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.

This article discusses the effect of using unsuitable alloys, metallurgical discontinuities, fabrication practices, and stress raisers on the failure of a pressure vessel. It provides information on pressure vessels made of composite materials and their welding practices. The article explains the failure of pressure vessels with emphasis on stress-corrosion cracking, hydrogen embrittlement, brittle and ductile fractures, creep and stress rupture, and fatigue with examples.

The boom lift equalizer hose on an excavator failed and the resultant release of high-pressure hydraulic fluid damaged the operator cabin. The hose was a heavy duty, high-impulse, multiple-spiral wire-reinforced, rubber covered hydraulic hose equivalent to 100R13 specifications as set in AS3791-1991. It had a maximum operating pressure of 34.5 MPa (5000 psi). The failure occurred adjacent to one of the couplings, although some of the wire strands had not broken. The two outer layers of reinforcement wire on the failed end had experienced extensive corrosion, corroding away completely in most areas. This corrosion was fairly uniform around the circumference of the hose. The loss of two spirals/layers of wire reinforcement effectively reduced the pressure carrying capacity of the hose to below that of the maximum operational pressure experienced. Either the hose (or assembly) was already corroded prior to being fitted, or, the hose experienced aggressive conditions causing rapid corrosion of the exposed wire strands.

A copper condenser dashpot in a refrigeration plant failed prematurely. The dashpot was a long tubular component with a cup brazed at each end. Stereomicroscopic examination of the fracture surface at low magnification revealed a typical ductile mode of failure. The failure was attributed to insufficient component thickness, which made the dashpot unable to withstand internal operating pressure, and to extensive annealing in the heat-affected zones of the brazed joints. It was recommended that the condenser dashpot design take into account the annealing effects of brazing. Hydrostatic testing at a pressure times greater than the maximum operating pressure prior to placing the component in service was also suggested.

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.

A heat exchanger failed five years after going into service in an ammonia synthesis plant. Its container, made of Cr-Mo alloy steel (Material No. 1.7362), operated in an environment that did not exceed 400 deg C or 600 atm of hydrogen partial pressure. X-ray examination revealed a fissure in one of the welded seams, which according to microscopic examination, originated in the base material of the container. Higher magnification revealed a narrow zone adjacent to the weld seam permeated with intergranular cracks, the result of hydrogen attack. It also showed the structure to be completely martensitic. Thus, the failure was due to hardening of the base material during welding, and recommendation was made to temper or anneal the welded regions to reduce the effects of hydrogen under pressure.

During autofrettage of a thick-wall steel pressure vessel, a crack developed through the wall of the component. Certain forged pressure vessels are subjected to autofrettage during their manufacture to induce residual compressive stresses at locations where fatigue cracks may initiate. The results of the autofrettage process, which creates a state of plastic strain in the material, is an increase in the fatigue life of the component. Analysis (visual inspection, 50x/500x unetched micrographs, and electron microprobe analysis) supports the conclusion that the fracture toughness of the steel was exceeded, and failure through the wall occurred because of the following reason: the high level of iron oxide found is highly abnormal in vacuum-degassed steels. Included matter of this nature (exogenous) most likely resulted from scale worked into the surface during forging. Therefore, it is understandable that failure occurred during autofrettage when the section containing these defects was subjected to plastic strains. Because the inclusions were sizable, hard, and extremely irregular, this region would effect substantial stress concentration. No recommendations were made.

This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

The bottom flange of a vertical pipe coupled to an isolating valve in a steam supply line to a turbine failed. Steam pressure was 1,500 psi and the temperature 416 deg C (780 deg F). Multiple cracking occurred in the bore of the flange. A quarter-segment was cut out and examined. The cracks were located in the part of the flange that formed a continuation of the pipe bore. The majority of them originated at the end of the flange bore and extended axially along the pipe and radially across the flange face. Magnetic crack detection revealed a further number of cracks in the weld deposit. While the fracture in the weld metal was of the ductile type exhibiting a fine fibrous appearance, that in the flange material was of the cleavage type. Microscopic examination revealed that the cracks were blunt-ended fissures of the type characteristic of corrosion-fatigue. It was concluded that cracking was due to corrosion-fatigue, which arose from the combined effect of a fluctuating tensile stress in the presence of a mildly corrosive environment.

