Two freshwater tanks (0.81 mm (0.032 in) thick, type 321 stainless steel) were removed from aircraft service because of leakage due to pitting and rusting on the bottoms of the tanks. One tank had been in service for 321 h, the other for 10 h. There had been departures from the specified procedure for chemical cleaning of the tanks in preparation for potable water storage. The sodium hypochlorite sterilizing solution used was three times the prescribed strength, and the process exposed the bottom of the tanks to hypochlorite solution that had collected near the outlet. Investigation (visual inspection, 95x unetched images, chemical testing with a 5% salt spray, chemical testing with sodium hypochlorite at three strength levels, samples were also pickled in an aqueous solution containing 15 vol% concentrated nitric acid (HNO3) and 3 vol% concentrated hydrofluoric acid (HF) and were then immersed in the three sodium hypochlorite solutions for several days) supported the conclusion that failure of the stainless steel tanks by chloride-induced pitting resulted from using an overly strong hypochlorite solution for sterilization and neglecting to rinse the tanks promptly afterward. Recommendations included revising directions for sterilization and rinsing.

Aluminum alloy BS.1476-HE.15 by virtue of its high strength and low density finds application in the form of bars or sections for cranes, bridges, and other such structures where a reduction in dead weight load and inertia stresses is advantageous. Bars and sections in H.15 alloy are mostly produced by extrusion. Some material processed this way has been prone to exfoliation corrosion. Extended aging for 24 h at a temperature of 185 deg C (365 deg F) virtually suppresses the tendency for exfoliation corrosion to develop. Also, the use of a sprayed coating, either of aluminum or Al-1Zn alloy, was effective in halting and preventing this form of attack. While alarming, the appearance of exfoliation corrosion provides a valuable warning to the engineer or inspector before a severe weakening of the particular sections has occurred.

The Rocky Point Viaduct, located near Port Orford, OR, was replaced after only 40 years of service. A beam from the original viaduct was studied in detail to determine the mechanisms contributing to severe corrosion damage to the structure. Results are presented from the delamination survey, potential and corrosion mapping, concrete chemistry, and concrete physical properties. The major cause of corrosion damage appears to have been the presence of both pre-existing and environmentally-delivered chlorides in the concrete.

High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.

This article presents a general overview of outdoor weather aging factors, their effects on the performance of polymeric materials, and the accelerated test methods that can be used to investigate those effects. These test methods are used to characterize material performance when subjected to specific, often controlled, and well-defined factors. The article also presents an overview of weathering instrument types that simulate outdoor stress factors.

Diagnosis of environmentally induced failures is greatly facilitated by metallographic analysis. As an example, a failure analysis of ASTM A574 material grade bolts is presented. The bolts served as bonnet screws in underground valves and failed due to stress-corrosion cracking. Metallographic methods were used to diagnose and provide solutions for the service failure. Included are photos showing crack propagation morphology and fracture surface appearance.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

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.

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.

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.

Accelerated life testing and aging methodologies are increasingly being used to generate engineering data for determining material property degradation and service life (or fitness for purpose) of plastic materials for hostile service conditions. This article presents an overview of accelerated life testing and aging of unreinforced and fiber-reinforced plastic materials for assessing long-term material properties and life expectancy in hostile service environments. It considers various environmental factors, such as temperature, humidity, pressure, weathering, liquid chemicals (i.e., alkalis and acids), ionizing radiation, and biological degradation, along with the combined effects of mechanical stress, temperature, and moisture (including environmental stress corrosion). The article also includes information on the use of accelerated testing for predicting material property degradation and long-term performance.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.

A storage tank had been in service at a petrochemical plant for 13 years when inspectors discovered cracks adjacent to weld joints and in the base plate near the foundation. The tank was made from AISI 304 stainless steel and held styrene monomer, a derivative of benzene. The cracks were subsequently welded over with 308 stainless steel filler wire and the base plate was replaced with new material. Soon after, the tank began leaking along the weld bead, triggering a full-scale investigation; spectroscopy, optical and scanning electron microscopy, fractography, SEM-EDS analysis, and microhardness, tensile, and impact testing. The results revealed transgranular cracks in the HAZ and base plate, likely initiated by stresses developed during welding and the presence of chloride from seawater used in the plant. It was also found that the repair weld was improperly done, nor did it include a postweld heat treatment to remove weld sensitization and minimize residual stresses.

A crack was detected in one arm of the right-hand horizontal brace of the nose landing gear shock strut from a large military aircraft. The shock strut was manufactured from a 7049 aluminum alloy forging in the shape of a delta. A laboratory investigation was conducted to determine the cause of failure. It was concluded that the arm failed because of the presence of an initial defect that led to the initiation of fatigue cracking. The fatigue cracking grew in service until the part failed by overload. The initial defect was probably caused during manufacture. Fleet-wide inspection of the struts was recommended.

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

This article discusses failures in shafts such as connecting rods, which translate rotary motion to linear motion, and in piston rods, which translate the action of fluid power to linear motion. It describes the process of examining a failed shaft to guide the direction of failure investigation and corrective action. Fatigue failures in shafts, such as bending fatigue, torsional fatigue, contact fatigue, and axial fatigue, are reviewed. The article provides information on the brittle fracture, ductile fracture, distortion, and corrosion of shafts. Abrasive wear and adhesive wear of metal parts are also discussed. The article concludes with a discussion on the influence of metallurgical factors and fabrication practices on the fatigue properties of materials, as well as the effects of surface coatings.

The various methods of furnace, torch, induction, resistance, dip, and laser brazing are used to produce a wide range of highly reliable brazed assemblies. However, imperfections that can lead to braze failure may result if proper attention is not paid to the physical properties of the material, joint design, prebraze cleaning, brazing procedures, postbraze cleaning, and quality control. Factors that must be considered include brazeability of the base metals; joint design and fit-up; filler-metal selection; prebraze cleaning; brazing temperature, time, atmosphere, or flux; conditions of the faying surfaces; postbraze cleaning; and service conditions. This article focuses on the advantages, limitations, sources of failure, and anomalies resulting from the brazing process. It discusses the processes involved in the testing and inspection required of the braze joint or assembly.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

This article addresses electrical testing and characterization of plastics and presents a number of techniques for evaluating the electrical properties of insulating materials, with a special focus on plastics, accompanied by a list of the electrical properties of different types of plastics. It provides the reader with sufficient information to select the appropriate electrical test(s) for a specific application. The tests covered in this article are widely used in industry to determine the electrical properties of insulating materials, particularly plastics. The article lists and defines terms used in connection with testing and specification of plastics for electrical applications.

This article commences with a discussion on the characteristics of stress-corrosion cracking (SCC) and describes crack initiation and propagation during SCC. It reviews the various mechanisms of SCC and addresses electrochemical and stress-sorption theories. The article explains the SCC, which occurs due to welding, metalworking process, and stress concentration, including options for investigation and corrective measures. It describes the sources of stresses in service and the effect of composition and metal structure on the susceptibility of SCC. The article provides information on specific ions and substances, service environments, and preservice environments responsible for SCC. It details the analysis of SCC failures, which include on-site examination, sampling, observation of fracture surface characteristics, macroscopic examination, microscopic examination, chemical analysis, metallographic analysis, and simulated-service tests. It provides case studies for the analysis of SCC service failures and their occurrence in steels, stainless steels, and commercial alloys of aluminum, copper, magnesium, and titanium.