Abstract
The microstructure, micrograph of the fracture sections and the alloy elements distribution of the fractured flange-connecting bolts of 3# circulating pump in a power plant were analyzed by the scanning electron microscopy, the optical microscopy and the electron probe microanalysis. The results showed that the failed bolts’ material is not the design material, and failure of the bolts is due to the stress corrosion crack propagation of the bolts’ austenitic material by chloride ions in seawater.
Highlights
During the time of other 20 flange-connecting bolts dismantled, 12 bolts were fallen off, and other 4 bolts were fractured
According to the analysis results shown in Tab.1, the material brands corresponding to similar elements in the world steel brands manual are listed in Tab.2[1]
Based on the above tests, the analysis conclusions are summarized as follows: (1) According to the chemical composition analysis of the bolts, the fractured bolt material belongs to high manganese steel
Summary
Some fractured bolts were collected for analysis, and the macrographs of these bolts are shown in Fig.. It can be observed that the screw threads of these bolts are in good condition basically. No crack defect is observed in the screw threads. All these bolts fractured at the smooth part in the middle of the bolts. The bolts fractured part don’t have the axial necking deformation by the appearance analysis, and don’t have the bending deformation. These characteristics indicate that the bolts fractured under low loads, which is generally considered as brittle fracture under low stress[2]
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