During natural gas drilling in the EMS region in 1956, considerable numbers of longitudinal cracks and transverse fractures occurred in the connecting pieces of the bore rods. The connectors were screwed onto the rods by means of a fine thread and tightly joined with it by shrinkage at 530 deg C. The connectors were made of SAE 4140 Cr-Mo steel. The material for the rod pipes was Fe-0.4C-1Mn steel. Structural stresses played a role in the cracking. Iron sulfide formed on the fracture planes and flake-like stress cracks occurred in the steel. The hydrogen sulfide content of the gas was the cause of damage. Hydrogen liberated by reaction with the iron caused the formation of iron sulfide after penetration of the steel, which had an explosive effect during molecular separation under high pressure. This in turn caused the crack formation in conjunction with the external and residual stresses.

Cavitation damage of diesel engine cylinder liners is due to vibration of the cylinder wall, initiated by slap of the piston under the combined forces of inertia and firing pressure as it passes top dead center. The occurrence on the anti-thrust side may possibly result from bouncing of the piston. The exact mechanism of cavitation damage is not entirely clear. Two schools of thought have developed, one supporting an essentially erosive, and the other an essentially corrosive, mechanism. Measures to prevent, or reduce, cavitation damage should be considered firstly from the aspect of design, attention being given to methods of reducing the amplitude of the liner vibration. Attempts have been made to reduce the severity of attack by attention to the environment. Inhibitors, such as chromates, benzoate/nitrite mixtures, and emulsified oils, have been tried with varying success. Attempts have been made to reduce or prevent cavitation damage by the application of cathodic protection, and this has been found to be effective in certain instances of trouble on propellers.

River water was pumped into a brine plant by a battery of vertical pumps, each operating at 3600 rpm and at a discharge pressure of 827 kPa (120 psi). The pumps were lubricated by means of controlled leakage. The 3.8 cm (1 in.) OD pump sleeves were made of an austenitic stainless steel and were hard faced with a fused nickel-base hardfacing alloy (approximately 58 HRC). Packing for the pumps consisted of a braided PTFE-asbestos material. After several weeks of operation, the pumps began to leak and to spray water over the platforms on which they were mounted at the edge of the river. Analysis supported the conclusions that the leaks were caused by excessive sleeve wear that resulted from the presence of fine, abrasive silt in the river water. The silt, which contained hard particles of silica, could not be filtered out of the inlet water effectively.

Piping and structural components used in space launch facilities such as NASA's Kennedy Space Center and the Air Force's Cape Canaveral Air Station face extreme operating conditions. Launch effluent and residue from solid rocket boosters react with moisture to form hydrochloric acid that settles on exposed surfaces as they are being subjected to severe mechanical loads imparted during lift-off. Failure analyses were performed on 304 stainless steel tubing that ruptured under such conditions, while carrying various gases, including nitrogen, oxygen, and breathing air. Hydrostatic testing indicated a burst strength of 13,500 psi for the intact sections of tubing. Scanning electron microscopy and metallographic examination revealed that the tubing failed due to corrosion pitting exacerbated by stress-corrosion cracking (SCC). The pitting originated on the outer surface of the tube and ranged from superficial to severe, with some pits extending through 75% of the tube's wall thickness. The SCC emanated from the pits and further reduced the service strength of the component until it could no longer sustain the operating pressure and final catastrophic fracture occurred. Corrosion-resistant coatings added after the investigation have proven effective in preventing subsequent such failures.

