Type 316L (UNS S31603) austenitic stainless steel piping was installed as part of a storm-sewer treatment collection system in a manufacturing facility. Within six months of start-up, leaks were discovered. Investigation (on-site current flow testing, visual inspection, water tests, and 5x/10x images etched in ASTM 89 reagent) supported the conclusion that the pitting in the austenitic stainless steel pipe was believed to be caused by damage to the passive layer brought about by a combination of MIC, high chloride levels, and high total dissolved solids. The low-flow and stagnant conditions present in the piping were primary contributors to the pit progression. Recommendations included replacing the pipe. Several alloys, nonmetallic materials, and lining materials were proposed for coupon testing to determine which would operate best in an environment with high levels of aerobic bacteria.

The paper describes the findings from a damaged propeller blade made from Mn-Ni-Al-bronze, commercially known as Superston 70 (ABS Type 5). The blade had broken at the 0.65 pitch radius location, and the fracture occurred in a brittle mode. The findings reported here point to two potential contributors to the propeller blade failure, viz., the presence of casting flaws at the low pressure side of the propeller blade and service stresses at this surface that reached approximately 400 MPa. This stress value exceeded the yield strength at the corresponding location of the unbroken blade by approximately 40%.

Threads of a bone screw (Co-Cr-Mo alloy, type ASTM F75) had broken off, and other threads had cracked. 15x sectioning showed porosity, and 155x magnification showed gas holes, segregation, and dissolved oxides. This supports the conclusion that manufacturing defects caused the failure.

A neck fitting (cast equivalent of AISI type 317) exhibited extreme corrosion with large, deeply pitted areas. It had been in service in a sulfite digester at 140 deg C (285 deg F) and 689 kPa (100 psi). The liquor was calcium bisulfite, and chloride content was reported to be low. Investigation (visual inspection, and micrographs of sections with electrolytic etching using 10 N KOH and then again after re-polishing and etching with Murakami's reagent) supported the conclusions that the casting never received a proper solution anneal. Recommendations included possible corrosion-screening tests in accordance with ASTM A 262 to ensure adequate corrosion resistance.

A lever (machined from a casting made of AISI type 410 stainless steel, then surface hardened by nitriding) that was a component of the main fuel-control linkage of an aircraft engine fractured in flight after a service life of less than 50 h. Investigation (radiographic inspection) supported the conclusions that the lever broke at a cold shut extending through approximately 95% of the cross section. The normally applied load constituted an overload of the remainder of the lever. Recommendations included adding magnetic-particle inspection to the inspection procedures for this cast lever.

Cracks formed on cylinder inserts from a water-cooled locomotive diesel engine, on the water side in the neck between the cylindrical part and the collar. Cracks were revealed by magnetic-particle inspection. As a rule, several parallel cracks had appeared, some of which were very fine. The part played by corrosion in the formation of the cracks was demonstrated with the help of metallographic techniques. The surface regions of the cracks widened into funnel form, which is a result of the corrosive influence of the cooling water. Actual corrosion pits could not be found indicating that the vibrational stresses had a greater share in the damage than the corrosive influence. Cracks appeared initially only in those engines in which no corrosion inhibitor had been added to the cooling water. The cracking was caused by corrosion fatigue. The combined presence of a corrosive medium and cyclical operating stress was needed to cause cracks. No cracks appeared when corrosion inhibitor was added to the cooling water.

A sand-cast steel eye connector used to link together two 54,430 kg capacity floating-bridge pontoons failed prematurely in service. The pontoons were coupled by upper and lower eye and clevis connectors that were pinned together. The eye connector was found to be cast from low-alloy steel conforming to ASTM A 148, grade 150-125. The crack was found to have originated along the lower surface initially penetrating a region of shrinkage porosity. It was observed that cracking then propagated in tension through sound metal and terminated in a shear lip at the top of the eye. The fracture of the eye connector was concluded to have occurred by tensile overload because of shrinkage porosity. Sound metal was ensured by radiographic examination of subsequent castings.

