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By
B.V. Krishna, R.K. Sidhu
By
Friedrich Karl Naumann, Ferdinand Spies
By
Friedrich Karl Naumann, Ferdinand Spies
By
A. Hudgins, C. Roepke, B. James, B. Kondori, B. Whitley
By
C. H. Hsu
By
Carmine D'Antonio
By
S. L. West, D. Z. Nelson, M. R. Louthan, Jr.
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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
... 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...
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.bldgs.c9001017
EISBN: 978-1-62708-219-8
... steel with carbon content toward the high side of the range. The mechanical properties of the parent metal in split and unsplit lengths were satisfactory. Weld strength, on the other hand, without removal of reinforcement was about 70% of parent metal strength in areas immediately adjacent to one...
Abstract
A 10-in. diam, spiral-welded AISI 1020 carbon steel pipe carrying water under pressure developed numerous leaks over a four mile section. The section was fabricated using submerged-arc welding from the outside surface. Each welded length of pipe had been subjected to a proof pressure approximately twice the specified design pressure and two-thirds the approximate yield point of the parent metal. No failures or leakage were observed during proof testing. Metallurgical examination corroborated visual checks, indicating a distinct lack of root penetration in the split areas. Splitting occurred as a result of inadequate root penetration. The most likely source of difficulty in the welding process was the linear speed. Probably, the failures would not have occurred in absence of the welding problem. Also, the pipe was inadequate for the specified design pressure, as well as the reported maximum system pressure.
Image
Fatigue strength as a function of slag inclusions for as-welded carbon-mang...
Available to PurchasePublished: 30 August 2021
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0047072
EISBN: 978-1-62708-217-4
... the shell in the annealed condition. During welding, the weld zones distorted under the welding pressure and increased the contact area, which changed the current distribution and resulted in low or inconsistent weld strength. Conclusion The outer shell of the bullet assembly separated from...
Abstract
Postflight inspection of a gas-turbine aircraft engine that had experienced compressor stall revealed that the engine air-intake bullet assembly had dislodged and was seated against the engine-inlet guide vanes at the 3 o'clock position. The bullet assembly consisted of an outer aerodynamic shell and an inner stiffener shell, both of 1.3 mm (0.050 in.) thick aluminum alloy 6061-T6, and four attachment clips of 1 mm (0.040 in.) thick alclad aluminum alloy 2024-T42. Each clip was joined to the outer shell by 12 spot welds and was also joined to the stiffener. Analysis (visual inspection, dye-penetrant inspection, and 10x/150x micrographs of sections etched with Keller's reagent) supports the conclusion that the outer shell of the bullet assembly separated from the stiffener because the four attachment clips fractured through the shell-to-clip spot welds. Fracture occurred by fatigue that initiated at the notch created by the intersection of the faying surfaces of the clip and shell with the spot weld nuggets. The 6061 aluminum alloy shell and stiffener were in the annealed (O) temper rather than T6, as specified. Recommendations included heat treating the shell and stiffener to the T6 temper after forming.
Book Chapter
Failures Related to Welding
Available to PurchaseSeries: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003509
EISBN: 978-1-62708-180-1
... as the heat input of the process are not addressed in detail. Planar Imperfections Planar imperfections are sharp cracklike features that can substantially reduce the fatigue strength of a welded joint or cause initiation of brittle fractures. Examples include hydrogen cracks, lamellar tears, lack...
Abstract
This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001041
EISBN: 978-1-62708-214-3
... to be fatigue cracking that initiated at the toes of the fillet welds. Secondary fatigue cracking occurred at the torque rod mounting holes. Failure was attributed to cyclic stresses at the weld toes that exceeded the lowered fatigue strength at this location. A design change that eliminated the fillet welds...
Abstract
Four truck cross members intended for use in heavy-duty transport trucks were investigated. Two of the members had cracked on a prototype vehicle and two had been fatigue tested in the laboratory. The cross members were fabricated from SAE 950X plate and consisted of a formed channel section and an internal fillet-welded diaphragm. Sections from each of the cross members were subjected to a complete analysis, including chemical analysis, magnetic particle testing, mechanical testing, scanning electron microscope/fractography, and metallography. The primary mode of failure was found to be fatigue cracking that initiated at the toes of the fillet welds. Secondary fatigue cracking occurred at the torque rod mounting holes. Failure was attributed to cyclic stresses at the weld toes that exceeded the lowered fatigue strength at this location. A design change that eliminated the fillet welds alleviated the problem.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.bldgs.c0047694
EISBN: 978-1-62708-219-8
... Abstract Extra high strength zinc-coated 1080 steel welded wire was wound into seven-wire cable strands for use in aerial cables and guy wires. The wires and cable strands failed tensile, elongation, and wrap tests, with wires fracturing near welds at 2.5 to 3.5% elongation and through...
