Volume 51, Issue 6

This paper first introduces the structure of multiple-anticorrosive bolts and the anticorrosive mechanism. To thoroughly analyze the durability of multiple-anticorrosive bolts in a corrosive environment, different corrosive environments were simulated and experiments on the durability of double- and multiple-anticorrosive bolts were conducted. Apparent changes were observed and the bond strength after corrosion was measured. From these test data, the resistance to corrosion was compared for the two types of bolts, and formulae for the service life of double- and multiple-anticorrosive bolts were derived in different corrosive environments. At the same time, a number of modification coefficients for optimization of the service-life formulae were put forward. The anticorrosion performance of the multiple-anticorrosive bolt was mainly studied and compared with that of the double-anticorrosion bolt, and the multiple-anticorrosive bolt was verified to have superior durability in a corrosive environment. The conclusions drawn in this study can be applied in the design of anticorrosive bolts to be used in an underground structure and later applied in durability analysis, providing reference values for actual engineering.

The three dimensional microstructural evolution of cast B206 (AlCu5Mg0.3Mn0.3) and AlCu7 (AlCu7Mn0.4) alloys is studied as a function of solution treatment time by synchrotron tomography. Both alloys are formed by an α-Al matrix, Al 2 Cu and Al 7 Cu 2 (FeMn). 3D microstructural parameters of the aluminides such as volume fraction and interconnectivity are presented for the alloys in as-cast condition and after 4 h, 8 h and 16 h of solution treatment at 530 °C. Morphological evolution is obtained from the mean and Gauss curvature distribution. Finally, target metallography is combined with energy dispersive x-ray analysis to identify the phases remaining after 16 h of solution treatment.

A number of retaining rings used in fuel gas piping assemblies of large stationary heavy-duty industrial gas turbines were found broken upon reception at the gas turbine manufacturer's plant. While the pipes were made of AISI 321 austenitic stainless steel, 1.4541, X6CrNiTi18-10, the specified material of the subject locking rings is the martensitic stainless chromium steel X39CrMo17-1, 1.4122. In fact, however, the failed snap rings consisted of the lower-chromium X39Cr13, 1.4031. The fractured retaining rings all originated from a particular North American supply chain. In contrast, the same pipe assemblies delivered by an alterna­tive second-source European supplier did not show these remarkable fractures in their retain­ing rings. Also, they were indeed made of the specified higher-chromium material. It was later discovered that the supplier that shipped the faulty product employed a peculiar wet cleaning process without proper post-cleaning drying. The conclusion of the metallurgical failure analysis was that the subject retaining rings failed by intergranular corrosion due to sensitisation from heat treatment and wet cleaning residues that remained on the product and caused corrosion during shipment. The erroneous material selection, violating the specifica­tion, contributed to the failure.