The structural collapse of an iron-ore bucket-wheel stacker reclaimer at the beginning of operation was investigated by means of mechanical tests, microstructural characterization, and computational structural analysis. The mechanical failure was a consequence of a brittle fracture by cleavage. The crack followed the heat-affected zone of a welded joint connecting a rectangular hollow section member and a plate flange. The main factors contributing to failure were related with a combination of design-in and manufacturing-in factors like high load-strength ratio at the point of failure, local stress concentration as a result of geometry restrictions, and weld defects. This particular section was responsible for the load transfer between the front tie member and the boom extremity, and its failure was the main cause of the catastrophic failure of the equipment.

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.

A multi-million dollar, four-color printing press used to produce a major weekly magazine was breaking pinions (shouldered shafts) on rolls. The cause of fracture was cyclic fatigue. Steel quality and heat treatment met expected standards. The pinion fracture showed multiple origins indicating rotational vibration fatigue. Keeping bolts tight solved this problem. In another case, grinding machines were unable to produce surfaces of uniform quality and smoothness on steel bearing products. Measurements showed that self-excited vibrations were created when particular steels were ground. It was found that the natural frequency of the wheel truing device was the culprit. A tuned damped absorber was designed and built to modify the resonance. This eliminated the problem.

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.

In TAKR 300 (Bob Hope) Class transport ships, the builder observed cracking of steel cloverleaf vehicle tie-down deck sockets following installation. Sockets were made from AH36 steel plate by flame cutting and cold coining, then submerged-arc welded to the shop deck. Cracks initiated from the tip of the cloverleaf pattern in >300 cases aboard several cargo vessels in various stages of construction. Consultants who analyzed the situation concluded that the problem may have been corrosion and hydrogen embrittlement. Three possible mechanisms of failure were considered: overload failure; fatigue fracture; and, environmentally-assisted cracking. Testing indicated overload failure was the cause. Remedial actions were taken to improve the fracture properties of the deck socket. A modified manufacturing process was developed involving milling and cutting instead of coining to round the comers of the flame-cut cloverleaf lobe. This new manufacturing process solved the problem.

A railway tank car developed a fracture in the region of the sill and shell attachment during operation at -34 deg C (-30 deg F). On either side of the sill-support member, cracking initiated at the weld between a 6.4 mm thick frontal cover plate and a 1.6 mm thick side support plate. The crack then propagated in a brittle manner upward through the side plate, through the welds attaching the side plate to a 25 mm (1 in.) thick shell plate (ASTM A212, grade B steel), and continued for several millimeters in the shell plate before terminating. Other plates involved were not positively identified but were generally classified as semi-killed carbon steels. Investigation (visual inspection, hardness testing, chemical analysis, Charpy V-notch testing, and drop-weight testing) supported the conclusions that the fracture was initiated by weld imperfections and propagated in a brittle manner as a result of service stresses acting on the plate having low toughness at the low service temperatures encountered. Recommendations included that the specifications for the steel plates be modified to include a toughness requirement and that improved welding and inspection practices be performed to reduce the incidence of weld imperfections.

Single 6.4 mm (0.25 in.) post-tensioning wires failed in a parking garage in the southern portion of the United States. Several failed wires were removed and the lengths were examined for signs of corrosion using SEM metallography. The scans showed localized shallow pitting, and chloride was detected in some of the pits. The test also revealed an initial crack that was probably caused by hydrogen embrittlement. Since no chloride was detected on the fracture surface, and none was detected in the overlying concrete, the corrosion appears to have begun prior to the wires' placement in the concrete.

During construction of a revolving sky-tower observatory, a 2.4 m (8 ft) diam cylindrical column developed serious circumferential cracks overnight at the 14 m (46 ft) level where two 12 m (40 ft) sections were joined by a girth weld. The temperatures ranged from 12 deg C (53 deg F) to 7 deg C (45 deg F) that night. The column was shop fabricated in 12 m (40 ft) long sections of 19 mm (3/4 in.) thick steel plate of ASTM A36 steel. Crack initiation was caused by high residual stress during girth welding, and the presence of notches formed by the termination of the incomplete welds. Continuation of the cracks was attributed to the brittle condition of the steel when cooled by the night air. A steel with a much lower ductile-to-brittle transition temperature is essential for this type of structure. Other necessary steps include better control of the girth-welding, choice of a more favorable electrode to avoid porosity, careful termination of all welds to avoid formation of notches, and completion of all welds before other sections of the column are erected.

