Search Results for 1230

A portion of the wall of a reactor vessel used in burning impurities from carbon particles failed by localized melting. The vessel was made of Hastelloy X (Ni-22Cr-9Mo-18Fe). Considering the service environment, melting could have been caused either by excessive carburization (which would have lowered the melting point of the alloy markedly) or by overheating. A small specimen containing melted and unmelted metal was removed from the vessel wall and examined metallographically. It was observed that the interface between the melted zone and the unaffected base metal was composed of large grains and enlarged grain boundaries. An area a short distance away from the melted zone was fine grained and relatively free of massive carbides. This evidence supported the conclusion that the vessel failed by melting that resulted from heating to about 1230 to 1260 deg C (2250 to 2300 deg F), which exceeded normal operating temperatures, and carburization was not the principal cause of failure. No recommendations were made.

On 16 July 1999, a Boeing 737-800 on final approach for landing sustained a major lightning strike. Damage to the fuselage structure primarily was in the form of melting or partial melting of widely-separated rivets and adjacent Alclad 2024-T3 fuselage skin. The damage was confined to a 0.25-in. (6.4-mm) radii around the affected rivets. The repair process involved removal of the locally-affected material and addition of a skin doubler to restore the aircraft structure to the originally designed condition. Damage features are described briefly.

Military aircraft use a cartridge ignition system for emergency engine starts. Analysis of premature failures of steel (AISI 4340) breech chambers in which the solid propellant cartridges were burned identified corrosion as one problem with an indication that stress-corrosion cracking may have occurred. A study was made for stress-corrosion cracking susceptibility of 4340 steel in a paste made of the residues collected from used breech chambers. The constant extension rate test (CERT) technique was employed and SCC susceptibility was demonstrated. The residues, which contained both combustion products from the cartridges and corrosion products from the chamber, were analyzed using elemental analysis and x-ray diffraction techniques. Electrochemical polarization techniques were also utilized to estimate corrosion rates.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.

A heat transport pump in a heavy water reactor failed (exhibiting excessive vibration) during a restart following a brief interruption in coolant flow due to a faulty valve. The pump had developed a large crack across the entire length of a bearing journal. An investigation to establish the root cause of the failure included chemical and metallurgical analysis, scanning electron fractography, mechanical property testing, finite element analysis of the shrink fitted journal, and a design review of the assembly fits. The journal failure was attributed to corrosion fatigue. Corrective actions to make the journals less susceptible to future failures were implemented and the process by which they were developed is described.

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.