A ductile iron T-hook hook was reported to have fractured in service. It was further reported that the hook had been subjected to a load that did not exceed 5900 kg (13,000 lb) at the time of fracture. No information was provided regarding the type of metal used to manufacture the hook. A failure analysis was requested to determine the cause of fracture. Two hooks were submitted for examination. Analysis (visual inspection, 2.7x light fractography, chemical analysis, 110x SEM fractography, 27x/110x/215x nital-etched micrographs) supported the conclusions that this component fractured in service as a consequence of ductile tensile overload. Evidence indicates that the fractured region was subjected to a load exceeding the capacity of the material. Because the information available from the service application indicated that the component had not been subjected to a stress that exceeded 5900 kg (13,000 lb), the observations made in this investigation suggested that either the load was underestimated or that the indicated load was applied at a more rapid rate (perhaps with a jerk), which would tend to increase the effective force of the load.

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.

Two type 316L stainless steel orthopedic screws broke approximately 6 weeks after surgical implant. The screws had been used to fasten a seven-hole narrow dynamic compression plate to a patient's spine. The broken screws and screws of the same vintage and source were examined using macrofractography, SEM fractography, and hardness testing. Fractography established that fracture was by fatigue and that the fatigue cracking originated at corrosion pits. Hardness while below specification, still indicated that the screws were in the cold-worked condition and notch sensitive during fatigue loading. Use of a steel with a higher molybdenum content (317L) in the annealed condition was recommended.

A steam heated exchanger was designed for concentrating sulfuric acid. Tantalum was selected for the tubing and the tube sheet liner because of its outstanding corrosion resistance. However, although the exchanger passed a searching shop inspection, it leaked during site testing. Considerable argument ensued about whether the cracking observed was due to poor welding during fabrication, or through abuse during handling on site. An SEM examination of the fractures revealed high cycle, low amplitude fatigue, and the problem was traced to vibration during road transport. Further failures were avoided by improved design and packing. This paper illustrated the value of SEM fractography when a rapid investigation is needed under the pressures of a fast moving project.

Several AISI type 321 stainless steel welded oil tank assemblies used on helicopter engine systems began to leak in service. One failure, a fracture on the aft side of a spot weld, was submitted for analysis. SEM fractography examination revealed fatigue failure. The failure initiated at an overload fracture near the root of the weld and was followed by mode III fatigue crack propagation (tearing) around the periphery of the weld. The initial overload fracture was caused by a high external load, which produced a concentrated stress and fracture at the weld root. The subsequent fatigue fracture was caused by engine vibrations during operation of the aircraft. Fracture characteristics indicated that the fatigue would not have occurred if the initial damage had not taken place.

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.

The failure during use of a seat on a heavy-duty swing set at an elementary school was investigated. The seat contained a perforated reinforcing sheet metal (galvanized type 430 stainless steel) insert covered by an elastomeric material. Specimens of the reinforcing sheet from the failed seat were examined using SEM fractography, tensile and ductility tests, and spectrographic chemical analysis. The test results showed that the steel used did not meet the manufacturer's specifications for ductility (elongation). In addition, the small-diameter punched holes caused a stress concentration factor that aggravated the brittleness of the steel.

An ASTM A391 steel chain link of an over head hoist failed catastrophically, causing damage to both property and personnel. Macrofractography identified the sequence of fractures within the chain link. The first fracture occurred at the welded joint, a second occurred opposite the weld. SEM fractography and metallography indicated that the link failed in a ductile manner because of tensile overload, which occurred when the hoist hook contacted the hoist's housing and prevented uptake of the chain. It was recommended that a load-sensing device be installed to prevent future occurrences and that a dye penetrant inspection be performed on the renwinder of the chain.

The causes of internal cracking that occurred in 9% Ni steel castings during manufacture were investigated using a series of eight laboratory castings containing varying amounts of molybdenum. The effect of mold thickness was also investigated. The laboratory castings were subjected to three-point bend testing, and fracture surfaces were examined using SEM fractography, metallography, and depth analysis (SIMS) of the fracture surface. The cracks were found to originate at austenitic grain boundaries that coincided with primary dendrite interfaces. The cracking was attributed to a decrease in grain-boundary cohesion resulting from sulfur segregation. Addition of molybdenum proved effective in preventing cracking. The molybdenum promoted MnS precipitation in the grain and preferentially segregated to the interfaces.

