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Suranjeeta Dhar, Fameeda Mohammed, Laura Xu, Raymond Fontana
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A.C. Raghuram, S. Radhakrishnan, R.V. Krishnan, V. Ramachandran
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S.J. Suess
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Suranjeeta Dhar, Fameeda Mohammed, Laura Xu, Raymond Fontana
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Friedrich Karl Naumann, Ferdinand Spies
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Book Chapter
Failure of a Polyoxymethylene Gear Wheel
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0092103
EISBN: 978-1-62708-234-1
... started mainly at the mechanically stressed tooth flanks. In addition, oil vapors, humidity, and other degradative agents could also have contributed to the observed failure. No recommendations were made. Boilers Gear teeth Microporisty Polyoxymethylene (Other, miscellaneous, or unspecified...
Abstract
A polyoxymethylene gear wheel that had been in operation in a boiler room failed. Investigation (visual inspection and 305x images) supported the conclusion that failure was due to postcrystallization causing considerable shrinkage. Breakdown along the crystalline superstructure started mainly at the mechanically stressed tooth flanks. In addition, oil vapors, humidity, and other degradative agents could also have contributed to the observed failure. No recommendations were made.
Book Chapter
Failure of a Nylon Driving Gear
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0092102
EISBN: 978-1-62708-234-1
... (frictional wear). No recommendations were made. Gears Lubrication Nylon (Other, miscellaneous, or unspecified) wear Figure 1 shows pitting on the tooth flank of a nylon oil-lubricated driving gear. The pitting produced numerous surface microcracks in association with large-scale fragmentation...
Abstract
A nylon oil-lubricated driving gear showed pitting upon visual inspection. The pitting produced numerous surface microcracks. Further investigation (visual inspection and 37x images) supported the conclusion that failure occurred in association with large-scale fragmentation (frictional wear). No recommendations were made.
Book Chapter
Poor Alloy Selection as a Cause of Failure
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0047387
EISBN: 978-1-62708-225-9
... composition Gear teeth Hardenability Sprockets Low-alloy steel (Other, miscellaneous, or unspecified) failure Induction-hardened teeth on a sprocket cast of low-alloy steel wore at an unacceptably high rate. A surface hardness of 50 to 51 HRC was determined; 55 HRC minimum had been specified...
Abstract
Induction-hardened teeth on a sprocket cast of low-alloy steel wore at an unacceptably high rate. A surface hardness of 50 to 51 HRC was determined; 55 HRC minimum had been specified. Analysis revealed that the alloy content of the steel was adequate for the desired hardenability but that the specified carbon content (0.29%) was too low. The low specified carbon content resulted in unacceptably low hardness. Because hardness largely controls wear rate, an early failure occurred. The specification for this part was changed so that a higher carbon content (0.45% C) was required.
Book Chapter
Pitting of TiN-Coated Back Surgery Wires
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.med.c9001573
EISBN: 978-1-62708-226-6
.... Arcing Pitting (wear) Surgical implants Wire Ti-6Al-4V Titanium nitride coating UNS R56406 Surface treatment related failures (Other, miscellaneous, or unspecified) wear Background The TiN coated back surgery wires were made of Ti6A14V. The reported failure was the presence of pits...
Abstract
TiN coated back surgery wires were made of Ti-6Al-4V. The reported failure was the presence of pits located in the uncoated area of the wires. The uncoated area of the wire is where the wire is fixtured in the coating chamber during coating. Examination and analysis of the pits using SEM/EDX detection unit revealed significant peaks of B, O, Zr and Fe. Moreover, the shape of the pits was similar to an arc crater. The formation of pits in the wire was caused during coating due to microarcing. A contaminated fixture used during the coating most likely caused the microarcing.
Book Chapter
Pitting Failure of Ball Bearings in an Electric Motor by Static Electrical Discharges
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0047935
EISBN: 978-1-62708-225-9
..., miscellaneous, or unspecified) wear (Other, miscellaneous, or unspecified) failure The electric motor in an office machine was producing intermittent noise. Ball bearings were suspected as the source of the noise and were removed from the motor and sent to the laboratory for examination. The bearings...
