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Handles welded to the top cover plate of a chemical-plant downcomer broke at the welds when the handles were used to lift the cover. The handles were fabricated of low-carbon steel rod; the cover was of type 502 stainless steel plate. The attachment welds were made with type 347 stainless steel filler metal to form a fillet between the handle and the cover. The structure was found to contain a zone of brittle martensite in the portion of the weld adjacent to the low-carbon steel handle; fracture had occurred in this zone. The brittle martensite layer in the weld was the result of using too large a welding rod and too much heat input, melting of the low-carbon steel handle, which diluted the austenitic stainless steel filler metal and formed martensitic steel in the weld zone. Because it was impractical to preheat and postheat the type 502 stainless steel cover plate, the low-carbon steel handle was welded to low-carbon steel plate, using low-carbon steel electrodes. This plate was then welded to the type 502 stainless steel plate with type 310 stainless steel electrodes. This design produced a large weld section over which the load was distributed.

The welds joining the liner and shell of a fluid catalytic cracking unit failed. The shell was made of ASTM A515 carbon steel welded with E7018 filler metal. The liner was made of type 405 stainless steel and was plug welded to the shell using ER309 and ER310 stainless steel filler metal. Fine cracks starting inside the weld zone and spreading outward through the weld and toward the surface were observed during examination. Decarburization and graphitization of the carbon steel at the interface was noted. The high carbon level was found to allow martensite to form eventually. The structure was found to be austenitic in the area where the grain-boundary precipitates appeared heaviest. The composition of the precipitates was analyzed using an electron microprobe to reveal presence of sulfur. Microstructural changes in the weld alloy at the interface were interpreted to be caused by dilution of the alloy and the presence of sulfur caused hot shortness. The necessary internal stress to produce extensive cracking was produced by the differential thermal expansion of the carbon and stainless steels. Periodic careful gouging of the affected areas followed by repair welding was recommended.

An extensive metallurgical investigation was carried out on samples of a failed roller bearing from the support and tilting system of a basic oxygen furnace converter used in the steel melting shop of an integrated steel plant. The converter bearing was fabricated from low-carbon, carburizing grade steel and had failed in service within a year of fitting to a repaired shaft. Microscopic observations of both the broken roller and inner-race samples revealed subsurface cracking and preponderance of brittle oxide and other macroinclusions. Electron probe microanalysis studies confirmed that the brittle oxides that formed stringers were alumina, and the other macroinclusions were complex silicates. Both the alumina and silicate inclusions were deleterious to contact-fatigue properties. Microstructurally, the carburized regions of the broken roller and of inner-race samples contained high-carbon tempered martensite. Microhardness measurements revealed that. Although the core hardness of the roller and the inner-race samples were similar, the surface hardness of the roller was approximately 8.5 HRC units harder than that of the inner-race. SEM observations of the roller fracture surface revealed striations indicative of fatigue, and EDS analyses corroborated a high incidence of silicate inclusions at crack sites. The study suggests that the failure of the bearing occurred because the hardness difference between the roller bearing and the inner-race surfaces resulted in wear of the inner-race. The wear led to shaft misalignment and play during service. The misalignment, coupled with the presence of inclusions, caused fatigue failure of the roller bearing.

The stub-shaft assembly which was part of the agitator shaft in a polyvinyl chloride reactor, fractured in service after a nut that retained a loose sleeve around the smaller-diam section of the shaft had been tightened several times to reduce leakage. The shaft was made of ASTM A105, grade 2 steel, and the larger-diam section was covered with a type 316 stainless steel end cap. The cap was welded to each end using type ER316 stainless steel filler metal. The forged steel shaft was revealed to have fractured at approximately 90 deg to the shaft axis in the weld metal and not in the heat-affected zone of the forged steel shaft. Microscopic investigation and chemical analysis of the steel shaft revealed presence of martensite (offered a path of easy crack propagation) around the fusion line and dilution of the weld metal by the carbon steel shaft. The microstructure was found to be martensitic as the fusion line was approached. The forged steel shaft was concluded to have failed by ductile fracture and possible reasons were discussed. Corrective measures adopted in the replacement shaft were specified.

