Time filter

Source Type

Hamakita, Japan

Naruse I.,Nagoya University | Yoshiie R.,Nagoya University | Matsuura M.,Nagoya University | Ueki Y.,EcoTopia Science Institute | And 2 more authors.
Journal of Chemical Engineering of Japan | Year: 2010

A thermal spraying technique was adopted to change the surface properties of heat exchanger tubes in pulverized coal fired boilers in order to reduce ash deposition. Initially, four types of coal ash with different melting points were tested as samples for ash deposition experiments.As a result, ash particles with higher fouling factor selectively adhered on the tube surface. Even for the ash particles with lower melting point, Ni alloy as a thermal spraying material played an effective role in reducing deposition. Ni alloy can reduce the ash deposition by limiting formation of molten slag at high temperature. In addition, long-term ash adhesion experiments were also carried out using a precise tension tester at high temperature. The effectiveness of the Ni alloy was also proved after long term contact between an ash pellet and a rod thermally sprayed Ni alloy at high temperature. This is because the Ni alloy can control the diffusion of Fe compounds from the tube rod to the ash deposition layer. © 2010 The Society of Chemical Engineers, Japan. Source

Nishikawa S.,Japan Power Engineering and Inspection Corporation | Ooi K.,Shibaura Institute of Technology | Ooi K.,Nippon Welding Rod Co. | Takahashi M.,Osaka University | Furukawa T.,Japan Power Engineering and Inspection Corporation
Yosetsu Gakkai Ronbunshu/Quarterly Journal of the Japan Welding Society | Year: 2015

Shielded metal arc weld metal for type 600 nickel base alloy (alloy 182) is used for weld components in nuclear power plants. To evaluate the intergranular corrosion resistance of alloy 182 after application of shot peening and subsequent thermal aging treatment at 593-793 K, we conducted the corrosion test (immersed in boiled 16% sulfuric acid + 5.7% copper sulfate aqueous solution at 57.6 ks) using specimens of alloy 182. The results show that the intergranular corrosion resistance of alloy 182 subjected to heat treatment at 893 K for 72 ks was improved by shot peening. Also, the intergranular corrosion resistance was not changed by thermal aging treatment at 593-793 K subsequent to shot peening. Because remaining chromium depletion layers along grain boundaries were still observed by transmission electron microscope (TEM) after shot peening, disappearance of chromium depletion layers cannot be a factor in the improvement of the intergranular corrosion resistance. The results of measurement of surface residual stress by the X-ray diffraction method show that the compressive residual stress introduced by shot peening still remained on the surface of the specimens. Based on these observations, we assumed that chromium depletion layers along grain boundaries near the surface were dissolved by the environment of the corrosion test, the dissolved regions were closed by the compressive residual stress on the surface, and then the remaining chromium depletion layers were protected from the corrosive environment. This assumption explains why the intergranular corrosion resistance was improved although chromium depletion layers remained. Source

Ohata M.,Osaka University | Ueno S.,Osaka University | Namekata T.,Nippon Steel and Sumikin Welding Co. | Satoh S.,Nippon Welding Rod Co. | And 4 more authors.
Welding in the World | Year: 2014

A finite element (FE) analysis of tensile test for a welded joint of austenitic stainless steel for a building structure SUS304A predicts necking in the weld metal as well as lower tensile strength than that of the base metal, even though the joints has the strength-overmatched weld metal. The FE analytical studies also suggest that such an anticipated deformation behavior comes from large difference in uniform elongation between the base metal and the weld metal. Experimental works for overmatched welded joints using SUS 304A and welding wire TS308MoJ supports the joint strength and the necking behavior demonstrated by the FE analysis. On the basis of parametric FE analyses, mechanical parameters that should be controlled to ensure the base metal necking and the tensile strength of a base metal in tensile test of the overmatched joint are proposed. © 2014 International Institute of Welding. Source

Naganuma H.,Tohoku Electric Power Co. | Ikeda N.,Tohoku Electric Power Co. | Ito T.,Nippon Welding Rod Co. | Matsuura M.,Nagoya University | And 4 more authors.
Fuel | Year: 2013

Some ash particles in solid fuels adhere on heat exchanger tube surfaces inside coal and/or biomass combustion boilers. The authors have already proposed a surface treatment on tubes, using a thermal spraying technique, to reduce ash deposition. Understanding reduction mechanisms of the ash deposition is necessary to evaluate effects of the surface treatment technique on the reduction of ash deposition. The reduction mechanisms of the ash deposition were elucidated due to physical and chemical aspects, measuring adhesion forces between the ash particles and some alloy specimens of the tube at high temperature under the simulated boiler conditions. As a result, the adhesion force increased with time and depended on both the ash types and the alloy specimens. The thermal spraying of Ni-alloy, in particular, could reduce the adhesion force. Moreover interface reactions between the ash particles and the alloy specimen played an effective role in increasing the adhesion force, alkali metal compounds in the ash samples also related to an increase of the adhesion force. Fe, which was one of the main alloy elements, diffused into the ash deposition layer beyond the interface. This observation result suggested that the interface reactions of the ash particles with the alloy caused an increase of the adhesion force. © 2012 Elsevier Ltd. All rights reserved. Source

Provided is a high Cr Ni-based alloy welding wire with which tensile strength and weld cracking resistance of a welded portion, the integrity of the microstructure of a welded metal, and inhibition of scale generation are improved. The high Cr Ni-based alloy welding wire is configured to have an alloy composition comprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si: 0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%, Ta: 1 to 10%, and Mo: 1 to 6%, and as inevitable impurities, Ca+Mg: less than 0.002%, N: 0.1% or less, P: 0.02% or less, O: 0.01% or less, S: 0.0015% or less, H: 0.0015% or less, Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni. Then, the high CrNi-based alloy welding wire is configured such that the contents of S, Ta, Al, and Ti satisfy the following relation (1) and the contents of Ta, Mo, and N satisfy the following relation (2):

Discover hidden collaborations