Cylinder fatigue can result from abnormal heating in service. Fatigue can be experienced also by piston heads, exhaust valves, and turbosupercharger housings (castings). Pistons from different engines series can sometimes fit, but because of slight design modifications, they may not function properly. Circumferential cracks and fractures near the head-to- barrel junctions have occurred on numerous cylinders of reciprocating piston engines. In most instances, cracks were caused by high cyclic pressures and high temperatures resulting most probably from detonation. At times, fractures or cracks (or both) were also caused by a combination of unfavorable temperature distribution (and possibly excessive pressures around the cylinder barrel), un-nitrided internal surfaces of cylinder barrels, and inadequate thread contours, which caused high stress concentrations at the thread roots. One example of the most common type of cylinder failure is illustrated.

An eddy current survey of the copper evaporator (chiller) tubes in an absorption air-conditioning unit revealed two tubes in the evaporator bundle with indications typical of longitudinal cracks. Significant necking down and grain distortion at the fracture surfaces was revealed by metallographic examination. The fracture features were found to be characteristic of an overload failure in a ductile material. The ruptured tubes were concluded as a result of examination to have failed as a result of excessive internal pressure. The source of the excessive internal pressure was assumed to be a freeze-up of the tube side water that occurred during interruption of the tube side flow or misoperation of the unit.

Three bearing bosses from the cover of scrap shears were sent in for examination. They had torn off the base plate to which they had been welded by fillet welds all around. Two of these were examined. They showed entirely the same symptoms. The bosses had broken away on three sides along the welds. The cleaved fractures in the burned notches propagated partially above and partially below several incipient cracks which may have been fatigue fractures. Metallographic sections showed that the fractures had occurred either at the burned notches near the transition from the weld to the sheet, or else they ran in the sheet material next to the weld. The quality of the welds could not be judged because the opposite fracture pieces to which they adhered had not been sent in. It was concluded that the breakaway of these bosses was at least favored by overheating and hardening.

A broken cross-recessed die was examined. Examination of the unetched, polished section for impurities revealed several coarse streaks of slag. The purity did not therefore correspond to the requirements set for a high speed tool steel of the given theoretical quality DMo 5. After etching with 5% nital the polished surface exhibited a pronounced, easily-visible, fibrous structure. Microscopic examination revealed that this etch pattern was produced by marked segregation bands. The very unfavorable structure for a high speed steel tool of these dimensions and subject to such stresses together with the low purity favored the fracture of the tool.

An elbow of 70 mm OD and 10 mm wall thickness made from St 35.29, and exposed to 315 atmospheres internal pressure in an oil hydraulic shear installation, cracked lengthwise after a short operating period. Because the stress was not sufficient to explain the fracture of this elbow under this pressure, an investigation was conducted to establish whether material or processing errors had occurred. Microscopic examination showed that a ferritic-pearlitic structure in select locations was very fine-grained. Other signs of fast cooling as compared to normally formed structure of the core zone were noted. It was also possible that the pipe was resting on a cold plate during bending or that it came in touch with a cold tool. This apparently caused the strains at the transition to the cross-sectional part that had been cooled more slowly. The location of the crack at just this point gave rise to the conclusion that it was formed either by the sole or contributive effect of these stresses.

Two 25 x 40 mm (1 x 1.5 in.) AISI 4150 hot-rolled steel bars that cracked during heat treatment were examined to determine whether the heat treating procedure had contributed to the failure. Metallographic examination of a cross section taken through the fracture revealed an oxide coating on both sides of the fracture surface. The oxide was also found on the top and bottom sides of the sample. Sawcut sides of the bar did not exhibit the oxide layer The presence of the oxide in the fracture, combined with its absence on all exterior surfaces, indicated that the fracture occurred as a result of an oxide seam in the original material rather than from oxide from heat treating. Nondestructive testing prior to machining and heat treatment was recommended.

Several cases of failures in gray cast iron paper machine dryer rolls were evaluated. The rolls were found have ground outer cylindrical surfaces on which the paper web is dried. They were found to rotate about their longitudinal axes at speeds from 50 to 250 rpm while containing saturated steam from 35 to 380 kPa. Failures were found to occur in the shell body, in a head near a hand hole or a manhole opening, or in a head near the journal-to-head interface. A cleavage fracture was revealed by scanning electron microscopy regardless of the driving stress for failure. Fracture surface were found to exhibit chevron marks typical of fatigue or raised points or tears pointing in the direction of the probable origin of failure. The characteristics of the thinwall cast iron structures like the variation in composition due to pouring from multiple ladles, variation in solidification rates, and variation in tensile strength to be noted during inspection were described.

