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B.V. Krishna, R.K. Sidhu
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Gary Wechsler, Victor K. Champagne, Marc Pepi
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D. G. Chakrapani
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Rakesh Kaul, N.G. Muralidharan, K.V. Kasiviswanathan, Baldev Raj
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Friedrich Karl Naumann, Ferdinand Spies
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Friedrich Karl Naumann, Ferdinand Spies
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Surface of the heating coil. Cracks shown up by the colour penetration proc...
Available to Purchase
in Leaky Heating Coils of an Austenitic Chromium-Nickel-Molybdenum Steel
> ASM Failure Analysis Case Histories: Failure Modes and Mechanisms
Published: 01 June 2019
Book Chapter
Catastrophic Failure of a Fan in a Diesel Engine Cooler
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.auto.c9001612
EISBN: 978-1-62708-218-1
... during operation. The propensity to crack initiation and failure was accentuated by improper cleaning of the surfaces prior to welding and to inadequate nugget-to-sheet edge distance. Heat penetration Nugget-to-edge distance Resistance spot welding Weld strength Welded steel Joining-related...
Abstract
The fan used to cool a diesel engine fractured catastrophically after approximately 100 h of operation. The fan failed at a spider, which was resistance spot welded to a shim placed between two circular spiders of 3 mm thickness. The detailed analysis of the fracture indicated that the premature failure of the fan was due to inadequate bonding between the sheets at the weld nugget. The fracture was initiated from the nugget-plate interface. The inadequate penetration and lack of fusion between the steel sheets during resistance spot welding led to poor weld strength and the fracture during operation. The propensity to crack initiation and failure was accentuated by improper cleaning of the surfaces prior to welding and to inadequate nugget-to-sheet edge distance.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0046022
EISBN: 978-1-62708-217-4
... that the presence of chromic acid stain on the fracture surface proved that the forging had cracked before anodizing. This suggest that the crack initiated during straightening, either after machining or after heat treatment. The structure and composition of the alloy appear to have been acceptable. Ductility...
Abstract
A forged aluminum alloy 2014-T6 catapult-hook attachment fitting (anodized by the chromic acid process to protect it from corrosion) from a naval aircraft broke in service. Spectrographic analysis, visual examination, microscopic examination, and tensile analysis showed minute cracks on the inside surface of a bearing hole, and small areas of pitting corrosion were visible on the exterior surface of the fitting. The analysis also revealed a small number of rosettes, suggestive of eutectic melting, in an otherwise normal structure. These examinations and analyses support the conclusion that the presence of chromic acid stain on the fracture surface proved that the forging had cracked before anodizing. This suggest that the crack initiated during straightening, either after machining or after heat treatment. The structure and composition of the alloy appear to have been acceptable. Ductility was acceptable so rosettes found in the microstructure are believed to have been nondamaging. Had they contributed to the failure, the ductility would have been very low. The recommendations included inspection for cracks and revising the manufacturing process to include a fluorescent liquid-penetrant inspection before anodizing, because chromic acid destroys the penetrant. This inspection would reduce the possibility of cracked parts being used in service.
Book Chapter
Failure of a Cast Conveyor Chain Link
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.matlhand.c0047432
EISBN: 978-1-62708-224-2
... Abstract The conveyor chain link failed by fracturing through a fabrication weld after some time in service. The link was made of cast low-alloy steel heat treated to a hardness of 285 HRB. The fabrication weld was made using E7018 electrodes. The fracture surfaces were almost entirely covered...
Abstract
The conveyor chain link failed by fracturing through a fabrication weld after some time in service. The link was made of cast low-alloy steel heat treated to a hardness of 285 HRB. The fabrication weld was made using E7018 electrodes. The fracture surfaces were almost entirely covered with beach marks, indicating fatigue cracking. The beach marks emanated from a 6.4 mm (1/4 in.) wide band of unusual appearance running across the center of the fracture. Saw cuts were made perpendicular to both of the fracture surfaces and across the unusual-looking bands. The cut surfaces were ground and etched with ammonium persulfate solution revealing that complete penetration had not been achieved at the weld root. The band observed in the fracture was apparently part of the unfused weld-preparation surface at the root of the weld. This failure was caused by fatigue that initiated at an incomplete penetration defect at the root of the fabrication weld. As a result of this failure, steps were taken to ensure that good welding practice (back-gouging) would be followed in the future fabrication of these links.
Book Chapter
Cracking of a Pressure Vessel Due to Penetration by Solder
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001440
EISBN: 978-1-62708-235-8
..., and it is not to be expected that heating to this extent would be visualised when the method of attachment was decided upon, as it is so far outside the range of normal service conditions. There is, however, always the possibility that solder penetration may occur even if only to a limited extent during the soldering...