A flanged 100 mm (4 in.) diam low-carbon steel spool piece lined with Teflon was removed from a sulfuric acid denitrification system after cracks were observed in the painted coating. Visual and microstructural examination along with SEM fractography revealed scaled iron oxides on all opened crack surfaces. The surfaces had a faceted morphology, indicating intergranular fracture. Cracks originated at the interface between the tube and the Teflon liner Corrosion products were found caked into the intergranular region between the liner and the spool. The portion of the liner that had been exposed to the process stream was discolored. Failure of the spool was attributed to stress-corrosion cracking promoted by the presence of nitrates. Nitric acid contaminant in the sulfuric acid stream had diffused through the liner and accumulated in the annular space. Use of a liner that is more impermeable to the diffusion of ionic species was recommended.

Failure analysis was performed on a fractured impeller from a boiler feed pump of a fossil fuel power plant. The impeller was a 12% Cr martensitic stainless steel casting. The failure occurred near the outside diameter of the shroud in the vicinity of a section change at the shroud/vane junction. Sections cut from the impeller were examined visually and by SEM fractography. Microstructural, chemical, and surface analyses and surface hardness tests were conducted on the impeller segments. The results indicated that the impeller failed in fatigue with casting defects increasing stress and initiating fracture. In addition, the composition and hardness of the impeller did not meet specifications. Revision of the casting process and institution of quality assurance methods were recommended.

A stainless steel flexible connector failed after a short period of service. Visual examination of the failed part revealed that a fracture had occurred in the thin-walled stainless steel bellows brazed into the flanges at each end. Surface examination by SEM fractography showed that failure of the bellows occurred via fatigue. The crack in the bellows had widened considerably after the fracture, and the bellows had been severely compressed on the fracture side prior to failure. Based on these observations, it was concluded that bellows had been damaged prior to installation. The damage resulted in high mean tensile stresses upon which were superimposed cyclic stresses, with fatigue failure the final result.

An ASTM A193-83a grade B7 (AISI 4140) steel turbine impeller shaft fractured after 2 months of service. Failure had initiated at three separate points around the periphery of the shaft, each associated with one of three keyways. SEM fractography, metallography, and chemical analysis indicated that the mechanism of fracture initiation was torsional fatigue. Intermittent deceleration and acceleration resulting from power surges during operation of the turbine caused torsional vibration and was considered the most probable source of the required cyclic stress. Final failure took place by torsional shear.

A type 410 stainless steel circulating water pump shaft used in a fossil power steam generation plant failed after more than 7 years of service. Visual examination showed the fracture surface to be coated with a thick, spalling, rust-colored scale, along with evidence of pitting. Samples for SEM fractography, EDS analysis, and metallography were taken at the crack initiation site. Hardness testing produced a value of approximately 27 HRC. The examinations clearly established that the shaft failed by fatigue. The fatigue crack originated at a localized region on the outside surface where pitting and intergranular cracking had occurred. The localized nature of the initial damage indicated that a corrosive medium had concentrated on the surface, probably due to a leaky seal. Reduction of hardness to 22 HRC or lower and inspection of seals were recommended to prevent future failures.

The draw-in bolt and collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after a relatively long service life. The collet ejected at a high rotational speed due to loss of its vertical support and shattered one of its arms upon impact with the work table. SEM fractography and metallographic examinations conducted on the bolt revealed hairline indications along grain facets on the fracture surface and stepwise cracking in the material, both indicating failure by hydrogen embrittlement. Similar draw-in bolts were discarded and replaced with bolts manufactured using controlled processes.

Six galvanized high-tensile steel bolts were used to hold the wheels of a four-wheel drive vehicle. The right hand rear wheel of this vehicle detached causing the vehicle to roll and resulting in considerable damage to the body. The wheel was detached by shearing of four of the bolts and stripping the nuts from the other two bolts, which remained unbroken. SEM fractography of the fracture surfaces of the four broken bolts indicated that the failure was due to reversed bending fatigue. Optical microscopy indicated that the bolts were heat treated to a tempered martensite structure and that the nuts were manufactured from low carbon steel. The paper discusses the influence of the microstructure on the failure process the events surrounding the nature of incident and the analysis of in-service failure of the failed components utilizing conventional metallurgical techniques.