A sand-cast steel eye connector used to link together two 54,430 kg capacity floating-bridge pontoons failed prematurely in service. The pontoons were coupled by upper and lower eye and clevis connectors that were pinned together. The eye connector was found to be cast from low-alloy steel conforming to ASTM A 148, grade 150-125. The crack was found to have originated along the lower surface initially penetrating a region of shrinkage porosity. It was observed that cracking then propagated in tension through sound metal and terminated in a shear lip at the top of the eye. The fracture of the eye connector was concluded to have occurred by tensile overload because of shrinkage porosity. Sound metal was ensured by radiographic examination of subsequent castings.

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.

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.

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.

Macrofractographs of the fracture surface from a multibladed fan showed that cracks started at the corner where bending stress was concentrated and propagated through the blade by fatigue. Peak stress at the monitoring position was less than 10 MPa. To simulate crack growth, the rotor was repeatedly deformed by a hydraulic fatigue tester. Comparison of striations of the failed blade with that of the tested one revealed the failed blade was loaded with more than 30 MPa of stress. These tests confirmed that the rotor and blades had sufficient strength to withstand up to 3x the stress of normal operation. The casing of the fan was vibrated at 10 to 60 Hz. Peak stress easily overcame 30 MPa, which was enough to initiate cracking. The fracture surfaces and starting position were the same as those on the failed fan. It was concluded that the exciting force from an air compressor caused blade failure.

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.

Fasteners, made in high-production progressive dies from 0.7 mm thick cold-rolled 1060 steel, were used to secure plastic fabric or webbing to the aluminum framework of outdoor furniture. It was found that approximately 30% of the fasteners cracked and fractured as they were compressed to clamp onto the framework prior to springback. The heat treatment cycle of the fasteners consisted of austenitizing, quenching, tempering to obtain a tempered martensite microstructure, acid cleaning, zinc electroplating, coating with a clear dichromate and thereafter baking to remove the nascent hydrogen. It was revealed that fasteners treated in this manner were brittle due to hydrogen embrittlement as the baking process was found to not be able to remove all the nascent hydrogen which had induced during acid cleaning and electroplating. The heat treatment cycle was modified to produce a bainitic structure and the method of plating the fastener with zinc was changed from electroplating to a mechanical deposition process to thus avoid hydrogen embrittlement.

Mower blades manufactured from grade 1566 high-manganese carbon steel failed a standard 90 deg test. The blades had been austempered and reportedly fractured in a brittle manner during testing. The austempering treatment was intended to produce a bainitic microstructure, but investigation (visual inspection, 2% nital etched 8.9x/196x images) showed that the typical core microstructure contained alternating bands of martensite and bainite. The conclusion was that the nonuniform microstructure was likely responsible for the atypical brittle behavior of the blades, and the observed structure suggests that the austempering heat treatment was performed too close to the nominal martensite start temperature. Recommendations included raising the austempering salt-bath temperature 56 deg C (100 deg F) to account for localized compositional variation.

Housings (being tested as part of a material conversion) from an electrical appliance failed during an engineering evaluation. They had been injection molded from a commercial polycarbonate/PET blend. Parts produced from the previous material, a nylon 6/6 resin, had consistently passed the testing regimen. Grease was applied liberally within the housing assembly during production. Investigation included visual inspection, 24x SEM images, micro-FTIR in the ATR mode, and analysis using DSC. No signs of material contamination were found, but the thermograms showed a crystallization of the PET resin. The grease present within the housing assembly, analyzed using micro-FTIR, was composed of a hydrocarbon-based oil, a phthalate-based oil, lithium stearate, and an amide-based additive. The conclusion was that the appliance housings failed through environmental stress cracking caused by a phthalate-based oil that was not compatible with the PC portion of the resin blend. Thus, the resin conversion was the root cause of the failures. Additionally, during the injection molding process the molded parts had been undercrystallized, reducing their mechanical strength. More importantly, the resin had been degraded, producing a reduction in the molecular weight and reducing both the mechanical integrity and chemical-resistance properties of the parts.