Abstract
A portable propane container with a name-plate soldered onto it exploded in service. When the vessel was inspected afterwards, it was found to have developed a crack in the top end plate. A portion of the end plate cut out to include the midlength and one termination of the crack was examined microscopically. This revealed that the crack was associated with intergranular penetration by molten metal. The microstructure in general was indicative of a good-quality mild steel. It was evident from that solder that was responsible for the penetration and that fused brass from the hand wheel had not played any part. Tensile stress was present at the time of the failure sufficiently high to enable solder penetration to take place. The use of soft solder as a medium for attaching name-plates directly on to stressed steel parts is not recommended. It would be preferable to use a welded-on patch plate or to employ one of the high-strength, non-metallic adhesives.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001822
EISBN: 978-1-62708-180-1
... and lead with a minor amount of tin. These elements are the major constituents of the bronze friction bearing. The copper-penetration failure occurred in the following sequence: The bearing surface was heated by friction because of loss of lubrication The babbitt metal lining melts between about...
Abstract
This article provides a background of friction-bearing failures due to overheating. The failures of locomotive axles caused by overheated traction-motor support bearings are discussed. The article also describes liquid-metal embrittlement (LME) in steel. It examines the results of various axle studies, with illustrations and concludes with information on the simulation of the LME mechanism.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0048791
EISBN: 978-1-62708-234-1
... Abstract Linear indications on the outer surface of a cross in a piping system were revealed by dye-penetrant examination. The cross was specified to be SA403 type WP 304 stainless steel. The cross had been subjected to induction-heating stress improvement. The linear indications on the cross...
Abstract
Linear indications on the outer surface of a cross in a piping system were revealed by dye-penetrant examination. The cross was specified to be SA403 type WP 304 stainless steel. The cross had been subjected to induction-heating stress improvement. The linear indications on the cross were located in wide bands running circumferentially below the cross-to-cap weld and above the cap-to-discharge-pipe weld. The material was found to conform to the requirements both in terms of hardness and strength. Intergranular cracks filled with oxide were observed on metallographic analysis of a sectioned and oxalic acid etched sample. The grain size was found to exceed the ASTM standard. No indications of sensitization were observed during testing with practice A of ASTM A 262. Definitive evidence of contaminants to support SCC as the failure mechanism was not disclosed during analysis. It was concluded that overheating or burning of the forging, which classically results in large grain size, intergranular fractures, and fine oxide particles dispersed throughout the grains was the possible reason for the failure.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0047756
EISBN: 978-1-62708-235-8
..., producing a grain-boundary network of braze metal in the tube and the resultant embrittlement that rendered the penetrated region vulnerable to fatigue cracking. Fatigue stresses acting in combination with additional heating and possible overtempering of the tube during torch debrazing and subsequent...
Abstract
Waspaloy (AMS 5586) fabricated inner ring of a spray-manifold assembly failed transversely through the manifold tubing at the edge of the tube and support sleeve brazed joint. The assembly was brazed with AWS BAu-4 filler metal (AMS 4787). Fatigue beach marks propagating from extremities of a granular gold-tinted surface region adjacent to the tube-to-sleeve brazed joint and extending circumferentially were revealed by microscopic examination. Embrittlement of the tube caused by molten braze metal penetration along grain boundaries was evidenced by micrographs of a granular portion of the fracture. It was revealed by the initial fracture profile that fatigue cracks begun as an intergranular separation and subsequently became transgranular. It was concluded that failure of the tube was caused by excessive alloying between the braze metal and the Waspaloy. Reduced temperatures during torch debrazing or rebrazing were recommended to minimize molten braze metal penetration.
Book Chapter
Failure of an Oil-Line Subassembly Because of Poor Welding
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0047636
EISBN: 978-1-62708-217-4
... the welding heat. Additional support for the oil line was installed to reduce vibration and minimize fatigue of the elbow. Gas tungsten arc welding Overaging Penetration Pipe bends Repair welding 6061-T6 UNS A96061 Fatigue fracture Joining-related failures Several elbow subassemblies...