A large fan assembly deformed and broke at multiple locations. The user wanted to know whether the bearing pillow block fracture caused the fan blade assembly to crack, or whether a fan blade assembly fracture caused the pillow block to crack. Close inspection of the entire length of the crack showed the crack probably grew quite a while before it was large enough to cause the final catastrophic event. No evidence of fatigue cracks was visible on the broken pillow blocks. In the absence of some other contradictory information, the usual conclusion would be to presume that the fatigue crack predated the single overload crack.

A ceiling in a concrete structure was hung on flat bars with a cross section of 30 x 80 mm. The bars were borne by a slit steel plate and supported by tabs that were welded onto the flat sides. One of the bars fractured during mounting when it was dropped from a height of about 1 m onto the opposite support. The fracture was a grainy forced rupture that propagated from one of the fillet welds. Investigation showed a steel was selected for this important construction that was prone to aging and that in fact had aged through cold deformation during straightening and then was welded yet. The bar could withstand mounting and subsequent static loading as long as it was treated with care, as could be expected from the good deformation characteristics of the static tensile test. The question is, however, whether occasional impacts or shocks can be assuredly avoided. This risk could have been eliminated if a killed steel of quality groups 2 or 3 according to DIN 17 100 had been used.

A portion of the roof of a single story building collapsed during a thunder storm. A failure analysis was conducted to determine whether this structural failure was due to improper design, substandard construction materials, faulty erection, or extreme weather conditions. The failure analysis consisted of an onsite inspection, macrofractographic examination of the fractures where the girders were welded to the columns, macrofractographic examination of the fractured trusses, metallographic examination of the girder and truss materials, chemical analysis of the low-carbon steel girder and truss materials, and mechanical testing of the truss material. It was concluded that substandard structural components in combination with faulty construction was responsible for this service failure.

A portion of a 19 mm (0.75 in.) diam structural steel bolt was found on the floor of a manufacturing shop. This shop contained an overhead crane system that ran on rails supported by girders and columns. Inspection of the crane system revealed that the bolt had come from a joint in the supporting girders and could be considered one of the principal fasteners in the track system. Analysis (visual inspection, metallographic exam, and hardness testing) supported the conclusions that fatigue induced by the overhead movement of the crane produced failure of the bolt. The bolt was deficient in strength for the cyclic applied loads in this case and probably was not tightened sufficiently. Recommendations included removing the remaining bolts in the crane support assembly and replacing them with a higher-strength, more fatigue-resistant bolt, for example, SAE grade F, 104 to 108 HRB. The bolts should be tightened according to the specifications of the manufacturer, and the system should be periodically inspected for correct tightness.

In 1979, during a routine bridge inspection, a fatigue crack was discovered in the top flange plate of one tie girder in a tied arch bridge crossing the Mississippi River. Metallographic analysis indicated a banding or segregation problem in the middle of the plate, where the carbon content was twice what it should have been. Based on this and results of ultrasonic testing, which revealed that the banding occurred in 24-ft lengths, it was decided to close the bridge and replace the defective steel. The steel used in the construction of this bridge was specified as ASTM A441, commonly used in structural applications. Testing showed an increase in hardness and weight percent carbon and manganese in the banded region. Further testing revealed that the area containing the segregation and coarse grain structure had a lower than expected toughness and a transition temperature 90 deg F higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size.

Some corrosion processes in the presence of chlorides, for steel embedded in concrete, are described and illustrated with the aid of scanning electron microscope EDXA data. Observations made of failure surfaces of reinforcements removed from the concrete beams after being subjected to sinusoidal load fluctuations at 6.7 Hz in air, 3% NaCl solution, and natural sea water are described. Reinforcement types studied included: hot-rolled mild steel bar, hot-rolled alloyed high strength bar, cold-worked high strength bar, galvanized bar of all these three types, nickel-clad bar and epoxy-coated bar.