Abstract
Extra high strength zinc-coated 1080 steel welded wire was wound into seven-wire cable strands for use in aerial cables and guy wires. The wires and cable strands failed tensile, elongation, and wrap tests, with wires fracturing near welds at 2.5 to 3.5% elongation and through the welded joints in wrap tests. The welded wire was annealed by resistance heating. The wire ends had a chisel shape, produced by the use of sidecutters. Tests of the heat treatment temperatures showed that the wire near the weld area exceeded 775 deg C (1425 deg F). Metallographic examination revealed martensite present in the weld area after the heat treatment. The test failures of the AISI 1080 steel wire butt-welded joints were due to martensite produced in cooling from the welding operation that was not tempered adequately in postweld heat treatment, and to poor wire-end preparation for welding that produced poorly formed weld burrs. The postweld heat treatment was standardized on the 760 deg C (1400 deg F) transformation treatment. The chisel shape of the wire ends was abandoned in favor of flat filed ends. The wrap test was improved by adopting a hand-cranked device. Under these conditions, the welded joints withstood the tensile and wrap tests.
Book Chapter
Fatigue Failures of Shafts Repaired by Welding
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001430
EISBN: 978-1-62708-236-5
... to heat-affected zone cracking, residual stresses, the lower fatigue strength of the weld deposited metal, and weld defects. Repair welding Shafts (power) Weld defects Fe-0.6C Joining-related failures Fatigue fracture It is true to say that the construction of engineering plant — vessels...
Abstract
An intermediate shaft (3 in. diam), part of a camshaft drive on a large diesel engine, broke after two weeks of service. Failure occurred at the end of the taper portion adjacent to the screwed thread. The irregular saw-tooth form of fracture was characteristic of failure from torsional fatigue. A second shaft carried as spare gear was fitted and failure took place in a similar manner in about the same period of time. Examination revealed that the tapered portion of the Fe-0.6C carbon steel shaft had been built up by welding prior to final machining. A detailed check by the engine-builder established that the manufacture of these two shafts had been subcontracted. It was ascertained that the taper portions had been machined to an incorrect angle and then subsequently built-up and remachined to the correct taper. The reduction in fatigue endurance following welding was due to heat-affected zone cracking, residual stresses, the lower fatigue strength of the weld deposited metal, and weld defects.
Book Chapter
Overload Failure of a Bronze Worm Gear
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.bldgs.c0090943
EISBN: 978-1-62708-219-8
... that consisted of both dimple rupture and grain-boundary dimple-rupture evidence. The base metal exhibited rather large-grain intergranular brittle cracking features with many types of inclusions. Chemical analysis revealed a standard high-strength, manganese bronze composition, and the weld filler metal...
Abstract
A very large diameter worm gear that had been in service in a dam for more than 60 years exhibited cracks and was removed. It was reported that the high-strength, low-ductility cast bronze gear was only rarely stressed during service, associated with infrequent opening and closing of gates. Due to the age of the gear and the time frame of its manufacture, no original material specifications or strength requirements could be located. Likewise, no maintenance records of possible repairs to the gear were available. Investigation (visual inspection, chemical analysis, tension and hardness testing, 119x SEM images, and potassium dichromate etched 297x metallographic images) supported the conclusion that the bronze gear cracked via mixed-mode overload, rather than by a progressive mechanism such as fatigue or stress-corrosion cracking. The cracking was not associated with regions that would be highly stressed and did not appear to be consistently correlated to casting imperfections, repair welds, or associated heat-affected zones. Cracking across the gear face suggested that bending forces from misalignment were likely responsible for the cracking. Recommendations included further review of the potential root cause.