A sand-cast medium-carbon steel heavy-duty axle housing, which had been quenched and tempered to about 30 HRC, fractured after almost 5000 h of service. Investigation (0.4x magnification) revealed that the fracture had been initiated by a hot tear that formed during solidification of the casting. The mass of a feeder-riser system located near the tear retarded cooling in this region, creating a hot spot. This supported the conclusion that the tear causing the fracture of the axle housing was formed during solidification by hindered contraction and was enlarged in service by fatigue. Recommendations were to change the feeder location to eliminate the hot spot and thus the occurrence of hot tearing.

A welded elbow assembly (AISI type 321 stainless steel, with components joined with ER347 stainless steel filler metal by gas tungsten arc welding) was part of a hydraulic-pump pressure line for a jet aircraft. The other end of the tube was attached to a flexible metal hose, which provided no support and offered no resistance to vibration. The line was leaking hydraulic fluid at the nut end of the elbow. Investigation supported the conclusion that failure was by fatigue cracking initiated from a notch at the root of the weld and was propagated by cyclic loading of the tubing as the result of vibration and inadequate support of the hose assembly. Recommendations included changing the joint design from a cylindrical lap joint to a square-groove butt joint. Also, an additional support was recommended for the hose assembly to minimize vibration at the elbow.

During 5.7 years of service, dye penetrant inspection of Inconel 800H pigtail connections regularly showed cracks at weld toes. Weld repairs were not able to prevent reoccurrence but often aggravated the condition. Samples containing small, but detectable, reducer-to-pigtail cracks showed intergranular cracks originating at weld toes and filled with oxidation product, which precluded determination of the cracking mechanism. All weldments exhibited high degrees of secondary precipitates, with original fabrication welds exhibiting higher apparent levels than repair welds. SEM/EDS analysis showed base metal grain boundary precipitates to be primarily chromium carbides, but some titanium carbides were also observed. Failure was believed to result from the synergism of thermally driven tube distortion, which resulted in over-stress, and from the intergranular oxidation products and intergranular carbides which contributed to cracking. It was recommended that stresses be reduced and /or that materials and components be changed. Refinements in welding procedures and implementation of preweld/postweld heat treatments were recommended also.

The case and stiffener of an inner-combustion-chamber case assembly failed by completely fracturing circumferentially around the edge of a groove arc weld joining the case and stiffener to the flange. The assembly consisted of a cylindrical stiffener inserted into a cylindrical case that were both welded to a flange. The case, stiffener, flange, and weld deposit were all of nickel-base alloy 718. It was observed that a manual arc weld repair had been made along almost the entire circumference of the original weld. Investigation (visual inspection, 0.5x macrographs, and 10x etched with 2% chromic acid plus HCl views) supported the conclusions that failure was by fatigue from multiple origins caused by welding defects. Ultimate failure was by tensile overload of the sections partly separated by the fatigue cracks. Recommendations included correct fit-up of the case, stiffener, and flange and more skillful welding techniques to avoid undercutting and unfused interfaces.

A pipe in a chip conveyor cracked at the toe of an exterior fillet weld connecting a flange to the pipe. The chip conveyor consisted of several spool sections. Each section was made up of a length of low-alloy steel pipe and two flanges, which were welded to each end. The composition specified for the pipe steel was 0.25C-0.98Mn-3.52Ni-1.34Cr-0.24Mo, which approximates a 9300 steel with high molybdenum. Investigation supported the conclusion that the conveyor pipe failed by brittle fracture, which was attributed to the stresses induced in forcing the circular flange over the elliptical section of the pipe. The toe of the weld and the adjacent undercut were stress raisers that determined the point of major crack origin. Under residual stress, the internal point of incomplete fusion also initiated additional cracks. Recommendations included ensuring a proper fit between an elliptical flange and pipe end to eliminate the cracking.

While undergoing vibration testing, a type 347 stainless steel inlet header for a fuel-to-air heat exchanger cracked in the header tube adjacent to the weld bead between the tube and header duct. Investigation (visual inspection and liquid penetrant inspection) supported the conclusion that the crack in the header tube was the result of a stress concentration at the toe of the weld joining a doubler collar to the tube. The stress concentration was caused by undercutting from poor welding technique and an unfavorable joint design that did not permit a good fit-up. Recommendations included manufacturing the doubler collar so that it could be placed in intimate contact with the header duct, and a revised weld procedure was recommended to result in a smaller, controlled, homogeneous weld joint with less distortion.

