Corrosion in Natural Waters

Copper is resistant to seawater, with the corrosion rate in temperate climates being about 0.5-1. Ogmd (0.001-0.002 ipy) in quiet water and somewhat higher in moving water. In tropical climates, the rate increases by IV2-2 times. It is one of the very few metals that remains free of fouling organisms, with normal corrosion being sufficient to release copper ions in concentrations that poison marine life. 

It is possible to avoid the damaging effects of Cu contamination of water by using copper piping coated on the inside surface with tin (tinned copper). For this reason, copper tanks for holding distilled water or for water storage on ships 

To protect copper hot-water tanks from pitting, sacrificial anodes of aluminum are sometimes used, particularly in certain areas of Great Britain [15]. 

Fresh waters, hot or cold. Copper is especially suited to convey soft, aerated waters that are low in carbonic and other adds. 

Deaerated, hot or cold, dilute H2SO4, H3PO4, acetic acid, and other nonoxidizing acids. 

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Corrosion in Natural Waters, ASTM STP 1086, C. H. Baloun, Ed., ASTM International, West Conshohocken, PA, 1990. 

The Various Forms of Aluminium Corrosion in Natural Waters... 

THE VARIOUS FORMS OF ALUMINIUM CORROSION IN NATURAL WATERS... 

Actually, the successful use of cationic surfactants (cSurf), as flotation reagents, frothers, metal corrosion inhibitors, pharmaceutical products, cosmetic materials, stimulates considerable increase in their production and as a result increases their content in natural water. As cationic surfactants are toxic pollutants in natural water and their maximum contaminant level (MCL) of natural water is 0.15-4.0 mg/dm, it is necessary to use methods for which provide rapid and reliable determination with sensitivity equal to at least 0.1 of MCL. Practically most sensitive methods of cationic surfactant determination include the preconcentration by extraction or sorption. Analytical methods without using organic solvents are more preferable due to their ecological safety. 

In natural waters, cold-worked commercial carbon steels of the same composition corrode at more or less the same rate as annealed steels, presumably because the corrosion rate in this case is controlled by the diffusion of oxygen. Unprotected carbon steels are sometimes exposed to natural waters, and it is this latter situation which is of greater practical importance than the behaviour of steels in acids, since steels should never be used in these environments unless they are protected. 

Murray, G. A. W., Artificial Pits for Quantitative Studies of Corrosion of Aluminium Alloys in Natural Waters , Corrosion, 20, 329 (1964)... 

Dissolved mineral salts The principal ions found in water are calcium, magnesium, sodium, bicarbonate, sulphate, chloride and nitrate. A few parts per million of iron or manganese may sometimes be present and there may be traces of potassium salts, whose behaviour is very similar to that of sodium salts. From the corrosion point of view the small quantities of other acid radicals present, e.g. nitrite, phosphate, iodide, bromide and fluoride, have little significance. Larger concentrations of some of these ions, notably nitrite and phosphate, may act as corrosion inhibitors, but the small quantities present in natural waters will have little effect. Some of the minor constituents have other beneficial or harmful effects, e.g. there is an optimum concentration of fluoride for control of dental caries and very low iodide or high nitrate concentrations are objectionable on medical grounds. 

Reference has previously been made to pH in connection with calcium carbonate, but it has also a more general significance. The pH of natural waters is, in fact, rarely outside the fairly narrow range of 4.5 to 8.5. High values, at which corrosion of steel may be suppressed, and low values, at which gaseous hydrogen evolution occurs, are not often found in natural waters. 

The above catalogue of difficulties, in relating the aggressivity of natural waters to their chemical composition, arises precisely because of the low corrosion rates that are usually found with most metals. Under such circumstances, water composition is only one of many factors that determine the rate of attack. The other factors include flow regime, temperature and the conditions under which the initial corrosion product is laid down. The best summary of the behaviour of metals commonly used in natural waters is still that produced by Campbell for the Society of Water Treatment and Examination... 

All ordinary ferrous structural materials, mild steels, low-alloy steels and wrought irons corrode at virtually the same rate when totally immersed in natural waters. Wrought iron may be slightly more resistant than mild steel in a test in sea-water at Gosport, Scottish wrought-iron specimens lost about 15% less weight after 12 months immersion than specimens of ordinary mild steel. As shown in Table 3.5, the process of manufacture and the composition of mild steel do not affect its corrosion rate appreciably . 