Book Chapter
Fractured Post of a Loading Gear
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.marine.c9001210
EISBN: 978-1-62708-227-3
... was a construction steel of 60 to 75 kp/sq mm strength. Thick-walled parts of steels of such high strength must be preheated to approximately 200 deg C along the edges prior to welding to minimize the strong heat losses by the cold mass of the part. In the case under investigation this either was not done at all...
Abstract
In a shipyard one of the two posts of a loading gear fractured under a comparatively small load at the point where it was welded into the ship’s deck. The post consisted of several pipe lengths that were produced by longitudinal seam welding of 27 mm thick sheets. The sheet metal was a construction steel of 60 to 75 kp/sq mm strength. Thick-walled parts of steels of such high strength must be preheated to approximately 200 deg C along the edges prior to welding to minimize the strong heat losses by the cold mass of the part. In the case under investigation this either was not done at all or the preheating was not high enough or sufficiently uniform. This damage was therefore caused by a welding defect.
Book Chapter
Broken Structural Bolt
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.bldgs.c9001204
EISBN: 978-1-62708-219-8
... outside of the weld seam closely under the head. Neither one had been particularly deformed before fracture. The composition of the head pieces corresponded approximately to manganese steel (Material No. 1 0845), a weldable construction steel with increased yield point and strength, while the shafts were...
Abstract
Two bolts from the stressed structure of a church building that had broken during stressing were examined to establish the cause of fracture. The fracture of one of the first bolt occurred in a double-vee groove weld whose root was not completely welded. The second bolt had cracked outside of the weld seam closely under the head. Neither one had been particularly deformed before fracture. The composition of the head pieces corresponded approximately to manganese steel (Material No. 1 0845), a weldable construction steel with increased yield point and strength, while the shafts were made from Cr-Mo steel (Material No. 1.7225) according to DIN 17200. It was found that the bolts were not made from a suitable alloy steel, but were welded together from two unsuitable steels, one of which lacked sufficient strength. The austenitic weld seams showed hot tears and were not welded through to the root. Also, the pieces were not preheated before welding, so that stress cracks occurred in the transition zones. The second bolt was overstressed during the impact caused by the breaking of the first bolt.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006808
EISBN: 978-1-62708-329-4
... the test sample is completed, a mechanical test of some sort is typically made to demonstrate that the two materials being welded have at least the minimum tensile strength of one of the two being joined. Also, ductility of the weld is frequently tested by means of weld bend tests to demonstrate...
Abstract
This article describes some of the welding discontinuities and flaws characterized by nondestructive examinations. It focuses on nondestructive inspection methods used in the welding industry. The sources of weld discontinuities and defects as they relate to service failures or rejection in new construction inspection are also discussed. The article discusses the types of base metal cracks and metallurgical weld cracking. The article discusses the processes involved in the analysis of in-service weld failures. It briefly reviews the general types of process-related discontinuities of arc welds. Mechanical and environmental failure origins related to other types of welding processes are also described. The article explains the cause and effects of process-related discontinuities including weld porosity, inclusions, incomplete fusion, and incomplete penetration. Different fitness-for-service assessment methodologies for calculating allowable or critical flaw sizes are also discussed.
Book Chapter
Failure of a Steam Accumulator Due to Lack of Complete Weld Penetration
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0048782
EISBN: 978-1-62708-235-8
... Several sections through a girth weld in a field steam accumulator showing lack of weld penetration. A hardness traverse on the shell yielded values from 84.1 to 86.5 HRB, corresponding to an approximate tensile strength of 550 MPa (80 ksi), which is within the 515- to 620-MPa (75- to 90-ksi) range...
Abstract
A steam accumulator, constructed with 10.3 mm thick SA515-70 steel heads and an 8 mm thick SA455A steel shell, ruptured after about three years of service. The accumulator was used in plastic molding operations. An extensive lack of weld penetration in this the head-to-shell girth weld was revealed by laboratory examination. Some misalignment of the head to the shell because of radial displacement of the shell and head centerlines was observed which was found to result in excessive clearances between the two parts and a slight difference in the thicknesses of the parts. Transgranular fracture with occasional secondary branching was revealed. It was interpreted by stress analysis that a small amount of misalignment added to lack of penetration increased the stresses to near the tensile strength of the material. The failure was judged to be a short-cycle high-stress notch-fatigue failure.
