The types of metal components used in lifting equipment include gears, shafts, drums and sheaves, brakes, brake wheels, couplings, bearings, wheels, electrical switchgear, chains, wire rope, and hooks. This article primarily deals with many of these metal components of lifting equipment in three categories: cranes and bridges, attachments used for direct lifting, and built-in members of lifting equipment. It first reviews the mechanisms, origins, and investigation of failures. Then the article describes the materials used for lifting equipment, followed by a section explaining the failure analysis of wire ropes and the failure of wire ropes due to corrosion, a common cause of wire-rope failure. Further, it reviews the characteristics of shock loading, abrasive wear, and stress-corrosion cracking of a wire rope. Then, the article provides information on the failure analysis of chains, hooks, shafts, and cranes and related members.

A wire hoisting rope on a drilling rig failed during a lift, after a few cycles of operation, causing extensive damage to support structures. The failure investigation that followed included mechanical property testing and chemical, metallurgical, and finite element analysis. The rope was made from multiple strands of 1095 steel wire. Its chemical composition, ferrite-pearlite structure, and high hardness indicate that the wire is a type of extra improved plow steel (EEIPS grade). The morphologies of the fracture surfaces suggest that the wires were subjected to tensile overloading. This was confirmed by finite element analysis, which also revealed compressive contact stresses between the wires and between the rope and sheave surface. Based on the results, it was concluded that a tensile overload, due to the combined effect of a sudden load and undersized sheave, is what ultimately caused the rope to fail.

Failed ferrous components were analyzed from a crane that operated on an offshore platform. The crane failed during operation and fell into the sea. The brake spring on the boom hoist was found to have fractured in four places. The spring contained a line defect (seam) that was the source of each crack. The fracture of the oil quenched and tempered (HRC 50 ASTM A229) spring was by stress-corrosion cracking after the crane fell into the sea because fatigue cannot account for the fractures observed. The crane failure was caused by an overload created by the operator catching a free-falling load.

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.

A stepped drive axle (hardened and tempered resulfurized 4150 steel forging) used in a high-speed electric overhead crane (rated at 6800 kg, or 7 tons, and handling about 220 lifts/day with each lift averaging 3625 to 5440 kg, or 4 to 6 tons) broke after 15 months of service. Visual examination of the fracture surface revealed three fracture regions. The primary fracture occurred approximately 50 mm (2 in.) from the driven end of the large-diam keywayed section on the stepped axle and approximately 38 mm (1 in.) from one end of the keyway where the crane wheel was keyed to the axle. Macroscopic, microscopic, and chemical examination revealed composition that was basically within the normal range for 4150 steel. This evidence supports the conclusion that cracking initiated at a location approximately opposite the keyway, and final fracture was due to mixed ductile and brittle fracture. Axial shift of the crane wheel during operation, because of insufficient interference fit, was the major cause of fatigue cracking. Recommendations included redesigning the axle to increase the critical diameter from 140 to 150 mm (5.5 to 6 in.) and to add a narrow shoulder to keep the drive wheel from shifting during operation.

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.

The T-section cross member of the lifting sling failed in service while lifting a 966 kg (2130 lb) load. The L-section sling body and the cross member were made of aluminum alloy 5083 or 5086 and were joined by welding using aluminum alloy 4043 filler metal. The fracture was found by visual examination to have occurred at the weld joining the sling body and the cross member. Inadequate joint penetration and porosity was revealed by macrographic examination of the weld. Lower silicon content and a higher magnesium and manganese content than the normal for alloy 4043 filler metal were found during chemical analysis. It was revealed by examination of the ends of the failed cross member that a rotational force that had been applied on the cross member caused it to fracture near the sling body. It was concluded that brittle fracture at the weld was caused by overloading which was attributed to the misalignment of the sling during loading. Aluminum alloy 5183 or 5356 filler metal was recommended to be used to avoid brittle welds.

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.

A 10,890-kg coil hook torch cut from 1040 steel plate failed while lifting a load of 13,600 kg after eight years of service. The normal ironing (wear) marks were exhibited by the inner surface of the hook. It was revealed by visual examination that cracking had originated at the inside radius of the hook. Beach marks (typical of fatigue fracture) were found extending over approximately 20% of the fracture surface. Numerous cracks were revealed by macroscopic examination of the torch-cut surfaces. It was revealed by macrograph of an etched specimen that the cracks had initiated in a hardened martensitic zone at the torch-cut surface and had extended up to the coarse pearlite structure beneath the martensitic zone. The fatigue fracture was concluded to have initiated in the brittle martensitic surface while failure was contributed by the 25% overload. As a corrective measure, the coil hooks were flame cut from ASTM A242 fine-grain steel plate, ground to remove the material damaged by flame cutting and stress relieved at 620 deg C.

