Search Results for plasma

An investigation of wear and failure of babbitt bushes was completed in this study. The results showed that wear at dry sliding of babbitt obtained by plasma spraying was less than that of babbitt in the as-cast state and after a deformation heat treatment. The failure of babbitt bushes was caused by a simultaneous and interrelated exhibition of fatigue and wear processes that depend considerably on cohesion strength between the bush and the bearing base and accumulation of defects on the contact surface between the bush and the shaft.

Identification of alloys using quantitative chemical analysis is an essential step during a metallurgical failure analysis process. There are several methods available for quantitative analysis of metal alloys, and the analyst should carefully approach selection of the method used. The choice of appropriate analytical techniques is determined by the specific chemical information required, the condition of the sample, and any limitations imposed by interested parties. This article discusses some of the commonly used quantitative chemical analysis techniques for metals. The discussion covers the operating principles, applications, advantages, and disadvantages of optical emission spectroscopy (OES), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray spectroscopy, and ion chromatography (IC). In addition, information on combustion analysis and inert gas fusion analysis is provided.

River water was pumped into a brine plant by a battery of vertical pumps, each operating at 3600 rpm and at a discharge pressure of 827 kPa (120 psi). The pumps were lubricated by means of controlled leakage. The 3.8 cm (1 in.) OD pump sleeves were made of an austenitic stainless steel and were hard faced with a fused nickel-base hardfacing alloy (approximately 58 HRC). Packing for the pumps consisted of a braided PTFE-asbestos material. After several weeks of operation, the pumps began to leak and to spray water over the platforms on which they were mounted at the edge of the river. Analysis supported the conclusions that the leaks were caused by excessive sleeve wear that resulted from the presence of fine, abrasive silt in the river water. The silt, which contained hard particles of silica, could not be filtered out of the inlet water effectively.

A tri-lobe cylindrical roller bearing was submitted for investigation to determine the cause of uniformly spaced axial fluting damages on its rollers and outer raceway surfaces. The rollers and raceways were made from premium-melted M50 and M50NiL, aircraft quality steels often used in bearings to minimize the effects of orbital slippage and rolling-contact fatigue. The damaged areas were examined under a scanning electron microscope, which revealed a high density of microcraters, characteristic of local melting and material removal associated with bearing currents. Investigators also examined the effect of electrical discharge on crater dimensions and density and the role that thermoelectric voltage potentials may have played.

A brackish water pump impeller was replaced after four years of service, while its predecessor lasted over 40 years. The subsequent failure investigation determined that the nickel-aluminum bronze impeller was not properly heat treated, which made the impeller susceptible to aluminum dealloying. The dealloying corrosion was exacerbated by erosion because the pump was slightly oversized. The investigation recommended better heat treating procedures and closer evaluation to ensure that new pumps are properly sized.

Erosion of solid surfaces can be brought about solely by liquids in two ways: from damage induced by formation and subsequent collapse of voids or cavities within the liquid, and from high-velocity impacts between a solid surface and liquid droplets. The former process is called cavitation erosion and the latter is liquid-droplet erosion. This article emphasizes on manifestations of damage and ways to minimize or repair these types of liquid impact damage, with illustrations.

A back wall riser tube in a high pressure boiler failed, interrupting operations in a cogeneration plant. The failure occurred in a tube facing the furnace, causing eight ruptured openings over a 1.8 m section. The investigation consisted of an on-site visual inspection, nondestructive testing, energy dispersive x-ray analysis, and inductively coupled plasma mass spectrometry. The tube was made from SA 210A1 carbon steel that had been compromised by wall thinning and the accumulation of fire and water-side scale deposits. Investigators determined that the tube failed due to prolonged caustic attack that led to ruptures in areas of high stress. The escaping steam eroded the outer surface of the tube causing heavy loss of metal around the rupture points.

The operator of an electric transit system purchased a large number of tin-plated copper connectors, putting some in service and others in reserve. Later, when some of the reserve connectors were inspected, the metal surfaces were covered with spots consisting of an ash-like powder and the plating material had separated from the substrate in many areas. Several connectors, including some that had been in service, were examined to determine what caused the change. The order stated that the connectors were to be coated with a layer of tin-bismuth (2% Bi) to guard against tin pest, a type of degradation that occurs at low temperatures. Based on the results of the investigation, which included SEM/EDS analysis, inductively coupled plasma spectroscopy, and x-ray diffraction, the metal surfaces contained less than 0.1% Bi and thus were not adequately protected against tin pest, which was confirmed as the failure mechanism in the investigation.

Two clamps that support overhead power lines in an electrified rail system fractured within six months of being installed. The clamps are made of CuNiSi alloy, a type of precipitation-strengthening nickel-silicon bronze. To identify the root cause of failure, the rail operator led an investigation that included fractographic and microstructural analysis, hardness testing, inductively coupled plasma spectroscopy, and finite-element analysis. The fracture was shown to be brittle in nature and covered with oxide flakes, but no other flaws relevant to the failure were observed. The investigation results suggest that the root cause of failure was a forging lap that occurred during manufacturing. Precracks induced by the forging defect and the influence of preload stress (due to bolt torque) caused the premature failure.

High-level radioactive wastes generated during the processing of nuclear materials are kept in large underground storage tanks made of low-carbon steel. The wastes consist primarily of concentrated solutions of sodium nitrate and sodium hydroxide. Each of the tanks is equipped with a purge ventilation system designed to continuously remove hydrogen gas and vapors without letting radionuclides escape. Several intergranular cracks were discovered in the vent pipe of one such system. The pipe, made of galvanized steel sheet, connects to an exhaust fan downstream of high-efficiency particulate air filters. The failure analysis investigation concluded that nitrate-induced stress-corrosion cracking was the cause of the failure.

Metallurgical SEM analysis provides many insights into the failure of biomedical materials and devices. The results of several such investigations are reported here, including findings and conclusions from the examination a total hip prosthesis, stainless steel and titanium compression plates, and hollow spinal rods. Some of the failure mechanisms that were identified include corrosive attack, corrosion plus erosion-corrosion, inclusions and stress gaps, production impurities, design flaws, and manufacturing defects. Failure prevention and mitigation strategies are also discussed.

Rolling-contact fatigue (RCF) is a common failure mode in components subjected to rolling or rolling-sliding contact. This article provides a basic understanding of RCF and a broad overview of materials and manufacturing techniques commonly used in industry to improve component life. A brief discussion on coatings to improve surface-initiated fatigue and wear is included, due to the similarity to RCF and the increasing criticality of this failure mode. The article presents a working knowledge of Hertzian contact theory, describes the life prediction of rolling-element bearings, and provides information on physics and testing of rolling-contact fatigue. Processes commonly used to produce bearings for demanding applications are also covered.