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.

Stress-corrosion cracking (SCC) is a form of corrosion and produces wastage in that the stress-corrosion cracks penetrate the cross-sectional thickness of a component over time and deteriorate its mechanical strength. Although there are factors common among the different forms of environmentally induced cracking, this article deals only with SCC of metallic components. It begins by presenting terminology and background of SCC. Then, the general characteristics of SCC and the development of conditions for SCC as well as the stages of SCC are covered. The article provides a brief overview of proposed SCC propagation mechanisms. It discusses the processes involved in diagnosing SCC and the prevention and mitigation of SCC. Several engineering alloys are discussed with respect to their susceptibility to SCC. This includes a description of some of the environmental and metallurgical conditions commonly associated with the development of SCC, although not all, and numerous case studies.

A storage tank had been in service at a petrochemical plant for 13 years when inspectors discovered cracks adjacent to weld joints and in the base plate near the foundation. The tank was made from AISI 304 stainless steel and held styrene monomer, a derivative of benzene. The cracks were subsequently welded over with 308 stainless steel filler wire and the base plate was replaced with new material. Soon after, the tank began leaking along the weld bead, triggering a full-scale investigation; spectroscopy, optical and scanning electron microscopy, fractography, SEM-EDS analysis, and microhardness, tensile, and impact testing. The results revealed transgranular cracks in the HAZ and base plate, likely initiated by stresses developed during welding and the presence of chloride from seawater used in the plant. It was also found that the repair weld was improperly done, nor did it include a postweld heat treatment to remove weld sensitization and minimize residual stresses.

A ring-type joint in a reactor pipeline for a hydrocracker unit had failed. Cracks were observed on the flange and the associated ring gasket during an inspection following a periodic shutdown of the unit. The components were manufactured from stabilized grades of austenitic stainless steel; the flange from type 321, and the ring gasket from 347. Examination revealed that the failure occurred by transgranular stress-corrosion cracking, initiated by the presence of polythionic acid. Detailed metallurgical investigation was subsequently conducted to identify what may have caused the formation of polythionic acid in the process gas.

Copper electrical feedthrough pins used in a bolting application in a refrigeration compressor had functioned without failure for years of production and thousands of units. When some of the pins began to fail, an investigation was conducted to determine the cause. Visual examination revealed that the observed fractures were mixed brittle intergranular with ductile microvoid dimples. An extensive analysis of failed samples combined with a process of elimination indicated that the fractures were due to stress-corrosion cracking caused by an unidentified chemical species within the sealed compressor chamber. A unique combination of applied stress, residual stress, stress riser, and grain size helped isolate the failure mechanism to a single production lot of material.

A heat transport pump in a heavy water reactor failed (exhibiting excessive vibration) during a restart following a brief interruption in coolant flow due to a faulty valve. The pump had developed a large crack across the entire length of a bearing journal. An investigation to establish the root cause of the failure included chemical and metallurgical analysis, scanning electron fractography, mechanical property testing, finite element analysis of the shrink fitted journal, and a design review of the assembly fits. The journal failure was attributed to corrosion fatigue. Corrective actions to make the journals less susceptible to future failures were implemented and the process by which they were developed is described.

High-level radioactive wastes generated during the processing of nuclear materials are kept in large underground storage tanks made of low-carbon steel. The wastes consist primarily of concentrated solutions of sodium nitrate and sodium hydroxide. Each of the tanks is equipped with a purge ventilation system designed to continuously remove hydrogen gas and vapors without letting radionuclides escape. Several intergranular cracks were discovered in the vent pipe of one such system. The pipe, made of galvanized steel sheet, connects to an exhaust fan downstream of high-efficiency particulate air filters. The failure analysis investigation concluded that nitrate-induced stress-corrosion cracking was the cause of the failure.

An air system on a marine platform unexpectedly shut down due to the failure of a union nut, which led to an investigation to quantify the material limitations of bronze alloys in corrosive marine environments. The study focused on two alloys: Al-Si bronze, as used in the failed component, and Ni-Al bronze, which has a history of success in naval applications. Material samples were examined using chemical analysis, SEM imaging, and corrosion testing. Investigators also analyzed precracked tension specimens, exposing them to different conditions to quantify stress intensity thresholds for environmentally assisted cracking. Al-Si bronze was found to be susceptible to subcritical intergranular cracking in air and seawater, whereas Ni-Al bronze was unaffected. Both materials, however, are susceptible to cracking in the presence of ammonia, although the subcritical crack growth rate is two to three times higher in Ni-Al bronze. Based on the results of this work, the likelihood of subcritical cracking under various conditions can be reasonably estimated, which, in the case at hand, proved to be quite high.

