Corrosion amount, equation

Attack by alkali solution, hydrofluoric acid and phosphoric acid A common feature of these corrosive agents is their ability to disrupt the network. Equation 18.1 shows the nature of the attack in alkaline solution where unlimited numbers of OH ions are available. This process is not encumbered by the formation of porous layers and the amount of leached matter is linearly dependent on time. Consequently the extent of attack by strong alkali is usually far greater than either acid or water attack. 

Sodium hydroxide, NaOH, is a soft, waxy, white, corrosive solid that is sold commercially as lye. It is an important industrial chemical because it is an inexpensive starting material for the production of other sodium salts. The amount of electricity used to electrolyze brine to produce NaOH in the chloralkali process (Section 12.13) is second only to the amount used to extract aluminum from its ores. The process produces chlorine and hydrogen gases as well as aqueous socFinn hydroxide (Fig. 14.17). The net ionic equation for the reaction is... 

Sharma et al. [153] have devised a gentle accelerated corrosion test using a kinetic rate equation to establish appropriate acceleration factors due to relative humidity and thermal effects. Using an estimate for the thermal activation energy of 0.6 eV and determining the amount of adsorbed water by a BET analysis on Au, Cu and Ni, they obtain an acceleration factor of 154 at 65°C/80% RH with respect to 25 °C/35-40% RH. 

When the number of concentrations of the circulating water is in the order of 3-7, some of the salts dissolved can exceed their solubility limits and precipitate, causing scale formation in pipes and coolers. The purpose of the treatment of the cooling water is to avoid scale formation. This is achieved by the injection of sulfuric acid to convert Ca and Mg carbonates (carbonate hardness) into more soluble sulfates. The amount of acid used must be limited to maintain some residual alkalinity in the system. If the system pH is reduced to far below 7.0, it would result in an accelerated corrosion within the system. As stated earlier, scale formation and/or corrosion tendency is defined by the Saturation Index (Langelier Index) and Stability Index (Ryznar equation). 

Sand entrainment will reduce the C value greatly. The applicability of this equation to high-pressure gas-oil-water mixtures is highly questionable. No account is taken of the relative velocities or relative amounts of the phases. Currently, the best approach to minimize erosion-corrosion is to select conditions that maintain annular flow by use of the graph in Figure 5.22, in which the parameters are the following ... 

In facL only small amounts of hydrochloric add are required to activate the aluminum chloride. Hence, to reduce the risks of corrosion, use is made of an initiator, ethyl chloride, whose action mechanism corresponds to the foUouine equation ... 

The Influence of Dissolved Salts upon Corrosion.—The presence of salts dissolved m water may greatly influence the manner in which the iron is attacked. Many salts exert a distinct chemical action on the metal. Thus, for example, when immersed in solutions of copper sulphate, iron readily dissolves, an equivalent amount of copper being precipitated in accordance with the equation —... 

Apparent porosity is very important in connection with flux corrosion and with thermal insulation which may be unfavourably affected by permeation of hot gases. The total volume of open pores can be determined, for example, by measuring the amount of absorbed water, but this value provides no information on pore size which is important with respect to these properties. The permeability for gases is therefore measured. The test specimen is fixed in a special vessel so that it allows a gas or air to be driven through. The gas permeation rate and the pressure difference are measured. The permeability coefficient K is then given by the equation... 

This equation shows that with other conditions equal, the thickness of the tube has very little influence on the transmission of heat, and with a copper tube K in. thick, the amount of heat transmitted would be 66,300 B.t.u. For an iron tube He in. thick, and A = 35, Q would be 61,812 B.t.u. The smaU theoretical advantage of copper over iron is also true in actual practice, except that usually iron tubes are more easily corroded than copper tubes, and the corrosion forms an insulating film on the iron which greatly reduces the heat transmission. For practical purposes iron of the same thickness will transmit about 80 per cent of the heat transmitted by copper. 

Experimental estimates of b are given in Table II. Except for galvanized steel, these values were calculated using gravimetric results and Equation 6. For galvanized steel, b was calculated from wet chemical results for the amount of zinc in the corrosion film, i.e., Equation 8, The number of data points,... 

Equation 10 is used to calculate the dry deposition velocity for NO2. It is assumed that all of the N02 in the dew came from the dissolution of NO2. A value of 0.03 cm/s is found for the deposition velocity. To calculate the dry deposition velocity for HNO3, it is assumed that the source of dew N03 was the dry deposition of HNO3. The calculated value, 2.0 cm/s, appears high relative to the velocities of other soluble gases such as HCHO (see Tables II and IV) and likely reflects that HNO3 can be adsorbed onto a dry surface. Evidence to substantiate this point appears in the next section. It is also possible that some of the NO3 and/or NO2 arose from the deposition of small amounts of PAN however, the ionic fate of dissolved PAN is not known and therefore more information is required for an assessment of its role in atmospheric corrosion. 

