A 6 x 19 fiber core steel wire rope failed as it was being used to lower a steel television tower. Fracture of the rope occurred at a point under one of two clips used to fashion a spliced loop that was directly connected to the top of the tower. Microscopic examination of the fracture surfaces and the condition of the individual wires revealed that 59% of the wires failed by shear, 39% failed in tension, and 2% had been cut. In addition, 87% of the wires showed some degree of crushing damage, ranging from mild to severe. The failure was attributed to improper installation of the clips.

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.

An AISI type 303(Se) stainless steel eye terminal that was roll swaged on the end of a 9.5 mm diam wire rope cracked extensively after one year of service. A hairline crack that had initiated at the inner surface of the fitting was revealed by metallographic examination of a sectioned terminal specimen. It was indicated by the holes in the region adjoining the crack and rough texture of the crack surface that a corrosive medium (presumably seawater) had entered the crack from the inner surface of the fitting and coupled with the hairline crack to develop crevice corrosion. The crack propagated toward the outer surface due to high residual stresses in the swaged metal and was followed closely by corrosion. Stress corrosion as result of a combination of residual stresses plus load stress and corrosion was found to cause the failure. Rotary swaging or swaging in a punch press was recommended instead of roll swaging as they made deformation more symmetrical.

The 11 mm diam 8 x 19 fiber-core rope, constructed from improved plow steel wire, on the cleaning-line crane failed while lifting a normal load of coils after five weeks of service. Several broken wires and fraying of the fiber core were revealed by visual examination of a section of the wire rope adjacent to the fracture. Fatigue cracks originating from both sides of the wire were revealed by microscopic examination of a longitudinal section of a wire. The diam of the sheave on the bale (27 cm) was found to be slightly below that specified for the 11 mm diam rope. It was observed that the sudden shock received by the hook in rolling the coils over the edge of the rinse tank after pickling caused vibration which was most severe at the clamped end of the rope. It was concluded that this caused the fatigue failure of the rope. As a corrective measure, the diam of the sheave was increased to 33 cm and pitched roll plates were installed between the tanks where rolling of coils was required.

Locked coil wire ropes, by virtue of their unique design and construction, have specialized applications in aerial ropeways, mine hoist installations, suspension bridge cables, and so forth. In such specialty ropes, the outer layer is constructed of Z-profile wires that provide not only effective interlocking but also a continuous working surface for withstanding in-service wear. The compact construction and fill-factor of locked coil wire ropes make them relatively impervious to the ingress of moisture and render them less vulnerable to corrosion. However, such ropes are comparatively more rigid than conventional wire ropes with fiber cores and therefore are more susceptible to the adverse effects of bending stresses. The reasons for premature in-service wire rope failures are rather complex but frequently may be attributed to inappropriate wire quality and/or abusive operating environment. In either case, a systematic investigation to diagnose precisely the genesis of failure is desirable. This article provides a microstructural insight into the causes of wire breakages on the outer layer of a 40 mm diam locked coil wire rope during service. The study reveals that the breakages of Z-profile wires on the outer rope layer were abrasion induced and accentuated by arrays of fine transverse cracks that developed on a surface martensite layer.

A 13 mm diam 18 x 7 fiber-core improved plow steel nonrotating wire rope, brought into service as a replacement for 6 x 37 improved plow steel ropes, failed after 14 months of service on a stacker crane. The change was reported to have been caused by difficulties twisting of the 6 x 37 rope. The hoist arrangement for this crane was found to consist of one rope with each end attached to a separate drum and the rope was wound around two 30-cm diam sheaves in the block and back up around an equalizer sheave. The rope section that had been in contact with the sheaves was deduced by measurement checks. The presence of broken wire ends, which indicated that the rope failed by fatigue, was revealed by reverse bending of the section of the rope which was normally subjected to this flexing. It was found that minimum sheave diam for a 13-mm 18 x 7 wire rope was 43 cm and hence the currently used smaller sheaves caused excessive bending stresses in the rope. The 18 x 7 rope was replaced by two 6 x 37 side-by-side counter-stranded steel-core ropes as a corrective measure.

The 16 mm diam 6 x 37 fiber-core improved plow steel wire rope on a scrapyard crane failed after two weeks of service under normal loading conditions. This type of rope was made of 0.71 to 0.75% carbon steel wires and a tensile strength of 1696 to 1917 MPa. The rope broke when it was attached to a chain for pulling jammed scrap from the baler. The rope was heavily abraded and several of the individual wires were broken. a uniform cold-drawn microstructure, with patches of untempered martensite in regions of severe abrasion and crown wear was revealed by metallographic examination. As a result of abrasion, a hard layer of martensite was formed on the wire. The wire was made susceptible to fatigue cracking, while bending around the sheave, by this brittle surface layer. The carbon content and tensile strength of the wire was found lower than specifications. As a corrective measure, this wire rope was substituted by the more abrasion resistant 6 x 19 rope.

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.

Mechanical properties of wire ropes, their chemical composition, and the failure analysis process for them are described. The wires are manufactured from high-carbon, plain carbon steel, with high-strength ropes most often manufactured from AISI Grade 1074. During visual failure examination, the rope, strand, and wire diameters should all be measured. Examination should also address the presence or absence of lubricant, corrosion evidence, and gross mechanical damage. Failed wires can exhibit classic cup-and-cone ductile features, flat fatigue features, and various appearances in-between. However, wires are often mechanically damaged after failure. Most nondestructive evaluation (NDE) techniques are not applicable to wire rope failures. Electron microscope fractography of fracture surfaces is essential in failure analysis. Fatigue is the most important fracture mode in wire ropes. Metallographic features of wire ropes that failed because of ductile overload and fatigue are described.

This article focuses on the mechanisms and common causes of failure of metal components in lifting equipment in the following three categories: cranes and bridges, particularly those for outdoor and other low-temperature service; attachments used for direct lifting, such as hooks, chains, wire rope, slings, beams, bales, and trunnions; and built-in members such as shafts, gears, and drums.