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.

Extra high strength zinc-coated 1080 steel welded wire was wound into seven-wire cable strands for use in aerial cables and guy wires. The wires and cable strands failed tensile, elongation, and wrap tests, with wires fracturing near welds at 2.5 to 3.5% elongation and through the welded joints in wrap tests. The welded wire was annealed by resistance heating. The wire ends had a chisel shape, produced by the use of sidecutters. Tests of the heat treatment temperatures showed that the wire near the weld area exceeded 775 deg C (1425 deg F). Metallographic examination revealed martensite present in the weld area after the heat treatment. The test failures of the AISI 1080 steel wire butt-welded joints were due to martensite produced in cooling from the welding operation that was not tempered adequately in postweld heat treatment, and to poor wire-end preparation for welding that produced poorly formed weld burrs. The postweld heat treatment was standardized on the 760 deg C (1400 deg F) transformation treatment. The chisel shape of the wire ends was abandoned in favor of flat filed ends. The wrap test was improved by adopting a hand-cranked device. Under these conditions, the welded joints withstood the tensile and wrap tests.

The secondary cooling water system pressure boundary of Savannah River Site reactors includes expansion joints utilizing a thin-wall bellows. While successfully used for over thirty years, an occasional replacement has been required because of the development of small, circumferential fatigue cracks in a bellows convolute. One such crack was recently shown to have initiated from a weld heat-affected zone liquation microcrack. The crack, initially open to the outer surface of the rolled and seam welded cylindrical bellows section, was closed when cold forming of the convolutes placed the outer surface in residual compression. However, the bellows was placed in tension when installed, and the tensile stresses reopened the microcrack. This five to eight grain diameter microcrack was extended by ductile fatigue processes. Initial extension was by relatively rapid propagation through the large-grained weld metal, followed by slower extension through the fine-grained base metal. A significant through-wall crack was not developed until the crack extended into the base metal on both sides of the weld. Leakage of cooling water was subsequently detected and the bellows removed and a replacement installed.

A welded joint between lengths of 4 in. OD x 13 SWG copper pipe which formed part of a cold-water main failed by cracking over one-third of the circumference. Microscopic examination of the filler metal showed that it had a structure corresponding to a brass of the 60:40 type commonly used for bronze welding. Failure resulted from dezincification of the joint material from the internal side of the tube. Also, a selective attack on the beta phase had occurred. It was evident that the loss in mechanical strength arising from the corrosion had resulted in the development of cracking in service. The filler metal used was not resistant to the conditions to which it was exposed. Copper welding rods as per BS 1077 or a Cu-Ag-P brazing alloy as recommended in BS 699, would have been preferable.

A tie rod, nut, and bellows from a failed 610 mm (24 in.) diam tied universal expansion joint that carried tail gases consisting of N 2 + O 2 with slight traces of nitrogen oxides and water were examined. The materials were SA 193-B7 (AISI 4140), SA 194–214, and Incoloy 800H, respectively. Visual examination of the bellows revealed cracks in heavily cold-worked areas (both inside and outside) and considerable corrosion. SEM analysis showed a classical intergranular failure pattern with microcracking. The threaded tie rod microstructure contained spheroidized carbide that was more pronounced at the tie rod end of the failure. Energy-dispersive X-ray analysis of fracture surfaces from the bellows showed the presence of chlorine and sulfur. Failure of the bellows was attributed to stress-corrosion cracking, with chlorine and sulfur being the corroding agents. The rod damage was the result of failure of the bellows, which allowed escaping hot gases to impinge on the tie rods and heat them to approximately 595 deg C (1100 deg F). It was recommended that the insulation be analyzed to determine the origin of the chlorine and sulfur and that it be replaced if necessary.

The various methods of furnace, torch, induction, resistance, dip, and laser brazing are used to produce a wide range of highly reliable brazed assemblies. However, imperfections that can lead to braze failure may result if proper attention is not paid to the physical properties of the material, joint design, prebraze cleaning, brazing procedures, postbraze cleaning, and quality control. Factors that must be considered include brazeability of the base metals; joint design and fit-up; filler-metal selection; prebraze cleaning; brazing temperature, time, atmosphere, or flux; conditions of the faying surfaces; postbraze cleaning; and service conditions. This article focuses on the advantages, limitations, sources of failure, and anomalies resulting from the brazing process. It discusses the processes involved in the testing and inspection required of the braze joint or assembly.

