Two broken ball-mill liners from a copper-mine ore operation were submitted for failure analysis. These liners failed prematurely, having reached less than 20% of their expected life. The chemical composition of the liners was within specifications for high-chromium white cast iron. The two broken liners were sand blasted for visual inspection and subsequent metallography and hardness testing. Many cracks were found externally and on the undersides. There were also signs of mechanical damage that occurred inside the mill before detection of the failures. The underside cracking is significant because the user advised that the liners were not backed in the installation. Cracking was present in the microstructures of both liners. These cracks tend to fracture the brittle carbide phase first; once nucleated, the sharp cracks can propagate and grow to critical dimensions, which eventually induces complete failure to the load-bearing section. The premature failure of these liners was caused by severe localized overstress conditions due to localized impact in service. Proper backing of shell liners should be ensured to reduce the effect of impact forces in the ball mill.

Several deburring drums that fractured were filled with abrasive, water, and small parts, such as roller bearing rollers, and rotated on their axis at 36 rpm. Cracks were discovered very early in the service lives of these high-chromium white iron cast structures. All of the fractures were through bolt holes in the mounting flange. The holes had a sharp edge and exhibited uneven wear on the inside diameter. In operation, the mounting bolts were frequently found to be loose and in at least one case broken off. A 25x scanning electron microscopy (SEM) fractograph from near this fracture-initiation area showed fatigue striations. No casting or metallurgical structural defects were found that could explain the failures. This evidence supports the conclusion that cracking was a result of the stress-concentration site at the bolt holes where a fatigue-initiated fracture occurred. Recommendations included that the radii be increased at the sharp corners and that lock-wiring be used to secure against bolt loosening.

A white cast iron water-line plug in a fire sprinkler systems split during leak repair. Examination revealed no material flaws, fatigue, or excessive corrosion. The plug head exhibited signs of excessive loads used in attempts to force the plug farther into the pipe. The evidence obtained indicated that the failure resulted from human error.

A high-chromium white cast iron shell liner installed in an ore crusher sustained impact damage in the course of operation. Visual-optical examination revealed horizontal cracks on the surface of the liner along with particles that had fractured off. Metallographic examination indicated a heavily deformed surface layer with chip formation at the wear surface. The chemical composition of the liner was found to be Fe-2.74C-0.75Mn-0.55Si-0.51Ni-19.4Cr-1.15M. This alloy is highly resistant to abrasive wear, yet at the same time, prone to chipping because little plastic displacement will occur at the surface. The liner failed as a result of severe abrasion caused by the impact of taconite rock. This was a material-selection problem in that the wrong alloy was used for a condition not anticipated in the original choice.

The right front spring hanger on a dual rear axle of the tractor of a tractor-trailer combination failed, causing the vehicle to roll-over. The hanger was made from malleable cast iron that had been heat treated to produce a decarburized surface layer and a pearlitic transition layer. It had been repair welded after breaking into two pieces longitudinally in a prior incident, using cast iron as weld metal. The repair weld bead on both surfaces missed the fracture over 15 to 20% of their lengths. The incomplete repair weld and brittleness of the weld metal and heat-affected zones led to the failure.

Wear, a form of surface deterioration, is a factor in a majority of component failures. This article is primarily concerned with abrasive wear mechanisms such as plastic deformation, cutting, and fragmentation which, at their core, stem from a difference in hardness between contacting surfaces. Adhesive wear, the type of wear that occurs between two mutually soluble materials, is also discussed, as is erosive wear, liquid impingement, and cavitation wear. The article also presents a procedure for failure analysis and provides a number of detailed examples, including jaw-type rock crusher wear, electronic circuit board drill wear, grinding plate wear failure analysis, impact wear of disk cutters, and identification of abrasive wear modes in martensitic steels.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

In this article, we report the outcome of an investigation made to uncover the premature fracture of crusher jaws produced in a local foundry. A crusher jaw that had failed while in service was studied through metallographic techniques to determine the cause of the failure. Our investigation revealed that the reason for the fracture was the presence of large carbides at the grain boundaries and in the grain matrix. This led to the formation of microcracks that propagated along the grain boundaries under in-service working forces. It is also believed that the precipitation of carbides at the grain boundaries may have occurred because of improper heat treatment, but not because of a deficiency in composition.