Book Chapter
Failures of Pipelines
Available to PurchaseSeries: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006822
EISBN: 978-1-62708-329-4
... penetration Inclusions Undercut Toe cracks Solidification cracks Girth-weld-specific flaws Low strength Hydrogen-assisted cold cracking Mechanical damage Gouges Dents Wrinkles External corrosion Uniform corrosion Localized corrosion Selective seam weld corrosion...
Abstract
This article discusses the failure analysis of several steel transmission pipeline failures, describes the causes and characteristics of specific pipeline failure modes, and introduces pipeline failure prevention and integrity management practices and methodologies. In addition, it covers the use of transmission pipeline in North America, discusses the procedures in pipeline failure analysis investigation, and provides a brief background on the most commonly observed pipeline flaws and degradation mechanisms. A case study related to hydrogen cracking and a hard spot is also presented.
Book Chapter
The Failure of Titanium Clad Tube Sheet in Heat Exchanger by Fatigue Cracking and Corrosion
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001570
EISBN: 978-1-62708-220-4
.... The primary objective of tube expansion in tubesheet is to increase the residual contact pressure and thus increase the holding strength of the joints. The expanded joint should hold and guide the tube in the tube hole to eliminate the undesirable longitudinal load imposed by exchanger tube on the seal weld...
Abstract
Corrosion failure occurred in a titanium clad tubesheet because of a corrosive tube-side gas-liquid mixture leaking through fatigue cracks in the seal welds at tube-to-tubesheet joints. The tubesheet was a carbon steel plate clad with titanium on the tube side face. The seal weld cracks were initiated by cyclic stress imposed by exchanger tubes. The gas-liquid mixture passed through cracks under tube-side pressure, resulting in severe corrosion of the steel backing plate. The failure started with the loosening of the expanded tube-to-tubesheet joints. Loose joints allowed the exchanger tubes to impose load on seal welds and the shell side cooling water entered the crevice between the tubesheet and the tubes. The cooling water in the crevice caused galvanic reaction and embrittlement of seal welds. Brittle crack opening and crack propagation in seal welds occurred due to the cyclic stress imposed by the tubes. The cyclic stress arised from the thermal cycling of the heat exchanger. The possible effects of material properties on the failure of the tubesheet are discussed.
Book Chapter
Failure of a Large Cast Dragline Bucket Shackle
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c0047423
EISBN: 978-1-62708-236-5
... not been used to make the weld. Repair welds in high-strength steel castings should always be made with low-hydrogen filler materials. Filler metals Heat affected zone Repair welding Fe-0.18C-1.37Ni-0.42Cr-0.31Mo Fatigue fracture Joining-related failures A large shackle used in operating...
Abstract
A large shackle used in operating a dragline bucket failed in service. The shackle was made of a cast low-alloy steel (similar to AISI 4320) heat treated to a hardness of 415 BN. The shackle failed by fracturing through the load-bearing region. Examination of the fracture surface revealed a fatigue crack through about one-third of the cross section. A secondary fatigue crack, perpendicular to the main fracture, was also observed. The composition of the weld deposit corresponded to a heat treatable flux-cored arc welding filler material that was known to have been used for repair welding of these products. This shackle failed because of fatigue initiating at hydrogen cracks that had occurred in the HAZ of a repair weld. The weld had been made with a heat-treatable filler material, and a full postweld heat treatment had been performed. However, a low-hydrogen filler material had not been used to make the weld. Repair welds in high-strength steel castings should always be made with low-hydrogen filler materials.
Book Chapter
Fracture of a Brine-Heater Shell at Welds
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0048733
EISBN: 978-1-62708-235-8
... for the heater-shell wall between the welds and the hot well outside the welds. These values exceeded the actual yield strength of the shell material at operating pressures of 331 kPa (48 psi) and greater. The material was no longer in the elastic region, and it deformed plastically to relieve or transfer...
Abstract
The brine-heater shell in a seawater-conversion plant failed by bursting along a welded joint connecting the hot well (C70600 per ASTM B 466) to the heater shell (ASTM A285, grade C steel). Three cracks in the welded joints between the heater shell and the hot well were revealed by visual inspection. It was observed that crack 1 and 2 were covered with high-temperature oxidation products which revealed that the surfaces had been separated for quite some time. A very high discontinuity stress which existed at the longitudinal welds between the hot well and the heater shell was revealed by stress analysis. It was interpreted that the cracks had originated shortly after the heater was put into operation and propagated slowly initially. The rate of propagation was interpreted to have increased due to discontinuity stresses greater than yield strength of the material. It was concluded that the brine heater cracked and fractured because it was overstressed in normal operation. The heater design was modified to make the heater shell and the hot well two separate units. A relief valve was recommended in the heater or in the steam line near the heater.
