Corrosion products high-temperature water

Because of its neuronic, mechanical, and physical properties, hafnium is an excellent control material for water-cooled, water-moderated reactors. It is found together with zirconium, and the process that produces pure zirconium produces hafnium as a by-product. Hafnium is resistant to corrosion by high-temperature water, has adequate mechanical strength, and can be readily fabricated. Hafnium consists of four isotopes, each of which has appreciable neutron absorption cross sections. The capture of neutrons by the isotope hafnium-177 leads to the formation of hafnium-178 the latter forms hafnium-179, which leads to hafnium-180. The first three have large resonance-capture cross sections, and hafnium-180 has a moderately large cross section. Thus, the element hafnium in its natural form has a long, useful lifetime as a neutron absorber. Because of the limited availability and high cost of hafnium, its use as a control material in civilian power reactors has been restricted. 

Corrosion products are another source of error in the potentiostatic determination of polarisation curves in high-temperature water. In stagnant tests Fe could be converted to FejO,, causing a false anodic current... 

K. Makela, T. Buddas, M. Zmitko, J. Kysela, The effect of hydrazine on high temperature water chemistry and corrosion product transport in primary circuit of a VVER 440 unit, Water Chemistry Conference, Nice, France, 1994. 

Lister [1981] states that Equation 7.31 has formed the basis of some reasonable predictions of corrosion product deposits in various high temperature water systems [Brusakov 1971]. 

Corrosion refers to the degradation of a metal by electrochemical reaction with the environment. At room temperature, the most important corrosion reactions involve water, and the process is known as aqueous corrosion. (Corrosion at high temperatures in dry air, called oxidation tarnishing, or direct corrosion, is considered in Section 8.5.) Aqueous corrosion involves a set of complex electrochemical reactions in which the metal reverts to a more stable condition, usually an oxide or mixture of oxides and hydroxides (Figure 9.15). In many cases the products are not crystalline and are frequently mixtures of compounds. Aside from the loss of metal, the corrosion products may be voluminous. In this case, they force overlying protective layers away from the metal and so allow corrosion to proceed unchecked, which exacerbates the damage. 

The oxide layers mentioned above are generated by oxidation of the Zircaloy base material by high-temperature water or steam. They must not be confused with the layers formed by deposition of corrosion product oxides originating from the surfaces of the other primary circuit components and structures these corrosion... 

Lister, D. H. (b) The transport of radioactive corrosion products in high-temperature water. 

Lister, D. H., Kushneriuk, S. A., Campbell, R. H. The transport of radioactive corrosion products in high-temperature water. — III. The interaction of dissolved cobalt with heated surfaces. Nucl. Sci. Engng. 85, 221—232 (1983)... 

Ishigure, K., Fujita, N., Tamura, T, Oshima, K. Effect of gamma radiation on the release of corrosion products from carbon steel and stainless steel in high-temperature water. Nucl. Technology 50, 169-177 (1980)... 

Since zinc does not form a protective scale, it is attacked by distilled and high purity water [64]. The corrosion products in distilled water at room temperature are zinc hydroxide and a little zinc oxide, at 85 °C zinc oxide which can contain zinc hydroxide [177]. In high purity water dissolved carbon dioxide attacks zinc however as soon as the CO2 content reaches 27 nig/1 a protective scale of zinc carbonate is formed [178]. The corrosion behaivour of zinc in distilled water (up to 3 bar, up to 100 °C) free from air and aerated shows two corrosion maxima one at 30-40 °C which increased with increasing pressure and another at 65-70 °C which decreased with increasing pressure [179]. Paint containing a zinc pigment on steel does not give adequate protection to distilled water. 

On the low pressure side 90/10 cupronickel was used to tube Nos 1 and 2 LP heater, and the deaerator vent condenser, as at low temperatures of operation no serious corrosion was expected on the steam side even In the presence of oxygen. On the water side most of the released corrosion products will be removed by the full flow Ion exchange treatment given by Powdex resin Interposed beyond the second LP heater. Typical analysis for water which has been given this treatment are 5 ppb maximum for metals normally encountered In feed-water circuits. Unfortunately It Is clear from power station experience that a significant pick-up of corrosion products on the water side takes place In the high pressure feed heaters downstream of the clean-up plant. 

Calcium carbonate has normal pH and inverse temperature solubilities. Hence, such deposits readily form as pH and water temperature rise. Copper carbonate can form beneath deposit accumulations, producing a friable bluish-white corrosion product (Fig. 4.17). Beneath the carbonate, sparkling, ruby-red cuprous oxide crystals will often be found on copper alloys (Fig. 4.18). The cuprous oxide is friable, as these crystals are small and do not readily cling to one another or other surfaces (Fig. 4.19). If chloride concentrations are high, a white copper chloride corrosion product may be present beneath the cuprous oxide layer. However, experience shows that copper chloride accumulation is usually slight relative to other corrosion product masses in most natural waters. 

The acidic catalysts used for these reactions include formic acid, HX (X = F, Cl, Br), oxalic acid, phosphoric acid, sulfuric acid, sulfamic acid, and p-toluenesulfonic acid.4 Oxalic acid is preferred since resins with low color can be obtained. Oxalic acid also decomposes at high temperatures (>180°C) to C02, CO, and water, which facilitates the removal of this catalyst thermally. Typically, 1-6 wt % catalyst is used. Hydrochloric acid results in corrosive materials and reportedly releases carcinogenic chloromethyl ether by-products during resin synthesis.2... 

A corrosion inhibitor that is the adduct of a carbonyl compound, an amine, and a thiocyanate has been described [1431]. The product provides protection against ferrous corrosion in severe environments. 500 ppm by weight is sufficient. The inhibitor is employed in wells producing both oil and water and in high-temperature environments around 120° C. 

The production of biodiesel from low quality oils such as animal fats, greases, and tropical oils is challenging due to the presence of undesirable components especially FFA and water. A pre-treatment step is required when using such high fatty-acid feedstock. Generally, this esterification pre-treatment employs liquid sulfuric acid catalyst which must subsequently be neutralized and either disposed of or recycled. However, requirement of high temperature, high molar ratio of alcohol to FFA, separation of the catalyst, enviromnental and corrosion related problems make its use costly for biodiesel production. 

The early sources of phenol were the destructive distillation of coal and the manufacture of methyl alcohol from wood. In both cases, phenol was a by-product. Recovered volumes were limited by whatever was made accidentally in the process. Initial commercial routes to on-purpose phenol involved the reaction of benzene with sulfuric acid (1920), chlorine (1928), or hydrochloric acid (1939) all these were followed by a subsequent hydrolysis step (reaction with water to get the -OH group) to get phenol. These processes required high temperatures and pressures to make the reactions go. They re multistep processes requiring special metallurgy to handle the corrosive mixtures involved. None of these processes is in commercial use today. 

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