가압형 경수로 압력용기 재료인 저합금강의 동적 붕산 부식 실증 연구

In present study mass loss behaviour of base metal and heat-treated API X70 pipeline steel in different environments such as fresh water, sea water and sodium thiosulphate medium were observed for 50 days. Corrosion is the main failure in pipeline steel which need to be reduced with the use of suitable heat treatment process. In present study two heat treatment such as HT-1 900 °C (2 hour) with tempering at 450 °C (4 hour) and HT-2 800 °C (2 hour) with tempering at 450 °C (4 hour) was used. Mechanical, microstructure and corrosion rate of HT-1 and HT-2 specimen in different environments were observed. Maximum corrosion rate (0.306 mm/y) in fresh water while minimum corrosion rate (0.181 mm/y) in sodium thiosulphate medium was observed for base metal. Maximum corrosion rate (0.224 mm/y) in sodium thiosulphate while minimum corrosion rate (0.106 mm/y) in fresh water medium was observed for HT-1 specimen. For HT-2 specimen, Maximum corrosion rate (0.192 mm/y) in sea water while minimum corrosion rate (0.099 mm/y) in fresh water medium was observed. For HT-2 specimen, maximum average hardness of (30.3 HRC) in sea water while minimum average hardness of (28 HRC) of base metal was observed. In fresh water also HT-2 specimen, maximum average hardness is (26.3 HRC) while minimum average hardness of (24.6 HRC) of base metal was observed. After that maximum average hardness of base metal (26.6 HRC) in sodium thiosulphate while minimum average hardness of (21 HRC) of HT-2 specimen was observed.

Borated water leakage through spent fuel pools (SFPs) at pressurized water reactors is a concern because it could cause corrosion of reinforcement steel in the concrete structure and compromise the integrity of the structure. Because corrosion rate of carbon steel in concrete in the presence of boric acid is lacking in published literature and available data are equivocal on the effect of boric acid on rebar corrosion, corrosion rate measurements were conducted in this study using several test methods. Rebar corrosion rates were measured in (i) borated water flowing in a simulated concrete crack, (ii) borated water flowing over a concrete surface, (iii) borated water that has reacted with concrete, and (iv) 2,400 ppm boric acid solutions with pH adjusted to a range of 6.0 to 7.7. The corrosion rates were measured using coupled multielectrode array sensor (CMAS) and linear polarization resistance (LPR) probes, both made using carbon steel. The results indicate that rebar corrosion rates are low (~1 µm/yr or less) when the solution pH is ~7.1 or higher. Below pH ~7.1, the corrosion rate increases with decreasing pH and can reach ~100 µm/yr in solutions with pH less than ~6.7. The threshold pH for carbon steel corrosion in borated solution is between 6.8 and 7.3.

The primary purpose of this research is to examine the stress corrosion cracking (SCC) resistance of Alloy 800NG in pressurized water reactor (PWR) primary water and pressurized heavy water reactor (PHWR) primary water. Rates of SCC growth of 20% cold-worked (CW) Alloy 800NG measured over the temperature range between 270°C and 360°C were compared with previously reported results for 20% CW Alloy TT690 and 20% CW Alloy 600 in order to consider which material is the most SCC resistant among materials presently being used for steam generator (SG) tubing worldwide. The secondary purpose is to examine the effect of chromium addition on SCC growth in PWR primary water of a series of alloys based on the Alloy 800 composition. SCC growth measurements were performed in PWR primary water over the chromium concentration range from 16% to 27% to obtain fundamental knowledge useful for considering a future alternative SCC-resistant material for SG tubing in extended life PWRs and PHWRs. The third objective is to examine the rate of cavity formation of 20% CW Alloy 800NG to obtain basic knowledge of one possible mechanism for SCC initiation after long-term operation. Measured rates of cavity formation in 20% CW Alloy 800NG were compared with previously reported results of 20% CW Alloy TT690 to compare the rate of SCC initiation caused by cavity formation. Four important patterns were observed. First, excellent SCC growth resistance was observed for 20% CW Alloy 800NG compared to 20% CW Alloy TT690 at 320°C, 340°C, and 360°C. Second, an inverse temperature dependence on SCC growth was observed in Alloy 800NG. The rate of SCC growth increased with decreasing temperature which was completely different from the trend for Alloy 600. Third, a significant beneficial effect by chromium addition in 800 series alloys on SCC growth resistance was observed in PWR primary water in the operating temperature range of PWRs and PHWRs. The rate of SCC growth decreased with increasing chromium concentration in the chromium concentration range between 16% and 27% chromium at 270°C, 290°C, and 320°C. However, no beneficial effect of chromium addition in these alloys was observed at 340°C and 360°C. Finally, a more than 10 times slower rate of cavity formation was observed in 20% CW Alloy 800NG than for 20% CW Alloy TT690. Results suggested that because of cavity formation, a more than 10-fold faster crack initiation occurred in Alloy TT690 than in Alloy 800NG. Further, carbide coverage and grain size significantly affected the rate of cavity formation. Detailed and comprehensive studies of long-term SCC initiation are necessary to ensure the future reliability of life-extended PWRs and PHWRs.