Coaxial cable connectors made of brass were failing at a high rate after less than one year of service in an outdoor industrial environonment. The observed failures, which consisted of cracks in the body and end cap, were analyzed and found to be brittle fractures due to stress-corrosion cracking. Two common stress-corrosion cracking tests for copper materials were conducted on new connectors from the same manufacturing lot, confirming the initial determination of the fracture mode. Additional testing as was done in the investigation is often helpful when analyzing corrosion failures.

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.

A return bend (made from ASTM A213, grade T11, ferritic steel) from a triolefin-unit heater ruptured after two years in service. The unit operated at 2410 kPa, with a hydrocarbon feed stream (85% propylene) entering at 260 to 290 deg C and leaving at 425 to 480 deg C. The fracture was found to terminate at the welds that joined the bend to the pipeline. A high concentration of both small and large inclusions was exhibited by the metallographic examination of the steel near the fracture. Branched cracks similar to those produced by stress corrosion of steel were observed in a section through the fireside edge of the fracture surface. Scale was observed over most of the crack path which acted as a stress raiser. The effect of the oxide was magnified during thermal cycles because of differential thermal expansion, with the steel having a greater expansion coefficient than the scale. It was recommended that material that is intended for critical applications where failure cannot be tolerated should be non-destructively examined.

A forged pressure vessel made from high temperature austenitic steel X8Cr-Ni-MoVNb 16 13 K (DIN 1.4988) failed. The widest part of the burst had fine cracks on the internal wall running longitudinally. When the internal wall was cleaned, numerous even finer cracks were exposed. On the fracture surfaces in this region an irregularly formed zone was visible in the direction of the internal wall and a fibrous oriented fracture zone towards the external wall. The fracture was typical of stress-corrosion cracking in austenitic steels. Vanadium trichloride was present and tensile stresses were of necessity set up by the internal pressure. Stress-corrosion cracking does not occur if one of the basic requirements is lacking. Because the chloride agent and tensile stresses were inevitably present, the only possible way to prevent future reoccurrence is to forge the entire pressure vessel from a material immune to stress-corrosion cracking or to use interchangeable linings of such a material. A nickel alloy could be considered.

Following disruption of the austenitic stainless steel basket of a hydro-extractor used for the separation of crystals of salt (sodium chloride) from glycerin, samples of the broken parts were analyzed. Examination revealed that the fish-plates joining the reinforcing hoops had broken, the shell had split from top to bottom adjacent to the weld, the top and bottom cover plates had become loose, all the rivets having pulled out, and the shaft was also found to be bent. Fracture took place in an irregular manner and was of the shear type towards both ends; it occurred immediately adjacent to the weld or a short distance from it and on alternate sides. Microscopical examination did not reveal any intergranular carbide precipitation, such as is well known to result in the weld-decay mode of failure. It was concluded that the primary cause of failure was stress-corrosion cracking arising from the combined effect of residual stresses and the corrosive effect of the material being centrifuged. If the shell had been stress-relieved after fabrication, the failure likely would not have occurred.

Weld-decay and stress-corrosion cracking developed in several similar all-welded vessels fabricated from austenitic stainless steel. During a periodic examination cracks were revealed at the external surface of one of the vessels. External patch welds had been applied at these and several other corresponding locations. Cracks visible on the external surface developed from the inside in a region close to the toe of the internal fillet weld to the deflector plate, and another deep crack associated with a weld cavity is visible slightly to the right of the main fissure. Microscopic examination revealed that precipitation of carbides at the grain boundaries had taken place in the vicinity of the cracks, but that the paths of the cracks were not wholly intergranular. Conditions present in the vicinity of the internal fillet weld must have been such as to favor both inter- and transgranular cracking. It is probable that the heating associated with the repair welds made from time to time also contributed to the trouble. The transgranular cracks, however, were indicative of stress-corrosion cracking.

A 680,000 kg (750 ton) per day ammonia unit was shut down following a fire near the outlet of the waste heat exchanger. The fire had resulted from leakage of ammonia from the type 316 stainless steel outlet piping. The outlet piping immediately downstream from the waste heat exchanger consisted of a flange made from a casting, and a reducing cone, a short length of pipe, and a 90 deg elbow, all made of 13 mm thick plate. A liner wrapped with insulation was welded to the smaller end of the reducing cone. All of the piping up to the flange was wrapped with insulation. Investigation (visual inspection, 10x unetched images, liquid-penetrant inspection, and chemical analysis of the insulation) supported the conclusion that the failure occurred in the area of the flange-to-cone weld by SCC as the result of aqueous chlorides leached from the insulation around the liner by condensate. Recommendations included eliminating the chlorides from the system, maintaining the temperature of the outlet stream above the dewpoint at all times, or that replacing the type 316 stainless steel with an alloy such as Incoloy 800 that is more resistant to chloride attack.

