Brass rods (mainly C36000, C38500, and C37700) are used in a great variety of applications, from machine component/hydraulic part manufacturing to architecture and fine arts. The chemical composition of these alloys is carefully designed to enhance machinability and/or hot formability (for free machining and hot stamping operations, respectively). This article reviews the principal defects that lead to in-process and in-service failures of brass rods and related components. The review is focused on defects caused by selected metalforming processes for the production of brass rods (extrusion and cold drawing) and on the role of these defects in failures during component processing and use.
A premix feeder line on a land-based gas turbine was found to be leaking, and the source of the leakage was traced back to a crack in a pipe-to-fitting weld. The weld joined a coupling made from the X6CrNiMoTi17-12-2 austenitic stainless steel to a type 316L austenitic stainless steel reducer. A root-cause assessment was conducted to determine the cause of the crack. Evidence of fatigue and corrosive attack was found. Various factors that influence the susceptibility to corrosion and cracking, such as heat tints, geometry of the weld, and surface finish of the component, are discussed. Recommendations are made for corrective actions and failure prevention.
Two titanium alloy wing attachment bolts from a commercial jetliner failed during the course of a routine service operation. Failure of the bolts occurred during the re-torque process as the wing was being reattached. Metallurgical failure analysis indicated that the fracture mechanism was ductile overload and that the mechanical properties of the bolts were consistent with exemplar bolts that had been supplied. After eliminating other sources of excessive load application, the most probable cause of failure was ascribed to variances between the frictional characteristics of the bolt at the time of re-torque and at the time of initial torque application several years earlier.
It is well known that corrosion can weaken structures over time, but because corrosion rates can differ significantly from location to location, it is difficult to predict the amount of weakening that can occur for a particular structure used outdoors in a given location. Over the years, salt fog testing has been used to help predict how a structure might degrade over time resulting from exposure. The most common tests are based upon MIL-STD 810 “Environmental Engineering Considerations and Laboratory Tests,” and ASTM B117 “Standard Practice for Operating Salt Spray (Fog) Apparatus.” Although these standards give guidelines on conducting accelerated tests, they provide no insight as to the real world exposure level corresponding to a test condition, i.e. an acceleration factor.
he Oak Ridge National Laboratory (ORNL) spiral notch torsion test (SNTT) system measures the intrinsic fracture toughness (K Ic) of structural materials, overcomes many of the limitations inherent in traditional techniques, and introduces new possibilities for standardizing fracture toughness testing. The system is uniquely suited to test a wide variety of materials, such as metals and alloys, ceramics, composites, polymers, carbon foam, and concrete. The SNTT system operates by applying pure torsion to cylindrical secimens machined with a notch line that spirals around the specimen at a 45° pitch (Fig. 1). Results are obtained with the aid of TOR3D-KIC, a three-dimensional finite-element computer code developed at ORNL, which may be obtained by contacting the author.
Two train rail elements at a switch location broke as part of a locomotive derailment. Preexisting cracks present in the elements most likely had developed as a result of wear in the switch system. The cracks were not the principal reason for the system failure, but they did define a plane of weakness. No other material defects were noted. The steel elements were severely deformed, but the final breaks included some brittle character, most likely a result of a high rate of loading during the incident. The rolling wheels were already outside of the constraints provided by the wheel flange and track configuration in order to cause the twisting and rolling deformation of the leading ends of the thin switch rails, which then led to breaking and separation of the pieces. Nondestructive examination was performed on an additional 199 switch rails. Cracks and/or linear indications were found on 27 switch points or switch point protectors. The flawed or damaged rails were removed, and spare rails that had passed the examination were substituted.
