Several newly developed liquid propane gas (LPG) cylinders made from Fe-0.13C-0.42Mn steel failed, each fracturing in the longitudinal direction. One of the cylinders was thoroughly analyzed to determine the cause. Deep-drawing flaws were observed on the inner wall of the cylinder, oriented in the direction of the fracture and roughly equal in length. Flaws about 1.3 mm deep, steps, and a chevron pattern were observed on the fractured surface as were cleavage facets, revealed by SEM. Hardness was relatively high and the microstructure near the fracture surface appeared elongated. In addition, the stress intensity factor KI calculated from the value of the internal pressure was lower than that estimated by the fracture toughness test. All of this suggests that the tanks were not sufficiently annealed and prone to brittle fracture. The analysis thus proves that cracks initiated by deep-drawing flaws were the primary cause of failure.

A 2 ft. diam 20 ft. long cylinder with a wall thickness of 1 in. used for the transportation of a compressed gas failed by cracking. The cylinder was forged in a low ally steel. The working pressure was 3000 psi and it had been in service for about seven years. A longitudinal crack, about 2 in. long, developed at the approximate mid-length of the vessel, and allowed slow de-pressurization. Subsequent examination by radiography and ultrasonic means indicated the crack was associated with an irregularly shaped, laminar type of defect located within the wall of the vessel. It was concluded that failure of this vessel resulted from the development of a radial crack orientated in the axial direction. This appeared to have originated on the bore surface in a region where the laminar defect closely approached this surface. The defect was introduced during the manufacture of the vessel, probably originating as a secondary pipe in the ingot which was subsequently displaced and forced into the wall of the vessel during the piercing operation.

Failure of three C22000 commercial bronze rupture discs was caused by mercury embrittlement. The discs were part of flammable gas cylinder safety devices designed to fail in a ductile mode when cylinders experience higher than design pressures. The subject discs failed prematurely below design pressure in a brittle manner. Fractographic examination using SEM indicated that failure occurred intergranularly from the cylinder side. EDS analysis indicated the presence of mercury on the fracture surface and mercury was also detected using scanning auger microprobe (SAM) analysis. The mercury was accidentally introduced into the cylinders during a gas-blending operation through a contaminated blending manifold. Replacement of the contaminated manifold was recommended along with discontinued use of mercury manometers, the original source of mercury contamination.

Two new chrome-plated CDA 377 brass valves intended for inert gas service failed on initial installation. After a pickling operation to clean the metal, the outer surfaces of the valves had been flashed with copper and then plated with nickel and chromium for aesthetic purposes. One of the valves failed by dezincification. The porous copper matrix could not sustain the clamping loads imposed by tightening the pressure relief fitting. The second valve failed by shear overload of the pressure relief fitting. Overload was facilitated by a reduction of cross-sectional area caused by intergranular attack and slight dezincification of the inner bore surface of the fitting. Dezincification and intergranular attack were attributed to excessive exposure to nonoxidizing acids in the pickling bath.

An engine cylinder head failed after operating just 3.2 km (2 mi) because of coolant leakage through the exhaust port. Visual examination of the exhaust ports revealed a casting defect on the No. 7 exhaust-port wall. A 0.9x examination of an unpolished, unetched longitudinal section through the defect indicated shrinkage porosity. This defect was found to interconnect the water jacket and the exhaust gas flow chamber. No cracks were found by magnetic-particle inspection. The gray iron cylinder head had a hardness of 229 HRB on the surface of the bottom deck. The microstructure consisted of type A size 4 flake graphite in a matrix of pearlite with small amounts of ferrite. this evidence supported the conclusion that the cylinder-head failure resulted from the presence of a casting defect (shrinkage) on the No. 7 cylinder exhaust-port wall interconnecting the water jacket with the exhaust-gas flow chamber. No recommendations were made.

Occasional failures were experienced in spool-type valves used in a hydraulic system. When a valve would fail, the close-fitting rotary valve would seize, causing loss of flow control of the hydraulic oil. The rotating spool in the valve was made of 8620 steel and was gas carburized. The cylinder in which the spool fitted was made of 1117 steel, also gas carburized. Investigation (visual inspection, low magnification images, 400x images, metallographic exam, and hardness testing) supported the conclusion that momentary sliding contact between the spool and the cylinder wall caused unstable retained austenite in the failed cylinder to transform to martensite. The increase in volume resulted in sufficient size distortion to cause interference between the cylinder and the spool, seizing, and loss of flow control. The failed parts had been carburized in a process in which the carbon potential was too high, which resulted in a microstructure having excessive retained austenite after heat treatment. Recommendations included modifying the composition of the carburizing atmosphere to yield carburized parts that did not retain significant amounts of austenite when they were heat treated.