The structural collapse of an iron-ore bucket-wheel stacker reclaimer at the beginning of operation was investigated by means of mechanical tests, microstructural characterization, and computational structural analysis. The mechanical failure was a consequence of a brittle fracture by cleavage. The crack followed the heat-affected zone of a welded joint connecting a rectangular hollow section member and a plate flange. The main factors contributing to failure were related with a combination of design-in and manufacturing-in factors like high load-strength ratio at the point of failure, local stress concentration as a result of geometry restrictions, and weld defects. This particular section was responsible for the load transfer between the front tie member and the boom extremity, and its failure was the main cause of the catastrophic failure of the equipment.

A steam accumulator, constructed with 10.3 mm thick SA515-70 steel heads and an 8 mm thick SA455A steel shell, ruptured after about three years of service. The accumulator was used in plastic molding operations. An extensive lack of weld penetration in this the head-to-shell girth weld was revealed by laboratory examination. Some misalignment of the head to the shell because of radial displacement of the shell and head centerlines was observed which was found to result in excessive clearances between the two parts and a slight difference in the thicknesses of the parts. Transgranular fracture with occasional secondary branching was revealed. It was interpreted by stress analysis that a small amount of misalignment added to lack of penetration increased the stresses to near the tensile strength of the material. The failure was judged to be a short-cycle high-stress notch-fatigue failure.

A drive-line assembly failed during vehicle testing. The vehicle had traveled 9022 km (5606 mi) before the failure occurred. Both the intact and fractured parts of the assembly were analyzed to determine the cause and sequence of failure. Visual examination of the assembly showed three of four bearing caps, two cap screws, and one universal-joint spider had fractured. Examination of the three fractured bearing caps and the spider showed no evidence of fatigue but showed that fracture occurred in a brittle manner. The bearing cap that was not destroyed still contained portions of the two fractured cap screws. It was found that the two cap screws failed in fatigue under service stresses. The three bearing caps and the universal-joint spider broke in a brittle manner. The properties of the material in the cap screws did not fulfill the specifications. The modified 1035 steel was of insufficient alloy content. Also, the tensile strength and endurance limit were lower than specified and were inadequate for the application. The material for the cap screw was changed from modified 1035 steel to 5140 steel.

This article discusses different types of mechanical fasteners, including threaded fasteners, rivets, blind fasteners, pin fasteners, special-purpose fasteners, and fasteners used with composite materials. It describes the origins and causes of fastener failures and with illustrative examples. Fatigue fracture in threaded fasteners and fretting in bolted machine parts are also discussed. The article provides a description of the different types of corrosion, such as atmospheric corrosion and liquid-immersion corrosion, in threaded fasteners. It also provides information on stress-corrosion cracking, hydrogen embrittlement, and liquid-metal embrittlement of bolts and nuts. The article explains the most commonly used protective metal coatings for ferrous metal fasteners. Zinc, cadmium, and aluminum are commonly used for such coatings. The article also illustrates the performance of the fasteners at elevated temperatures and concludes with a discussion on fastener failures in composites.

A portion of a 19 mm (0.75 in.) diam structural steel bolt was found on the floor of a manufacturing shop. This shop contained an overhead crane system that ran on rails supported by girders and columns. Inspection of the crane system revealed that the bolt had come from a joint in the supporting girders and could be considered one of the principal fasteners in the track system. Analysis (visual inspection, metallographic exam, and hardness testing) supported the conclusions that fatigue induced by the overhead movement of the crane produced failure of the bolt. The bolt was deficient in strength for the cyclic applied loads in this case and probably was not tightened sufficiently. Recommendations included removing the remaining bolts in the crane support assembly and replacing them with a higher-strength, more fatigue-resistant bolt, for example, SAE grade F, 104 to 108 HRB. The bolts should be tightened according to the specifications of the manufacturer, and the system should be periodically inspected for correct tightness.