Corrosion failure occurred in a titanium clad tubesheet because of a corrosive tube-side gas-liquid mixture leaking through fatigue cracks in the seal welds at tube-to-tubesheet joints. The tubesheet was a carbon steel plate clad with titanium on the tube side face. The seal weld cracks were initiated by cyclic stress imposed by exchanger tubes. The gas-liquid mixture passed through cracks under tube-side pressure, resulting in severe corrosion of the steel backing plate. The failure started with the loosening of the expanded tube-to-tubesheet joints. Loose joints allowed the exchanger tubes to impose load on seal welds and the shell side cooling water entered the crevice between the tubesheet and the tubes. The cooling water in the crevice caused galvanic reaction and embrittlement of seal welds. Brittle crack opening and crack propagation in seal welds occurred due to the cyclic stress imposed by the tubes. The cyclic stress arised from the thermal cycling of the heat exchanger. The possible effects of material properties on the failure of the tubesheet are discussed.

After 10 to 20 months of service, the carbon steel hoppers on three trucks used to transport bulk ammonium nitrate prills developed extensive cracking in the upper walls. The prills were discharged from the steel hoppers using air superchargers that generated an unloading pressure of approximately 11 kPa (7 psi). Each hopper truck held from 9,100 to 11,800 kg (10 to 13 tons) of prills when fully loaded and handled approximately 90,700 kg (100 tons) per month. The walls of the hoppers were made of 2.7 mm (0.105 in.) thick flat-rolled carbon steel sheet of structural quality, conforming to ASTM A 245 (obsolete specification replaced by A 570 and A 611). Investigation (visual inspection and 100x micrographs polished and etched with nital) supported the conclusion that failure of the hoppers was the result of intergranular SCC of the sheet-steel walls because of contact with a highly concentrated ammonium nitrate solution. Recommendations included the cost-effective solution of applying a three-coat epoxy-type coating with a total dry thickness of 0.3 mm (0.013 in.) to the interior surfaces of the hoppers.

Failure of a case hardened steel shaft incorporated fuel pump in a turbine-powered aircraft resulted in damage to the aircraft. The disassembled pump was found to be dry and free of any contamination. Damage was exhibited on the pressure side of each spline tooth in the impeller and the relatively smooth cavities and undercutting of the flank on this side indicated that the damage was caused by an erosion or abrasion mechanism. A relatively smooth worn area was formed at the center of each tooth due to an abrasive action and an undulating outline with undercutting was observed on the damaged side. Particles of sand, paint, or plastic, fibers from the cartridge, brass, and steel were viewed in the brown residue on the filter cartridge under a low power microscope and later confirmed by chemical analysis. Large amount of iron was identified by application of a magnet. It was concluded that the combined effect of vibration and abrasive wear by sand and metal particles removed from the splines damaged the shaft. Case hardened spline teeth surface was recommended to increase resistance to wear and abrasion.

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

Erosion of a solid surface can be brought about by liquid droplet impingement (LDI), which is defined as "progressive loss of original material from a solid surface due to continued exposure to erosion by liquid droplets." In this article, the emphasis is placed on the damage mechanism of LDI erosion under the influence of a liquid film and surface roughness and on the prediction of LDI erosion. The fundamentals of LDI and processes involved in initiation of erosion are also discussed.

This article offers an overview of fatigue fundamentals, common fatigue terminology, and examples of damage morphology. It presents a summary of relevant engineering mechanics, cyclic plasticity principles, and perspective on the modern design by analysis (DBA) techniques. The article reviews fatigue assessment methods incorporated in international design and post construction codes and standards, with special emphasis on evaluating welds. Specifically, the stress-life approach, the strain-life approach, and the fracture mechanics (crack growth) approach are described. An overview of high-cycle welded fatigue methods, cycle-counting techniques, and a discussion on ratcheting are also offered. A historical synopsis of fatigue technology advancements and commentary on component design and fabrication strategies to mitigate fatigue damage and improve damage tolerance are provided. Finally, the article presents practical fatigue assessment case studies of in-service equipment (pressure vessels) that employ DBA methods.

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.