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.

Welded low-carbon steel bomb fins were rejected because of poor weld practice. Visual and metallographic examination revealed that the resistance plug welds that attach the outer skin to the inner spar displayed inadequate weld penetration. Recommended changes to the resistance welding parameters resulted in acceptable welds.

An exhaust diffuser assembly failed prematurely in service. The failure occurred near the intake end of the assembly and involved fracture in the diffuser cone (Corten), diffuser in take flange (type 310 stainless steel), diffuser exit flange (type 405 stainless steel), expansion bellows (Inconel 600), and bellows intake flange (Corten). Individual segments of the failed subassemblies were examined using various methods. The analysis indicated that the weld joint in the diffuser intake flange (type 310 stainless steel to Corten steel) contained diffusion-zone solidification cracks. The joints had been produced using the mechanized gas-metal arc welding process. Cracking was attributed to improper control of welding parameters, and failure was attributed to weld defects.

This case study describes the failure analysis of a steel nozzle in which cracking was observed after a circumferential welding process. The nozzle assembly was made from low-carbon CrMoV alloy steel that was subsequently single-pass butt welded using gas tungsten arc welding. Although no cracks were found when the welds were visually inspected, X-ray radiography showed small discontinuous surface cracks adjacent to the weld bead in the heat affected zone. Further investigation, including optical microscopy, microhardness testing, and residual stress measurements, revealed that the cracks were caused primarily by the presence of coarse untempered martensite in the heat affected zone due to localized heating. The localized heating was caused by high welding heat input or low welding speed and resulted in high transformation stresses. These transformation stresses, working in combination with thermal stresses and constraint conditions, resulted in intergranular brittle fracture.

Several compressor diaphragms from five gas turbines cracked after a short time in service. The vanes were constructed of type 403 stainless steel, and welding was performed using type 309L austenitic stainless steel filler metal. The fractures originated in the weld heat-affected zones of inner and outer shrouds. A complete metallurgical analysis was conducted to determine the cause of failure. It was concluded that the diaphragms had failed by fatigue. Analysis suggests that the welds contained high residual stresses and had not been properly stress relieved. Improper welding techniques may have also contributed to the failures. Use of proper welding techniques, including appropriate prewelding and postwelding heat treatments, was recommended.

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.

A fluorescent liquid-penetrant inspection of an experimental stator vane of a first-stage axial compressor revealed the presence of a longitudinal crack over 50 mm (2 in.) long at the edge of a resistance seam weld. The vane was made of titanium alloy Ti-6Al-4V (AMS 4911). The crack was opened by fracturing the vane. The crack surface displayed fatigue beach marks emanating from the seam-weld interface. Both the leading-edge and trailing-edge seam welds exhibited weld-metal expulsions up to 3.6 mm (0.14 in.) in length. Metallographic examination confirmed that metal expulsion from the resistance welds was generally present. The stator vane failed by a fatigue crack that initiated at internal surface discontinuities caused by metal expulsion from the resistance seam weld used in fabricating the vane. Expulsion of metal from seam welds should be eliminated by a slight reduction in welding current to reduce the temperature, by an increase in the electrode force, or both.

A series of resistance spot welds joining Z-shape and C-shape members of an aircraft drop-tank structure failed during ejection testing. The members were fabricated of alclad aluminum alloy 2024-T62. The back surface of the C-shape members showed severe electrode-indentation marks off to one side of the spot weld, suggesting improper electrode contact. Visual examination of the weld fractures showed that the weld nuggets varied considerably in size, some being very small and three exhibiting an HAZ but no weld. Of 28 welds, only nine had acceptable nugget diameters and fusion-zone widths. The weld deficiencies were traced to problems in forming and fit-up of the C-shape members and to difficulties in alignment and positioning of the weld tooling. The failure of the resistance spot welds was attributed to poor weld quality caused by unfavorable fit-up and lack of proper weld-tool positioning. The problem could be solved by better forming procedures to provide an accurate fit-up that would not interfere with electrode alignment.