Nondestructive metallographic examination of materials frequently must be performed on-site when the component in question cannot be moved or destructively examined. Often, it is imperative that specific microstructural information (i.e., material type, heat treatment condition, homogeneity, etc.) be obtained either before initial use of a component, or before the use of a component can be safely resumed. In this paper, the use of standard metallurgical laboratory equipment, and the procedures required to conduct nondestructive on-site metallographic analyses of engineering materials, is presented. As an example, the materials and metallographic techniques employed in an actual on-site investigation of a gas tungsten-arc weldment joining two large diameter Ti-6Al-4V alloy cylinders are discussed in depth to illustrate what can be accomplished.

Door-closer cylinder castings manufactured of class 30 gray iron were breaking during machining. The manufacturing source reported that a random sampling of castings from this lot had hardnesses from 180 to 210 HRB. Based on the color of the components, heat treatment of these castings was suspected. Metallurgical examination on two representative castings supported the conclusions that the cracks in these gray iron door closers that were present either before or during the heat treatment were attributed to a substandard microstructure of the wrong type of graphite combined with excessive ferrite. This anomalous structure is caused by shortcomings in the foundry practice of chemical composition, solidification, and inoculation control. Judging from the microstructure, the strength of the material was lower than desired for class 30 gray iron, and the suspected heat treatment further reduced the strength. Recommendations included that the chemistry and inoculation should be controlled to produce type A graphite structure. The chemistry control should aim for a carbon equivalent close to 4.3% to achieve adequate fluidity for thin sections and to alleviate gas defects.

Several pressurized air containers (i.e., diving tanks) made of non-heat-treatable Al-5Mg aluminum alloy failed catastrophically. Catastrophic failure occurred when a subcritical stress corrosion crack reached a critical size. Critical crack size for unstable propagation was reached prior to wall penetration, which could have led to subsequent loss of pressure, resulting in explosion of the cylinder. It was recommended that more stress corrosion resistant alloys be used for sea diving applications. Furthermore, cylinders should have a reduced wall thickness that can be determined employing the “leak-before-break” design philosophy, developed using fracture mechanics, to eliminate the possibility of catastrophic ruptures.

A portable propane container with a name-plate soldered onto it exploded in service. When the vessel was inspected afterwards, it was found to have developed a crack in the top end plate. A portion of the end plate cut out to include the midlength and one termination of the crack was examined microscopically. This revealed that the crack was associated with intergranular penetration by molten metal. The microstructure in general was indicative of a good-quality mild steel. It was evident from that solder that was responsible for the penetration and that fused brass from the hand wheel had not played any part. Tensile stress was present at the time of the failure sufficiently high to enable solder penetration to take place. The use of soft solder as a medium for attaching name-plates directly on to stressed steel parts is not recommended. It would be preferable to use a welded-on patch plate or to employ one of the high-strength, non-metallic adhesives.

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.

A nozzle in a wastewater vaporizer began leaking after approximately three years of service with acetic and formic acid wastewaters at 105 deg C (225 deg F) and 414 kPa (60 psig). The shell of the vessel was weld fabricated from 6.4 mm (0.25 in.) E-Brite stainless steel plate and measured 1.5 m (58 in.) in diameter and 8.5 m (28 ft) in length. Investigation (visual inspection, chemical analysis, radiography, dye-penetrant inspection, and hydrostatic testing of all E-Brite welds, 4x images, 100x/200x images electrolytically etched with 10% oxalic acid, and V-notch Charpy testing) supported the conclusion that failure of the nozzle weld was the result of intergranular corrosion caused by the pickup of interstitial elements and subsequent precipitation of chromium carbides and nitrides. Carbon pickup was believed to have been caused by inadequate joint cleaning prior to welding. The increase in the weld nitrogen level was a direct result of inadequate argon gas shielding of the molten weld puddle. Two areas of inadequate shielding were identified: improper gas flow rate for a 19 mm (0.75 in.) diam gas lens nozzle, and contamination of the manifold gas system. Recommendations included changes in the cleaning and welding process.