Although a precise understanding of roll failure genesis is complex, the microstructure of a broken roll can often unravel intrinsic deficiencies in material quality responsible for its failure. This is especially relevant in circumstances when, even under a similar mill-operating environment, the failure involves a particular roll or a specific batch of rolls. This paper provides a microstructural insight into the cause of premature breakage of a second-intermediate Sendzimir mill drive roll used at a stainless steel sheet rolling plant under the Steel Authority of India Limited. Microstructural issues influencing roll quality, such as characteristics of carbides, tempered martensite, retained austenite, etc., have been extensively studied through optical and scanning electron microscopy, electron-probe microanalysis, image analysis, and x-ray diffractometry. These are discussed to elucidate specific microstructural inadequacies that accentuated the failure. The study reveals that even through retained austenite content is low (6.29 vol%) and martensite is non-acicular, the roll breakage is a consequence of intergranular cracking caused by improper carbide morphology and distribution.

A storage tank had been in service at a petrochemical plant for 13 years when inspectors discovered cracks adjacent to weld joints and in the base plate near the foundation. The tank was made from AISI 304 stainless steel and held styrene monomer, a derivative of benzene. The cracks were subsequently welded over with 308 stainless steel filler wire and the base plate was replaced with new material. Soon after, the tank began leaking along the weld bead, triggering a full-scale investigation; spectroscopy, optical and scanning electron microscopy, fractography, SEM-EDS analysis, and microhardness, tensile, and impact testing. The results revealed transgranular cracks in the HAZ and base plate, likely initiated by stresses developed during welding and the presence of chloride from seawater used in the plant. It was also found that the repair weld was improperly done, nor did it include a postweld heat treatment to remove weld sensitization and minimize residual stresses.

A spiral heat exchanger made from 316L stainless steel developed a leak after eight years of service as a condenser on a distillation tower. Examination identified the leak as being located on the cooling water side in the heat affected zone (HAZ) of a weld joining two plates. Cooling water deposits were observed in a V-shaped corner formed by the weld. A metallurgical examination identified the presence of transgranular cracks in the HAZ on the cooling water side. Analysis of the cooling water revealed the presence of chlorides. Based on the metallurgical analysis and other findings, it was determined that the cracks and associated leak were the result of chloride stress-corrosion cracking.

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.

Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.

Spalled fragments from the work rolls of a steel bar straightening machine were received for failure analysis. Visual inspection coupled with optical and scanning electron microscopy were used as the principal analytical techniques for the investigation. Fractographic analysis revealed the presence of a characteristic fatigue crack propagation pattern (beach marks) and radial chevron marks indicating the occurrence of final overload through a brittle intergranular fracture. The collected evidence suggests that surface-initiated cracks propagated by fatigue led to spalling, resulting in severe work roll damage as well as machine downtime and increased maintenance costs.

A deformed steel tube was received for failure analysis after buckling during a heat-treat operation. The tube was subjected to various metallurgical tests as well as nondestructive testing to confirm the presence of residual stresses. The microstructure of the tube was found to be homogenous and had no banded structure. However, x-ray diffraction analysis confirmed the presence of up to 6% retained austenite which likely caused the tube to buckle during the 910 °C heat treating procedure.

Graphitization, the formation of graphite nodules in carbon and low alloy steels, contributes to many failures in high-temperature environments. Three such failures in power-generating systems were analyzed to demonstrate the unpredictable nature of this failure mechanism and its effect on material properties and structures. In general, the more randomly distributed the nodules, the less effect they have on structural integrity. In the cases examined, the nodules were found to be organized in planar arrays, indicating they might have an effect on material properties. Closer inspection, however, revealed that the magnitude of the effect depends on the relative orientation of the planar arrangement and principle tensile stress. For normal orientation, the effect of embrittlement tends to be most severe. Conversely, when the orientation is parallel, the nodules have little or no effect. The cases examined show that knowledge is incomplete in regard to graphitization, and the prediction of its occurrence is not yet possible.

