The stub-shaft assembly which was part of the agitator shaft in a polyvinyl chloride reactor, fractured in service after a nut that retained a loose sleeve around the smaller-diam section of the shaft had been tightened several times to reduce leakage. The shaft was made of ASTM A105, grade 2 steel, and the larger-diam section was covered with a type 316 stainless steel end cap. The cap was welded to each end using type ER316 stainless steel filler metal. The forged steel shaft was revealed to have fractured at approximately 90 deg to the shaft axis in the weld metal and not in the heat-affected zone of the forged steel shaft. Microscopic investigation and chemical analysis of the steel shaft revealed presence of martensite (offered a path of easy crack propagation) around the fusion line and dilution of the weld metal by the carbon steel shaft. The microstructure was found to be martensitic as the fusion line was approached. The forged steel shaft was concluded to have failed by ductile fracture and possible reasons were discussed. Corrective measures adopted in the replacement shaft were specified.

During the pre-test inspection following the stress calculation check on a 7-ton capacity Scotch derrick crane, it was noted that threads on the back stay anchorage bolts were of unusually fine pitch (11 tpi) and that the machined faces of the nuts showed irregular pits or depressions disposed in an annular manner. When sectioned, the nuts showed a surprising method of construction. The nuts for the bolts had been made by using conventional pipe couplings inserted into sleeves made from hexagonal bar and the coupling secured to the sleeve by welding at each outer face. The ends of the sleeve bore were chamfered to form a weld preparation. After welding, the faces were machined which resulted in the removal of most of the weld metal and revealed a pronounced lack of penetration. All bolts used to anchor derrick crane back stays should be designed in accordance with the recommendations of British Standard 327:1964 (Clauses 10 and 18).

A sand-cast gray iron flanged nut was used to adjust the upper roll on a 3.05 m (10 ft) pyramid-type plate-bending machine. The flange broke away from the body of the nut during service. Analysis (visual inspection and 150x micrographs of sections etched with nital) supported the conclusions that brittle fracture of the flange from the body was the result of overload caused by misalignment between the flange and the roll holder. The microstructure contained graphite flakes of excessive size and inclusions in critical areas; however, these metallurgical imperfections did not appear to have had significant effects on the fracture. Recommendations included carefully and properly aligning the flange surface with the roll holder to achieve uniform distribution of the load. Also, a more ductile metal, such as steel or ductile iron, would be more suitable for this application and would require less exact alignment.

A steam turbine developed excessive noise and vibration during routine operation. It was found that the nut that locked the turbine disk In place had worked its way out from the threads and the disk had come of the shaft. Examination of the locking mechanism indicated that its design was responsible for the loosening of the nut. It was recommended that the locking mechanism be redesigned and changed in all existing turbines.