Abstract
Ball bearings made of type 440C stainless steel hardened to 60 HRC and suspected as the source of intermittent noise in an office machine were examined. A number of spots on the inner-ring raceway were revealed by scanning electron microscopy. The metal in the area around the spot was evidenced to have been melted and welded to the inner-ring raceway. It was revealed by randomly spaced welded areas on the raceways that the welding was the result of short electrical discharges between the bearing raceways and the balls. The use of an electrically nonconductive lubricant in the bearings was suspected to have caused the electric discharge by accumulation and discharge of static charge. The electrical resistance between the rotor and the motor frame lubricated with electrically conductive grease and the grease used in the current case was measured and compared to confirm the fact the currently used grease was nonconductive. It was concluded that the pits were formed by momentary welding between the ball and ring surfaces. The lubricant was replaced by electrically conductive grease as a corrective measure.
Book Chapter
Failure of Steel Wire Rope Because of Overheating
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.matlhand.c0048035
EISBN: 978-1-62708-224-2
.... Thus, a 50% loss in tensile strength of the wires was caused by overheating which lead to failure of the rope. It was recommended that prolonged exposure of wire ropes to extreme conditions should be avoided. Cranes Slags Tensile strength Steel wire rope (Other, miscellaneous, or unspecified...
Abstract
A 3.8-cm diam 6 x 37 rope of improved plow steel wire failed in service during dumping of a ladle of hot slag. A heavy blue oxide extending 0.6 to 0.9 m back from each side of the break was revealed on examination of the rope. Tensile fractures were shown by the broken ends of the rope. Recrystallization of the steel was revealed during microscopic examination of the wires adjacent to the break which indicated that the wires had been heated in excess of 700 deg C (1292 deg F). The tensile strength of the wires in the rope that broke was 896 MPa whereas the specification required it to be 1724 MPa. Thus, a 50% loss in tensile strength of the wires was caused by overheating which lead to failure of the rope. It was recommended that prolonged exposure of wire ropes to extreme conditions should be avoided.
Book Chapter
Failure of a Hastelloy X Reactor-Vessel Wall
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c0046953
EISBN: 978-1-62708-220-4
...), which exceeded normal operating temperatures, and carburization was not the principal cause of failure. No recommendations were made. Chemical reactors Melting Overheating Hastelloy X UNS N06002 (Other, miscellaneous, or unspecified) failure A portion of the wall of a reactor vessel used...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c9001900
EISBN: 978-1-62708-225-9
... the residue of partial melting was seen. Ball bearings Electric arcs Electric motors Grounding (electrical) Martensite Melting Scanning electron microscopy 52100 UNS G52986 (Other, miscellaneous, or unspecified) failure Incorrect grounding of an electric motor resulted in electric current...
Abstract
Incorrect grounding of an electric motor resulted in electric current passing through a 52100 steel ball bearing and caused multiple arcing between the rolling elements. The multiple arcing developed a pattern on the outer race known as ‘fluting’. A section of ball race outer showed the distinct banding (fluting) resulting from spark discharges while the bearing was rotating. The severe distress of the surface resulted in unacceptable levels of vibration. An SEM photograph of the banded regions showed smoothing of the asperities from continued operation is evident. In the craters the residue of partial melting was seen.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c9001748
EISBN: 978-1-62708-225-9
..., miscellaneous, or unspecified) wear Made of AMS 6740, the shaft of Fig. 1 was nitrided to a depth of 0.009 to 0.013 in. It failed due to abnormal wear; spline failure of the power turbine gear caused an engine overspeed and disintegration. Excessive spline wear ( Fig. 2 ) resulted from a new coupling...