A die-cast zinc adapter used in a snowthrower failed catastrophically in a brittle overload manner. The component had a chemical composition similar to standard zinc alloy ZA-27 (UNS Z35840), although the iron content was much higher and the copper slightly lower. The mechanical properties and alloy designation were not specified. Investigation (visual inspection, 187x SEM images, unetched 30x images, hardness testing, and chemical analysis) of both the failed adapter and an exemplar casting from known-good lot supported the conclusion that the casting failed as a result of brittle overload fracture due to excessive iron-zinc phase and gross porosity. These conditions acted synergistically to reduce the strength of the material. The composition was nonstandard, and the inherent brittleness suggested that it was unlikely that this material was an intentional proprietary alloy. No recommendations were made.

Cerclage wire, which was used with two screws and washers for a tension band in a corrective internal fixation, was found broken at several points and corroded after nine months in service. The material was examined using energy-dispersive x-ray analysis and determined not to be in compliance with standards (type 304 stainless steel without molybdenum). The screws and washers were found to be made of remelted implant-quality type 316L stainless steel and were intact. Signs of sensitization, characterized by chromium carbide precipitates at the grain boundaries, were revealed by the microstructure. Intercrystalline corrosion with pitted grains was indicated by SEM fractography. Improper heat treatment of the steel was interpreted to have led to intercrystalline corrosion and implant separation.

TiN coated back surgery wires were made of Ti-6Al-4V. The reported failure was the presence of pits located in the uncoated area of the wires. The uncoated area of the wire is where the wire is fixtured in the coating chamber during coating. Examination and analysis of the pits using SEM/EDX detection unit revealed significant peaks of B, O, Zr and Fe. Moreover, the shape of the pits was similar to an arc crater. The formation of pits in the wire was caused during coating due to microarcing. A contaminated fixture used during the coating most likely caused the microarcing.

After being in service for ten years, two admiralty brass heat-exchanger tubes from a cooler in a refinery catalytic reforming unit cracked circumferentially in the area of U-bends. A blunt transgranular cracking with minimal branching propagating from the inside surface of the tube was revealed by metallography which was typical of cracking by corrosion fatigue mechanism. Corrosion deposits on both the inside- and outside-diam surfaces were found in the tubes. The presence of copper, zinc, iron, and small amounts of chloride, sulfur, silicon, tin, and manganese was revealed by energy-dispersive analysis of the deposits. It was interpreted by the hardness values (higher than typical for annealed copper tubing) that the tubes may not have been annealed after the U-bends were formed and thus the role of residual stresses in the crack was revealed. It was concluded that the tubes failed by corrosion fatigue initiated by pitting at the inside-diam surface. The tubes were recommended to be annealed after bending to reduce residual stresses from the bending operation to an acceptable level.

A tubular heat exchanger in a refinery reformer unit leaked after one month of service. The exchanger contained 167 type 304 stainless steel U-bent integral-finned tubes. Cracks in the tube wall were revealed during examination. Hardness of the tube was found to be 30 HRC at the inside surface and up to 40 HRC at the base of the fin midway between the roots which indicated that the fins were cold formed and not subsequently annealed thus susceptible to SCC because of a high residual stress level. It was revealed by metallographic examination that the fracture was predominantly by transgranular branched cracking and had originated from the inside surface. It was concluded that the tubes failed in SCC caused by chlorides in the presence of high residual stresses. The finned tubes were ordered in the annealed condition as a corrective measure.

A case of continual product refinement stimulated by product failures was described. Brittle fracture of gas transmission line pipe steels occurred demonstrating a poor combination of materials, environment, manufacturing and installation problems, and loads. Initial efforts were concentrated towards decreasing the Charpy ductile-to-brittle transition temperature to avoid brittle fracture. It was subsequently revealed that the absorbed energy on the upper shelf of the Charpy energy-temperature curve was critical for arresting a moving crack. Both fracture initiation and fracture propagation were needed be controlled. It was concluded that improved steel processing procedures, chiefly hot-working temperature and deformation control, were also required to optimize microstructure and properties.

