Long-term trends in the corrosion state and surface properties of the stainless steel tubes of steam generators decontaminated chemically in VVER-type nuclear reactors

Our previous studies have revealed that a ”hybrid” structure of the amorphous and crystalline phases is formed in the outermost surface region of the austenitic stainless steel tubes of steam generators (SGs) as an undesired consequence of the industrial application of the AP-CITROX (AP: alkaline permanganate; CITROX: citric and oxalic acid) decontamination technology. The formation of this mobile oxide-layer increased the amount of the corrosion products in the primary circuit significantly, resulting in magnetite deposition on fuel assemblies. Owing to the fact that there is no investigation method available for the in-situ monitoring of the inner surfaces of heat exchanger tubes, a research project based on sampling as well as on ex-situ electrochemical and surface analytical measurements was elaborated. Within the frame of this project, comprehensive investigation of the general corrosion state and metallographic features of 36 stainless steel specimens, cut out from various locations of the 21 steam generators of the Paks NPP in the time period of 2000-2007 has been performed. The present work gives a brief overview on the general corrosion state of the heat exchanger tubes of SGs, concerning the long-term effects of the AP-CITROX procedure on the chemical composition and structure of the protective oxide-layer.

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Comprehensive investigation of the corrosion state and surface properties of the stainless steel tubes of steam generators

Nova Biotechnologica et Chimica ◽

10.36547/nbc.1131 ◽

2021 ◽

Vol 9 (3) ◽

Author(s):

Andrea Szabó Nagy ◽

Kálmán Varga ◽

Bernadett Baja ◽

Zoltán Németh ◽

Deszo Oravetz ◽

...

Keyword(s):

Stainless Steel ◽

Heat Exchanger ◽

Chemical Composition ◽

Oxide Layer ◽

General Corrosion ◽

Steam Generators ◽

Protective Oxide ◽

Comprehensive Investigation ◽

Protective Oxide Layer ◽

Corrosion State

Evaluating the water chemistry in the primary circuit and the effect of chemical econtamination of the heat exchanger tubes performed by the AP-CITROX (AP: alkaline permanganate; CITROX: citric and oxalic acid) procedure at Paks NPP (Hungary), a project dealing with the comprehensive investigation of the general corrosion state of the steam generators (SGs) has been initiated. Owing to the fact that there is no investigation method available for the in-situ monitoring of the inner surfaces of heat exchanger tubes, a research program based on sampling as well as on ex-situ electrochemical (voltammetric) and surface analytical measurements (SEM-EDX, CEMS, XRD, XPS) was developed and elaborated. In the time period of 2000-2008 - within the frame of the above project - 45 stainless steel specimens, cut out from various locations of the steam generators of the Paks NPP were investigated. Based on the measured corrosion characteristics (corrosion rate, thickness and chemical composition of the protective oxide-layer) it was found that these parameters are strongly dependent on the decontamination history of steam generators. The present work gives a brief overview on the general corrosion state of the heat exchanger tubes of SGs, concerning the long-term effects of the AP-CITROX procedure on the chemical composition and structure of the protective oxide-layer.

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Residual Stresses in Bent Tubes for Nuclear Steam Generators

CORROSION ◽

10.5006/0010-9312-32.9.357 ◽

1976 ◽

Vol 32 (9) ◽

pp. 357-364 ◽

Cited By ~ 4

Author(s):

Ph. BERGE ◽

H. D. BUI ◽

J. R. DONATI ◽

D. VILLARD

Keyword(s):

Stainless Steel ◽

Residual Stresses ◽

Stress Corrosion ◽

Strain Gauge ◽

Corrosion Test ◽

Steam Generators ◽

Steel Tubes ◽

Inconel 600 ◽

Stress Relieving ◽

Very High

Abstract Residual stresses in Inconel 600 tubes for PWR steam generators were measured using the strain gauge technique, and the results were checked by a stress corrosion test in boiling MgCl2 performed on stainless steel tubes manufactured according to the same process as the Inconel 600 tubes. It was shown that very high tensile stresses, equal to or even exceeding the yield stress, could exist as a result of the straightening, bending or roll expanding operations. The efficiency of possible stress relieving treatments was also investigated.

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Pyrolytic carbon filaments and associated catalytic particles formed in steel tubes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113196 ◽

1984 ◽

Vol 42 ◽

pp. 662-663

Author(s):

Y. L. Chen ◽

J. R. Bradley

Keyword(s):

Stainless Steel ◽

Carbon Steel ◽

Catalyst Particle ◽

Pyrolytic Carbon ◽

Plain Carbon Steel ◽

304 Stainless Steel ◽

Hydrocarbon Gases ◽

Steel Tubes ◽

Filamentous Carbon ◽

Carbon Filaments

Considerable effort has been directed toward an improved understanding of the production of the strong and stiff ∼ 1-20 μm diameter pyrolytic carbon fibers of the type reported by Koyama and, more recently, by Tibbetts. These macroscopic fibers are produced when pyrolytic carbon filaments (∼ 0.1 μm or less in diameter) are thickened by deposition of carbon during thermal decomposition of hydrocarbon gases. Each such precursor filament normally lengthens in association with an attached catalyst particle. The subject of filamentous carbon formation and much of the work on characterization of the catalyst particles have been reviewed thoroughly by Baker and Harris. However, identification of the catalyst particles remains a problem of continuing interest. The purpose of this work was to characterize the microstructure of the pyrolytic carbon filaments and the catalyst particles formed inside stainless steel and plain carbon steel tubes. For the present study, natural gas (∼; 97 % methane) was passed through type 304 stainless steel and SAE 1020 plain carbon steel tubes at 1240°K.

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