“…3 agrees with the potential-pH diagrams [29,30]. Meanwhile, the corrosion rate is well known to be related to protective chromium oxide layer is still maintained even at 500 °C by supplying enough chromium to the surface.…”
Section: Chemical Analysis Of Corrosion Layersupporting
A mechanically alloyed austenitic stainless steel (MA304LZ) was produced from pre-alloyed SUS304L powder with a small amount of zirconium addition. Coupon-type specimens of MA304LZ and SUS304L steels were subjected to hot water at 300 °C/25 MPa and supercritical pressurized water (SCW) at 500 °C/25 MPa for 1000 hr. MA304LZ is significantly less susceptible to corrosion weight gain in SCW than SUS304L which follows the parabolic rule between weight gain and elapsing time. The reduction of weight gain in MA304LZ can be attributed to much smaller grains which enhance chromium diffusion through grain boundaries and consequently accelerate the formation of a protective chromium oxide layer. Nickel oxides were observed in SUS304L but not in MA304LZ after the test at 500 °C. It is considered that zirconium addition suppresses nickel diffusion as well as oxygen diffusion because of the strong interaction of zirconium/nickel and zirconium/oxygen. Electrochemical potentiodynamic reactivation (EPR) measurement of the degree of sensitization (DOS) of annealed and non-annealed samples indicates that both steels were resistant to sensitization of grain boundary corrosion. However, the annealing of MA304LZ at 1050 °C diminishes the beneficial grain size effect of MA304LZ.
“…3 agrees with the potential-pH diagrams [29,30]. Meanwhile, the corrosion rate is well known to be related to protective chromium oxide layer is still maintained even at 500 °C by supplying enough chromium to the surface.…”
Section: Chemical Analysis Of Corrosion Layersupporting
A mechanically alloyed austenitic stainless steel (MA304LZ) was produced from pre-alloyed SUS304L powder with a small amount of zirconium addition. Coupon-type specimens of MA304LZ and SUS304L steels were subjected to hot water at 300 °C/25 MPa and supercritical pressurized water (SCW) at 500 °C/25 MPa for 1000 hr. MA304LZ is significantly less susceptible to corrosion weight gain in SCW than SUS304L which follows the parabolic rule between weight gain and elapsing time. The reduction of weight gain in MA304LZ can be attributed to much smaller grains which enhance chromium diffusion through grain boundaries and consequently accelerate the formation of a protective chromium oxide layer. Nickel oxides were observed in SUS304L but not in MA304LZ after the test at 500 °C. It is considered that zirconium addition suppresses nickel diffusion as well as oxygen diffusion because of the strong interaction of zirconium/nickel and zirconium/oxygen. Electrochemical potentiodynamic reactivation (EPR) measurement of the degree of sensitization (DOS) of annealed and non-annealed samples indicates that both steels were resistant to sensitization of grain boundary corrosion. However, the annealing of MA304LZ at 1050 °C diminishes the beneficial grain size effect of MA304LZ.
“…This fact is identical with the result inferred from the Pourbaix diagram for Fe-Cr-H 2 O in BWR water. 30) Mössbauer spectra of Zn x Fe 2+ 1−x Fe 3+ 2 O 4 in the range of 0<x≤0.6 prepared from aqueous solution show a doublet and two sextets attributed to irons of A and B sites, whereas the spectra in the range of x≥0.8 show only doublet. 31) Considering these facts, the obtained CEMS spectra of the zinc added samples in Figs.…”
Section: Conversion Electron Mössbauer Spectroscopymentioning
Effect of zinc and/or nickel addition on cobalt deposition was studied under simulated normal water chemistry condition of boiling water reactor. Type 316L stainless steel coupon was exposed to high temperature water including cobalt ion, together with zinc and/or nickel ions up to 1,000 h using experimental recirculating loops. Either addition of zinc or nickel ions reduced amounts of cobalt deposition on stainless steel. Simultaneous addition of both zinc and nickel ions showed the synergy effect; less amounts of cobalt deposition were observed for simultaneous addition of zinc and nickel ions comparing to individual addition at equivalent concentration. Glow discharge spectrometry and conversion electron Mössbauer spectroscopy revealed that the different mechanism of reducing cobalt deposition prevails between zinc and nickel ions.
“…From the basic equations by Tetelman 35 ) and Dugdale 36 ) it follows that With this link between the electrochemical and mechanical module, a respective fracture strain ε f is provided for a given value of Q H .…”
Section: Mechanical Module and Hydrogen Crackingmentioning
As an extension of recently presented SCC models for pure nickel and iron in high temperature water, the anodic path -hydrogen assisted stress corrosion cracking of a Cr-Ni alloy is presented simulating alloy 600 properties. With the local anodic path corrosion as the crack initiation phase, the respective oxides precipitate while the crack tip solution will acidify and establish local hydrogen ion reduction conditions. Depending on the applied global stress, local plastic straining will then provide an active crack tip surface that transfers atomic hydrogen to the plastic zone ahead of the crack tip.Hydrogen assisted crack propagation is then controlled by the calculated local hydrogen ion reduction charge and the plastic strain distribution ahead of the crack tip. The resultsshow that for global stress levels close to the yield stress and at constant dissolved oxygen contents the increasing dissolved hydrogen contents are providing peak crack growth rates at hydrogen levels that decrease both with increasing temperatures and bulk pH. The peak crack growth rates decrease also with decreasing global stress as well as with increasing temperature and increasing bulk pH. The results are in accordance with published experimental investigations and operational experiences regarding the effects of dissolved hydrogen on stress corrosion rates in high temperature waters of nuclear reactors. They are explained by the interaction between the electrochemical parameters of the respective reactions.
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