Three separate corrosion mechanisms were involved in the failure of an AISI type 304 stainless steel pipe elbow. The major cracks, including the one that penetrated the wall, tend to be wide-mouthed, tapering to a blunt tip, with corrosion products filling much of the crack space. This was characteristic of corrosion fatigue. The second type of cracking originated at some of the major cracks. These cracks were branched and transgranular, which is characteristic of stress-corrosion caused by chlorides. The third crack mode, an intergranular network, was most probably the result of hydrogen sulphide attack. The 13-year service life of the elbow made it difficult, if not impossible, to determine the order of the corrosion mechanisms or the length of time it took to reach the present state of degradation after the initiation of corrosion. Based on the long service life the present material has given, it was recommended that it be used again.

AISI type 321 stainless steel heat exchanger tubes failed after only three months of service. Macroscopic examination revealed that the leaks were the result of localized pitting attack originating at the water side surfaces of the tubes. Metallographic sections were prepared from both sets of tubes. Microscopic examination revealed that the pits had a small mouth with a large subsurface cavity which is typical of chloride pitting of austenitic stainless steel. However, no pitting was found in other areas of the system, where the chloride content of the process water was higher. This was attributed to the fact that they were downstream from a deaeration unit. It was concluded that the pitting was caused by a synergistic effect of chlorine and oxygen in the make-up water. Because it was not possible to install a deaeration unit upstream of the heat exchangers, it was recommended that a molybdenum-bearing stainless steel such as 316L or 317L be used instead of 321.

This investigation involved two AISI 304L acid storage tanks and one AISI 304L spent solvent tank from a sewage treatment facility. After installation, these tanks were hydrostatically tested using sewage effluent. No leaks were found and after a year or two, the tanks were drained and filled with nitric acid in preparation for service. Three weeks later the two acid tanks were found to be leaking from the bottom. Samples from the spent solvent tank revealed that pitting was located in a depressed area near a suction hole, beneath a black residue. It was concluded that the acid tanks failed by chloride-induced pitting initiated by microbial activity. Further, the spent solvent tank failed by a similar, but anaerobic mechanism. The use of the effluent for the hydrostatic test and the failure to remove it and clean and dry the tanks was the primary cause of failure. Localized carbide segregation in the original plate served as preferential corrosion sites. Had the tanks been hydrostatically tested in a proper manner, the pitting may not have occurred.

Some of the admiralty brass tubes were failing in a heat exchanger. The heat exchanger cooled air by passing river water through the inside of the tubes. The wall thickness of all tubes ranged between 1.19 to 1.27 mm (0.047 to 0.050 in.). General intergranular corrosion occurred at the inside surfaces of the tubes. Transgranular stress-corrosion cracking, probably the result of sulphates under basic conditions, and dezincification occurred also as the result of galvanic corrosion under the deposits in the tubes. Recommendations were to use a closed-loop water system to eliminate sulphates, ammonia, etc., and to run trials on one unit with tubes of other alloys such as 80-20 Cu-Ni or 70-30 Cu-Ni to evaluate their performance prior to any large scale retubing operations.

The self-powered flux detectors used in some nuclear reactors are Pt or V-cored co-axial cables with MgO as an insulator and Inconel 600 as the outer sheath material. The detectors are designed to operate in a He atmosphere; to maximize the conduction of heat (generated from the interaction with gamma radiation) and to prevent corrosion. A number of failures have occurred over the years because of a loss of the He cover gas in the assembly. This has resulted in either acid attack on the Inconel 600 sheath in a wet environment or gaseous corrosion in a dry environment. In the latter case, nitriding and embrittlement occurred at temperatures as low as 300 to 400 deg C (determined from an examination of the oxidation of the Zircaloy-2 carrier rod on which the detectors were mounted). Recent results are described and discussed in terms of the oxidation and nitriding kinetics of Zircaloy-2 and Inconel 600, respectively.

Several air heat exchangers failed in service in a pulp and paper operation. The tubes were made from AISI 316 stainless steel with an extruded aluminum fin mechanically bonded to the outside. Originally, the failures were blamed on poor tube to header welds. The units were sent back to the manufacturer for repair. Some of the units failed the hydrostatic test after they were repaired. Microscopic examination revealed the presence of branched transgranular cracks characteristic of stress-corrosion cracking. Only some of the tubes failed and these did so by stress-corrosion cracking. The most probable primary cause of the stress-corrosion cracking was local high residual stresses indicated by the areas of high hardness in the tubes. Low halogens in the water and airborne corrodents found normally in a pulp and paper mill were all that were required in the presence of high residual stresses in the tubes to initiate stress-corrosion cracking. Use of a low-carbon grade of stainless steel such as 316L was recommended to facilitate formation of the tube without producing excessive residual stresses. It was recommended also that failed units be segregated until it can be determined if the failure was related to operating pressure or some other unique cause.