The shafts on two centrifugal pumps failed during use in a petroleum refinery. Light optical microscopy and scanning electron microscopy were used to analyze the damaged materials to determine the cause of failure. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.

This case study describes the failure analysis of a steel nozzle in which cracking was observed after a circumferential welding process. The nozzle assembly was made from low-carbon CrMoV alloy steel that was subsequently single-pass butt welded using gas tungsten arc welding. Although no cracks were found when the welds were visually inspected, X-ray radiography showed small discontinuous surface cracks adjacent to the weld bead in the heat affected zone. Further investigation, including optical microscopy, microhardness testing, and residual stress measurements, revealed that the cracks were caused primarily by the presence of coarse untempered martensite in the heat affected zone due to localized heating. The localized heating was caused by high welding heat input or low welding speed and resulted in high transformation stresses. These transformation stresses, working in combination with thermal stresses and constraint conditions, resulted in intergranular brittle fracture.

Stainless steel pipe (273-mm OD x 8-mm wall thickness) used in the fabrication of large manifolds developed crack-like decohesions during a routine inductive bending procedure. The imperfections, which were found near the outside diameter, were around 3 mm in length oriented in the circumferential direction and penetrated nearly 2 mm into the pipe wall. The pipes were made of titanium-stabilized austenitic stainless steel X6CrNiMoTi17-12-2. Six hypotheses were considered during the investigation, which ultimately concluded that the failure was caused by liquation cracking due to overheating.

Several stainless steel coils cracked during a routine unwinding procedure, prompting an investigation to determine the cause. The analysis included optical and scanning electron microscopy, energy-dispersive x-ray spectrometry, and tensile testing. An examination of the fracture surfaces revealed a brittle intercrystalline mode of fracture with typical manifestations of clear grain facets. Branched and discrete stepwise microcracks were also found along with unusually high levels of residual hydrogen. Mechanical tests revealed a marked loss of tensile ductility in the defective steel with elongations barely approaching 8%, compared to 50% at the time of delivery weeks earlier. Based on the timing interval and the fact that failure occurred at operating stresses well below the yield point of the material, the failure is being attributed to hydrogen-induced damage. Potential sources of hydrogen are considered as are remedial measures for controlling hydrogen content in steels.

A masonry type drill bit, designed for impact drilling in rock, fractured after a short time in service. Samples of the failed bit were analyzed using optical and scanning electron microscopy, quantitative metallography, and chemical analysis. The composition was found to be that of 18CrNi3Mo steel. Investigators also found evidence of inclusions and prior austenite grain size, although it was determined that neither played a role in the failure. Rather, according to test data, the failure occurred because of stress concentration (due to geometric discontinuities along the tooth profiles) and the cumulative effect of torque and force loading (the byproduct of continuous twisting and axial impact). Cracks readily initiate under these conditions then propagate quickly through what was found to be networks of tempered martensite, thus resulting in premature failure.

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.

A section from a stop-block guide fell to the floor on a crane runway after it failed. A brittle crystalline-type break was disclosed by examination of the fracture surface. The point of initiation was in a hardened heat-affected layer that had developed during flame cutting and welding. The metal was identified to be 1020 steel. It was indicated by the coarse as-rolled structure (grain size of ASTM 00 to 4) of the base metal that the weldment (stop block and guide) had not been normalized. The brittle failure was evaluated to have been initiated at a metallurgical and mechanical notch produced by flame cutting and welding. As corrective measures, fully silicon-killed 1020 steel with a maximum grain size of ASTM 5 were used to make new stop-block weldments. The weldments were normalized at 900 deg C after flame cutting and welding to improve microstructure and impact strength. All flame-cut surfaces were ground to remove notches.

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.