A fuel-nozzle-support assembly showed transverse indications after fluorescent liquid-penetrant inspection of a repair-welded area at a fillet on the front side of the support neck adjacent to the mounting flange. Visual examination disclosed an irregular crack. The crack through the neck was sectioned; examination showed that the crack had extended through the repair weld. The crack had followed an intergranular path. The crack was opened, and binocular-microscope examination of the fracture surface showed that the surface contained dendrites with discolored oxide films that were typical of exposure to air when very hot. Several additional subsurface cracks, typical of hot tears, were observed in and near the weld. There had been too much local heat input in making the repair weld. The result was localized thermal contraction and hot tearing. The cracking of the repair weld was attributed to unfavorable welding practice that accentuated thermal contraction stresses and caused hot tearing. Recommendations involved use of a small-diameter welding electrode, a lower heat input, and deposition in shallow layers that could be effectively peened between passes to minimize internal stress.

Handles welded to the top cover plate of a chemical-plant downcomer broke at the welds when the handles were used to lift the cover. The handles were fabricated of low-carbon steel rod; the cover was of type 502 stainless steel plate. The attachment welds were made with type 347 stainless steel filler metal to form a fillet between the handle and the cover. The structure was found to contain a zone of brittle martensite in the portion of the weld adjacent to the low-carbon steel handle; fracture had occurred in this zone. The brittle martensite layer in the weld was the result of using too large a welding rod and too much heat input, melting of the low-carbon steel handle, which diluted the austenitic stainless steel filler metal and formed martensitic steel in the weld zone. Because it was impractical to preheat and postheat the type 502 stainless steel cover plate, the low-carbon steel handle was welded to low-carbon steel plate, using low-carbon steel electrodes. This plate was then welded to the type 502 stainless steel plate with type 310 stainless steel electrodes. This design produced a large weld section over which the load was distributed.

AM350 stainless steel bellows used in the control rod drive mechanism of a fast breeder reactor failed after 1000 h of service in sodium at 550 deg C (1020 deg F). Helium leak testing indicated that leaks had occurred at various regions of the welded joints between the convolutes in the bellows. The weld failure was attributed to poor quality assurance during fabrication, which resulted in cracklike openings at the fusion zone. The openings extended during tensile loading. Use of proper welding procedures and quality control measures were recommended to prevent future failures.

Several of the welds in a hoist carriage tram-rail assembly fabricated by shielded metal arc welding the leg of a large T-section 1020 steel beam to the leg of a smaller T-section 1050 steel rail failed in one portion of the assembly. Four weld cracks and several indefinite indications were found by magnetic-particle inspection. The cracks were revealed by metallographic examination to have originated in the HAZs in the rail section. Cracks in welds and in HAZs resulting from arcing the electrode adjacent to the weld and weld spatter were also revealed. The tram-rail assembly was concluded to have failed by fatigue cracking in HAZs. The fatigue cracking was initiated and propagated by vibration of the tram rail by movement of the hoist carriage on the rail. As a corrective measure, welding procedures were improved and the replacement rail assemblies were preheated and postheated.

A failed crosshead of an industrial compressor was examined using optical and scanning electron microscope. The crosshead was an ASTM A148 grade 105-85 steel casting. On the basis of the observations reported and available background information, it was concluded that the failure began with the initiation of cracks at slag inclusions and sharp fillets in weld-repair areas in the casting. The weld-repair procedures were unsatisfactory. The cracks propagated in a fatigue mode. he casting quality was judged unacceptable because of the presence of excessive shrinkage porosity. It was recommended that crosshead castings be properly inspected before machining. Revision of foundry practice to reduce or eliminate porosity was also recommended.

The failure of a 45 Mg (50 ton) rail crane bolster was investigated. Spectrochemical analysis indicated that the material was a 0.25C-1.24Mn-0.62Cr-0.24Mo cast steel. SEM examination revealed the presence of fatigue, as well as intergranular and ductile fractures. Microstructural analysis focused on an area where an antisway device had been welded to the structure and revealed the presence of coarse, untempered martensite that had resulted from faulty weld repair techniques. It was suggested that the use of proper welding procedures, including preheating and postheating, would have prevented the failure.

Schedule 80 low-carbon steel pipes used to transfer kraft liquor in a Kamyr continuous pulp digester failed within 18 months after installation. Visual and metallographic examinations established that the cracking initiated on the internal surfaces of the equalizer pipes in the welds and heat-affected zones (HAZs). Fracture/crack morphology was brittle and primarily intergranular and deposits at crack tips were primarily iron oxides with significant amounts of sodium compounds. On these bases, the cracking was characterized as intergranular stress-corrosion cracking (IGSCC). Corrosion-related deterioration was not found, indicating that the material was generally suitable for the intended service. High residual tensile stresses in the welds and HAZS, resulting from field welding under highly constrained conditions using inadequate weld procedures, were the most probable cause of the failures. Minimizing residual stresses through use of welding procedures that include appropriate preweld and interpass temperatures and postweld stress relief heat treatment at 650 deg C (1200 deg F) was recommended to prevent further failures.