A large crack developed at a girder-truss joint area of the Fremont bridge in Portland, OR, on 28 Oct 1971. It occurred during a positioning procedure involving a junction piece welded to a girder, starting as a brittle fracture and terminating in plastic hinges in the girder web welds. The arch rib top plate, as it met the main girder, formed a composite beam of A588/A36 composition. Investigation showed the original design of the failed component called for an angle of high geometric stress concentration (90 deg with no radius) in a region of substantial transverse weld joints. While the material met chemical and mechanical property requirements, tests showed it had low fracture toughness and critical-sized flaws oriented normal to the principal stress in the failed junction piece. Fabrication procedures resulted in high residual stresses and a metallurgical notch at the radius in the junction piece. Stresses induced during jacking (the procedure used to raise bridge components into position) applied the stresses in the critical radius that triggered the cracking.

During the construction of a prestressed concrete viaduct, several 12.2 mm diam wires ruptured after tensioning but before the channels were grouted. They were made of heat treated prestressed concrete steel St 145/160. While the wire bundles, each containing over 100 wires, were being drawn into the channels they were repeatedly pulled over the sharp edges of square section guide blocks. The fractures were initiated at these chafe zones. It was concluded that the chafing of the wires on the edges of the guide blocks, particularly the resulting martensite formation, caused the wires to rupture.

Cold cracking of structural steel weldments is a well-documented failure mechanism, and extensive work has been done to recognize welding and materials selection parameters associated with it. These efforts, however, have not fully eliminated the occurrence of such failures. This article examines a case of cold cracking failure in the construction industry. Fortunately, the failure was identified prior to final erection of the structural members and the weld was successfully reworked. The article explains how various welding parameters, such as electrode/wire selection, joint design, and pre/postheating, played a role in the failure. Human factors and fabrication practices that contributed to the problem are covered as well.

Microstructure, corrosion, and fracture morphologies of prestressed steel wires that failed in service on concrete siphons at the Central Arizona Project (CAP) are discussed. The CAP conveys water for municipal, industrial, and agricultural use through a system of canals, tunnels, and siphons from Lake Havasu to just south of Tucson, AZ. Six siphons were made from prestressed concrete pipe units 6.4 m (21 ft) in diam and 7.7 m long, making them the largest circular precast structures ever built. The pipe was manufactured on site and consisted of a 495-mm thick concrete core, wrapped with ASTM A648 steel prestressing wire. All of the CAP failures evaluated were attributed to corrosion. Longitudinal splits reduced the service life of the pipe significantly by facilitating corrosion and introducing sharp cracks into the microstructure of the wire. A few failures were attributed to general corrosion, where the cross section of the wire is reduced until the strength of the wire is exceeded. Most of the failures evaluated were attributed to stress-corrosion cracking.

A tool used to stretch reinforcement wires in prestressed concrete failed. All eight individual jaws were broken. Visual examination of the fracture surfaces indicated that about half of the broken parts had a partially dendritic appearance. Further, fracture surfaces near the exteriors of the parts were clean and smooth, and there was evidence of a case. Examination of the flat surfaces of the parts revealed surface cracking where actual failure had not occurred. Chemical analysis showed the material to be a low-alloy carburizing steel. The microstructure was compatible with a steel which is cast, carburized, quenched, and tempered. The structure was generally satisfactory, except for the presence of severe shrinkage porosity. It was concluded that the presence of shrinkage porosity in critical areas was the primary cause of fracture. Extremely high hardness indicating a lack of adequate tempering was the secondary cause.

Coiled tubing with 80 ksi yield strength manufactured to a maximum hardness of 22 HRC to meet NACE Standard MR0175 requirement for sour gas service failed after being on 38 jobs (70% of its estimated fatigue life). A transverse crack where a leak occurred was identified as the primary failure point. Numerous OD surface fissures were revealed by a low-power microscope. A brittle zone near the OD, identified as a sulfide stress crack with additional fatigue cracking was revealed by SEM. Sulfide stress cracking defined as brittle failure by cracking under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide was concluded to have initiated the failure which was propagated by fatigue. It was recommended that in the presence of known corrosive environments the tubing should not be used above 50% of its theoretical fatigue life.