An investigation has been made of the influence of amount and distribution of precipitate phase on the corrosion kinetics of “low purity” zirconium in 20 percent hydrochloric acid at 200 C. It was found that minimum corrosion rates, coincident with minimum values of activation energy and frequency factor in the Arrhenius relationship, were obtained by solution heat treatment at 700 C followed by water quenching. Such heat treatment gave a corrosion rate equivalent to that of alpha annealed iodide zirconium. A maximum corrosion rate was obtained by a beta solution treatment at 890 C followed by water quenching, whereas beta solution treatment at 1000 C gave sharply reduced corrosion rates. Nature of distribution of the precipitate phase profoundly influenced corrosion rate. A discontinuous pattern of intergranular and transgranular globular particles was substantially less deleterious than the same amount of impurity phase finely disseminated throughout the microstructure. The results of the investigation are discussed in terms of the possible roles of chlorine and hydroxyl ions in the corrosion mechanism. Relative effects on corrosion kinetics of statistical distributions of active sites (each characteristic of lattice configurations produced by lattice defects, solute atoms and precipitation phenomena) are also considered.

Soil is the most diverse environment that can cause metal corrosion. Many researchers claim that soil is a corrosive environment that has complexity compared to other environments. With a background knowledge of soil engineering properties in a specific area and their effects on the metal corrosion process then corrosion problems can be prevented. This paper presents the relationship between andesitic volcanic soil engineering properties with an average corrosion rate based on geotechnical and statistical methods. In this paper, we propose a new average corrosion rate per year on that soil. The study area took place on the Sekincau-Way Tenong Transect Road, West Lampung, Sumatra, Indonesia. This area was composed of silty clay to clayey silt soils which weathering products from andesitic-basaltic volcanic breccia. This soil can store water that is moderate to high and has high plastic properties. Based on the statistical approach, it can be concluded that the corrosion rate in andesitic volcanic soils is 1.132 mm/yr. Soil engineering properties (water content, index plasticity, and clay content) simultaneously affect the average corrosion rate. The effective contribution of each independent variable (soil engineering properties) to the corrosion rate is a plasticity index of 39.5%, the water content of 24.79%, and clay content of 26.04%. Index plasticity and water content were found to raise the average corrosion rate at the soil samples, while clay content was on the side that lowered the average corrosion rate.

Effect of residual tensile stress and crystallographic structure on corrosion behavior of AZ31 Mg alloy rolled sheets

The main purpose of the present study was to develop a comprehensive model that can predict the pitting corrosion rate of oil and gas pipelines containing CO2, H2S, and bacteria. Pitting corrosion has been described using a diffusion model in a unidirectional pit. The model considers 22 ionic species and the potential value inside the pit. The diffusion coefficient values of these ions, which strongly affect the corrosion rate, were found in the literature. This model predicts whether pitting will occur and the maximum corrosion rate at the time of the formation of a corrosion protective scale. The presence of H2S allows for the formation of FeS film, which has a suppressive effect on the CO2 corrosion rate. This suppressive effect on CO2 corrosion rate is more dramatic with increasing temperature and concentration of H2S. In the presence of bacteria, the concentration of sulfates at the bottom of the pit goes to zero when convergence occurs. The sulfate reducing bacteria reduces sulfate to sulfide and produces acetic acid at the bottom of the pit, which accelerates corrosion. These acetates also form complexes with iron, which increase the acidity of the pit. This comprehensive model provides information such as the corrosion rate in mils per year, if the system is CO2 or H2S dominated, and if the system is in a pitting or non-pitting condition. It was observed that the primary parameters that affect the model predictions are temperature, bulk pH, concentration of acetates, concentration of sodium chloride, concentration of hydrogen sulfide, concentration of sulfates, and metal wall thickness.