Abstract
Several elbow subassemblies comprising segments of oil-line assemblies that recycled aircraft-engine oil from pump to filter broke in service. The components of the subassemblies were made of aluminum alloy 6061-T6. Two subassemblies were returned to the laboratory to determine cause of failure. In one, the threaded boss had separated from the elbow at the weld. In the other, the failure was by fracture of the elbow near the flange. The separation of the threaded boss from the elbow was due to a poor welding procedure. Crack propagation was accelerated by fatigue caused by cyclic service stresses. The fracture of the second elbow near the flange was caused by overaging during repair welding of the boss weld. Satisfactory weld penetration was achieved by improved training of the welders plus more careful inspection. Repair welding was prohibited, to avoid recurrence of overaging from the welding heat. Additional support for the oil line was installed to reduce vibration and minimize fatigue of the elbow.
Book Chapter
Failed Missile Launcher Detent Spring
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001268
EISBN: 978-1-62708-215-0
... plastically deformed while two of the deformed leafs did not meet minimal hardness or tensile requirements. Liquid penetrant testing revealed no cracks or other surface discontinuities on the leaf springs. Material sectioned from the soft spring leafs was heat-treated according to specifications...
Abstract
A missile detached from a Navy fighter jet during a routine landing on an aircraft carrier deck because of a faulty missile launcher detent spring. Visual inspection of Inconel 718 detent spring assembly revealed that four of the nine spring leafs comprising the assembly were plastically deformed while two of the deformed leafs did not meet minimal hardness or tensile requirements. Liquid penetrant testing revealed no cracks or other surface discontinuities on the leaf springs. Material sectioned from the soft spring leafs was heat-treated according to specifications in the laboratory. The resultant increase in mechanical properties of the re-heat-treated material indicated that the original heat treatment was not performed correctly. The failure was attributed to improper heat treatment. Recommendations focused on more stringent quality control of the heat-treat operations.
Book Chapter
Stress-Corrosion Cracking of Stainless Steel Falling Film Black Liquor Evaporator
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.pulp.c9001567
EISBN: 978-1-62708-230-3
... Abstract A falling film black liquor evaporator consisted of flat twin plate heat exchangers and was used to increase black liquor solids content prior to its burning in the recovery boiler. Several plate heat exchangers were fabricated of AISI type 316L stainless steel by electric resistance...
Abstract
A falling film black liquor evaporator consisted of flat twin plate heat exchangers and was used to increase black liquor solids content prior to its burning in the recovery boiler. Several plate heat exchangers were fabricated of AISI type 316L stainless steel by electric resistance welding. Cracks initiated at the inside surface of the welded areas and penetrated through the wall thickness. In several locations, the weld fractured and the plates separated with significant spring back, indicative of high residual stresses attributed to fabrication and weld procedures. The cracks had extended radially from the electric resistant weld into the base metal. Metallographic examination revealed the cracks were transgranular and branching, characteristic of SCC in austenitic stainless steels. The fracture surfaces had a brittle cleavage-like appearance, typical of SCC in austenitic stainless steels. Chlorides in the service environment were a contributory factor. The primary factor causing SCC localized at the electric resistant welds was substantial residual stresses as a result of fabrication procedures. It was recommended that the heat exchanger plates be subjected to stress-relief heat treatment following fabrication and welding.
Book Chapter
Failure of a Martensitic Stainless Steel Ball Valve
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001352
EISBN: 978-1-62708-215-0
... of the crack during operation. Proper weld heat treatment was recommended, along with avoidance of abrupt change in cross section near the weld. Due penetrant testing at the ball stem junction before and after heat treatment was also suggested. Austenitic stainless steels Chemical processing equipment...
Abstract
Repeated failures of high-pressure ball valves were reported in a chemical plant. The ball valves were made of AFNOR Z30C13 martensitic stainless steel. Initial examination of the valves showed that failure occurred in a weld at the ball/stem junction end of austenitic stainless steel sleeves that had been welded to the valve stem at both ends. Metallographic examination showed that a crack had been introduced into the weld by improper weld heat treatment. Stress concentration at the weld location resulting from an abrupt change in cross section facilitated easy propagation of the crack during operation. Proper weld heat treatment was recommended, along with avoidance of abrupt change in cross section near the weld. Due penetrant testing at the ball stem junction before and after heat treatment was also suggested.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0091528
EISBN: 978-1-62708-229-7
... the conclusion that the failure was caused by SCC due to stress, sensitization, and environment. Recommendations included replacing all pipe sections and installing them using low-heat-input, multiple-pass welding procedures. Heat affected zone Integranular fracture Piping 304 UNS S30400 Joining...
