A forged alloy steel arm of a lifting fork with an approximate cross section of 150 x 240 mm (5.92 x 9.45 in.) fractured after only a short service life on a lift truck. The fracture surface had the appearance of a fracture originating from a surface crack. Analysis (visual inspection, 200x micrographs, chemical analysis, and metallographic examination) supported the conclusion that the primary cause of the failure was the brittleness (lack of impact toughness) of the steel. The coarse bainitic microstructure was inadequate for the service application. The microstructure resulted from either improper heat treatment or no heat treatment after the forging operation. The surface cracks in the lifting-fork arm acted as starter notches (stress raisers), assisting in the initiation of fracture. No recommendations were made.

A 22 m (72 ft) diameter filled grain storage bin made from a 0.2% carbon steel collapsed at a temperature of −1 to 4 deg C (30 to 40 deg F). Failure analysis indicated that fracture occurred in a two-step process: first downward, by ductile failure of small ligament from a bolt hole near the bottom of the tank to create a crack 25 mm (1 in.) long, and then upward, by brittle fracture through successive 1.2 m (4ft) wide sheets of ASTM A446 material. Site investigation showed that the concrete base pad was not level. Chemical analysis indicated that the material had a high nitrogen content (0.020%). The allowable stress based on yield was estimated using four different design criteria. Correlation among those results was poor. The different criteria indicated that the material was loaded from the maximum allowable to approximately 30% less than allowable. Nevertheless, at this stress level, fracture mechanics indicated that the 25 mm (1 in.) starter crack exceeded or was very near the critical crack length for the material. Additional factors not taken into account in the design equations included cold work from a hole punching operation, thread imprinting in bolt holes, and an additional hoop stress created by forcing an incorrectly formed panel to fit the pad base radius. These factors increased the nominal design stress to a sufficiently large value to cause the critical crack length to be exceeded.

The repeated failure of a welded ASTM A283 grade D pipe that was part of a 6 km (4 mi) line drawing and conducting river water to a water treatment plant was investigated. Failure analysis was conducted on sections of pipe from the third failure. Visual, macrofractographic, SEM fractographic, metallographic, chemical, and mechanical property (tension and impact toughness) analyses were conducted. On the basis of the tests and observations, it was concluded that the failure was the combined result of poor notch toughness (impact) properties of the steel, high stresses in the joint area, a possible stress raiser at the intersection of the spiral weld and girth weld, and sudden impact loading, probably due to water hammer. Use of a semi- or fully killed steel with a minimum Charpy V-notch impact value of 20 J (15 ft·lbf) at 0 deg C (32 deg F) was recommended for future water lines. Certified test results from the steel mill, procedure qualification tests of the welding, and design changes to reduce water hammer were also recommended.

Creep crack growth and fracture toughness tests were performed using test material machined from a seam welded ASTM A-155-66 class 1 (2.25Cr-1Mo) steel steam pipe that had been in service for 15 years. The fracture morphology was examined using SEM fractography. Dimpled fracture was found to be characteristic of fracture toughness specimens. Creep crack growth generally followed the fusion line region and was characterized as dimpled fracture mixed with cavities. These fracture morphologies were similar to those of an actual steam pipe. It was concluded that creep crack growth behavior was the prime failure mechanism of seam-welded steam pipes.

A catastrophic brittle fracture occurred in a welded steel (ASTM A517 grade H) trapezoidal cross-section box girder while the concrete deck of a large bridge was being poured. The failure occurred across the full width of a 57 mm (2 1 4 in.) thick, 760 mm (30 in.) wide flange and arrested 100 mm (4 in.) down the slant web. Failure analysis revealed a major deficiency in fracture toughness. The failure occurred as a brittle fracture after the formation of a welding hot crack and approximately 40 mm (1 1 2 in.) of slow crack growth. It was recommended that bridges fabricated from this grade of steel undergo frequent inspection and that stringent test requirements be imposed as a condition of use in non-redundant main load-carrying components.

An API type 2 steel clamp located on the riser of a semisubmersible drilling rig between the lower ball joint and riser blowout preventer (BOP) conductor failed after 7 years of service. Failure analysis revealed the cause of failure to be the low toughness of the clamp material. Contributing factors included the presence of a hard, brittle, heat-affected zone and weld defects at the handling pad eye. It was recommended that the replacement clamp be made from a material with good toughness and that any installation of attachments by welding be done according to qualified procedures.

The spontaneous breakage of tempered glass spandrel panels used to cover concrete wall panels on building facades was investigated. Between January 1988 and August 1990, 19 panel failures were recorded. The tinted panels were coated on their exterior surfaces with a reflective metal oxide and covered on the back surfaces with an adherent black polyethylene plastic. Macro fractography, SEM fractography, EDX analysis, and photo elasticimetry were conducted on four of the shattered panels. Small nickel sulfide inclusions were found at the failure origins. Failure of the panels was attributed to growth of the inclusions, coupled with high residual stresses. Fracture mechanics analysis showed that the residual stresses alone were high enough to cause fracture of the glass, with a flaw of the size observed.