Abstract
A pinion gear made of AMS 6470 steel, nitrided all over, lost internal splined teeth due to wear. Spline failure of the power turbine gear caused an engine overspeed and disintegration. Excessive spline wear resulted from a new coupling being mated during overhaul with a worn gear spline. Wear on the spline teeth flanks of the coupling was attributed to severe wear on the mating gear (internal) spline teeth. The assigned cause was an inadequate maintenance procedure which resulted in a wear-damaged component being retained in the power train during engine overhaul. To prevent reoccurrence, specific inspection criteria were issued defining maximum limits for spline wear. A procedure and requirements were specified for installing the coupling and pinion gear at the next overhaul.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0047939
EISBN: 978-1-62708-225-9
... 4620 UNS G46200 (Other, miscellaneous, or unspecified) failure The roller bearing shown in Fig. 1 was one of two that were mounted in an electric motor/gearbox assembly. Rough operation of the bearing was observed, and the unit was shut down. The bearing was removed and submitted...
Abstract
Rough operation of the roller bearing mounted in an electric motor/gearbox assembly was observed. The bearing components made of low-alloy steel (4620 or 8620) and the cup, cone and rollers were carburized, hardened and tempered. The contact surfaces of these components (cup, cone and roller) were revealed to be uniformly electrolytically etched by visual examination. The action similar to anodic etching was believed to have occurred as a result of stray currents in the electric motor (not properly grounded) and the presence of an electrolyte (moisture) between the cup and roller surfaces of the bearing. As a remedial action, the bearing was insulated for protection from stray currents by grounding of the motor and the moisture was kept out by sealing both bearings in the assembly.
Book Chapter
Rapid Wear of an Impact Breaker Bar Due to Excessive Retained Austenite
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c0047307
EISBN: 978-1-62708-223-5
... hardenability for the section size involved. Breaker bars Castings Retained austenite Wear resistance Fe-2.75C-19.5Cr-1.1Mo (Other, miscellaneous, or unspecified) wear The nominal composition of this chromium alloy cast iron was Fe-2.75C-0.75Mn-0.5Si-0.5Ni-19.5Cr-1.1Mo. The measured hardness...
Abstract
An impact breaker bar showed signs of rapid wear. The nominal composition of this chromium alloy cast iron was Fe-2.75C-0.75Mn-0.5Si-0.5Ni-19.5Cr-1.1Mo. The measured hardness of this bar was 450 to 500 HRB. The desired hardness for this material after air hardening is 600 to 650 HRB. The microstructure consisted of eutectic chromium carbides (Cr7C3) in a matrix of retained austenite and martensite intermingled with secondary carbides. Analysis (visual inspection and 500x view of sections etched with Marble's reagent) supported the conclusion that the low hardness resulted from an excessive amount of retained austenite. This caused reduced wear resistance and thus rapid wear in service. Recommendations included avoiding an excessive austenitizing temperature and excessive cooling rates from the austenitizing temperature and controlling the chemical composition to avoid excessive hardenability for the section size involved.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001015
EISBN: 978-1-62708-217-4
... Carburetors Clamps Helicopters Turbochargers Metal (Other, miscellaneous, or unspecified) failure Careful investigation of the flight log and accident reports indicated that a helicopter rapidly lost altitude and struck a tree, causing a fire and severe damage. In cases of this kind, it is common...
Abstract
A helicopter rapidly lost altitude and struck a tree, causing a fire and severe damage. The hose clamp which was the subject of this investigation was one of two used on a short length of hose between the turbocharger and the carburetion system. The purpose of this examination was to determine whether the hose failed during or before the accident. Fracture in the failed clamp was accompanied by obvious permanent deformation and evidence of local shearing at the ends of the perforation where fracture occurred, and in the adjacent perforation. The first test involved tightening the clamps to failure with a torque wrench. In no case did the band material fracture. In a second attempt to duplicate the failure, a tensile testing machine was used to pull the two fittings apart while the hose was clamped in place. When the testing machine was operated at maximum head travel (approximately 20 in. per min.), one of the hose clamps broke in the same manner as the clamp in question. The manner of failure during the tension test indicated this clamp failed at the time of the crash because of a sudden separation between the turbocharger and the remainder of the aircraft.
Book Chapter
Failure of a Steam Turbine Due to a Design Flaw
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001080
EISBN: 978-1-62708-214-3
... was responsible for the loosening of the nut. It was recommended that the locking mechanism be redesigned and changed in all existing turbines. Locking Nuts (fasteners) Turbine disks Turbine steel (Other, miscellaneous, or unspecified) failure Background A290 mm (10 in.) diam horizontal steam...