The repeated failure of a welded ASTM A283 grade D pipe that was part of a 6 km (4 mi) line drawing and conducting river water to a water treatment plant was investigated. Failure analysis was conducted on sections of pipe from the third failure. Visual, macrofractographic, SEM fractographic, metallographic, chemical, and mechanical property (tension and impact toughness) analyses were conducted. On the basis of the tests and observations, it was concluded that the failure was the combined result of poor notch toughness (impact) properties of the steel, high stresses in the joint area, a possible stress raiser at the intersection of the spiral weld and girth weld, and sudden impact loading, probably due to water hammer. Use of a semi- or fully killed steel with a minimum Charpy V-notch impact value of 20 J (15 ft·lbf) at 0 deg C (32 deg F) was recommended for future water lines. Certified test results from the steel mill, procedure qualification tests of the welding, and design changes to reduce water hammer were also recommended.

Repeated failures of high-pressure ball valves were reported in a chemical plant. The ball valves were made of AFNOR Z30C13 martensitic stainless steel. Initial examination of the valves showed that failure occurred in a weld at the ball/stem junction end of austenitic stainless steel sleeves that had been welded to the valve stem at both ends. Metallographic examination showed that a crack had been introduced into the weld by improper weld heat treatment. Stress concentration at the weld location resulting from an abrupt change in cross section facilitated easy propagation of the crack during operation. Proper weld heat treatment was recommended, along with avoidance of abrupt change in cross section near the weld. Due penetrant testing at the ball stem junction before and after heat treatment was also suggested.

The source of cracking in the circumferential weld seam in a JIS-SM50B carbon-manganese steel pipe used in a CO2 absorber was investigated, the absorber had been in service for 18 years. The seam had been weld-repaired twice, and the repair welds had been locally stress relieved. Longitudinal seams in the same vessel, which had been stress relieved in a furnace, showed no tendency toward cracking. The solution passing through the vessel contained CO2-CO-H20, KHCO, and Cl− ions. Nondestructive testing revealed that the cracks originated in the heat-affected zone and propagated into the base metal and weld. Severe branching of the cracks characteristic of stress-corrosion cracking was observed. Microexamination revealed that crack propagation was transgranular further supporting the possibility of stress-corrosion cracking. Simulation tests carried out in the vessel confirmed this mode of cracking. It was recommended that weld seams be furnace heat treated at a temperature of 600 to 640 deg C (1110 to 1180 deg F) for a minimum of 1 h per inch of section thickness.

A front-wheel drive hatchback automobile was involved in a severe front end impact. Failure analysis of the automobile revealed only a single sound spot weld in each of two 66 cm (26 in.) sections of both upper and lower floor sill flanges. Consequently, upon impact, the floor pan separated from the rocker panel, buckled and rotated upward and forward. This introduced slack in the seat belts since their retractors, being anchored to the floor pan, also rotated forward. Although not contributory to the accident itself, the faulty welds were responsible in part for the severity of the injuries sustained by the driver. The faulty welds in the unit body were apparently a consequence of improper settings of parameters on a multihead electrical resistance spot welding machine. Lack of appreciation of the hazard associated with failure of this weldment may have contributed to the low frequency of their physical inspection during production. A similar case involving faulty welds in a fuel delivery truck is also discussed.

An E-Brite /Ferralium explosively bonded tube sheet in a nitric acid condenser was removed from service because of corrosion. Visual and metallographic examination of tube sheet samples revealed severe cracking in the heat-affected zone between the outer tubes and the weld joining the tube sheet to the floating skirt. Cracks penetrated deep into the tube sheet, and occasionally into the tube walls. The microstructures of both alloys and of the weld appeared normal. Intergranular corrosion characteristic of end-grain attack was apparent. A low dead spot at the skirt / tube sheet joint allowed the Nox to condense and subsequently reboil. This, coupled with repeated repair welding in the area, reduced resistance to acid attack. Intergranular corrosion continued until failure. Recommendations included changing operating parameter inlet to prevent HNO3 condensation outside the inlet and replacement of the floating skirt with virgin material (i.e., material unaffected by weld repairs).