After six years of service, three water shut-off valves on a copper water line in a residential building were found to be inoperative. Macroscopic examination of the valves after disassembly revealed that all three failed at the key that holds the spindle in the gate. In addition, the color near the key changed from yellow to red-brown. The gate was made from leaded red brass (85-5-5-5) while the spindle was made from silicon brass. It was concluded that the valves failed by dezincification resulting from bimetallic galvanic corrosion. It is common in the valve industry to use components made of different alloys in the same valve, but this is not the best approach for all applications.

Soft-soldered copper pipe joints used in refrigerating plants failed. The solder had not adhered uniformly to the pipe surface. In addition, there were some longitudinal grooves on the pipe surfaces, parts of which were not filled with solder. The unsoldered areas formed cavities within the joints, some of which had been in direct communication with the outsides via the grooves or interconnected cavities. On cooling, moisture condensed on the external surfaces. Some of this was drawn by capillary action into the cavities in open communication with the external surface. On continued cooling to below freezing-point, water that entered the cavities solidified. This was accompanied by a slight increase in volume, which collapsed the pipe walls. In the examples, the pipe ends had not been properly tinned. The solder used was found to be of the tin-antimony type, containing about 5% antimony, which is more difficult to use than the usual tin-lead alloys. The use of this particular type of solder was a contributory factor in the production of unsound joints in the samples examined.

This article is a compilation of terms related to analysis and prevention of engineering failures.

This glossary is a compilation of terms related to the analysis and prevention of component and equipment failures. It is intended to help promote clear thinking and useful failure analysis. The definitions presented are those used in this Volume and reflect a common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts.

This article is a compilation of terms and definitions related to failure analysis and prevention. This glossary is intended to help promote clear thinking and useful failure analysis. The definitions presented are those used in this volume and reflect common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts.

This article focuses on the mechanisms of microbiologically influenced corrosion as a basis for discussion on the diagnosis, management, and prevention of biological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It begins with an overview of the scope of microbial activity and the corrosion process. Then, various mechanisms that influence corrosion in microorganisms are discussed. The focus is on the incremental activities needed to assess the role played by microorganisms, if any, in the overall scenario. The article presents a case study that illustrates opportunities to improve operating processes and procedures related to the management of system integrity. Industry experience with corrosion-resistant alloys of steel, copper, and aluminum is reviewed. The article ends with a discussion on monitoring and preventing microbiologically influenced corrosion failures.

This article provides assistance to a failure analyst in broadening the initial scope of the investigation of a physical engineering failure in order to identify the root cause of a problem. The engineering design process, including task clarification, conceptual design, embodiment design, and detail design, is reviewed. The article discusses the design process at the personal and project levels but takes into consideration the effects of some higher level influences and interfaces often found to contribute to engineering failures.

The intent of this article is to assist the failure analyst in understanding the underlying engineering design process embodied in a failed component or system. It begins with a description of the mode of failure. This is followed by a section providing information on the root cause of failure. Next, the article discusses the steps involved in the engineering design process and explains the importance of considering the engineering design process. Information on failure modes and effects analysis is also provided. The article ends with a discussion on the consequence of management actions on failures.

Failure analysis is a process that is performed in order to determine the causes or factors that have led to an undesired loss of functionality. This article is intended to demonstrate proper approaches to failure analysis work. The goal of the proper approach is to allow the most useful and relevant information to be obtained. The discussion covers the principles and approaches in failure analysis work, objectives and scopes of failure analysis, the planning stages for failure analysis, the preparation of a protocol for a failure analysis, practices used by failure analysts, and procedures of failure analysis.

Failure analysis is a process that is performed to determine the causes or factors that have led to an undesired loss of functionality. This article describes some of the factors and conditions that might be considered when approaching a failure analysis problem. It focuses on the key principles, objectives, practices, and procedures of failure analysis. The article provides guidelines on the preparation of a protocol for a failure analysis. It also demonstrates the proper approaches to failure analysis.