A portion of the roof of a single story building collapsed during a thunder storm. A failure analysis was conducted to determine whether this structural failure was due to improper design, substandard construction materials, faulty erection, or extreme weather conditions. The failure analysis consisted of an onsite inspection, macrofractographic examination of the fractures where the girders were welded to the columns, macrofractographic examination of the fractured trusses, metallographic examination of the girder and truss materials, chemical analysis of the low-carbon steel girder and truss materials, and mechanical testing of the truss material. It was concluded that substandard structural components in combination with faulty construction was responsible for this service failure.

A type 17-4PH stainless steel tube exhibited brown discoloration after a pickling operation. EDS analysis of the extracted substance revealed relatively high levels of iron and chromium, along with lower amounts of aluminum, silicon, sulfur, chlorine, calcium, manganese, and nickel. The iron, chromium, and nickel are likely in the form of dissolution products from the pickling solution. FTIR analysis revealed the presence of polypropylene and poly(ethylene:propylene). The EDS results showed that the discoloration of the tube was associated with oxidation products of the tube material, as well as adherent organic residue. Analysis by FTIR of the residue revealed detectable levels of two polymeric substances, which were later determined to be construction materials of the pickling tank. It was recommended that more frequent cleaning and/or replacement of the pickling solution be put into place and another type of tank material be considered.

Although field corrosion tests had indicated that type 316L stainless steel would be a suitable material for neutralization tanks, the vessels suffered severe corrosion when placed in service. Welded coupons of type 316L had been tested along with similar Alloy 20Cb® (UNS NO8020) specimens in a lead-lined tank equipped with copper coils that had served in this function prior to construction of the new tanks. Both materials exhibited virtually no corrosion and no preferential weld attack. Type 316L was selected for the project. The subsequent corrosion was the result of the borderline passivity of type 316L in hot dilute sulfuric acid (about 0.1%). Inaccuracy of the testing was attributed to the presence of cupric ions in the lead-lined vessel fluids, which had been released by corrosion of the copper coils. Careful control of both temperature and pH was recommended to reduce the corrosion to an acceptable limit.

Cold cracking of structural steel weldments is a well-documented failure mechanism, and extensive work has been done to recognize welding and materials selection parameters associated with it. These efforts, however, have not fully eliminated the occurrence of such failures. This article examines a case of cold cracking failure in the construction industry. Fortunately, the failure was identified prior to final erection of the structural members and the weld was successfully reworked. The article explains how various welding parameters, such as electrode/wire selection, joint design, and pre/postheating, played a role in the failure. Human factors and fabrication practices that contributed to the problem are covered as well.

In a shipyard one of the two posts of a loading gear fractured under a comparatively small load at the point where it was welded into the ship’s deck. The post consisted of several pipe lengths that were produced by longitudinal seam welding of 27 mm thick sheets. The sheet metal was a construction steel of 60 to 75 kp/sq mm strength. Thick-walled parts of steels of such high strength must be preheated to approximately 200 deg C along the edges prior to welding to minimize the strong heat losses by the cold mass of the part. In the case under investigation this either was not done at all or the preheating was not high enough or sufficiently uniform. This damage was therefore caused by a welding defect.

A recuperator for blast heating of a cupola furnace became unserviceable because of the brittle fracture of several finned tubes made of heat resistant cast steel containing 1.4C, 2.3Si and 28Cr. The service temperature was reported as 850 deg C. This led to the suspicion that the fracturing had something to do with the precipitation of sigma phase. Metallographic examination showed that the multiaxial stresses caused by sigma phase formation and the related embrittlement was the cause for the fracture of the recuperator. A steel of lower chromium content with no or little tendency for sigma phase formation would have had adequate corrosion resistance at the relatively low service temperature.

A failed laser mirror and another complete mirror of the same construction were analyzed. The laser mirror consisted of three layers of material brazed together to form channels through which the cooling water flows. Samples were analyzed with light optical and scanning electron microscopy. The corrosion product contained molybdenum and copper with a trace of gold. The base material was analyzed as molybdenum with negligible alloying additions. The primary mode of corrosion attack on the base material appeared to be intergranular, although uniform corrosion was evident also. It was concluded that corrosion attack sufficiently weakened the base material and the brazed joints, allowing catastrophic failure of the mirror due to the pressure of the cooling water. It was recommended that the mirrors be cleaned of all corrosion products present as a result of past service conditions and proof tested. It was recommended that the water system consisting of deionized water and formaldehyde be replaced with water having a low oxygen content and a cathodic inhibitor (oxygen scavenger).