A shaft which carried the diverter sheave wheel of an electric goods lift failed, resulting in the cage failing to the bottom of the well. Failure had taken place at a reduction in diam at which no filet radius existed. Metallurgical examination did not disclose any abnormal features. The material was a mild steel in the normalized condition. The appearance of the fracture indicated failure was due to bending stresses. The absence of any fillet radius at the reduction in diam provided a region of stress concentration from which fatigue cracks developed.

During the lifting of a piece of machinery by means of an overhead travelling crane the hook fractured suddenly. The load was attached to the hook by means of fiber rope slings and rupture occurred in a plane which appeared to coincide with the sling loop nearest to the back of the hook. The rated capacity of the crane was 15 tons. At the time of the mishap it was being used to lift one end of a hydraulic cylinder with a total weight of about 27 tons. Fracture was of the cleavage type throughout. There was no evidence of any prior deformation of the material in the vicinity, nor was there any indication of a pre-existing crack or major discontinuity at the point of origin. A sulfur print suggested the hook had been forged from a billet cogged down from an ingot of semi-killed steel. Failure of this hook was attributed to strain-age embrittlement of the material at the surface of the intrados.

A bridge wheel from a 272,160 kg stripper crane fractured in the web near the rim after one year of service. The wheel was forged from 1055 steel, and the tread, hub faces, and hub bore were machined. Beach marks indicative of fatigue at ten locations were revealed by macroscopic examination of the fracture surfaces. The surface of the web was heavily scaled and decarburized. A gross forging defect extending about 1.8 mm along the fracture surface was disclosed by examination of a micrograph of a section through one of the fatigue origins. Shallower forging defects were visible along the web surface. Fatigue cracking of the wheel was initiated at forging defects in the web. Replacement wheels were machined all over and were magnetic particle inspected to detect any cracks that could act as stress raisers.

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.

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.

A resistance-welded chain link made from 16 mm diam 4615 steel failed while lowering a 9070 kg load of billets into a rail car after being in service for 13 months. Beach marks, typical of fatigue were found to have originated at the inside of the link which broke at the weld. Cracks in the weld zone (up to 1.2 mm deep) were revealed during metallographic examination of a section through the fracture surface. The cracks were filled with scale which indicated that they had formed during resistance welding of the link. The defect was thus attributed to the weld defects which initiated the fatigue failure by acting as stress raisers. The welding method was changed by the manufacturer and all chains were replaced with defect free chains.

Several thousands of new 16 mm diam alloy steel sling chains used for handling billets failed by chain-link fractures. No failures were found to have occurred before delivery of the new chains. It was observed that the links had broken at the weld. It was found that all failures had occurred in links having hardness values in the range of 375 to 444 HRB. It was revealed by the supplier that the previous hardness level of 302 to 375 HRB was increased to minimize wear which made the links were made notch sensitive and resulted in fractures that initiated at the butt-weld flash on the inside surfaces of the links. A further reduction in ductility was believed to have been caused by lower temperatures during winter months. Thus, the failure was concluded to have been caused in a brittle manner caused by the notch sensitivity of the high hardness material at lower temperatures. The chains were retempered to a hardness of 302 to 375 HRB as a corrective measure and subsequently ordered chains had this hardness as a requirement.

A ductile iron T-hook hook was reported to have fractured in service. It was further reported that the hook had been subjected to a load that did not exceed 5900 kg (13,000 lb) at the time of fracture. No information was provided regarding the type of metal used to manufacture the hook. A failure analysis was requested to determine the cause of fracture. Two hooks were submitted for examination. Analysis (visual inspection, 2.7x light fractography, chemical analysis, 110x SEM fractography, 27x/110x/215x nital-etched micrographs) supported the conclusions that this component fractured in service as a consequence of ductile tensile overload. Evidence indicates that the fractured region was subjected to a load exceeding the capacity of the material. Because the information available from the service application indicated that the component had not been subjected to a stress that exceeded 5900 kg (13,000 lb), the observations made in this investigation suggested that either the load was underestimated or that the indicated load was applied at a more rapid rate (perhaps with a jerk), which would tend to increase the effective force of the load.

A drum pinion shaft (1030 steel) which was part of the hoisting gear of a crane (capacity 18,140-kg) operating in a blooming mill failed while lifting a 9070 kg load. Chatter marks, rough-machining marks, and sharp corner radii were revealed in the keyway which extended into a shoulder at a change in diam. A circular recess below the keyway surface was revealed at each end of the keyway. A sharp corner at the end of the keyway was revealed by examination to be the origin of fracture. Beach marks were found radiating from the origin over a large portion of the fracture surface which confirmed failure of the shaft by fatigue fracture. As a corrective measure the shaft was replaced with one made of 4140 steel, quenched and tempered to a hardness of 286 to 319 HRB. The keyway was moved away from the change in section and was machined with a 1.6-mm radius in the bottom corners and a larger-radius fillet was machined at the change in section.

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.