Abstract
A 150 mm (6 in.) schedule 80S type 304 stainless steel pipe (11 mm, or 0.432 in., wall thickness), which had served as an equalizer line in the primary loop of a pressurized-water reactor, was found to contain several circumferential cracks 50 to 100 mm (2 to 4 in.) long. Two of these cracks, which had penetrated the pipe wall, were responsible for leaks detected in a hydrostatic test performed during a general inspection after seven years of service. Investigation (visual inspection, visual and ultrasonic weld examination, water analysis, and chemical analysis) supported the conclusion that the failure was caused by SCC due to stress, sensitization, and environment. Recommendations included replacing all pipe sections and installing them using low-heat-input, multiple-pass welding procedures.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001314
EISBN: 978-1-62708-215-0
... because the system was thermally cycled some 1200 to 2400 times before cracking penetrated the wall and caused a sharp temperature rise due to combustion of the heat exchanger fluid. How Failure Could Have Been Prevented Flow conditions inside the tube were inadequate to prevent a dry wall...
Abstract
A gas-fired, ASTM A-106 Grade B carbon steel vaporizer failed on three different occasions during attempts to bring the vaporizer on line. Dye penetrant examination indicated the presence of multiple packets of ductile cracks on the inside of the coil radius at the bottom of the horizontal axis coils. Visual examination of the inside of the tubing indicated the presence of a carbonaceous deposit resulting from decomposition of the heat-exchanging fluid. Subsequent metallographic examination and microhardness testing indicated that the steel was heated to a temperature above the allowable operating temperature for the fluid. The probable cause for failure is thermal fatigue due to the localized overheating. Flow conditions inside the tubing should be reexamined to ensure suitable conditions for annular fluid flow.
Book Chapter
Crevice Corrosion of Tubing in a Hydraulic-Oil Cooler
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0048708
EISBN: 978-1-62708-229-7
... Abstract The horizontal heat-exchanger tubes made of copper alloy C70600, in one of two hydraulic-oil coolers in an electric power plant, leaked after 18 months of service. River water was used as the coolant in the heat-exchanger tubes. Several nodules on the inner surface and holes through...
Abstract
The horizontal heat-exchanger tubes made of copper alloy C70600, in one of two hydraulic-oil coolers in an electric power plant, leaked after 18 months of service. River water was used as the coolant in the heat-exchanger tubes. Several nodules on the inner surface and holes through the tube wall, which appeared to have formed by pitting under the nodules, were revealed by visual examination. Steep sidewalls, which indicated a high rate of attack, were revealed by microscopic examination of a section through the pit which had penetrated the tube wall. The major constituent of reddish deposit on the inner surfaces of the tubes was revealed to be iron oxide and slight manganese dioxide. Effluent from steel mills upstream was indicated by the presence of these and other constituents to be the source of most of the solids found in the tubes. It was concluded that the tubing failed by crevice corrosion. The tubing in the cooler was replaced, and cooling-water supply was changed from river to city water, which contained no dirt to deposit on the tube surfaces. An alternate solution of installing replacement tubes in the vertical position to make deposition of solids from river water less likely was suggested.
Book Chapter
Hot Cracks in a Repair Weld
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c0047586
EISBN: 978-1-62708-236-5
... typical of exposure to air when very hot. Several additional subsurface cracks, typical of hot tears, were observed in and near the weld. There had been too much local heat input in making the repair weld. The result was localized thermal contraction and hot tearing. The cracking of the repair weld...
Abstract
A fuel-nozzle-support assembly showed transverse indications after fluorescent liquid-penetrant inspection of a repair-welded area at a fillet on the front side of the support neck adjacent to the mounting flange. Visual examination disclosed an irregular crack. The crack through the neck was sectioned; examination showed that the crack had extended through the repair weld. The crack had followed an intergranular path. The crack was opened, and binocular-microscope examination of the fracture surface showed that the surface contained dendrites with discolored oxide films that were typical of exposure to air when very hot. Several additional subsurface cracks, typical of hot tears, were observed in and near the weld. There had been too much local heat input in making the repair weld. The result was localized thermal contraction and hot tearing. The cracking of the repair weld was attributed to unfavorable welding practice that accentuated thermal contraction stresses and caused hot tearing. Recommendations involved use of a small-diameter welding electrode, a lower heat input, and deposition in shallow layers that could be effectively peened between passes to minimize internal stress.
Book Chapter
Steel Socket Pipe Conduit Cracked Next to Weld Seam
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001257
EISBN: 978-1-62708-235-8
... of a low-carbon steel in which the zone heated during welding was delineated only slightly next to the seam, the other pipe was etched much darker, i.e., higher in carbon, and the heated zone appeared to stand out darkly against the basic material. The overlapping weld was defect-free and dense...
