Two tubular AISI 1025 steel posts (improved design) in a carrier vehicle failed by cracking at the radius of the flange after five weeks of service. The posts were two of four that supported the chassis of the vehicle high above the wheels. The original design involved a flat flange of low-carbon low-alloy steel that was welded to an AISI 1025 steel tube, and the improved design included placing the welded joint of the flange farther away from the flange fillet. Investigation (visual inspection and chemical analysis) supported the conclusion that the failures in the flanges of improved design were attributed to fatigue cracks initiating at the aluminum oxide inclusions in the flange fillet. Recommendations included retaining the improved design of the flange with the weld approximately 50 mm (2 in.) from the fillet, but changing the metal to a forging of AISI 4140 steel, oil quenched and tempered to a hardness of 241 to 285 HRB. Preheating to 370 deg C (700 deg F) before and during welding with AISI 4130 steel wire was specified. It was also recommended that the weld be subjected to magnetic-particle inspection and then stress relieved at 595 deg C (1100 deg F), followed by final machining.

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.

Four truck cross members intended for use in heavy-duty transport trucks were investigated. Two of the members had cracked on a prototype vehicle and two had been fatigue tested in the laboratory. The cross members were fabricated from SAE 950X plate and consisted of a formed channel section and an internal fillet-welded diaphragm. Sections from each of the cross members were subjected to a complete analysis, including chemical analysis, magnetic particle testing, mechanical testing, scanning electron microscope/fractography, and metallography. The primary mode of failure was found to be fatigue cracking that initiated at the toes of the fillet welds. Secondary fatigue cracking occurred at the torque rod mounting holes. Failure was attributed to cyclic stresses at the weld toes that exceeded the lowered fatigue strength at this location. A design change that eliminated the fillet welds alleviated the problem.

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.

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.