The onset of leakage adjacent to two butt welds in a 2 in. bore pipe was traced to the development of fine cracks. The pipe carried 40% sodium hydroxide solution. The actual temperature was not known, but the pipeline was steam traced at a pressure of 30 psi, equivalent to a temperature of 130 deg C (266 deg F). Magnetic crack detection revealed circumferential crack-like indications situated a short distance from the butt weld. Cracking originated on the bore surfaces of the tube and was of an intergranular nature reminiscent of caustic cracking in steam boilers. The strength of the solution of caustic soda and possibly the temperature also were in the range known to produce stress-corrosion cracking of mild steels in the presence of stresses of sufficient magnitude. In this instance the location of the cracking suggested that residual stresses from welding, which approach yield point magnitude, were responsible. As all other welds were suspect, the remedy was to remove the joints and to reweld followed by local stress relief.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

The century-old Harvard bridge spans the Charles River between Boston and Cambridge. About half of the 23 spans are suspended by wrought iron eyebars. Recent failures of some of these eyebars were examined. The primary cause of failure was the seizure of the joints at the eyebar pin locations as a result of the intrusion of water and salt, and the consequent heavy corrosion of the joint. The seizure of these joints led to high edgewise bending stress in the bars as the bridge underwent thermal movement. The cracking was enhanced by the presence of the corrosive medium so that the cracks were initiated and caused to grow by some combination of corrosion fatigue and stress-corrosion cracking, the former probably being predominant.

This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.

The brine-heater shell in a seawater-conversion plant failed by bursting along a welded joint connecting the hot well (C70600 per ASTM B 466) to the heater shell (ASTM A285, grade C steel). Three cracks in the welded joints between the heater shell and the hot well were revealed by visual inspection. It was observed that crack 1 and 2 were covered with high-temperature oxidation products which revealed that the surfaces had been separated for quite some time. A very high discontinuity stress which existed at the longitudinal welds between the hot well and the heater shell was revealed by stress analysis. It was interpreted that the cracks had originated shortly after the heater was put into operation and propagated slowly initially. The rate of propagation was interpreted to have increased due to discontinuity stresses greater than yield strength of the material. It was concluded that the brine heater cracked and fractured because it was overstressed in normal operation. The heater design was modified to make the heater shell and the hot well two separate units. A relief valve was recommended in the heater or in the steam line near the heater.

During a routine inspection on an aircraft assembly line, an airframe attachment bolt was found to be broken. The bolt was one of 12 that attach the lower outboard longeron to the wing carry-through structure. Failure occurred on the right-hand forward bolt in this longeron splice attachment. The bolt was fabricated from PH13-8Mo stainless steel heat treated to have an ultimate tensile strength of 1517 to 1655 MPa (220 to 240 ksi). A water-soluble coolant was used in drilling the bolt hole where this fastener was inserted. Investigation (visual inspection, 265 SEM images, hardness testing, auger emission spectroscopy and secondary imaging spectroscopy, tensile testing, and chemical analysis) supported the conclusion that failure of the attachment bolt was caused by stress corrosion. The source of the corrosive media was the water-soluble coolant used in boring the bolt holes. Recommendations included inspecting for corrosion all the bolts that were installed using the water-soluble coolant at the spliced joint areas, rinsing all machined bolt holes with a noncorrosive agent, and installing new PH13-8Mo stainless steel bolts with a polysulfide wet sealant.

An API type 2 steel clamp located on the riser of a semisubmersible drilling rig between the lower ball joint and riser blowout preventer (BOP) conductor failed after 7 years of service. Failure analysis revealed the cause of failure to be the low toughness of the clamp material. Contributing factors included the presence of a hard, brittle, heat-affected zone and weld defects at the handling pad eye. It was recommended that the replacement clamp be made from a material with good toughness and that any installation of attachments by welding be done according to qualified procedures.

Due to the recent requirement of higher integration density, solder joints are getting smaller in electronic product assemblies, which makes the joints more vulnerable to failure. Thus, the root-cause failure analysis for the solder joints becomes important to prevent failure at the assembly level. This article covers the properties of solder alloys and the corresponding intermetallic compounds. It includes the dominant failure modes introduced during the solder joint manufacturing process and in field-use applications. The corresponding failure mechanism and root-cause analysis are also presented. The article introduces several frequently used methods for solder joint failure detection, prevention, and isolation (identification for the failed location).

This article describes some of the welding discontinuities and flaws characterized by nondestructive examinations. It focuses on nondestructive inspection methods used in the welding industry. The sources of weld discontinuities and defects as they relate to service failures or rejection in new construction inspection are also discussed. The article discusses the types of base metal cracks and metallurgical weld cracking. The article discusses the processes involved in the analysis of in-service weld failures. It briefly reviews the general types of process-related discontinuities of arc welds. Mechanical and environmental failure origins related to other types of welding processes are also described. The article explains the cause and effects of process-related discontinuities including weld porosity, inclusions, incomplete fusion, and incomplete penetration. Different fitness-for-service assessment methodologies for calculating allowable or critical flaw sizes are also discussed.