Abstract
A steel socket pipe conduit NW 150 cracked open during pressure testing next to the weld seam almost along the entire circumference. The crack occurred in part in the penetration notch and in part immediately adjacent to it. While the uncracked pipe showed the light etch shading of a low-carbon steel in which the zone heated during welding was delineated only slightly next to the seam, the other pipe was etched much darker, i.e., higher in carbon, and the heated zone appeared to stand out darkly against the basic material. The overlapping weld was defect-free and dense. The uncracked pipe consisted of soft steel that obviously was made for this purpose, while the cracked pipe consisted of a strongly-hardenable steel which contained not only more carbon and manganese than customary but also a considerable amount of chromium. Therefore, the damage was caused by a mix-up of materials that allowed an unsuitable steel to be used for the weldment.
Book Chapter
Corroded Pipe Section of Oil Burner for Superheated Steam Generator
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001240
EISBN: 978-1-62708-234-1
... by erosion were noticeable. This was a typical case of crevice corrosion. The rolled joint evidently was not entirely tight, so that saturated steam condensate could penetrate into the gap. Heat exchangers Oil burners Pipe Fe-0.15C Pitting corrosion Erosion - corrosion Crevice corrosion...
Abstract
A heat exchanger made of a pipe in which oil was heated from the outside from approximately 90 deg C to 170 deg C, by superheated steam of about 8 to 10 atmospheres had developed a leak at the rolled joint of the pipe and pipe bottom. The pipes were supposed to be made from St 35.29 steel and annealed at the rolled joint to 100 mm length. The outer pipe surface was strongly pitted by corrosion all around the rolled joint. In the vicinity of the steam chamber the pipe wall had oxidized through from the exterior to the interior at one spot. Adjoining this spot, grooves caused by erosion were noticeable. This was a typical case of crevice corrosion. The rolled joint evidently was not entirely tight, so that saturated steam condensate could penetrate into the gap.
Book Chapter
Stress-Corrosion Cracking of Type 316 Stainless Steel Piping
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c0091617
EISBN: 978-1-62708-220-4
... Abstract A 680,000 kg (750 ton) per day ammonia unit was shut down following a fire near the outlet of the waste heat exchanger. The fire had resulted from leakage of ammonia from the type 316 stainless steel outlet piping. The outlet piping immediately downstream from the waste heat exchanger...
Abstract
A 680,000 kg (750 ton) per day ammonia unit was shut down following a fire near the outlet of the waste heat exchanger. The fire had resulted from leakage of ammonia from the type 316 stainless steel outlet piping. The outlet piping immediately downstream from the waste heat exchanger consisted of a flange made from a casting, and a reducing cone, a short length of pipe, and a 90 deg elbow, all made of 13 mm thick plate. A liner wrapped with insulation was welded to the smaller end of the reducing cone. All of the piping up to the flange was wrapped with insulation. Investigation (visual inspection, 10x unetched images, liquid-penetrant inspection, and chemical analysis of the insulation) supported the conclusion that the failure occurred in the area of the flange-to-cone weld by SCC as the result of aqueous chlorides leached from the insulation around the liner by condensate. Recommendations included eliminating the chlorides from the system, maintaining the temperature of the outlet stream above the dewpoint at all times, or that replacing the type 316 stainless steel with an alloy such as Incoloy 800 that is more resistant to chloride attack.
Book Chapter
Intergranular Cracking in an Air Bottle Because of Torch Overheating Before Welding
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0047632
EISBN: 978-1-62708-235-8
..., this included heating of the boss, which constituted a massive heat sink. The port fitting was then welded in place. Final full heat treatment to the T62 temper was followed by machining, pressure testing, and radiographic and liquid-penetrant inspection. Fig. 1 Aluminum alloy air bottle that failed...
Abstract
An air bottle, machined from a solid block of aluminum alloy 2219-T852, displayed liquid-penetrant crack indications after assembly welding. The air bottle was machined to rough shape, a 3.8 mm (0.15 in.) wall thickness cylindrical cup with a 19 mm (3/4 in.) wall thickness integral boss on one side. After annealing, hot spinning, annealing a second time, and tack welding a port fitting, the assembly was torch preheated to 120 to 150 deg C (250 to 300 deg F). The port fitting was then welded in place. Final full heat treatment to the T62 temper was followed by machining, testing, and inspection. The crack indications were found only on one side of the boss and on the lower portion of the hot-spun dome region. The metallographic specimens revealed triangular voids and severe intergranular cracks. The cracks displayed the glossy surfaces typical of melted and resolidified material. The localized cracks in the air bottle were from grain-boundary eutectic melting caused by local torch overheating used in preparation for assembly welding of a port fitting. A change in design was scheduled to semiautomatic welding without the use of preheating for the joining of the port fitting for the dome opening.
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