Banding wires of the rotor of an 1800 hp motor were renewed following replacement of the banding rings. After about six months of service, a breakdown occurred due to bursting of the banding wires in several places. The 0.064 in. diam wire was nonmagnetic and of the 18/8 Cr-Ni type of austenitic stainless steel. The fractures were short and partially crystalline, with no evidence of slowly developing cracks of the fatigue type. Microscopical examination of sections taken through the fractures showed the cracking to be of the multiple branching type. Because the material was in the heavily cold-worked condition, it was not possible to determine with certainty if the cracks were of the inter- or trans-granular type. It was concluded that failure was due to stress-corrosion cracking in a chloride environment. Failure of the wires was likely due to the use of a chloride-containing flux during the soldering operation.

A bomb retaining ring fabricated from type 302 stainless steel unwrapped during a practice flight, causing the bomb fins to deploy. The retaining ring was able to unwrap itself because it was thinner and softer than required. Hardness testing, metallography, and tensile testing confirmed that the component was in the annealed condition and not in the required work-hardened 1/4-hard condition.

Failure analysis was performed on threaded Ti-6Al-4V fasteners that had fractured in the threads during installation. Scanning electron microscopy (SEM) and optical metallography revealed that the fractures initiated in circumferential shear bands present at the thread roots. The fractures propagated by microvoid coalescence typical of that observed in notched tensile specimen fractures of the same material. For comparison, Ti-6Al-4V fasteners from various commercial sources were tested to failure in uniaxial tension and examined in the SEM. In all cases, the fracture appearances were similar to that exhibited by the fasteners that failed during installation. In addition, results of optical microscopy indicated that the geometry and extent of the shear bands appeared to depend on the fabrication process employed by the individual manufacturers. Causes of shear band formation are discussed along with potential methods to eliminate these microstructural in homogeneities.

The connecting end of two forged medium-carbon steel rods used in an application in which they were subjected to severe low-frequency loading failed in service. The fractures extended completely through the connecting end. The surface hardness of the rods was found to be lower than specifications. The fractures were revealed to be in areas of the transition regions that had been rough ground to remove flash along the parting line. The presence of beach marks, indicating fatigue failure, was revealed by examination. The fracture origin was confirmed by the location and curvature of beach marks to be the rough ground surface. An incipient crack 9.5 mm along with several other cracks on one of the fractured rods was revealed by liquid penetration examination. Metallographic examination of the fractured rods indicated a banded structure consisting of zones of ferrite and pearlite. It was established that the incipient cracks found in liquid-penetrant inspection had originated at the surface in the banded region, in areas of ferrite where this constituent had been visibly deformed by grinding. Closer control on the microstructure, hardness of the forgings and smooth finish in critical area was recommended.

A carbon-molybdenum (ASTM A209 Grade T1) steel superheater tube section in an 8.6 MPa (1250 psig) boiler cracked because of long-term overheating damage that resulted from prolonged exposure to metal temperatures between 482 deg C (900 deg F) and 551 deg C (1025 deg F). The outer diameter of the tube exhibited a crack (fissure) oriented approximately 45 deg to the longitudinal axis and 3.8 cm (1.5 in.) long. The inner diameter surface showed a fissure in the same location and orientation. Microstructure at the failure near the outer diameter surface exhibited evidence of creep cracking and creep void formation at the fissure. A nearly continuous band of graphite nodules was observed on the surface of the fissure. In addition to the graphite band formation, the microstructure near the failure exhibited carbide spheroidization from long-term overheating in all the tube regions examined. It was concluded that preferential nucleations of graphite nodules in a series of bands weakened the steel locally, producing preferred fracture paths. Formation of these graphite bands probably expedited the creep failure of the tube. Future failures may be avoided by using low-alloy steels with chromium additions such as ASTM A213 Grade T11 or T22, which are resistant to graphitization damage.

