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 CF-8M (cast type 316) neck liner or manway was removed from the top of a digester vessel. Repeated attempts to repair the part in the field during its life cycle of many years had failed to keep the unit from leaking. The casting was a CF-8M modified with the molybdenum level at the top end of the range. The plate was standard 317L material. The filler metal was type 316, although marginal in molybdenum content. Investigation (visual inspection, chemical analysis, micrographs, and metallographic examination) supported the conclusion that the damage to the neck liner was due to Cl-SCC in an area of debris buildup. It appeared the original casting suffered SCC in a low-oxygen area high in chlorides from repeated wet/dry cycles where there was a buildup of debris. Recommendations included redesigning the neck liner to eliminate the abrupt change where there was debris buildup. If redesign was impossible, an alloy more resistant to Cl-SCC, such as a duplex stainless steel or a high-molybdenum (4 to 6%) austenitic stainless steel, should be used.

Several back up rolls of 1400 mm barrel diam from a broad strip mill broke after a relatively short operating time as a result of bending stresses when the rolls were dismantled. The fracture occurred in the conical region of the neck at about 600 mm diam. The rolls were shaped steel castings with 0.8 to 1.0% C, 1% Mn, 1% Cr, 0.5% Mo and 0.4% Ni and were heat treated to a tensile strength of 950 N/sq mm. Because the bending stress on mounting was only 42 N/sq mm in the fracture cross section, it was evident at the outset that material defects had promoted the fracture. In the case of this roll and the other broken rolls, the cracking and fracture were promoted by various casting defects. Investigation of the rolls showed that both the breaking off of the neck and the disintegration of the barrel edges was caused by material defects, more exactly casting defects. The fractures on the other rolls examined were so badly rusted or contaminated that they were incapable of yielding any information.

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.

An oil scavenge pump was found to have failed when a protective shear neck fractured during the start of a jet engine. Visual inspection revealed that the driven gear in one of the bearing compartments was frozen as was the corresponding drive gear. Spacer wear and thermal discoloration (particularly on the driven gear) were also observed. The gears were made from 32Cr-Mo-V13 steel, hardened and nitrided to 750 to 950 HV. Micrographic inspection of the gear teeth revealed microstructural changes that, in context, appear to be the result of friction heating. The spacers consist of Cu alloy (AMS4845) bushings force fit into AA2024-T3 Al alloy spacing elements. It was found that uncontrolled fit interference between the two components had led to Cu alloy overstress. Thermal cycling under operating conditions yielded the material. The dilation was directed inward to the shaft, however, because the bushing had only a few microns of clearance. The effect caused the oil to squeeze out, resulting in metal-to-metal contact, and ultimately failure.

A system of carbon steel headers, handling superheated water of 188 deg C (370 deg F) at 2 MPa (300 psi) for automobile-tire curing presses, developed a number of leaks within about four months after two to three years of leak-free service. All the leaks were in shielded metal arc butt welds joining 200 mm (8 in.) diam 90 deg elbows and pipe to 200 mm (8 in.) diam welding-neck flanges. A flange-elbow-flange assembly and a flange-pipe assembly that had leaked were removed for examination. Investigation (visual inspection, hardness testing, chemical analysis, magnetic-particle testing, radiographic inspection, and 2% nital etched 1.7x views) showed varying IDs on the assemblies and supported the conclusions that the failures of the butt welds were the result of fatigue cracks caused by cyclic thermal stresses that initiated at stress-concentrating notches at the toes of the interior fillet welds on the surfaces of the flanges. Recommendations included using ultrasonic testing to identify the appropriate joints and then replacing them. Special attention to accuracy of fit-up in the replacement joints was also recommended to achieve smooth, notch-free contours on the interior surfaces.