The interior of a cylindrical tank used for the road transport of concentrated sulfuric acid revealed severe blistering of the plates, mainly over the crown and more particularly on the first ring. The tank, made in 1958, was of welded construction, the material being mild steel plate. Some of the blisters were pierced by drilling a hole in the center and at the same time applying a small flame. In several cases combustion of the escaping gas caused minor explosions, a result characteristic of hydrogen. Etching showed the material to be a low-carbon steel in the partly spheroidized condition. There was no evidence of cracking of the material in the region of the blisters and bend tests demonstrated it possessed satisfactory ductility. The primary cause of the blistering was ascribed to the presence of discontinuities within the plate. This provided cavities in which the hydrogen was able to accumulate and build up pressure. Had the material been free from discontinuities of appreciable size, the blistering would not have occurred.

Erosion of solid surfaces can be brought about solely by liquids in two ways: from damage induced by formation and subsequent collapse of voids or cavities within the liquid, and from high-velocity impacts between a solid surface and liquid droplets. The former process is called cavitation erosion and the latter is liquid-droplet erosion. This article emphasizes on manifestations of damage and ways to minimize or repair these types of liquid impact damage, with illustrations.

This article focuses on failure analyses of aircraft components from a metallurgical and materials engineering standpoint, which considers the interdependence of processing, structure, properties, and performance of materials. It discusses methodologies for conducting aircraft investigations and inspections and emphasizes cases where metallurgical or materials contributions were causal to an accident event. The article highlights how the failure of a component or system can affect the associated systems and the overall aircraft. The case studies in this article provide examples of aircraft component and system-level failures that resulted from various factors, including operational stresses, environmental effects, improper maintenance/inspection/repair, construction and installation issues, manufacturing issues, and inadequate design.

Corrosion in a closed-loop cooling water system constructed of austenitic stainless steel occurred during an extended lay up of the system with biologically contaminated water. The characteristics of the failure were those of microbiologically influenced corrosion (MIC). The corrosion occurred at welds and consisted of large subsurface void formations with pinhole penetrations of the surfaces. Corrosive attack initiated in the heat affected zones of the welds, usually immediately adjacent to fusion lines. Stepwise grinding, polishing, and etching through the affected areas revealed that voids generally grew in the wrought material by uniform general corrosion. Tunneling or worm-holing was also observed, whereby void extension occurred by initiating daughter voids probably at flaws or other inhomogeneities. Selective attack occurred within the fusion zone, i.e., within the cast two-phase structure of the weld filler itself. The result was a void wall which consisted of a rough and porous ferritic material, a consequence of preferential attack of the austenitic phase and slightly lower rate of corrosive attack of the ferrite phase. The three-dimensional spongy surface was studied optically and with the scanning electron microscope.

A longeron assembly constructed of Alclad 2024, some parts being in the T3 condition, others in the T42 condition, failed at a rivet hole. Plastic deformation at the crack site was found, but no plastic deformation was found in similar failed components. It was concluded that the numerous hairline cracks in the Alclad layer adjacent to the main fracture were fatigue cracks. In another case, bonded samples of 2024-T3 sheet were fatigue tested at various stress levels. Failures could be separated into three groups: those that failed in the adhesive bond, those that failed in the base material, and those that exhibited a dual failure. The last category failed in the adhesive bond and also showed a type of pitting on one face of the base material. In a third case, a 2024-T4 extrusion section was found to exhibit blistering after chemical milling. The presence of interconnecting microcracks between adjacent discontinuities supported a hydrogen blistering diagnosis.

Two bolts from the stressed structure of a church building that had broken during stressing were examined to establish the cause of fracture. The fracture of one of the first bolt occurred in a double-vee groove weld whose root was not completely welded. The second bolt had cracked outside of the weld seam closely under the head. Neither one had been particularly deformed before fracture. The composition of the head pieces corresponded approximately to manganese steel (Material No. 1 0845), a weldable construction steel with increased yield point and strength, while the shafts were made from Cr-Mo steel (Material No. 1.7225) according to DIN 17200. It was found that the bolts were not made from a suitable alloy steel, but were welded together from two unsuitable steels, one of which lacked sufficient strength. The austenitic weld seams showed hot tears and were not welded through to the root. Also, the pieces were not preheated before welding, so that stress cracks occurred in the transition zones. The second bolt was overstressed during the impact caused by the breaking of the first bolt.