At sufficiently high rates of flow in natural waters enough oxygen may reach the surface to cause partial passivity, in which case the corrosion rate may decrease. In sea-water, owing to the high concentration of chloride ions, the corrosion rate increases with velocity. In one series of tests, corrosion under static conditions was 0-125mm/y, 0-50mm/y at 5 ft/s and 0-83 mm/y at 15 ft/s. 

Skold and Larson" in studies of the corrosion of steel and cast iron in natural water found that a linear relationship existed between potential and the applied anodic and cathodic current densities, providing the values of the latter were low. However, the recognition of the importance of these observations is due to Stern and his co-workerswho used the term linear polarisation to describe the linearity of the rj — i curve in the region of E o , the corrosion potential. The slope of this linear curve, AE — AJ or Af - A/, is termed the polarisation resistance, / p, since it has dimensions of ohms, and this term is synonymous with linear polarisation in... 

The corrosion testing of metals in natural waters is most usually conducted in field or service tests since the conditions of flow are important and often rate-determining. Testing will be concerned with mains water (potable water), river-water and sea-water or combinations of these as in estaurine conditions. Test specimens of various geometries will be used, e.g. in the... 

Fresh water. Aluminum and its alloys are not prone to corrosion on exposure to distilled water up to 180°C. Thus storage tanks, piping and fittings of the alloy can be used for handling distilled water. The composition of natural fresh water is variable. In spite of this restriction, the alloys are not attacked, even at 180°C in natural waters. It should be noted that pitting may occur when a small thickness of the sample is exposed. In this case Alclad 3003 is recommended for use to avoid failure due to pitting. 

Copper alloys C44300, C44500, C61300, C68700, C70600 and C71500 series are more corrosion resistant than copper in natural waters. In general these alloys contain corrosion-resistant metals such as nickel or metals such as iron and aluminum, which... 

Nickel is resistant to chloride-induced SCC, but subject to caustic cracking in aerated solutions under high stress. Nickel is highly resistant to corrosion in natural fresh water and flowing seawater. Pitting occurs under stagnant or crevice conditions. 

The corrosion of lead in natural waters depends on the hardness of the waters, as evidenced by the data in Table 4.56. The natural waters of moderate hardness (i.e., less than 125 ppm calcium carbonate) tend to be less aggressive due to the formation of a protective film, which is also aided by the presence of silicates. On the other hand, nitrate ions disrupt the protective film and increase the corrosion rate. Corrosion of lead occurs in waters containing carbonic acid due to the conversion of carbonate in the film into... 

Electrochemistry is important in other less obvious ways. For example, the corrosion of iron, which has tremendous economic implications, is an electrochemical process. In addition, many important industrial materials such as aluminum, chlorine, and sodium hydroxide are prepared by electrolytic processes. In analytical chemistry, electrochemical techniques use electrodes that are specific for a given molecule or ion, including H+ (pH meters), F, Cl , and many others. These increasingly important methods are used to analyze for trace pollutants in natural waters or for the tiny quantities of chemicals in human blood that may signal the development of a specific disease. 

DOT CLASSIFICATION 2.2 Label Nonflammable Gas SAFETY PROFILE This material is chemically inert in the pure state and is considered to be physiologically inert as well. However, as it is ordinarily obtainable, it can contain variable quantities of the low-sulfur fluorides. Some of these are toxic, very reacdve chemically, and corrosive in nature. These materials can hydrolyze on contact with water to yield hydrogen fluoride, which is highly toxic and very corrosive. In high concentrations and when pure it may act as a simple asphjudant. Incompatible with disilane. Vigorous reaction with disilane. May explode. When heated to decomposition emits highly toxic fumes of F" and SOx. 

A negative attribute of orthophosphate is its tendency to precipitate with calcium hardness found in natural waters. In recent years, deposit control agents that prevent this deposition have been developed. Owing to its relatively low cost, orthophosphate is widely used as an industrial corrosion inhibitor. 

F. Mansfeld, M. W. Kendig, and S. Tsai, "Corrosion Kinetics in Low Conductivity Media I. Iron in Natural Waters," Corrosion Science, 22 (1982) 455-471. 

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