An oxygen line that was part of a mobile, truck -mounted oxygen-acetylene welding unit exploded in service. Analysis revealed that the failure occurred at the flexible hose-to-valve connection. It was further determined that a steel adapter had been installed at the point of failure to make the connection. Use of the adapter which joined with a brass nipple, created an unacceptable dissimilar metal joint. The steel also provided a source for the generation of sparks. Loctite, a hydrocarbon sealant that is highly flammable and explosive in contact with pure oxygen, had been used to seal the threaded joint. It was recommended that only brass fittings be used to assemble removable joints and that use of washers, sealants, and hydrocarbon lubricants be strictly avoided.

While an attempt was being made to start the diesel engine of a dragline type excavator, a severe explosion took place, the operator unfortunately being killed. The engine was normally started by compressed air from an air bottle or receiver charged to a pressure of 350 psi by a small auxiliary engine driven compressor fitted on the excavators. On an occasion when this had broken down, the air bottle was replenished by the engineer-in-charge from a cylinder of compressed air. The compressor engine remained unserviced and when the starting bottle again became depleted, the excavator operator re-charged it himself from another cylinder without the knowledge of the engineer. The engine was started satisfactorily, and the bottle charged again to 350 psi in readiness for the start on the following day. It was while an attempt was being made to start the engine on this occasion that the explosion took place. The cylinder used by the operator for re-charging the receiver contained not air but oxygen.

Damage to a passenger aircraft that resulted from a midair explosion and subsequent emergency landing was investigated to determine the cause and location of the explosion. Extensive damage had occurred in the front toilet and cockpit areas and to the undercarriage and underside of the aircraft. Fractographic and surface examination of metal fragments (stainless steel and aluminum alloy) from damaged areas indicated that the accident was caused by an explosion in the front toilet. A reconstruction exercise confirmed this conclusion. Damage to the undercarriage and underside resulted from the emergency landing.

After a quick-release fitting of an ejection seat broke, an investigation was performed to determine the manner and cause of crack propagation. Most fractography-based investigations aim to characterize only qualitative characteristics, such as the fracture orientation and origin position, topology, and details of interactions with microstructural features. The aim of this investigation was to use quantitative fractography as a tool to extract information, including striation spacing and size of the stretched zone, in order to make a direct correlation with fracture mechanic concepts. As the crack propagated, striations were created on the fracture surface as a result of service-induced load changes. The size of the striations were measured to estimate crack propagation rate. Remaining lifetime estimates were also made. The dimensions of plastically stretched zones found at the tips of the cracks were evaluated using electron micrograph stereo image pairs to characterize local fracture toughness. To complete the failure analysis, nondestructive evaluation, metallographic examination, and chemical investigations were carried out. No secondary cracks could be found. Most of the broken parts showed that the microstructure, the hardness, and the chemical composition of the Al-alloy were within the specification, but some of the cracked parts were manufactured using a different material than that specified.

A 127 cu m (4,480 cu ft) pressurized railroad tank car burst catastrophically. The railroad tank was approximately 18 m (59 ft) long (from 2:1 elliptical heads), 3 m (10 ft) in OD, and 16 mm (0.63 in.) thick. The chemical and material properties of the tank were to comply with AAR M-128 Grade B. As a result of the explosive failure of the tank car, fragments were ejected from the central region of the car between the support trucks from ground zero to a maximum of approximately 195 m (640 ft). The mode of failure was a brittle fracture originating at a preexisting lamination and crack in the tank wall adjacent to the tank nozzle. The mechanism of failure was overpressurization of the railroad tank car caused by a chemical reaction of the butadiene contents. The interrelationship of the mode, mechanism, and consequences of failure is reviewed to reconstruct the sequence of events that led up to the breach of the railroad tank car. Means to prevent similar reoccurrences are discussed.

On 13 Dec 1994, two massive detonations leveled portions of an ammonium nitrate plant near Sioux City, IA. The primary explosion allegedly occurred in defectively-designed titanium sparger piping inside the neutralizer vessel. Investigation however, revealed the explosion occurred because of unsafe plant operations and poor maintenance procedures. Specifically, the ammonium nitrate within the 18,000 gal capacity neutralizer vessel had become contaminated and made highly acidic. The operators then injected superheated steam directly into the ammonium nitrate in the neutralizer vessel.

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.

An explosion occurred in a portion of a horizontal, U-shaped expansion loop in a steam main approximately 10-in. diam which had been operating at 400 psi for six years. Steam conditions varied from 538 deg C (450 deg F) saturated to 343 deg C (650 deg F) superheated. Fracture occurred longitudinally through the upper wall over a length of approximately 68 in. The sample received for examination was ultrasonically tested, which indicated a band of internal defects extending 1 in. in from the edge. Subsequently, the portion of the pipe embodying the other side of the rupture was obtained for examination. Transverse sections through this and the mating portion already received, followed by magnetic crack detection, revealed the presence of defective zones. Subsequent ultrasonic examination of other sections of the steam main indicated suspect areas in a number of lengths of pipe. These defects were basically laminations of a similar form to those which resulted in the failure of the portion of pipe.

Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.

This article addresses the effects of damage to equipment and structures due to explosions (blast), fire, and heat as well as the methodologies that are used by investigating teams to assess the damage and remaining life of the equipment. It discusses the steps involved in preliminary data collection and preparation. Before discussing the identification, evaluation, and use of explosion damage indicators, the article describes some of the more common events that are considered in incident investigations. The range of scenarios that can occur during explosions and the characteristics of each are also covered. In addition, the article primarily discusses level 1 and level 2 of fire and heat damage assessment and provides information on level 3 assessment.

A fire in a storage yard engulfed several propane delivery trucks, causing one of them to explode. A series of elevated-temperature stress-rupture tears developed along the top of the truck-mounted tank as it was heated by the fire. Unstable fracture then occurred suddenly along the length of the tank and around both end caps, following the girth welds that connect them to the center portion of the tank. The remaining contents of the tank were suddenly released, aerosolized, and combusted, creating a powerful boiling liquid expanding vapor explosion (BLEVE). Based on the metallography of the tank pieces, the approximate tank temperature at the onset of explosion was determined. Metallurgical analysis provided additional insights as well as a framework for making tanks less susceptible to this destructive failure mechanism.