A recuperator for blast heating of a cupola furnace became unserviceable because of the brittle fracture of several finned tubes made of heat resistant cast steel containing 1.4C, 2.3Si and 28Cr. The service temperature was reported as 850 deg C. This led to the suspicion that the fracturing had something to do with the precipitation of sigma phase. Metallographic examination showed that the multiaxial stresses caused by sigma phase formation and the related embrittlement was the cause for the fracture of the recuperator. A steel of lower chromium content with no or little tendency for sigma phase formation would have had adequate corrosion resistance at the relatively low service temperature.

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 steel socket pipe conduit NW 150 cracked open during pressure testing next to the weld seam almost along the entire circumference. The crack occurred in part in the penetration notch and in part immediately adjacent to it. While the uncracked pipe showed the light etch shading of a low-carbon steel in which the zone heated during welding was delineated only slightly next to the seam, the other pipe was etched much darker, i.e., higher in carbon, and the heated zone appeared to stand out darkly against the basic material. The overlapping weld was defect-free and dense. The uncracked pipe consisted of soft steel that obviously was made for this purpose, while the cracked pipe consisted of a strongly-hardenable steel which contained not only more carbon and manganese than customary but also a considerable amount of chromium. Therefore, the damage was caused by a mix-up of materials that allowed an unsuitable steel to be used for the weldment.

A series of poppet-valve stems fabricated from 17-4 PH (AISI type 630) stainless steel failed prematurely in service during the development of a large combustion assembly. The poppet valves were part of a scavenging system that evacuated the assembly after each combustion cycle. The function of the valve is to open and close a port; thus, the valve is subjected to both impact and tensile loading. Analysis (visual inspection, hardness testing, and stress analysis) supported the conclusions that the valve stems were impact loaded to stresses in excess of their yield strength. That they failed in the threaded portion also suggests a stress-concentration effect. Recommendations included changing the material spec to a higher-strength material with greater impact strength. In this case, it was recommended that the stems, despite any possible design changes, be manufactured from an alloy such as PH 13-8Mo, which can be processed to a yield strength of 1379 MPa (200 ksi), with impact energies of the order of 81 J (60 ft·lbf) at room temperature.

A forged aluminum alloy 2014-T6 catapult-hook attachment fitting (anodized by the chromic acid process to protect it from corrosion) from a naval aircraft broke in service. Spectrographic analysis, visual examination, microscopic examination, and tensile analysis showed minute cracks on the inside surface of a bearing hole, and small areas of pitting corrosion were visible on the exterior surface of the fitting. The analysis also revealed a small number of rosettes, suggestive of eutectic melting, in an otherwise normal structure. These examinations and analyses support the conclusion that the presence of chromic acid stain on the fracture surface proved that the forging had cracked before anodizing. This suggest that the crack initiated during straightening, either after machining or after heat treatment. The structure and composition of the alloy appear to have been acceptable. Ductility was acceptable so rosettes found in the microstructure are believed to have been nondamaging. Had they contributed to the failure, the ductility would have been very low. The recommendations included inspection for cracks and revising the manufacturing process to include a fluorescent liquid-penetrant inspection before anodizing, because chromic acid destroys the penetrant. This inspection would reduce the possibility of cracked parts being used in service.

An irrigation pipe made of medium-density PE failed during service. This pipe was subjected to severe cyclic-bending strain of the order of 6% while under tensile stress of approximately 6.9 MPa (1000 psi) and a hoop stress of approximately 6.2 MPa (900 psi), far more stringent conditions than those encountered in most applications of PE pipes. Visual inspection and reflected-light optical micrographs were used to plot bandwidth as a function of crack length. The conclusion was that, contrary to the dominant belief that pipe failure initiates from surface defects, a critical size flaw within the pipe wall can also initiate failure as it did in this case. Recommendations included that similarity criteria should be established between the fracture behavior of a component in service and that observed in the laboratory.

A cracked 356 mm (14 in.) diam slip-on flange (Ni-Cr-Mo-V steel) was submitted for failure analysis. Reported results and observations indicated that the flange was not an integral forging or a casting, as specified. It had been fabricated by welding and machining a ring insert within a flange with a larger internal diameter. The flange cracked because the welds between the flange and the insert were inadequate to withstand the bolting pressures. A warning was issued to end users of the flanges, which are being inspected nondestructively for conformance to specifications.