Several newly developed liquid propane gas (LPG) cylinders made from Fe-0.13C-0.42Mn steel failed, each fracturing in the longitudinal direction. One of the cylinders was thoroughly analyzed to determine the cause. Deep-drawing flaws were observed on the inner wall of the cylinder, oriented in the direction of the fracture and roughly equal in length. Flaws about 1.3 mm deep, steps, and a chevron pattern were observed on the fractured surface as were cleavage facets, revealed by SEM. Hardness was relatively high and the microstructure near the fracture surface appeared elongated. In addition, the stress intensity factor KI calculated from the value of the internal pressure was lower than that estimated by the fracture toughness test. All of this suggests that the tanks were not sufficiently annealed and prone to brittle fracture. The analysis thus proves that cracks initiated by deep-drawing flaws were the primary cause of failure.

Type 316L stainless steel pipes carrying brine at 120 deg C (250 deg F) and at a pH of about 7, failed by perforation at or near circumferential butt-weld seams. The failure was examined optically and radiographically in the field. Specimens were removed and examined metallographically and with a SEM in the laboratory. The examinations revealed a combination of failure mechanisms. The pitting failure of the welds was attributed to localized attack of an activated surface, in which anodic pits corroded rapidly. Additionally, SCC driven by residual welding stresses occurred in the base metal adjacent to the welds. Use of highly stressed austenitic stainless steels in high-chloride environments having a temperature above 65 deg C (150 deg F) should be discouraged. Solution annealing or shot peening to reduce residual stresses may be advisable. If heat treatment is not feasible after welding, the substitution of a more corrosion-resistant alloy, such as Incoloy 800 or 825, may be necessary.

U-shaped leaf springs, intended to serve as spacers between oil tank floats and the inner walls of the containers, broke while being fitted, or after a short time in use, in the bend of the U. The springs were made of tempered strip steel of type C 88 with 0.84 % C, bent at room temperature, and electroplated with cadmium for protection against corrosion. Each fracture showed seven or eight kidney-shaped cracks. At the origins of these cracks on the concave inner surface of the springs, crater-like depressions and beads of melted and resolidified material were found. Fracture of the springs was caused by stress cracks as a consequence of local hardening. The hardening caused by melting and resolidification, and therefore the cracks in the springs, was the result of a faulty procedure during cadmium electroplating.

The genesis of failure of 6.1 mm thick electric resistance welded API 5L X-46 pipes during pretesting at a pressure equivalent to 90% of specified minimum yield strength was investigated. Cracks were found to initiate on the outer surface of the pipes in the fusion zone and propagate along the through-thickness direction. The presence of extensive decarburization and formation of a soft ferrite band within the fusion zone may have contributed to the nucleation of the cracks. Crack propagation was aided by the presence of exogenous inclusions entrapped within the fusion zone. Analysis of these inclusions confirmed the presence of Fe, Si, Ca, and O, indicating slag entrapment to be the most probable culprit.

Several deburring drums that fractured were filled with abrasive, water, and small parts, such as roller bearing rollers, and rotated on their axis at 36 rpm. Cracks were discovered very early in the service lives of these high-chromium white iron cast structures. All of the fractures were through bolt holes in the mounting flange. The holes had a sharp edge and exhibited uneven wear on the inside diameter. In operation, the mounting bolts were frequently found to be loose and in at least one case broken off. A 25x scanning electron microscopy (SEM) fractograph from near this fracture-initiation area showed fatigue striations. No casting or metallurgical structural defects were found that could explain the failures. This evidence supports the conclusion that cracking was a result of the stress-concentration site at the bolt holes where a fatigue-initiated fracture occurred. Recommendations included that the radii be increased at the sharp corners and that lock-wiring be used to secure against bolt loosening.