Characterization of Working Thicknesses of Some Bath-Dip-Produced Corrosion – Protective Bitumen Coatings on Polish-Prepared Low Carbon Steel Specimens
The coating thickness is an important variable that plays a role in product quality, process control and cost. Determination of the required working thicknesses for different service requirements is however a complicated task in the product finishing field. A previous study has shown that Nigeria is blessed with abundant bitumen resources for sustained exploitation as common, economical and effective coat-inhibitors of steelwork corrosion in her economy. This paper presents a testdetermination of the expected range of working thicknesses of coatings with proper bitumens from the resources. Bitumen samples were harvested at three different critical bitumen resource sites in the country for the tests. 30 specimens of the steel were properly prepared. Coatings of different thicknesses were produced on the specimens by dipping a different pair of them in each bitumen sample heated to each of five different temperatures in the range of 170 – 230 O C and removing and cooling them to 38 O C-room-temperature. The thickness of each produced coating was properly determined with a micrometer through dimensional change before and after coating. Analysis of the overall obtained data shows that the average working thicknesses of coatings with any bitumens of comparable quality to the as-harvested from the resources using temperatures in the range will decrease with increase in temperature from about 1.46 to 0.81mm respectively, and thicknesses of coatings with the separate bitumens using the same bath temperature will have minimal variations.
Marine Corrosion
This brief discussion will highlight the types of marine corrosion problems that are encountered in Naval service. Literally millions of parts are involved in the construction and use of Naval ships and all may be subject to the deleterious effects of seawater unless suitable precautions are taken. The important aspect of marine corrosion is to be aware of the limitations of materials and to understand the material/environment interactions in order to overcome such limitations.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.