Two sections of a galvanized cable 10.5 A 160 GR +NORM M 9533 (round stranded cable of normal type, h + 6, Langslay, right-handed) were examined. One had a 100 mm long blackish-brown tarnished zone obviously caused by localized heating at one end, inside which the hemp core was missing, and the other corresponded to the original condition of the cable. The cause of the damage was unknown. About a third of the wires had fractured and the rest had been cut. All were tensile fractures with a relatively high degree of necking. The cause of the localized heating was unknown. It can only be concluded from the investigation that the temperature did not exceed the Ac3 point of the wire material, which should be about 750 deg C, and that the heating lasted a fairly long time.

Three radially-cracked disks that circulated the protective gases in a bell-type annealing furnace were examined. During service they had been heated in cycles of 48 h to 720 deg C for 3 h each time, then were kept at temperature for 15 h followed by cooling to 40 deg C in 30 h, while rotating at 1750 rpm. Two disks were cracked at the inner face of the sheet metal rim while the rim of the third was completely cracked through. An analysis of the sheet metal rim of one of the disks showed the following composition: 0.06C, 1.98Si, 25.8Cr, and 35.8Ni. A steel of such high chromium content was susceptible to s-phase formation when annealed under 800 deg C. The material selected was therefore unsuitable for the stress to be anticipated. In view of the required oxidation resistance, a chromium-silicon or chromium-aluminum steel with 6 or 13% Cr would have been adequate. If the high temperature strength of these steels proved inadequate, an alloy lower in chromium would have been preferable.

Cracking was found in the heads on large Yankee dryers, large, cylindrical, rotating, pressurized, high-temperature, cast iron pressure vessels (ASME Boiler and Pressure Vessel Code Section VIII, Rules for Construction of Pressure Vessels), used to remove moisture from sheets of tissue paper during manufacturing. The typical components consist of a cast iron shell, two cast iron concave heads, and a large cast iron internal center stay attached to journals. The heads are attached to the shell and center stay with high-strength bolts. FEA and metallurgical investigation supported the conclusion that the cracking was caused by an unexpected type of load placed on the machine, namely corrosion product buildup at the head/shell interface causing the joint to displace open. It was also found that compressive bolting loads could slightly open the head/shell interface at the periphery. Recommendations included design changes in the head/shell joint, and detailed preventive maintenance inspection procedures were also suggested.

A crane long-travel worm drive shaft was found to be chipped during unpacking after delivery. Chemical analysis showed that the steel (EN36A with a case depth of 1 mm, or 0.04 inch did not meet specifications. Magnetic particle inspection revealed a crack on the side of the shaft opposite the chip. Metallographic examination indicated that the case depth was approximately 2 mm (0.08 in.) and that a repair weld of an earlier chip had been made in the cracked area. The chipping was attributed to excessive case depth and rough handling. It was recommended that the shaft be returned to the manufacturer and a replacement requested.

A 150 cm ID boiler drum made form ASTM A515, grade 70, steel failed during final hydrotesting at a pressure of approximately 26 MPa. Brittle fractures were revealed in between two SA-106C nozzles and remainder was found to involve tearing. Short, flat segments of fracture area, indicative of pre-existing cracks, were revealed by examination of the fracture surface at the drain grooves arc gouged at the nozzle sites. A thin layer of material with a dendritic structure was observed at the groove surface. The dendritic layer was revealed by qualitative microprobe analysis to contain over 1% C, higher than the carbon content of the base metal. The cracks in the drain groove surface could have occurred after arc gouging, during subsequent stress-relieving, or during the hydrostatic test. Flame cutting is not recommended for the type of steel used in the boiler drum because it can lead to local embrittlement and stress raisers, potentially initiating major failures.

In a steel foundry, tensile and bend specimens of castings made in a 2-ton basic arc furnace showed, at irregular intervals, regions with coarse-grained fractures where the specimens broke prematurely, so that the specified strength and toughness values could not be reached. Several cast tensile specimens and some forcibly-broken pieces of the flanges of armature yokes made of cast steel GS C 25 according to DIN 17 245 were investigated. Microscopic examination showed that the cause of damage was the superabundant use of aluminum as deoxidizer. According to recommendations, the aluminum addition was reduced by one-half. Since then, there have been no additional rejects due to insufficient tensile and bend values.