Two Z-shape impeller vanes failed. The vane material was 14-hard type 301 stainless steel. The vanes were of two-piece construction, with a longitudinal weld. Analyses indicated that the vanes had not been solution annealed after welding, leaving the heat-affected zone above the welds in a highly sensitized state. The sensitized material lost corrosion resistance, became embrittled along the grain boundaries, and finally failed by intergranular cracking. Use of type 410 martensitic stainless steel was recommended.

A ceiling in a concrete structure was hung on flat bars with a cross section of 30 x 80 mm. The bars were borne by a slit steel plate and supported by tabs that were welded onto the flat sides. One of the bars fractured during mounting when it was dropped from a height of about 1 m onto the opposite support. The fracture was a grainy forced rupture that propagated from one of the fillet welds. Investigation showed a steel was selected for this important construction that was prone to aging and that in fact had aged through cold deformation during straightening and then was welded yet. The bar could withstand mounting and subsequent static loading as long as it was treated with care, as could be expected from the good deformation characteristics of the static tensile test. The question is, however, whether occasional impacts or shocks can be assuredly avoided. This risk could have been eliminated if a killed steel of quality groups 2 or 3 according to DIN 17 100 had been used.

Thermal and transformation stresses, resulting from welding, adding up with operational stresses can result in failure. Examples involving the crankshaft of a shaft-drive to produce artificial waves in a swimming pool, the joint bar of a dredger cast out of a running non-alloyed steel with 39 kg/sq mm tensile strength, which had been strengthened by welding plate strips on both sides had fractured in service; an axle tube out of 40 Mn 4 after DIN 17 200 from a paper fabrication machine, which had three short longitudinal slits distributed uniformly over its surface; welding to repair worn out bearing or fits, and a broken rear axle tube of a bus are described.

Crane collapse due to bolt fatigue and fatigue failure of a crane support column, crane tower, overhead yard crane, hoist rope, and overhead crane drive shaft are described. The first four examples relate to the structural integrity of cranes. However, equipment such as drive and hoist-train components are often subject to severe fatigue loading and are perhaps even more prone to fatigue failure. In all instances, the presence of fatigue cracks at least contributed to the failure. In most instances, fatigue was the sole cause. Further, in each case, with regular inspection, fatigue cracks probably would have been detected well before final failure.

A special eyebolt was used to lift prefabricated concrete panels weighing approximately 16 cwt. Two eyebolts were used with a spreader bar to give a vertical lift on each eyebolt. Following failure of one eyebolt, which resulted in dropping of the load and subsequent failure of the other one, a complete eyebolt was submitted for assessment. Microscopic examination indicated a medium carbon-manganese steel had been used for the lower screwed portion of the eyebolt. Failure may have been due to brittle fracture or to fatigue, both of which could have been initiated at cracks in the hardened material in the region of the weld securing the screwed portion to the intermediate collar and which may have formed at the time of manufacture. Out-of-squareness of the thread with the collar, as was seen in the example submitted, gave rise to bending stresses when the bolt was tightened down, and this could have been a further factor which promoted failure. It was suggested that the design and construction could be improved by either making the component in one piece or, if it was desired, to adapt a standard eyebolt.

The maximum life of base-loaded headers and piping is not possible to be predicted until they develop microcracking. The typical elements of a periodic inspection program after the occurrence of the crack was described extensively. Cracks caused by creep swelling in the stub-to-header welds in the secondary superheater outlet headers (constructed of SA335-P11 material) of a major boiler were described as an example. The OD of the header was measured to detect the amount of swelling and found to have increased 1.6% since its installation. Ligament cracks extending from tube seat to tube seat were revealed by surface inspection. Cracks were found to originate from inside the header, extend axially in the tube penetrations and radially from those holes into the ligaments. Cracks in 94 locations, ranging from small radial cracks to full 360Ý cracks were revealed by dye-penetrant inspection. The unit was operated under reduced-temperature conditions and with less load cycling than previously until a redesigned SA335-P22 header was installed.

A superheater in a generator produced 80 t/h of steam at 400 deg C and 41 kPa. Failure took place at the connection from the collector to the vent line used during start up. The material of construction was carbon steel, and the unit had 240,000 h of operation at the time of failure, with 99 shutdowns. Widespread cracking on the inside was apparent, the most severe cracking being some distance from the nozzle connection in a downstream direction. Widespread cracking and pitting were observed also at the connections to the safety valve and soot blower. Pitting was most apparent on the downstream sides of the openings in the shell. In all the damaged areas the mechanism of failure involved surface pitting and subsequent SCC. This failure showed the problems that can develop where there are long lines in which condensation may occur and return periodically to a superheater or other hot component. In this particular case, control of dissolved solids in the boiler feedwater may have been inadequate.