Two failures of AP15A grade J-55 electric resistance welded (ERW) tubing in as our gas environment were investigated. The first failure occurred after 112 days of service. Replacement pipe failed 2 days later. Surface examination of the failed tubing indicated that fracture initiated at the outside surface. Metallographic analysis showed that the fracture originated in the upturned fibers adjacent to the ERW bond line. Cross sections of the weld were removed from three random locations in the test sample. At each location, the up turned fibers of the weld zone contained bands of hard-appearing microstructure. Hardness measurements confirmed these observations. The cracks followed these bands. It was concluded that the tubing failed from sulfide stress cracking, which resulted from bands of susceptible microstructure in the ERW zone. The banded microstructure in the pipe suggested that chemical segregation contributed to the hard areas. Postweld normalized heat treatment apparently did not sufficiently reduce the hardness of these areas.

In 1979, during a routine bridge inspection, a fatigue crack was discovered in the top flange plate of one tie girder in a tied arch bridge crossing the Mississippi River. Metallographic analysis indicated a banding or segregation problem in the middle of the plate, where the carbon content was twice what it should have been. Based on this and results of ultrasonic testing, which revealed that the banding occurred in 24-ft lengths, it was decided to close the bridge and replace the defective steel. The steel used in the construction of this bridge was specified as ASTM A441, commonly used in structural applications. Testing showed an increase in hardness and weight percent carbon and manganese in the banded region. Further testing revealed that the area containing the segregation and coarse grain structure had a lower than expected toughness and a transition temperature 90 deg F higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size.

A cross-recessed die of D5 tool steel fractured in service. The die face was found to be subjected to shear and tensile stresses as a result of the forging pressures from the material being worked. The presence of numerous slag stringers was revealed by microscopic examination of an unetched longitudinal section taken through the die. The pattern was microscopically revealed after etching with 5 % nital to be due to severe chemical segregation or banding. Considerable variation in the hardness, corresponding to the banded and non-banded regions across the face of the specimen was observed. The fracture was found to have originated near the high-stress region of the die face examination of the fracture surface. Failure of the die was concluded to have originated in an area of abnormally high hardness which is prone to microcracking during heat treatment for this grade of tool steel

A set of plastic grips from an electric consumer product failed while in service. The grips had been injection molded from a general-purpose grade of ABS resin. The parts had cracked while in use after apparent embrittlement of the material. Investigation (visual inspection, SEM imaging, and micro-FTIR in the ATR mode) showed that the spectrum representing the grip surface contained absorption bands associated with ABS as well as additional bands of significant intensity. A spectral subtraction removed the bands associated with the ABS resin resulting in a very good match with glyceride derivatives of fats and oils. This supported the conclusion that the grips failed via brittle fracture associated with severe chemical attack of the ABS resin. A significant level of glyceride derivatives of fatty acids, known to degrade ABS resins, was found on the part surface.

The conveyor chain link failed by fracturing through a fabrication weld after some time in service. The link was made of cast low-alloy steel heat treated to a hardness of 285 HRB. The fabrication weld was made using E7018 electrodes. The fracture surfaces were almost entirely covered with beach marks, indicating fatigue cracking. The beach marks emanated from a 6.4 mm (1/4 in.) wide band of unusual appearance running across the center of the fracture. Saw cuts were made perpendicular to both of the fracture surfaces and across the unusual-looking bands. The cut surfaces were ground and etched with ammonium persulfate solution revealing that complete penetration had not been achieved at the weld root. The band observed in the fracture was apparently part of the unfused weld-preparation surface at the root of the weld. This failure was caused by fatigue that initiated at an incomplete penetration defect at the root of the fabrication weld. As a result of this failure, steps were taken to ensure that good welding practice (back-gouging) would be followed in the future fabrication of these links.

A steel lifting eye, manufactured from grade 1144 steel, failed during service. The eye ring fractured in two places, adjacent to the threaded shank and diametrically opposite to this region. Woody overload features, typical for resulfurized steels were revealed by SEM. The directionality of the features was found to be suggestive of shear overload. It was observed that fracture preferentially followed the nonmetallic inclusions. The fracture was revealed to be parallel to the direction of the manganese sulfide stringer inclusions. The presence of significant banding of the ferrite and pearlite microstructure was revealed by etching. It was also observed that the fracture is primarily along the inclusions and through bands of ferrite. It was concluded that the lifting eye failed as a result of overload. Fracture occurred parallel to the rolling direction, through manganese-sulfide stringers and ferrite bands in the base metal matrix. The material used for this application was very anisotropic, exhibiting substantially poorer long and short transverse mechanical properties than longitudinal properties.

