A portion of the wall of a reactor vessel used in burning impurities from carbon particles failed by localized melting. The vessel was made of Hastelloy X (Ni-22Cr-9Mo-18Fe). Considering the service environment, melting could have been caused either by excessive carburization (which would have lowered the melting point of the alloy markedly) or by overheating. A small specimen containing melted and unmelted metal was removed from the vessel wall and examined metallographically. It was observed that the interface between the melted zone and the unaffected base metal was composed of large grains and enlarged grain boundaries. An area a short distance away from the melted zone was fine grained and relatively free of massive carbides. This evidence supported the conclusion that the vessel failed by melting that resulted from heating to about 1230 to 1260 deg C (2250 to 2300 deg F), which exceeded normal operating temperatures, and carburization was not the principal cause of failure. No recommendations were made.

An air bottle, machined from a solid block of aluminum alloy 2219-T852, displayed liquid-penetrant crack indications after assembly welding. The air bottle was machined to rough shape, a 3.8 mm (0.15 in.) wall thickness cylindrical cup with a 19 mm (3/4 in.) wall thickness integral boss on one side. After annealing, hot spinning, annealing a second time, and tack welding a port fitting, the assembly was torch preheated to 120 to 150 deg C (250 to 300 deg F). The port fitting was then welded in place. Final full heat treatment to the T62 temper was followed by machining, testing, and inspection. The crack indications were found only on one side of the boss and on the lower portion of the hot-spun dome region. The metallographic specimens revealed triangular voids and severe intergranular cracks. The cracks displayed the glossy surfaces typical of melted and resolidified material. The localized cracks in the air bottle were from grain-boundary eutectic melting caused by local torch overheating used in preparation for assembly welding of a port fitting. A change in design was scheduled to semiautomatic welding without the use of preheating for the joining of the port fitting for the dome opening.

A steel pot used as crucible in a magnesium alloy foundry developed a leak that resulted in a fire and caused extensive damage. Hypotheses as to the cause of the leak included a defect in the pot, overuse, overheating, and poor foundry practices. Scanning electron microscopy, transmission electron microscopy, optical microscopy, and x-ray microanalysis in conjunction with dimensional analysis, phase diagrams and thermodynamics considerations were employed to evaluate the various hypotheses. All evidence pointed to an oxide mass in the area where the hole developed, likely introduced during the steelmaking process.

On 16 July 1999, a Boeing 737-800 on final approach for landing sustained a major lightning strike. Damage to the fuselage structure primarily was in the form of melting or partial melting of widely-separated rivets and adjacent Alclad 2024-T3 fuselage skin. The damage was confined to a 0.25-in. (6.4-mm) radii around the affected rivets. The repair process involved removal of the locally-affected material and addition of a skin doubler to restore the aircraft structure to the originally designed condition. Damage features are described briefly.

Ball bearings made of type 440C stainless steel hardened to 60 HRC and suspected as the source of intermittent noise in an office machine were examined. A number of spots on the inner-ring raceway were revealed by scanning electron microscopy. The metal in the area around the spot was evidenced to have been melted and welded to the inner-ring raceway. It was revealed by randomly spaced welded areas on the raceways that the welding was the result of short electrical discharges between the bearing raceways and the balls. The use of an electrically nonconductive lubricant in the bearings was suspected to have caused the electric discharge by accumulation and discharge of static charge. The electrical resistance between the rotor and the motor frame lubricated with electrically conductive grease and the grease used in the current case was measured and compared to confirm the fact the currently used grease was nonconductive. It was concluded that the pits were formed by momentary welding between the ball and ring surfaces. The lubricant was replaced by electrically conductive grease as a corrective measure.

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.

An investigation of the impeller and deposit samples from a centrifugal compressor revealed that an aluminum IR-12 refrigerant reaction had occurred, causing extensive damage to the second-stage impeller and contaminating the internal compressor components. The spherical surface morphology of the impeller fragments suggested that the aluminum had melted and resolidified. The deposits were similar in composition and were identified by XRD as consisting primarily of aluminum trifluoride. In addition, EDS analysis detected major amounts of chlorine and iron. Results of a combustion test indicated that the compressor deposit was comprised of a 9. 8 wt% carbon and that the condenser deposit contained 8.7 wt% carbon. It was concluded that the primary cause of failure was the rubbing of the impeller against the casting and that a self-sustaining Freon fire had occurred in the failed compressor