Equation 16 is a transcendental equation that must be solved iteratively. The corrosion at exposure time t is the sum of the soluble and insoluble components however, the insoluble contribution depends on the amount of soluble products produced via its dependence on p ... 

Generally these compositions contain an epoxy-novolac, a hardener, a catalyst, silica fillers, and an internal lubricant/mold release compound. Brom-inated epoxies and antimony trioxide are included to provide the required flame retardant characteristics. Other, unspecified additives are used to promote adhesion or to reduce corrosion rates. Because of their superior thermal capabilities and electrical properties, epoxidized novolacs are preferred over epoxy homopolymers. Near stoichiometric amounts of hardeners such as novolacs (Equation 1), anhydrides, and primary amines can be used to cure the resins in the presence of a catalyst. The linkages which are formed include ethers, esters, or secondary amines, respectively. 

In order to determine the value of e the amount of corrosion product removed from the surface, it is necessary to integrate Equation 10.44. 

The presence of hypochlorous acid as opposed to the hypochlorite ion, is responsible for the biocidal activity. Hypochlorous acid is estimated to be twenty times more effective as a micro-biocide than the hypochlorite ion. Unfortunately however, in a cooling tower there is a tendency to strip chlorine from the water by the countercurrent flow of the air, so that Equation 14.23 moves to the left and it is likely that by the time the water reaches the basin of the tower all the chlorine will have been lost to the air in addition to reactions with organic matter within the tower. It will be necessary therefore for maximum utilisation of the available chlorine to ensure that the equilibrium of Equation 14.24, is over to the LHS. Since the ionisation process produces hydrogen ions the equilibrium will be affected by the pH of the solution. The effect of pH on HOCl stability is shown on Fig. 14.16 [Marshall and Bott 1988]. In the figure 100% HOCl indicates that the equilibrium is completely to the left in Equation 14.24 and there is no ionisation of the HOCl. From Fig. 14.16 this condition occurs at pH of around 5. At a pH 7.5 hypochlorite ion and acid co-exist in approximately equal amounts. It nll be seen that as the pH approaches 9 the hypochlorous acid content drops to a very low value and the biocidal effect is negligible. Values of pH lower than around 6.5 are not practical because of the potential risk of corrosion. 

In any case, single-layer inhibited pol mier films cannot substantially restrict the rate of corrosion processes by limiting their vapor or oxygen-penetrability. This becomes especially clear in comparison with the mean rate of steel corrosion in atmosphere (1.9g/(m days) [112]). The amounts of water and oxygen needed for the corrosion process to run at the indicated rate calculated by the equation... 

A Hmit state related to corrosion propagation considered in DuraCrete is the appearance of a crack with a width of 1 mm, which is taken as the start of spaUing. Equations are given [21] for the crack width caused by a corroding bar based on the amount of corrosion present, the amount needed to produce a crack, and some factors including the cover depth, the rebar diameter and the tensile strength of the concrete. After corrosion initiation, the amount of corrosion is given by the corro-... 

Potential measurements of protected structure, especially in soil, are comprised with an error resulting from the voltage drop between the structure and the reference electrode. This error depends on the resistance of layers of corrosion products and insulation, and the resistance of the electrolytic environment. Equation (1) shows the amount of ohmic potential drop in the measurement of the potential of a... 

From the stoichiometry of reactions (6.14) and (6.16) results that in some conditions the calcium hydroxide can be formed, which is the potentially substrate of the reaction (6.14), increasing the amount of gypsum formed. Ettringite produced according to the equation (6.16) is expansive too. The reaction (6.16) is dominating in the soluted gypsum containing solutions, it means at hmited sodium content. The calcium sulphate shows a weaker corrosive effect because of the lower solubility in water. 

Results equivalent to those available at atmospheric pressure can be achieved with lower acid concentrations. This fact can give the chlorine plant operator a wider choice. Less-concentrated feed acid might be used for example, 93% H2SO4 becomes a sound choice. The concentration of the spent acid can also be lower, provided that its increased corrosivity is acceptable. A wider spread between feed and waste acid concentrations reduces the consumption of acid and the amount of waste generated. Equation (9.38) gives the relationship. 

When a non-corroded steel surface is exposed to the atmosphere, the rate of corrosion is highest. It then diminishes with exposure time as the rust layer builds up. Empirically, the amount of mass corroded as a function of time can be described by the equation ... 

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