Abstract
A steam turbine developed excessive noise and vibration during routine operation. It was found that the nut that locked the turbine disk In place had worked its way out from the threads and the disk had come of the shaft. Examination of the locking mechanism indicated that its design was responsible for the loosening of the nut. It was recommended that the locking mechanism be redesigned and changed in all existing turbines.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001623
EISBN: 978-1-62708-232-7
... wool (Other, miscellaneous, or unspecified) failure Several glass wool insulation sections from a heat-treat furnace showed visible discoloration. The insulation was originally white but exhibited a gray discoloration in some areas, as shown in Fig. 1 . As in the coin example, this discoloration...
Abstract
Several glass wool insulation sections from a heat-treat furnace showed visible, but only cosmetic discoloration. EDS showed the presence of silicon, aluminum, and oxygen in the nondiscolored region, and these elements are consistent with glass wool. Relatively high levels of chromium and nickel were detected in the discolored area, along with lower amounts of iron, manganese, sodium, calcium, cobalt, and sulfur, in addition to the surrounding glass wool elements. Results of this limited evaluation showed the discoloration was caused by the presence of elevated levels of chromium, nickel, and aluminum. The visual appearance, along with the EDS findings, suggested these elements were present in the form of oxides. These oxides were likely deposited from adjacent structural components of the furnace, which had oxidized during operation.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.auto.c9001624
EISBN: 978-1-62708-218-1
..., which led to melting of the wire. Chemical analysis Corrosion products Discoloration Electric Sensors Wire Copper (Other, miscellaneous, or unspecified) failure An electronic sensor coil failed continuity testing, indicating that a break was present in the polymercoated wire...
Abstract
An electronic sensor coil failed continuity testing, indicating that a break was present in the polymer-coated wire. An area of the wire showed a green discoloration and the break in the wire was located in this same region. The discoloration was suspected to be an indicator of what caused the failure. SEM/EDS and FTIR results showed the break in the coil wire was associated with corrosion. The corrosion debris contained relatively high levels of sodium and chlorine, which were likely in the form of salt. Some salt deposits were noted also in other areas along the wire surface. The findings suggested salt or salt water had leaked into the sensor and caused localized corrosion to the wire, possibly at an area where preexisting damage was present in the coating. Separation occurred in the wire when the current density at the reduced cross section caused excessive localized heating, which led to melting of the wire.
Book Chapter
Discoloration of a Stainless Steel Tube after Pickling
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001626
EISBN: 978-1-62708-235-8
... into place and another type of tank material be considered. Chemical analysis Discoloration Pickling Tubes 17-4 PH UNS S17400 (Other, miscellaneous, or unspecified) failure A type 17-4PH stainless steel tube exhibited brown discoloration after a pickling operation. Although the discoloration...
Abstract
A type 17-4PH stainless steel tube exhibited brown discoloration after a pickling operation. EDS analysis of the extracted substance revealed relatively high levels of iron and chromium, along with lower amounts of aluminum, silicon, sulfur, chlorine, calcium, manganese, and nickel. The iron, chromium, and nickel are likely in the form of dissolution products from the pickling solution. FTIR analysis revealed the presence of polypropylene and poly(ethylene:propylene). The EDS results showed that the discoloration of the tube was associated with oxidation products of the tube material, as well as adherent organic residue. Analysis by FTIR of the residue revealed detectable levels of two polymeric substances, which were later determined to be construction materials of the pickling tank. It was recommended that more frequent cleaning and/or replacement of the pickling solution be put into place and another type of tank material be considered.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001499
EISBN: 978-1-62708-236-5
... position under a reverberating load for an extended period of time. Loads (forces) Reflection Spur gears Vibration 8622 UNS G86220 (Other, miscellaneous, or unspecified) wear Three spur gears that had formed a straight-line train in a speed reducer were brought in for examination...