Austenitic stainless steel (X 10 Cr-Ni-Mo-Ti 18 10, Material No. 1.4571) cooling coils were found leaking in 15 spots after eight weeks of service in an apparatus in which ammonium sulfide solution was converted into ammonium sulfate. The external temperature of the coil was approximately 175 deg C and it was cooled by water at 3 atm. Examination of two sections of the coil showed pinhead size pitting cavities at the exterior surface and partially parallel and partially angled array of fine cracks on external as well as the internal surfaces of the bend. Metallographic examination conducted on longitudinal and transverse sections showed predominantly transcrystalline cracks, originated from the pits at the external surfaces of the pipe. Their appearance suggested they were stress corrosion cracks that occur in austenitic steels under the combined effect of stresses and certain corrosion agents, especially chlorides. If chlorides were absent, hydrogen sulfide which causes similar pitting and is capable of causing cracks could be suspected. Favorable state of stresses, which could be residual or due to heat treating, bending or straightening operations, would be recommended for better behavior of the container.

A process vessel heating coil, consisting of several 3 ft diam turns, was supplied with steam at 400 psi and a temperature of 343 deg C (650 deg F). At bi-weekly intervals well water was introduced to effect rapid cooling of the contents. After about eight months, leakage developed from a circumferential crack on the underside of the uppermost turn. Shorter cracks were found at a similar location on the bottom turn, and further leakage occurred at pinhole perforations adjacent to the crack in the top turn and near to a butt-weld in the coil. Microscopic examination revealed that the cracks were predominantly of the intergranular variety. In addition, transgranular cracks were present. Material was an austenitic stainless steel of the type specified but the absence of columbium and titanium in significant amounts showed that it was not stabilized against intergranular carbide precipitation. The transgranular cracks indicated that failure was due partly to stress-corrosion. It was concluded that the chlorides provided the main corrodent for both the stress and intercrystalline-corrosion cracking.

Tube sheets (found to be copper alloy C46400, or naval brass, and 5 cm (2 in.) thick) of an air compressor aftercooler were found to be cracked and leaking approximately 12 to 14 months after they had been retubed. Most of the tube sheets had been retubed several times previously because of unrelated tube failures. Sanitary (chlorinated) well water was generally used in the system, although filtered process make-up water (river water) containing ammonia was occasionally used. Investigation (visual inspection, chemical analysis, mercurous nitrate testing, unetched 5X micrographs, and 250X micrographs etched in 10% ammonium persulfate solution) supported the conclusion that the tube sheets failed by SCC as a result of the combined action of internal stresses and a corrosive environment. The internal stresses had been induced by retubing operations, and the environment had become corrosive when ammonia was introduced into the system by the occasional use of process make-up water. Recommendations included making a standard procedure to stress relieve tube sheets before each retubing operation. The stress relieving should be done by heating at 275 deg C (525 deg F) for 30 min and slowly cooling for 3 h to room temperature.

After about four years of service, cracks appeared on the internal or process-side surfaces of four evaporator pans in a sugar concentrator. The pans consisted of a Mo stabilized austenitic stainless steel inner vessel surrounded by a mild steel steam jacket. Corrosion of the external surface had taken place in the form of confluent pitting over a band adjacent to the fillet weld which attached the pan to the blocking ring. Numerous cracks were present in this corroded zone. Microscopical examination of several specimens cut from the sample revealed that the internal cracks in the pan itself originated from the external side of the plate, i.e. from the region covered by the shrouding ring. They were predominantly of the transgranular type. Because the cracks were not of the intergranular type as usually found with weld decay, they were considered to be indicative of stress-corrosion cracking. Stresses responsible for the cracking resulted from weld contraction. The pans had been hosed down periodically with water from local boreholes to remove sugar from the external surfaces, which introduced the corrosive medium.

A corrosion resistant chromium nickel steel (X 2 Cr-Ni-Mo 18 10) worm drive used in a chemical plant at 80 deg C and 100 to 200 atm pressure to transport media containing chloride failed during normal operation. Visual inspections showed that the entire surface of the gear was covered with fine branching cracks and was flaking off. Microscopic examination showed that the unetched polished material had disintegrated to an average depth of 1 mm below the surface. A micrograph of the etched surface revealed numerous deformation lines and transgranular cracking. The failure was thus due to stress-corrosion cracking and additional corrosion due to ventilation elements. Because austenitic chromium nickel steels are prone to stress-corrosion cracking, particularly in the presence of chlorine compounds at high temperatures, and because austenitic rust- and acid-resistant steels are prone to smearing and work hardening during machining, it was recommended that these types of steels be machined only with sharp, short tools mounted in rigid structures. In addition, residual stresses should be eliminated by post-process annealing in a protective atmosphere.