On 14 April 1912, at 11:40 p.m., Greenland Time, the Royal Mail Ship Titanic on its maiden voyage was proceeding westward at 21.5 knots (40 km/h) when the lookouts on the foremast sighted a massive iceberg estimated to have weighed between 150,000 to 300,000 tons at a distance of 500 m ahead. Immediately, the ship’s engines were reversed and the ship was turned to port (left) in an attempt to avoid the iceberg. In about 40 sec, the ship struck the iceberg below the waterline on its starboard (right) side near the bow. The iceberg raked the hull of the ship for 100 m, destroying the integrity of the six forward watertight compartments. Within 2 h 40 min the RMS Titanic sank. Metallurgical examination and chemical analysis of the steel taken from the Titanic revealed important clues that allow an understanding of the severity of the damage inflicted on the hull. Although the steel was probably as good as was available at the time the ship was constructed, it was very inferior when compared with modern steel. The notch toughness showed a very low value (4 J) for the steel at the water temperature (-2 deg C) in the North Atlantic at the time of the accident.

Door-closer cylinder castings manufactured of class 30 gray iron were breaking during machining. The manufacturing source reported that a random sampling of castings from this lot had hardnesses from 180 to 210 HRB. Based on the color of the components, heat treatment of these castings was suspected. Metallurgical examination on two representative castings supported the conclusions that the cracks in these gray iron door closers that were present either before or during the heat treatment were attributed to a substandard microstructure of the wrong type of graphite combined with excessive ferrite. This anomalous structure is caused by shortcomings in the foundry practice of chemical composition, solidification, and inoculation control. Judging from the microstructure, the strength of the material was lower than desired for class 30 gray iron, and the suspected heat treatment further reduced the strength. Recommendations included that the chemistry and inoculation should be controlled to produce type A graphite structure. The chemistry control should aim for a carbon equivalent close to 4.3% to achieve adequate fluidity for thin sections and to alleviate gas defects.

Two plastic tank floats in separate toilets in one dwelling failed within a relatively brief period of time. Examination of the floats and of a brass connecting rod revealed that the fracture occurred at the base of the threaded hole in the nipple and was brittle in nature. The fracture surfaces were coated with zinc oxide. It was concluded that the failure resulted from improper repairs and/or adjustments, including the use of a cosmetic zinc oxide cream as a lubricant. The cream initiated deterioration of the originally ductile plastic, causing it to become brittle and fragile.

A section of pipe in a hydrocarbon pipeline was found to be leaking. The pipeline was installed several decades earlier and was protected by an external coating of extruded polyethylene and a cathodic protection system. The failed pipe section was made from API 5L X46 line pipe steel, approximately 22 cm (8.7 in.) OD x 0.5 cm (0.2 in.) wall thickness, which was electric resistance welded along the longitudinal seam. The pressure at the time and location of the failure was 2760 kPa, which corresponds to 20% of the specified minimum yield strength. The cause of failure (based on visual inspection, magnetic particle inspection, stereoscopic analysis, scanning electron microscopy, tensile and hardness testing, and chemical analysis) was attributed to damage resulting from a lightning strike.

Component slippage in the left-side final drive train of a tracked military vehicle was detected after the vehicle had been driven 13,700 km (8500 miles) in combined highway and rough-terrain service. The slipping was traced to the mating surfaces of the final drive gear and the adjacent splined coupling sleeve. Specifications included that the gear and coupling be made from 4140 steel bar oil quenched and tempered to a hardness of 265 to 290 HB (equivalent to 27 to 31 HRC) and that the finish-machined parts be single-stage gas nitrided to produce a total case depth of 0.5 mm (0.020 in.) and a minimum surface hardness equivalent to 58 HRC. Investigation (visual inspection, low-magnification images, 500X images of polished sections etched in 2% nital, spectrographic analysis, and hardness testing) supported the conclusion that the failure occurred by crushing, or cracking, of the case as a result of several factors. Recommendations included reducing the high local stresses at the pitch line to an acceptable level with a design modification. Also suggested was specification of a core hardness of 35 to 40 HRC to provide adequate support for the case and to permit attainment of the specified surface hardness of 58 HRC.

Impact or percussive wear is defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another body. Impact wear, however, has many analogies to the field of erosive wear. The main difference is that, in impact wear situations, the bodies tend to be large and contact in a well-defined location in a controlled way, unlike erosion where the eroding particles are small and interact randomly with the target surface. This article describes some generic features and modes of impact wear of metals, ceramics, and polymers. It discusses the processes involved in testing and modeling of impact wear, and includes two case studies.