This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

A group of control valves that regulate production in a field of sour gas wellheads performed satisfactorily for three years before pits and cracks were detected during an inspection. One of the valves was examined using chemical and microstructural analysis to determine the cause of failure and provide preventive measures. The valve body was made of A216-WCC cast carbon steel. Its inner surface was covered with cracks stemming from surface pits. Investigators concluded that the failure was caused by a combination of hydrogen-induced corrosion cracking and sulfide stress-corrosion cracking. Based on test data and cost, A217-WC9 cast Cr–Mo steel would be a better alloy for the application.

A shopping mall in South Carolina was originally constructed in 1988 and a second phase completed in 1989. The HVAC system inside the mall included an open, recirculating condenser water loop that served various fan coil units located within tenant spaces. The system had a recirculating capacity of about 44,000 gal (166,000 L) of water. It consisted primarily of steel pipes fitted with threaded connectors on the 2 in. (46 cm) pipes and bolted flanged couplings on the larger pipes. Seven years following the completion of the mall, corrosion problems were noted at the outer and inner surfaces of the pipe. Visual observations on the inner diametral surfaces revealed that the pipes were, in almost all cases, filled with corrosion products. A significant amount of base metal loss was documented in all of the samples. The cause of the observed corrosion was determined to be a lack of corrosion monitoring and poor water quality. Pipe replacement and a regular water testing program were recommended.

This article focuses on the corrosion-wear synergism in aqueous slurry and grinding environments. It describes the effects of environmental factors on corrosive wear and provides information on the impact and three-body abrasive-corrosive wear. The article also discusses the various means for combating corrosive wear, namely, materials selection, surface treatments, and handling-environment modifications.

This paper reviews several fatigue failures from the waterwall, superheater, and economizer portions of the boiler, their causes and how they were mitigated and monitored. Some cases required simple field modifications by cutting or welding, repair of existing controls, and/or changes in maintenance. Nondestructive inspections by visual, magnetic particle, ultrasonic, and radiographic methods for detecting and monitoring damage are discussed. These failures are presented to provide hindsight that will help others in increasing the success rate for anticipating and analyzing the remaining life of other units.

Practical examples of stress-corrosion cracking (SCC) and methods for its prevention were presented. Cracks in chloride-sensitive austenitic steels were very branched and transcrystalline. Etched cross sections of molybdenum-free samples showed chloride-induced cracks running out of the pitted areas. Alternatively polishing and etching micro-sections for viewing at high magnification made crack detail more visible. Optical and scanning electron micrographs showed cracking in austenitic cast steel and cast iron due to both internal tensile and critical residual stresses; the latter causes flake-like spalling. Measures to prevent SCC include stress reduction, use of austenitic steels or nickel alloys not susceptible to grain boundary attack, use of ferritic chromium steels, surface slag removal, control of temperature and chloride concentration, and cathodic protection.

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.

Leaks developed at random locations in aluminum brass condenser tubes within the first year of operation of a steam condenser in a nuclear power plant. One failed tube underwent scanning electron microscopy surface examination and optical microscope metallography. It was determined that the tube failed from crevice corrosion under seawater deposits that had formed on the inner surface. Mechanical cleaning of the condenser tubes every 6 months and installation of intake screens of smaller mesh size were recommended.

Several stainless steel bolts used on a Titan Space Launch Vehicle broke at the shank and failure was attributed to stress-corrosion cracking. But results could not be duplicated in the laboratory with salt-solution immersion tests until the real culprit was established: the secondary effect of galvanic coupling, hydrogen embrittlement.

The principal task of a failure analyst during a physical-cause investigation is to identify the sequence of events involved in the failure. Technical skills and tools are required for such identification, but the analyst also needs a mental organizational framework that helps evaluate the significance of observations. This article discusses the processes involved in the characterization and identification of damage and damage mechanisms. It describes the relationships between damage causes, mechanisms, and modes with examples. In addition, some of the more prevalent and encompassing characterization approaches and categorization methods of damage mechanism are also covered.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

This article provides a discussion on the structural ceramics used in gas turbine components, the automotive and aerospace industries, or as heat exchangers in various segments of the chemical and power generation industries. It covers the fundamental aspects of chemical corrosion and describes the corrosion resistance characteristics of specific classes of refractories and structural ceramics. The article also examines the prevention strategies that minimize corrosion failures of both classes of materials.

This article focuses on the mechanisms of microbially induced or influenced corrosion (MIC) of metallic materials as an introduction to the recognition, management, and prevention of microbiological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It discusses the degradation of various protective systems, such as corrosion inhibitors and lubricants. The article describes the failure analysis of steel, iron, copper, aluminum, and their alloys. It also discusses the probes available to monitor conditions relevant to MIC in industrial systems and the sampling and analysis of conditions usually achieved by the installation of removable coupons in the target system. The article also explains the prevention and control strategies of MIC in industrial systems.

This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.

A number of AISI 347 stainless steel bellows intended for use in the control rod drive mechanism of a fast breeder reactor were found to be leaking before being placed in service. The bellows, which had been in storage for one year in a seacoast environment, exhibited a leak rate on the order of 1 x 10−7 cu cm/s (6 x 10−8 cu in./s). Optical metallography revealed numerous pits and cracks on the surfaces of the bellow convolutes, which had been welded to one another using an autogenous gas tungsten arc welding process. Microhardness measurements indicated that the bellows had not been adequately stress relieved. It was recommended that a complete stress-relieving treatment be applied to the formed bellows. Improvement of storage conditions to avoid direct and prolonged contact of the bellows with the humid, chloride-containing environment was also recommended.

Alloy 430 stainless steel tube-to-header welds failed in a heat recovery steam generator (HRSG) within one year of commissioning. The HRSG was in a combined cycle, gas-fired, combustion turbine electric power plant. Alloy 430, a 17% Cr ferritic stainless steel, was selected because of its resistance to chloride and sulfuric acid dewpoint corrosion under conditions potentially present in the HRSG low-pressure feedwater economizer. Intergranular corrosion and cracking were found in the weld metal and heat-affected zones. The hardness in these regions was up to 35 HRC, and the weld had received a postweld heat treatment (PWHT). Metallographic examination revealed that the corroded areas contained undertempered martensite. Fully tempered weld areas with a hardness of 93 HRB were not attacked. No evidence of corrosion fatigue was found. Uneven temperature control during PWHT was the most likely cause of failure.

This article describes the two critical goals in a failure investigation: damage mechanisms and damage modes. It explains the determination of primary and secondary damage mechanisms and discusses the methodology used to classify the damage mechanisms.

This article explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.

Life assessment of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The failure investigator's input is essential for the meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into the determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed include industry perspectives on failure and life assessment of components, structural design philosophies, the role of the failure analyst in life assessment, and the role of nondestructive inspection. They also cover fatigue life assessment, elevated-temperature life assessment, fitness-for-service life assessment, brittle fracture assessments, corrosion assessments, and blast, fire, and heat damage assessments.