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Abstract:The aim of this work was to investigate the corrosion rate of welded carbon steel pipe (ASTM (American Society for Testing and Materials) A106 Grade B) by GTAW under the currents of 60, 70, and 80 A. All welded pipes satisfied weld procedure specifications and were verified by a procedure qualification record. The property of used materials was in agreement with the ASME standard: section IX. The welded pipe was used for schematic model corrosion measurements applied in 3.5 wt % NaCl at various flow rates and analyzed by using the electrochemical technique with Tafel's equation. The results showed the correlation between the flow rate and the corrosion rate of the pipe; the greater the flow rate, the higher corrosion rate. Moreover, the welded pipe from the welding current of 70 A exhibited higher tensile strength and corrosion resistance than those from currents of 60 and 80 A. It indicated that the welding current of 70 A produced optimum heat for the welding of A106 pipe grade B. In addition, the microstructure of the welded pipe was observed by SEM. The phase transformation and crystallite size were analyzed by XRD and Sherrer's equation. The results suggested that the welding current could change the microstructure and phase of the welded pipe causing change in the corrosion rate.

This work presents the improvement of hardfacing welding for American Society for Testing and Materials (ASTM) A572-based high-strength, low-alloy steel by controlling the heating/cooling conditions of welding process. In the welding process, the buffer and hardfacing layers were welded onto A572-based material by a nickel–chromium electrode and chromium carbide electrode, respectively. The base metal and electrode materials were controlled by the heating/cooling process during the welding to reduce excessive stress, which could result in a crack in the specimens. The welded specimens were examined by visual and penetrant inspections for evaluating the welding quality. The macro–micro structure of the deposited layer was investigated; scanning electron microscope with an energy-dispersive X-ray spectrometer (SEM-EDS) and XRD were used to characterize structural properties, elemental compositions, and crystallite sizes of the welded specimens. The surface properties, such as hardness, impact, and abrasive wear of the welded specimens, were tested for evaluation of the wear resistance of the welded specimens.

This paper presents a specific kind of failure in ethylene pyrolysis furnace tubes. It considers the case in which the tubes made of 35Cr-45Ni-Nb high temperature alloy failed to carburization, causing creep damage. The investigation found that used tubes became difficult to weld repair due to internal carburized layers of the tube. The microstructure and geochemical component of crystallized carbide at grain boundary of tube specimens were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) with back-scattered electrons mode (BSE), and energy dispersive X-ray spectroscopy (EDS). Micro-hardness tests was performed to determine the hardness of the matrix and the compounds of new and used tube material. The testing result indicated that used tubes exhibited a higher hardness and higher degree of carburization compared to those of new tubes. The microstructure of used tubes also revealed coarse chromium carbide precipitation and a continuous carbide lattice at austenite grain boundaries. However, thermal heat treatment applied for developing tube weld repair could result in dissolving or breaking up chromium carbide with a decrease in hardness value. This procedure is recommended to improve the weldability of the 35Cr-45Ni-Nb used tubes alloy.