Book Chapter
Failure of a Stainless Steel Hip Fracture Fixation Device
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001264
EISBN: 978-1-62708-215-0
... the condition of the material adjacent to the welds and substantially reduced yield strength, tensile strength, and attendant fatigue strength. The welds were placed at the point on the plate that experienced the most severe bending stresses in service. Thus, the plate was made weakest in the area where...
Abstract
A type 316L stainless steel “Jewett nail” hip implant failed after 2 months of service. Fracture occurred through the first of five screw holes in the plate section. Microscopic examination of mating fracture surfaces showed that failure had initiated at the outside (convex) surface of the plate and proceeded through its thickness. The fracture morphology was characteristic of fatigue. A beveled area on the inside surface of the plate indicated that the implant had been fractured for some time prior to removal. Metallographic examination of samples cut from the plate section revealed a series of hidden repair welds on the inside surface of the plate in the vicinity of the fracture. Comparison of the microstructure in the area of the fracture with that in an area away from the weld indicated that the repair welding had resulted in the creation of an annealed, softened zone. Manufacturers should never attempt to salvage this type of critical device by welding or any other procedure that might compromise its integrity.
Book Chapter
Brittle Fracture of a Soybean-Oil Storage Tank Caused by High Service Stresses
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.conag.c0047508
EISBN: 978-1-62708-221-1
... Abstract A riveted 0.25% carbon steel oil-storage tank in Oklahoma was dismantled and reassembled in Minnesota by welding to form a storage tank for soybean oil. An opening was cut in the side of the tank to admit a front-end loader. A frame of heavy angle iron was welded to the tank...
Abstract
A riveted 0.25% carbon steel oil-storage tank in Oklahoma was dismantled and reassembled in Minnesota by welding to form a storage tank for soybean oil. An opening was cut in the side of the tank to admit a front-end loader. A frame of heavy angle iron was welded to the tank and drilled for bolting on a heavy steel plate. The tank was filled to a record height. In mid-Jan the temperature dropped to -31 deg C (-23 deg F), with high winds. The tank split open and collapsed. The welding used the shielded metal arc process with E6010 electrodes, which could lead to weld porosity, hydrogen embrittlement, or both. At subzero temperatures, the steel was below its ductile-to-brittle transition temperature. These circumstances suggest a brittle condition. Steps to avoid this type of failure: For cold conditions, the steel plate should have a low carbon content and a high manganese-to-sulfur ratio and be in a normalized condition, low-hydrogen electrodes and welding practices should be used, all corners should be generously radiused, the welds should be inspected and ground or dressed to minimize stress concentrations, postweld heating is advisable, and radiographic and penetrant inspection tests should be performed.
Book Chapter
Reactor Cooling Water Expansion Joint Bellows: The Role of the Seam Weld in Fatigue Crack Development
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001682
EISBN: 978-1-62708-229-7
... from the Weld. The tensile tests of the portions of the bellows convolutes demonstrated that neither the welding nor the liquation cracking of the HAZ reduced the strength of the bellows. Three types of flat, reduced section test samples were prepared: base metal samples, samples which had...
Abstract
The secondary cooling water system pressure boundary of Savannah River Site reactors includes expansion joints utilizing a thin-wall bellows. While successfully used for over thirty years, an occasional replacement has been required because of the development of small, circumferential fatigue cracks in a bellows convolute. One such crack was recently shown to have initiated from a weld heat-affected zone liquation microcrack. The crack, initially open to the outer surface of the rolled and seam welded cylindrical bellows section, was closed when cold forming of the convolutes placed the outer surface in residual compression. However, the bellows was placed in tension when installed, and the tensile stresses reopened the microcrack. This five to eight grain diameter microcrack was extended by ductile fatigue processes. Initial extension was by relatively rapid propagation through the large-grained weld metal, followed by slower extension through the fine-grained base metal. A significant through-wall crack was not developed until the crack extended into the base metal on both sides of the weld. Leakage of cooling water was subsequently detected and the bellows removed and a replacement installed.
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