Metal-induced embrittlement is a phenomenon in which the ductility or fracture stress of a solid metal is reduced by surface contact with another metal in either liquid or solid form. This article summarizes the characteristics of solid metal induced embrittlement (SMIE) and liquid metal induced embrittlement (LMIE). It describes the unique features that assist in arriving at a clear conclusion whether SMIE or LMIE is the most probable cause of the problem. The article briefly reviews some commercial alloy systems where LMIE or SMIE has been documented. It also provides some examples of cracking due to these phenomena, either in manufacturing or in service.

Metal-induced embrittlement is a phenomenon in which the ductility or the fracture stress of a solid metal is reduced by surface contact with another metal in either the liquid or solid form. This article summarizes some of the characteristics of liquid-metal- and solid-metal-induced embrittlement. This phenomenon shares many of these characteristics with other modes of environmentally induced cracking, such as hydrogen embrittlement and stress-corrosion cracking. The discussion covers the occurrence, failure analysis, and service failures of the embrittlement. The article also briefly reviews some commercial alloy systems in which liquid-metal-induced embrittlement or solid-metal-induced embrittlement has been documented and describes some examples of cracking due to these phenomena, either in manufacturing or in service.

This article presents a failure analysis of an aluminum cylinder head on an automotive engine. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head, then propagated through the entire thickness of the component. Metallurgical examination of the crack origin revealed that casting pores played a role in initiating the crack. Stress components, identified by finite element analysis, also played a role, particularly the stresses imposed by the bolt assembly leading to plastic strain. It was concluded that the failure can be prevented by eliminating the bolt hole, using a different type of bolt, or adjusting the fastening torque.

The failures of two aircraft components, one from a landing gear and the other from an ejector rack mechanism, were investigated. Both were made from PH 13-8 Mo (UNS S13800) precipitation-hardening stainless steel which had been heat treated to the H1000 and H950 tempers respectively and then chromium plated. The parts were characterized metallographically and mechanically and were found to be compliant. Detailed fractographic examination revealed that the first stage of both failures was similar: subsurface initiation of numerous cracks with a wide range of orientations and cleavage like features. The cracking was followed by fatigue in one case and catastrophic failure in the other. Hydrogen embrittlement was identified as the most likely mechanism of failure.

A cylindrical spiral gear, part of a locomotive axle assembly, cracked ten days after it had been press-fit onto a shaft, after which it sat in place as other repairs were made. Workers at the locomotive shop reported hearing a sound, and upon inspecting the gear, found a crack extending radially from the bore to the surface of one of the tooth flanks. The crack runs the entire width of the bore, passing through an oil hole in the hub, across the spoke plate and out to the tip of one of the teeth. Design requirements call for the gear teeth to be carburized, while the remaining surfaces, protected by an anti-carburizing coating, stay unchanged. Based on extensive testing, including metallographic examination, microstructural analysis, microhardness testing, and spectroscopy, the oil hole was not protected as required, evidenced by the presence of a case layer. This oversight combined with the observation of intergranular fracture surfaces and the presence of secondary microcracks in the case layer point to hydrogen embrittlement as the primary cause of failure. It is likely that hydrogen absorption occurred during the gas carburizing process.

Initially, two vertical double-acting two-stage compressors delivering chlorine gas at a pressure of 100 psi appeared to be running satisfactorily. About six months later the LP piston-rod of the No. 2 compressor failed due to burning, the compressor being worked double-acting at the time. About five months later, the HP piston rod of the No. 1 compressor failed in a similar manner. Specimens for microscopic examination were cut from the rod in the region of the failure and from the extreme end that had been situated above the piston and hence not subjected to an appreciable rise in temperature. The material was a steel in the normalized condition with a 0.35% C content. It appears probable that deficient lubrication of the gland resulted in overheating of the rod due to friction. The presence of a sprayed-metal coating was probably an additional factor in promoting failure, as it would present to the gas a surface area considerably greater than that of a homogeneous material.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

Distortion failure occurs when a structure or component is deformed so that it can no longer support the load it was intended to carry. Every structure has a load limit beyond which it is considered unsafe or unreliable. Estimation of load limits is an important aspect of design and is commonly computed by classical design or limit analysis. This article discusses the common aspects of failure by distortion with suitable examples. Analysis of a distortion failure often must be thorough and rigorous to determine the root cause of failure and to specify proper corrective action. The article summarizes the general process of distortion failure analysis. It also discusses three types of distortion failures that provide useful insights into the problems of analyzing unusual mechanisms of distortion. These include elastic distortion, ratcheting, and inelastic cyclic buckling.