A spent nuclear fuel canister has been developed with the goal of no containment failure even during accidental drop conditions. This canister was designed to be loaded with U.S. Department of Energy spent nuclear fuel and then used for interim storage, transportation to the nation’s repository, and final disposal at the repository. The design required a high degree of confidence against failure if the canister were subjected to loads (e.g., accidental drop events) resulting in large plastic deformations and high strains. Significant testing of the canister clearly demonstrates that it can safely achieve the intended design goals without failure. The canister skirt and its attachment to the containment boundary are the key engineered elements of the design that allow significant impact damage without failure of the containment.
ondestructive evaluation is described as nondestructive testing (NDT), nondestructive inspection (NDI), and nondestructive examination (NDE). The activities associated with the evaluation include testing, inspection, and examination and primarily involve looking at (or through) and/or measuring some characteristic of an object. Frequently there is a desire to determine some characteristic of the object or to determine whether the object contains irregularities, discontinuities, or flaws. These examinations, inspections, or tests are used to determine the physical soundness of a material without impairing its usefulness. Nondestructive evaluation is a powerful tool that can help assure safety, quality, and reliability; increase productivity; decrease liability; protect the environment; and save money. In this article, nondestructive evaluation is represented by the acronym NDE.
Locked coil wire ropes, by virtue of their unique design and construction, have specialized applications in aerial ropeways, mine hoist installations, suspension bridge cables, and so forth. In such specialty ropes, the outer layer is constructed of Z-profile wires that provide not only effective interlocking but also a continuous working surface for withstanding in-service wear. The compact construction and fill-factor of locked coil wire ropes make them relatively impervious to the ingress of moisture and render them less vulnerable to corrosion. However, such ropes are comparatively more rigid than conventional wire ropes with fiber cores and therefore are more susceptible to the adverse effects of bending stresses. The reasons for premature in-service wire rope failures are rather complex but frequently may be attributed to inappropriate wire quality and/or abusive operating environment. In either case, a systematic investigation to diagnose precisely the genesis of failure is desirable. This article provides a microstructural insight into the causes of wire breakages on the outer layer of a 40 mm diam locked coil wire rope during service. The study reveals that the breakages of Z-profile wires on the outer rope layer were abrasion induced and accentuated by arrays of fine transverse cracks that developed on a surface martensite layer.
Proper operation of vector controlled induction motor drives over the entire speed range critically depends upon reliable operation of the feedback sensors. In the event of sensor failures, it is desirable that the induction motor system continues to operate, even if under a diminished performance capacity. This paper describes the development of a fault tolerant control system for an induction motor with automatic controller reconfiguration. The system adaptively reorganizes itself in the event of sensor loss or sensor recovery to sustain the best control performance given the complement of the remaining sensors. Theoretical and experimental results are presented
This paper describes the remote ultrasonic (UT) examinations of a high-level radioactive waste (HLW) storage tank at the Savannah River Site in South Carolina. The inspections, carried out by E.R. Holland, R.W. Vande Kamp, and J.B. Elder, were performed from the contaminated, annular space of the 46-year-old, inactive, 1.03 million gallon waste storage tank. A steerable, magnetic wheel wall crawler was inserted into the annular space through small (6 in., or 150 mm, diameter) holes/risers in the tank top. The crawler carried the equipment used to simultaneously collect data with up to four UT transducers and two cameras. The purpose of this inspection was to verify corrosion models and to investigate the possibility of previously unidentified corrosion sites or mechanisms. The inspections included evaluation of previously identified leak sites, thickness mapping, and crack detection scans on specified areas of the tank. No indications of reportable wall loss or pitting were detected. All thickness readings were above minimum design tank-wall thickness, although several small indications of thinning were noted. The crack detection and sizing examinations revealed five previously undetected indications, four of which were only partially through-wall. The cracks that were examined were found to be slightly longer than expected but still well within the flaw size criteria used to evaluate tank structural integrity.
The design of 3-piece steel pressurized containers includes double seams that connect the bottom and top of the container to the container body. These seams have some inherent design features, such as crevices, that can lead to corrosion and other forms of failure. Since the 3-piece containers are pressurized with liquefied propellants, such as propane, failure can lead to catastrophic separation of the top or bottom from the body. This creates a “rocket” effect with the potential to cause serious personal injury and/or property damage. This paper presents the analysis of several such failures and demonstrates that corrosion, weld cracking, and stress concentrations act to cause sudden, unexpected, explosive failures. Several changes in construction that could minimize the tendency for explosion are also discussed.
