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.

The crane hook (rated for 13000 kg) failed in the threaded shank while lifting a load of 9072 kg. The metal in the hook was revealed by chemical analysis to be killed 1020 steel. It was disclosed by visual examination that the fracture had at the last thread on the shank and rough machining and chatter marks were evident on the threads. Beach marks that emanated from the thread-root locations on opposite sides of the fracture surface identified these locations to be the origins of the fracture. A medium-coarse slightly acicular structure was revealed by metallographic examination which indicated that the material was in the as-forged condition (which meant lower fatigue strength). The fracture was concluded to have occurred due to stress concentration in the root of the last thread. Normalizing of the crane hook after forging was suggested as a corrective measure. A stress-relief groove with a diam slightly smaller than the root diam was placed at the end of the thread and a large-radius fillet was machined at the change in diameter of the shank.

Several of the welds in a hoist carriage tram-rail assembly fabricated by shielded metal arc welding the leg of a large T-section 1020 steel beam to the leg of a smaller T-section 1050 steel rail failed in one portion of the assembly. Four weld cracks and several indefinite indications were found by magnetic-particle inspection. The cracks were revealed by metallographic examination to have originated in the HAZs in the rail section. Cracks in welds and in HAZs resulting from arcing the electrode adjacent to the weld and weld spatter were also revealed. The tram-rail assembly was concluded to have failed by fatigue cracking in HAZs. The fatigue cracking was initiated and propagated by vibration of the tram rail by movement of the hoist carriage on the rail. As a corrective measure, welding procedures were improved and the replacement rail assemblies were preheated and postheated.

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.

The governor on an aircraft engine failed and upon disassembly of the unit, it was discovered that the retainer for the flyweight pivot pins was broken. The channel-shaped retainer was made of 0.8 mm (0.030 in.) thick 1018 or 1020 steel. The part was plated with copper, which acted as a stop-off during carburizing of the offset, circular thrust-bearing surface surrounding the 16-mm (0.637-in.) diam hole. The bearing surface was case hardened to a depth of 0.05 to 0.1 mm (0.002 to 0.005 in.), then austempered to obtain a minimum hardness of 600 Knoop (1-kg, or 2.2-lb, load). Considerable vibration was created in the installation because of the design of the mechanical device used to transmit power to the governor. The pins were permitted to slide axially a small distance. Analysis (visual inspection, microscopic examination, and ductility measurements) supported the conclusion that failure of the retainer was the result of fatigue caused by vibration in the flyweight assembly. Impact of the pivot pins on the retainer also contributed to failure. Recommendations included redesign of the flyweight assembly, and replacement of the channel-shaped retainer with a spring-clip type of pin retainer.

A hook on a two-leg chain (each 13 mm diam, included angle 60 deg) failed at the junction of the eye and shank while lifting a 4990 kg load. The diam of the hook at this junction was approximately 22 mm. Light intergranular oxidation at the surface on the side of the hook where cracking started was revealed by visual examination of the fracture region. Almost 50% of the fracture surface was found to contain beach marks (indicative of fatigue failure) while the remainder contained cleavage facets. A medium-coarse acicular as-forged structure was revealed by metallographic examination and the metal was showed by chemical analysis to be semikilled 1015 steel. The fatigue fracture was concluded to have initiated in the intergranular oxidation region and the failure of the hook was contributed by the poor fatigue and impact properties of the forged structure. As a corrective measure, the chain-sling hook was replaced with one made of normalized, fully killed, finegrain 1020 steel.

An 1100 aluminum alloy connector of a high-tension aluminum conductor steel-reinforced (ACSR) transmission cable failed after more than 20 years in service, in a region of consider able industrial pollution. The steel core was spliced with a galvanized 1020 carbon steel sheath. Visual examination showed that the connector had undergone considerable plastic deformation and necking before fracture. The steel sheath was severely corroded, and the steel splice was pressed off-center in the axial direction inside the connector. Examination of the fracture surface and micro-structural analysis indicated that the failure was caused by mechanical overload, which occurred because of weakening of the steel support cable by corrosion inside the fitting. The corrosion was ascribed to defective assembly of the connector which allowed moisture penetration.

AM350 stainless steel bellows used in the control rod drive mechanism of a fast breeder reactor failed after 1000 h of service in sodium at 550 deg C (1020 deg F). Helium leak testing indicated that leaks had occurred at various regions of the welded joints between the convolutes in the bellows. The weld failure was attributed to poor quality assurance during fabrication, which resulted in cracklike openings at the fusion zone. The openings extended during tensile loading. Use of proper welding procedures and quality control measures were recommended to prevent future failures.

Two AISI type 316 stainless steel dished ends failed through the formation of intergranular stress-corrosion cracks (IGSCC) within a few months of service. The dished ends failed in the straight portions near the circumferential welds that joined the ends to the cylindrical portions of the vessel. Both dished ends were manufactured from the same batch and were supplied by the same manufacturer One of the dished ends had been exposed to sodium at 550 deg C (1020 deg F) for 500 h before failure due to sodium leakage was detected. The other dished end was used to fabricate a second vessel that was kept in storage for 1 year Clear evidence of sensitization was found in areas where IGSCC occurred. Sensitization was extensive in the dished end that had been exposed to sodium at high temperature, and it occurred in a narrow band similar to that typical of weld decay in the dished end that had been kept in storage. Solution annealing was recommended to relieve residual stress, thereby reducing the probability of failure. It was also recommended that the carbon content of the steel be lowered, i.e., that a 316L grade be used.

A high-pressure steam pipe specified to be P22 low-alloy steel failed after 25 years of service. Located at the end of the steam line, the pipe reportedly received no steam flow during normal service. Visual examination of the failed pipe section revealed a window fracture that appeared brittle in nature. Specimens from the fracture area and from an area well away from the fracture were examined metallographically and chemically analyzed. Results indicated that the pipe had failed by hydrogen damage that resulted in brittle fracture. Chemical analysis indicated that the pipe material was 1020 carbon steel, not P22. The misapplication of pipe material was considered to be a contributing factor. Position of the pipe within the system caused the localized damage.