A coupling in a line-shaft vertical turbine pump installed in a dam foundation fractured after a very short time. The coupling material was ASTM A582 416 martensitic stainless steel. Visual, macrofractographic, and scanning electron microscopic examination of the coupling showed that the fracture was brittle and was initiated by an intergranular cracking mechanism. The mode of fracture outside the crack initiation zone was transgranular cleavage. No indication of fatigue was found. The failure was attributed to improper heat treatment during manufacture, which resulted in a brittle microstructure susceptible to corrosion. The crack initiated either by stress-corrosion or hydrogen cracking. It was recommended that the couplings in the system be examined for surface cracking and, if present, corrective measures be taken.

This paper describes the analysis of the failure of a Zr-2.5Nb pressure tube in a CANDU reactor. The failure sequence was established as: (1) the existence of an undetected manufacturing flaw in the form of a lamination, (2) in-service development of the flaw by oxidation of the lamination, (3) delayed hydride cracking, which extended the flaw through the wall of the tube, resulting in leakage, and (4) rupture of the tube by cold pressurization while the reactor was shut down. The comprehensive failure analysis led to a remedial action plan that permitted the reactor to be returned to full-power operation and ensured a low probability of a similar occurrence for all CANDU reactors.

A piece of wheel flange separated from the main landing gear wheel of a C130 aircraft as it taxied on a runway. The wheel was a 2014-T61 aluminum alloy forging and had been in service nearly 20 years. Fractographic evidence indicated that the initial crack growth was caused by high-cycle fatigue. The crack grew to approximately 8 in. in length before final catastrophic fracture. Fatigue analyses accurately predicted the cyclic life demonstrated by the failed wheel since its last inspection, assuming an initial crack length of 13 to 25 mm (0.5 to 1.0 in.). It was recommended that the inspection interval be reduced to one-third of its original duration for the current level of inspection reliability, or that inspection procedures be improved in order that cracks substantially smaller than 13 mm (0.5 in.) can be reliably detected.

The right landing gear on a twin-turboprop transport aircraft collapsed during landing. Preliminary examination indicated that the failure occurred at a steel-to-aluminum (7014) pinned drag-strut connection due to fracture of the lower set of drag-strut attachment lugs at the lower end of the oleo cylinder housing. Two lug fractures that were determined to be the primary fractures were analyzed. Results of various examinations indicated that stress-corrosion cracking associated with the origins of the principal fractures in the connection was the cause of failure. It was recommended that the design be modified to avoid dissimilar metal combinations of high corrosion potential.

A gray cast iron (ASTM 247 type A) gate valve in an oleum and sulfuric acid piping loop at a chemical process plant fractured catastrophically after approximately 10 years of service. The valve was a 150 mm (6 in.) bolted flange type rated to conform to ANSI B16.1 for service at 1034 kPa (150 psi) and 120 deg C (250 deg F) maximum in 93 to 99% sulfuric acid. The fracture originated at stress-corrosion cracks that occurred in a high-stress transition region at the valve body-to-flange juncture. The mechanical properties of the failed valve were below those of the manufacturer's cited specification, and the wall thickness through which the fracture occurred exceeded the minimum 9.5 mm (38 in.) thickness cited by the manufacturer The valve flange had been unbolted and rebolted to a maintenanced piping coil immediately prior to failure. It was recommended that the flange-to-valve body juncture be redesigned to reduce stress levels. A method of maintenance and inspection in concert with a criterion for life prediction for this and other valves and components in the system was also recommended.

A 127 cu m (4,480 cu ft) pressurized railroad tank car burst catastrophically. The railroad tank was approximately 18 m (59 ft) long (from 2:1 elliptical heads), 3 m (10 ft) in OD, and 16 mm (0.63 in.) thick. The chemical and material properties of the tank were to comply with AAR M-128 Grade B. As a result of the explosive failure of the tank car, fragments were ejected from the central region of the car between the support trucks from ground zero to a maximum of approximately 195 m (640 ft). The mode of failure was a brittle fracture originating at a preexisting lamination and crack in the tank wall adjacent to the tank nozzle. The mechanism of failure was overpressurization of the railroad tank car caused by a chemical reaction of the butadiene contents. The interrelationship of the mode, mechanism, and consequences of failure is reviewed to reconstruct the sequence of events that led up to the breach of the railroad tank car. Means to prevent similar reoccurrences are discussed.