Corrosion of platinum catalyst in alkaline solutions

<p>The pressurizer is the component in the reactor coolant system which provides a means of controlling the system pressure. The pressurizer has a function to keep the operational pressure of reactor coolant system in set point condition. For controlling primary coolant system pressure, the pressurizer has pressurizer spray, heater, safety relief valve and instrumentation to control level and pressurizer. The purpose of this study is to see the effect of boric acid, lithium hydroxide and temperature on SS 304 as PWR pressurizer material.The method that used in this research is to observe the corrosion rates of pressurizer material in several boric acid and lithium hydroxide concentration at several temperature conditions using Potentiostat. Tests were conducted in 28, 60, 80,and 100 °C in 2000, 2500, 3000 ppm boric acid and addition 2.0 and 2.5 ppm lithium hydroxide. The pressurizer material corrodes in solution containing boric acid solution. The corrosion rates increased if boric acid solution concentration and temperature also increased. The results showed that that corrosion rate for the material were very small and the highest corrosion rate occurred in 3000 ppm boric acid concentration at 80 °C ,that is 4.5913 x 10<sup>-1</sup> mpy.The corrosion rates increased until temperature 80 °C, but increasing the temperature from 80 °C to 100 °C decreased the corrosion rates from4.5913 x 10<sup>-1</sup> to 4.5264 x 10<sup>-1</sup>mpy. Lithium hidroxide addition in boric acid containing media generally decreased SS 304 corrosion rate as P W R pressurizer material.K.</p>

Reinforced mortar samples were exposed in humidity chambers with different relative humidity or exposed in cyclic moisture conditions. The rebars were in an “as received” condition meaning that the preexisting oxide scale were intact. The lowest chloride concentration that initiated corrosion was 1% Cl− by mass of cement, corrosion was then observed for samples exposed at 97% relative humidity. It is suggested that the corrosion rate decreases when samples are exposed to a relative humidity lower than 97%. The results indicate that threshold levels should be evaluated at rather humid conditions (97%) despite the fact that the maximum corrosion rate at higher chloride levels is observed in the interval 91–94%. For samples exposed to cyclic moisture conditions, a lower chloride concentration was needed to initiate corrosion compared to samples exposed in static moisture conditions.

In the context of increased pace of modern production, the role of heat treatment is increasing, as it is the main method for producing steels with a given structure and mechanical properties. Parts used in production must have a long service life not only at room temperature, but also have high strength characteristics at low and high temperatures. In this regard, special attention is paid to steel used for the manufacture of such parts. One of them is steel grade St52-3 (rus 17Г1C). The aim of the work was to determine the effect of quenching at various temperatures onto corrosion resistance of St52-3 steel. To achieve this goal, tasks such as studying the effect of different tempering temperatures of St52-3 steel on the value of hardness according to the Rockwell method were undertaken. After-treatment gravimetric studies were performed to identify the temperature regime of tempering that minimizes the corrosion rates. It was shown that after tempering, the hardness of the samples decreases with increasing temperature. To assess the corrosiveness of the medium for the test samples, the mass and depth corrosion indicators were calculated. The maximum corrosion rate is observed during quenching and subsequent tempering at a temperature of 300 °C, the minimum at a tempering temperature of 500 °C.

Kinetics of mild steel corrosion in aqueous formic acid solutions

Corrosion behaviour of mild steel in formic acid solutions

Corrosion and inhibition studies of copper in aqueous solutions of formic acid and acetic acid

Primary-to-secondary leaks in the U-bend regions of certain pressurized water reactor (PWR) steam generators prompted removal of 29 Inconel 600 U-bends from the Trojan Steam Generator D for examination. Metallurgical examinations clearly indicated that the cracks initiate from the primary system (inner) tube surface and propagate intergranularly. The cracks occur in the extrados side of the irregular* (also called opposite) transition. The cracking developed in the borated primary system water, suggesting that it is an example of Coriou-type cracking of Inconel 600.