost basis, a failure investigation is crucially important to the safety of critical systems and components, as well as those failures that can cause enterprise-threatening events like plant shut-downs. In a manufacturing environment, materials-related failures can imperil product lines if appropriate preventative or corrective action is not taken. The challenge is to accurately determine the root cause of failure to guide the appropriate corrective action.
Visual inspections of the failed part is useful to the experienced materials scientist or engineer in guiding the path of the investigation to collect the necessary information to make a root cause determination; but sometimes first impressions can be misleading. Occasionally, what was initially intended to be a confirmatory investigation turns out to provide unanticipated but important insight into the manufacture, application, or material that has larger implications than the single failure event. This paper will present multiple case studies that discuss failure analyses that discovered root causes that were not immediately obvious. The appropriate context of information about the events surrounding the failure will be discussed along with the need for data regarding the type of service environment in which the failed parts were operating. The discussion will include analysis of buried pipe thought to be the source of an explosion and a cracked water main that caused widespread distribution of hazardous material. Industrial equipment joining failures initially associated with corrosion will also be presented. Finally, suspected stress corrosion cracking failures from the chemical processing and oil/gas industries will be considered.