High-horsepower electric motors were utilized to drive large compressors (made of 4340 steel shafts and gear-type couplings) required in a manufacturing process. The load was transmitted by two keys 180 deg apart. Six of the eight compressor shafts were found cracked in a keyway and one of them fractured after a few months of operation. Visual examination of fractured shaft revealed that the cracks originated from one of the keyways and propagated circumferentially around the shaft. The shaft and coupling slippage was indicated by the upset keys and this type of fracture. The shaft surface both near and in the keyways indicated fretting which greatly reduced the fatigue limit of the shaft metal and initiated fatigue cracks. Fatigue marks were observed on the fractured key. Repetitive impact loading was responsible for propagation of the cracks. The high cyclic bending stresses were caused by misalignment between the electric motor and compressor and were transmitted to the shaft through the geared coupling. Flexible-disk couplings capable of transmitting the required horsepower were installed on the shafts as a corrective measure.

One of six cables on a passenger elevator was found fractured during a routine inspection. The cable is made of 16-mm steel wire rope designated 8 x 19 G Preformed Extra High Strength Special Traction Elevator Cable with fiber core. Samples of wire from the cable revealed two types of fractures: flat-type fractures were observed in 1.2 and 1 mm diam wires and cup-and-cone fractures were observed in 0.6 mm diam wires. A nick observed in the side of one of the larger wires was found to be rusted. Beach marks radiating inward, indicative of fatigue cracking, were also revealed. The smaller wires were found to be slightly oxidized and behaved in a ductile manner under excessive loads before ultimate failure. Flat-type fractures were believed to have resulted from cyclic torsional stresses along with longitudinal cracking. Restriction of free movement of the socket-end in the shackle was found to have promoted fracture due to increased magnitude of stresses. Mechanical damage to surfaces of wires was concluded to be sufficient to cause fatigue cracking under the stresses encountered in service.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.