A recuperator used for preheating the combustion air for a rolling mill furnace failed after a relatively short service time because of leakage of the pipes in the colder part. The 6 % chrome steel pipes used for the warmer part connected by means of welding with austenitic electrodes to the unalloyed mild steel pipe of larger diam. Visual inspection showed corrosion and deep, trench-like erosion over the entire circumference of the seam on the side of the thicker mild steel pipe. Examination using the V2-A solution for picral etch showed the microstructure of the unalloyed pipe had become coarse-grained and acicular, and the microstructure of the welding seam had become predominantly martensitic as a result of the mixing of the weld metal with the fused pipe material. The chrome steel pipe had become partially transformed to martensite or bainite at the transition to the weld. Thus, the failure occurred due to typical contact corrosion wherein the alloyed welding seam represented the less noble electrode. The martensitic structure may have contributed to the failure as well. Due to the typical nature of the failure, no recommendations were made.

An amusement ride failed when a component in the ride parted, permitting it to fly apart. The ride consisted of a central shaft supporting a spider of three arms, each of which was equipped with an AISI 1040 steel secondary shaft about which a circular platform rotated. The main shaft rotated at about 12 rpm and the platforms at a speed of 20 rpm. The accident occurred when one of the secondary shafts on the amusement ride broke. The point of fracture was adjacent to a weld that attached the shaft to a 16 mm thick plate, which in turn bore the platform support arms. Investigation (visual inspection, 0.4x magnification, and stress analysis) supported the conclusion that a likely cause for the fatigue failure was the combination of residual stresses generated in welding and centrifugal service stresses from operation that were accentuated by areas of stress concentration at the undercut locations. Without the excessive residual stress, the shaft dimensions appeared ample for the service load. Recommendations included applying the fillet weld with more care to avoid undercutting. The residual stresses could be minimized by pre-weld and post-weld heat application.

A stuffing box (sand cast from ASTM A 536, grade 60-45-10, ductile iron) began leaking water after two weeks of service. The machine was operating at 326 rpm with a discharge water pressure of 21.4 MPa (3100 psi). Investigation (visual inspection, mechanical analysis, and nital etched 100x magnification) supported the conclusion that the crack initiated at the inner edge of a lubrication hole and had propagated toward both the threaded and flange ends of the casting. An appreciable residual-stress concentration must have been present and caused propagation of the crack. The residual stress might have been caused when a fitting was tightly screwed into the lubrication hole, and it might have been concentrated by notches at the inner end of the hole created when the drill broke through the sidewall to the stuffing box.

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.

During the final shop welding of a large armature for a direct-current motor (4475 kW, or 6000 hp), a loud bang was heard, and the welding operation stopped. When the weld was cold, nondestructive evaluation revealed a large crack adjacent to the root weld. Investigation showed the main crack had propagated parallel to the fusion boundary along the subcritical HAZ and was associated with long stringers of type II manganese sulfide (MnS) inclusions. This supported the conclusion that the weld failed by lamellar tearing as a result of the high rotational strain induced at the root of the weld caused by the weld design, weld sequence, and thermal effects. Recommendations included removing the old weldment to a depth beyond the crack and replacing this with a softer weld metal layer before making the main weld onto the softer layer.

A railway tank car developed a fracture in the region of the sill and shell attachment during operation at -34 deg C (-30 deg F). On either side of the sill-support member, cracking initiated at the weld between a 6.4 mm thick frontal cover plate and a 1.6 mm thick side support plate. The crack then propagated in a brittle manner upward through the side plate, through the welds attaching the side plate to a 25 mm (1 in.) thick shell plate (ASTM A212, grade B steel), and continued for several millimeters in the shell plate before terminating. Other plates involved were not positively identified but were generally classified as semi-killed carbon steels. Investigation (visual inspection, hardness testing, chemical analysis, Charpy V-notch testing, and drop-weight testing) supported the conclusions that the fracture was initiated by weld imperfections and propagated in a brittle manner as a result of service stresses acting on the plate having low toughness at the low service temperatures encountered. Recommendations included that the specifications for the steel plates be modified to include a toughness requirement and that improved welding and inspection practices be performed to reduce the incidence of weld imperfections.