Effects of thermal history and segregation on the susceptibility of stress corrosion cracking (SCC) in the heat-affected zone (HAZ) of an alloy 182-A533B dissimilar weld joint in high temperature, oxygenated water doped with SO4 2- and Cl- was evaluated by creviced bent beam test. Results indicate that step cooling and the addition of Cl- promoted SCC propagation and reactivation in HAZ. It is also suggested that compositional changes induced by welding and step cooling, especially the segregation of ph...
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Correlation between phosphorus segregation and stress corrosion cracking susceptibility in the heat affected zone of an A533B-A182 dissimilar weld joint

Grain boundary (GB) segregation of phosphorus and alloying elements in the heat-affected zone (HAZ) of an Alloy182- A533B dissimilar weld joint used in nuclear reactor pressure vessels was studied quantitatively by three-dimensional atom probe tomography. Non-equilibrium segregation occurred during welding and post-weld heat treatment, leading to remarkable enrichment of P, C, Mn and Mo at GBs, of which the levels were all microstructure- dependent. After step cooling, P and Mn showed further increase ...
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Effects of thermal history and microstructure on grain boundary segregation in the heat-affected zone of an Alloy182-A533B dissimilar weld joint

To evaluate the rate of thermal embrittlement of type 316 low-carbon stainless steel weld metal at BWR operating temperature, aging test at 310°C, 335°C, and 400°C was carried out. Hardness of each ferrite and austenite phase of s pecimens was measured selectively by microhardness tester. Hardness of ferrite was increased apparently with all three aging temperatures, whereas hardness of austenite was not changed. Changes in the microstructure of ferrite ag ed at 310°C for 11,000h and 18,000h were analyzed ...
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Evaluation of aging embrittlement of low-carbon austenitic stainless steelweld metal near the BWR operating temperature

The crevice former which does not release anion impurities (e.g. Cl-) for SCC (Stress Corrosion Cracking) initiation experiment in simulated boiling water reactor water environment has been ev aluated. The creviced bent beam tests of sensitized stainless steel with using the crevice condition as an experimental parameter were carried out. Even SCC occurred at the part of specimen su rface which tested with only the spacer (no crevice former), it has been difficult to obtain the reproducible result. SCC ini...
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Evaluation of crevice former for SCC initiation experiment in simulated BWR water environment

The method for determining the repassivation potential for corrosion crevice of stainless steel is defined by JIS, but that of Alloy600 is not defined yet. In this paper, the method for determining the repassivation potential was considered based on the experiments with Alloy600 of nuclear constituent material by reference to JIS and intended to contribute to the establishment of it. In preparation for measuring the repassivation potential, the pitting potential dependence of Cl- concentration is measu...
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Study on the electrochemical method for determining the repassivation potential for corrosion crevice of Alloy600.

The purpose of this study is to investigate the following items focused on the microstructure near the fusion boundary of dissimilar weld joint with Ni-based weld metal and low alloy steel; (1) Microstructural characteristics near the fusion boundary, (2) Dominant factor that makes crack retardation near the fusion boundary. Main conclusions can be summarized as follows; (1) From the results of CBB tests, it has been understood that the low alloy s teel has no SCC susceptibility and that there is a differ...
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SCC propagation and cessation behavior near the fusion boundary of dissimilar weld jointwith Ni-based weld metal and low alloy steel

SCC behavior near the fusion boundary of dissimilar weld joint with Ni-based weld metal and low alloy steel in high temperature water has been investigated with special attention on relation t o the characteristics of microstructure. From the results of CBB test (1.0 ppm-Na2SO4 and 8 ppm dissolved oxygen), it has been obvious that the LAS has no SCC susceptibility. On the other hand, Alloy182 in the weld samples have SCC susceptibility. Most of crack tips have located at the fusion boundary, and the penetr...
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Characteristics of microstructure and SCC behavior near the fusion boundaryof Ni-base weld metal and low alloy steel

Crevice corrosion has been concerned in the Fukushima Daiichi Nuclear Power Station, since seawater was injected to make up water level as part of the emergency action. To evaluate structural integrity, it is important to inves tigate whether crevice corrosion occurred. The purpose of this study is to investigate conditions of crevice corrosion initiation and repassivation of SUS304L. SUS304L specimens with acrylic crevice were held at constant electr ochemical potentials in 1000ppm Cl- solution. It was in...
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Evaluation of crevice corrosion initiation condition and repassivation condition of SUS304L

Austenitic stainless steels are widely used as structural materials in many industries. However, stainless steels are susceptible to crevice corrosion in the solution including chloride ions. In this paper, at first, the most inhibitive anion against corrosion was investigated by anodic polarization measurement of type 316L stainless steel in the solution containing Cl- with candidate inhibitive anions (WO42-, MoO42-, VO3-). MoO42- was adopted as the most inhibitive anion in this study. Next, the effec...
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Effect on critical potentials for crevice corrosion initiation and repassivation of stainless steel by addition of inhibitive anion

1．はじめに 原子力発電プラントでは、安全性・信頼性を確保するために、毎年プラントを停止して電気事業法で義務付けられた定期検査を実施している。発電プラントの信頼性を確保しながら稼働率を高めるためには、保守作業の効率化が必要である。同時に、発電プラントの高経年化に伴い、メンテナンス技術の高度化が今後重要となってくる。一方、保守要員には高度な知識・技能・技術が要求され、ベテラン技能者のノウハウの伝承を含めた教育・訓練の効率化・高度化のための技術開発も必要とされている。これらを背景として、（株）東芝、（株）日立......