Oxidation behavior and cracking susceptibility of the Ni-Cr alloys (Ni-14Cr, Ni-22Cr and Ni-30Cr) under extremely-low oxygen partial pressure have been investigated by experiments used as plate specimen and Reverse U-Bend (RUB) specimen for 750 hours at 400 °C in two kinds of gas system (inert gas and dry steam) under various oxygen potential (Ni stable, Ni/NiO equilibrium and NiO stable).The Ni-Cr alloys cracked along grain boundary both in inert gas system (with trace O2, without H2O ) and in hydrogenat...
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Oxidation behavior under stress of Ni-Cr alloys in gas phase under extremely-low oxygen potential

Pipe wall thinning is one of the important degradation phenomena taking place in the nuclear power plant. Major mechanism of the mainly pipe wall thinning is Flow Accelerated Corrosion (FAC), where chemical process plays the primary role. But mechanism of FAC is not yet full y understood. Especially characteristics of oxide film formed in FAC is not well known although oxide film property would be strongly related to thinning rate in FAC. The main objective of this work is finding characteristics of oxide ...
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Relation of Thinning Rate and Characterization of The Oxide Film Formed in Flow Accelerated Corrosion of Carbon Steels

Wet polish with fine emery paper is most commonly used for final finish of SCC specimens and corrosion coupons. Although cold w ork introduced by the fine emery finish is slight, a series of experiments have demonstrated that the very slight cold work can ffect oxidation behaviors and apparent SCC susceptibility of Ni base alloys in hydrogenated steam. Oxidation tests and reverse type SCC experiments have been done in hydrogenated steam at 400C for Ni-Cr binary alloys with various Cr content from 14% t o 3...
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Effect of slight cold work introduced with fine emery finish on oxidation and cracking behaviours of Ni base alloys in hydrogenated steam

Corrosion rate of carbon steel SS400 was investigated in test solution (NaClaq, Cl-:200ppm) with a rotating cylinder electrode system. Polarization resistance measurement was used to determine variation of corrosion rate with time and specimens surface were observed after the measurements. Under aerated condition (dissolved oxygen: 7.3ppm), the corrosion rate increased with increasing rotating speed in low rotation speed ranges , but the corrosion rate decreased in high rotating speed ranges. The reas...
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Evaluation of corrosion of cooling system piping of Fukushima Daiichi NPP

It was reported that nitride layer formed on SUS310S heating tubes in the reactor of melamine production plant showed severe spalling susceptibility. After replacement to SUS304heating tubes, spalling and thinning was suppressed. According to previous studies, a crystal structure of the nitrided layers of SUS310S and SUS304 heating tubes mainly consist of γ’ and α’, respectively. The reason why the SUS304 heating tube showed low spalling susceptibility was considered to be a smaller expansion rate of α...
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Wastage mechanism of heating tubes made of austenitic stainless steels in a complex environment of nitriding, oxidizing, and carburizing

In this study, we investigate the effect of oxygen potential on oxide film, intergranular oxidation and cracking susceptibility on nickel base alloy in hydrogenated superheated steam at 400℃. Intergranular cracking occurred at oxygen potential of LOGPO2=-26.32(Ni/NiO equilibrium). In contrast, no cracking occurred at oxygen potential of LOGPO2=-24.09 and LOGPO2=-27.04(near the cracked condition). This result shows that oxygen potential range for cracking susceptibility seemed to be narrow in hydrogenat...
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Effect of oxygen potential on oxide film, intergranular oxidation and cracking susceptibility on nickel base alloy in superheated steam

内一 哲哉 Tetsuya UCHIMOTO Although electrochemical transients can provide very sensitive indication about the onset of localized corrosion, including initiation of stress corrosion cracking (SCC), information on location of the initiation site is not available. In the present study, we proposed an estimation method of location and m agnitude of SCC initiation events, where electrochemical transients associated with local anodic events are measured by multiple reference electrodes and location of the initi...
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Electrochemical Method for Monitoring Film Ruptures in SCC Initiation Processes