Chain link, a part of a mechanism for transferring hot or cold steel blooms into and out of a reheating furnace, broke after approximately four months of service. The link was cast from 2% Cr austenitic manganese steel and was subjected to repeated heating to temperatures of 455 to 595 deg C (850 to 1100 deg F). Examination included visual inspection, macrograph of a nital-etched specimen from an as-received chain link 1.85x, micrographs of a nital-etched specimen from an as-received chain link 100x/600x, normal microstructure of as-cast standard austenitic manganese steel 100x, micrograph of a nital-etched specimen that had been austenitized 20 min at 1095 deg C (2000 deg F) and air cooled 315x, and micrograph of the same specimen after annealing 68 h at 480 deg C (900 deg F) 1000x). Investigation supported the conclusions that the chain link failed in a brittle manner, because the austenitic manganese steel from which it was cast became embrittled after being reheated in the temperature range of 455 to 595 deg C (850 to 1100 deg F) for prolonged periods of time. The alloy was not suitable for this application, because of its metallurgical instability under service conditions.

Cracks were discovered in the cast 17-4 PH stainless steel outboard leading edge flap support of an aircraft wing during overhaul inspection. Failure analysis focused on an apparently intergranular area of fracture surface. It was determined that the original mode of crack growth was cleavage, probably caused by cast-in hydrogen. The intergranular appearance resulted from heat treatment of the already cracked part, which caused the formation of grain-boundary “growth figures” on the exposed crack surfaces. It was recommended that the castings be more closely inspected for defects before further processing and that foundry practices be reviewed to correct deficiencies leading to excessive hydrogen absorption during melting and casting.

Rollover accidents in light trucks and cars involving an axle failure frequently raise the question of whether the axle broke causing the rollover or did the axle break as a result of the rollover. Axles in these vehicles are induction hardened medium carbon steel. Bearings ride directly on the axles. This article provides a fractography/fracture mechanic approach to making the determination of when the axle failed. Full scale tests on axle assemblies and suspensions provided data for fracture toughness in the induction hardened outer case on the axle. These tests also demonstrated that roller bearing indentions on the axle journal, cross pin indentation on the end of the axle, and axle bending can be accounted for by spring energy release following axle failure. Pre-existing cracks in the induction hardened axle are small and are often difficult to see without a microscope. The pre-existing crack morphology was intergranular fracture in the axles studied. An estimate of the force required to cause the axle fracture can be made using the measured crack size, fracture toughness determined from these tests, and linear elastic fracture mechanics. The axle can be reliably said to have failed prior to rollover if the estimated force for failure is equal to or less than forces imposed on the axle during events leading to the rollover.

A number of failures involving carbon and alloy steels were analyzed to assess the effects of inclusions and their influence on mechanical properties. Inclusions, including brittle oxides and more ductile manganese sulfides (MnS), affect fatigue endurance limit, fatigue crack propagation rates, fracture toughness, notch toughness, and transverse tensile properties, and do so in an anisotropic manner with respect to rolling direction. Significant property anisotropy has been documented in the failures investigated, providing evidence that designers failed to account for it. Typical fracture morphologies observed in such cases and metallographic appearances of MnS-containing materials are illustrated.

Numerous flaws were detected in a steam turbine rotor during a scheduled inspection and maintenance outage. A fracture-mechanics-based analysis of the flaws showed that the rotor could not be safely returned to service. Material, samples from the bore were analyzed to evaluate the actual mechanical properties and to determine the metallurgical cause of the observed indications. Samples were examined in a scanning electron microscope and subjected to chemical analysis and several mechanical property tests, including tensile, Charpy V-notch impact, and fracture toughness. The material was found to be a typical Cr-Mo-V steel, and it met the property requirements. No evidence of temper embrittlement was found. The analyses showed that the observed flaws were present in the original forging and attributed them to lack of ingot consolidation. A series of actions, including overboring of the rotor to remove indications close to the surface and revision of starting procedures, were implemented to extend the remaining life of the rotor and ensure its fitness for continued service.

A fracture mechanics based failure analysis and life prediction of a large centrifugal fan made from low-carbon, medium-strength steel was undertaken following shortcomings in attempts to explain its fatigue life from start stop cycles alone. Measurements of the fracture toughness and flaw size at failure, coupled with quantitative SEM fractography using striation spacing methods, revealed that the cyclic stress amplitudes just prior to failure were much larger than expected, in this particular case. Subsequent improvements in fan design and fabrication have effectively alleviated the problem of slow, high cycle fatigue crack growth, at normal operating stresses in similar fans.

An I-beam of IS-226 specification—I-section dimensions of 450 x l50 x 10 mm (17.7 x 5.9 x 0.4 in.) and a length of 12.41 m (40.7ft)—was flame cut into two section in an open yard near these a coast under normal weather conditions. After approximately 112h, the shorter section of he I-beam split catastrophically along the entire length through the web. Detailed investigation revealed segregation of high levels of carbon, sulfur and phosphorus in the middle of the web and high residual stresses attributed to rolling during fabrication. Flame cutting caused a change in the distribution of the residual stresses, which, aided by low fracture toughness due to the poor quality of the beam, resulted in failure. It was recommended that segregation be avoided in cast ingots used for I-beam manufacture by implementing a better quality-control procedure.