Metallographic studies found that steel used to fabricate the U.S.S. Arizona battleship during original construction, 1913-1915 and reconstruction, 1929-1931 were consistent with the best materials available during each time period. Due to the force of the forward magazine detonation, the best steel available today would not have had any impact on the outcome. Heavy banding in steels from both periods could adversely affect the corrosion resistance under anaerobic conditions that prevail during a corrosion cycle that has developed under hard biofouling layers for over 58 years. Banding would have no effect on corrosion rate under aerobic conditions that may occur in local areas on the hull. In the part of the ship from which samples for this report were obtained, high temperatures above 1340 deg F did not occur. Hull plate samples from the submerged wreckage are not yet available. These samples will be important to confirm findings to this time and determine the remaining thickness of the hull plate and, indirectly, the integrity of the fuel oil tanks.

A main steam pipe was found to be leaking due to a large circumferential crack in a pipe-to-fitting weld in one of two steam leads between the superheater outlet nozzles and the turbine stop valves (a line made of SA335-P22 material). The main crack surface was found to be rough, oriented about normal to the outside surface, and had a dark oxidized appearance. The cracking was found to be predominantly intergranular. Distinct shiny bands that etched slower than the remainder of the sample at the top of each individual weld bead were revealed by microscopic examination. These bands were found contain small cracks and microvoids. A mechanism of intergranular creep rupture at elevated temperature was identified as a result of a series of stress-rupture and tensile tests. It was revealed by the crack shape that cracking initiated on the pipe exterior, then propagated inward and in the circumferential direction in response to a bending moment load. It was concluded that the primary cause of failure was the occurrence of bending stresses that exceeded the stress levels predicted by design calculations and that were higher than the maximum allowable primary membrane stress.

A large pressure vessel designed for use in an ammonia plant failed during hydrostatic testing. It was fabricated from ten Mn-Cr-Ni-Mo-V steel plates which were rolled and welded to form ten cylindrical shell sections and three forgings of similar composition. The fracture surfaces were metallographically examined to be typical for brittle steel fracture and associated with the circumferential weld that joined the flange forging to the first shell section. Featureless facets in the HAZ were observed and were revealed to be the fracture-initiation sites. Pronounced banding in the structure of the flange forging was revealed by examination. A greater susceptibility to cracking was interpreted from the higher hardenability found within the bands. Stress relief was concluded to have not been performed at the specified temperature level (by hardness and impact tests) which caused the formation of hard spots. The mode of crack propagation was established by microstructural examination to be transgranular cleavage. It was concluded that failure of the pressure vessel stemmed from the formation of transverse fabrication cracks in the HAZ fostered by the presence of hard spots. It was recommended that normalizing and tempering temperatures be modified and a revised forging practice explored.

Incorrect grounding of an electric motor resulted in electric current passing through a 52100 steel ball bearing and caused multiple arcing between the rolling elements. The multiple arcing developed a pattern on the outer race known as ‘fluting’. A section of ball race outer showed the distinct banding (fluting) resulting from spark discharges while the bearing was rotating. The severe distress of the surface resulted in unacceptable levels of vibration. An SEM photograph of the banded regions showed smoothing of the asperities from continued operation is evident. In the craters the residue of partial melting was seen.

The clapper in a 250 mm diam disk valve (made from ASTM A36 steel, stress relieved and cadmium plated) fractured at the welded joint between the clapper and a 20 mm diam support rod (also made of same material). The valve contained a stream of gas consisting of 55% H2S, 39% CO2, 5% H2, and 1% hydrocarbons at 40 deg C and 55 kPa during operation. Voids on the fracture surface and evidence of incomplete weld penetration were revealed by examination. Brittle fracture was indicated by the overall appearance through some fatigue beach marks were observed. Very narrow bands of high hardness were revealed at the edges of the weld metal. It was revealed by chemical analysis of this band that a stainless steel filler metal had been used which produced mixed composition at the weld boundaries. The plating material was revealed to be nickel by chemical analysis. It was concluded that clapper failed by fatigue and brittle fracture because it was welded with an incorrect filler metal. A clapper assembly was welded with a low-carbon steel filler metal, then cadmium plated.