Abstract
Three spur gears made from 8622 Ni-Cr-Mo alloy steel formed a straight-line train in a speed reducer on a rail-mounted overslung lumber carrier. The gears were submitted for nondestructive examination and evaluation, with no accompanying information or report. Two teeth on one of the gears were found to be pitted, one low on profile and the adjacent tooth high on profile. The mating gear had a similar characteristic, two adjacent teeth with evidence of pitting and the same difference in profile. It was correctly deduced that the pitting occurred because the gears were in a static position under a reverberating load for an extended period of time.
Book Chapter
Failure of a Muffle for a Brazing Furnace
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c0046956
EISBN: 978-1-62708-232-7
... boundaries Intermetallic phases Muffle furnaces Overheating Nickel-base high-temperature alloy (Other, miscellaneous, or unspecified) failure A brazing-furnace muffle 34 cm (13 1 4 in.) wide, 26 cm (10 3 8 in.) high, and 198 cm (78 in.) long, was fabricated from nickel-base high...
Abstract
A brazing-furnace muffle 34 cm (13 in.) wide, 26 cm (10 in.) high, and 198 cm (78 in.) long, was fabricated from nickel-base high-temperature alloy sheet and installed in a gas-fired furnace used for copper brazing of various assemblies. The operating temperature of the muffle was reported to have been closely controlled at the normal temperature of 1175 deg C (2150 deg F); a hydrogen atmosphere was used during brazing. After about five months of continuous operation, four or five holes developed on the floor of the muffle, and the muffle was removed from service. Analysis (visual inspection, x-ray spectrometry, and metallographic examination) supported the conclusion that the muffle failed by localized overheating in some areas to temperatures exceeding 1260 deg C (2300 deg F). The copper found near the holes had dripped to the floor from assemblies during brazing. The copper diffused into the nickel-base alloy and formed a grain-boundary phase that was molten at the operating temperature. The presence of this phase caused localized liquefaction and weakened the alloy sufficiently to allow formation of the holes. No recommendations were made.
Book Chapter
Failures of TiN-Coated Wobblers in a Hydraulic Assembly
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001572
EISBN: 978-1-62708-236-5
... in this case for the production acceptance tests. Coating removal Gouging Hydraulic assemblies Wobblers 52100E Titanium nitride coating UNS G52986 (Other, miscellaneous, or unspecified) failure Background Extensive slipper/wobbler failures had occurred in the integrated drive generators...
Abstract
Extensive slipper/wobbler failures occurred in the integrated drive generators that incorporated TiN coated wobblers, during the production acceptance test. Similar coated wobblers had passed the application tests. The nature of the failure was extensive gouging of the wobbler surface with discoloration and coating removal. The substrate material was E52100 which was through-hardened to HRC 55-60. The slippers that were in contact with the coated wobbler surface were made of AISI 06 material. A synthetic oil was used as the hydraulic fluid in the application. The failure in the wobblers was caused by lack of temperature control during application which resulted in localized surface rehardening. It was established that there was a significant difference in the grade of the hydraulic fluid that was used in the two test programs. Use of superior grade of hydraulic fluid was recommended in this case for the production acceptance tests.
Book Chapter
Investigation of Worn Chain Links
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.matlhand.c9001209
EISBN: 978-1-62708-224-2
... operating stress if they had been welded satisfactorily and hardened correctly, and whether it made any sense to case harden highly stressed chains of this type. Chains Gas carburizing Wear Welded joints Steel chain Joining-related failures (Other, miscellaneous, or unspecified) wear Heat...
Abstract
Three links of a chain showing unusually strong wear were examined. Corresponding to the stress, the wear was strongest in the bends of the links, but it was especially pronounced in the bend in which the butt weld seam was located. Investigation showed the links were manufactured from an unkilled carbon-deficient steel, and were case hardened to a depth of 0.8 to 0.9 mm. The peripheral structure at the places not showing wear consisted of coarse acicular martensite with a high percentage of retained austenite. The links therefore were strongly overheated, probably directly heated during case hardening. The butt weld seams were not tight and were covered with oxide inclusions. Given that wear occurred preferentially at the welds it may be concluded that this weld defect contributed to the substantial wear. This leaves unanswered whether these chains could have withstood the high operating stress if they had been welded satisfactorily and hardened correctly, and whether it made any sense to case harden highly stressed chains of this type.
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