Zinc alloys soil corrosion

In tests carried out by the National Bureau of Standards in the USA specimens of copper alloys, lead, zinc and zinc alloys were buried at a number of different sites for periods varying from 11 to 14 years. The soils tested covered a pH range from 2-6 to 9-4 and resistivities ranged from 62 to 17 800 fi cm. The weight losses and maximum depths of pitting were recorded, and the results indicated that the most severe corrosion occurred in soils of poor aeration having high acid and soluble-salt contents. 

Dissolution of steel or zinc in sulfuric or hydrochloric acid is a typical example of uniform electrochemical attack. Steel and copper alloys are more vulnerable to general corrosion than other alloys. Uniform corrosion often results from atmospheric exposure (polluted industrial environments) exposure in fresh, brackish, and salt waters or exposure in soils and chemicals. The rusting of steel, the green patina on copper, tarnishing silver and white mst on zinc on atmospheric exposure are due to uniform corrosion.14... 

In some of the more corrosive soils, corrosion of the steel (after the zinc has been completely destroyed) is considerably less than that observed on uncoated steel control specimens. Also, it appeared in some soils that the protection afforded to the steel was not due solely to sacrificial corrosion of the zinc but was supplemented by some other mechanism. A few tests indicated that a film, consisting primarily of zinc silicate formed by galvanic action between the zinc and the underlying zinc-iron alloy or bare steel, was responsible for the additional protection. 

In the case of brasses, consideration must be given to the risk of dezindfication, especially at high zinc levels. Soils contaminated with detergent solutions and ammonia also pose a higher corrosion risk for copper and copper alloys. Additional corrosion protection for copper and copper alloys is usually considered only in highly corrosive soil conditions. CP, the use of acid-neutralizing backfill such as limestone, and protective coatings can be used in these applications. 

Materials such as metals, alloys, steels and plastics form the theme of the fourth chapter. The behavior and use of cast irons, low alloy carbon steels and their application in atmospheric corrosion, fresh waters, seawater and soils are presented. This is followed by a discussion of stainless steels, martensitic steels and duplex steels and their behavior in various media. Aluminum and its alloys and their corrosion behavior in acids, fresh water, seawater, outdoor atmospheres and soils, copper and its alloys and their corrosion resistance in various media, nickel and its alloys and their corrosion behavior in various industrial environments, titanium and its alloys and their performance in various chemical environments, cobalt alloys and their applications, corrosion behavior of lead and its alloys, magnesium and its alloys together with their corrosion behavior, zinc and its alloys, along with their corrosion behavior, zirconium, its alloys and their corrosion behavior, tin and tin plate with their applications in atmospheric corrosion are discussed. The final part of the chapter concerns refractories and ceramics and polymeric materials and their application in various corrosive media. 

Natural soils vary too widely in composition to permit very specific advice to be given, but sandy, well-aerated soils with a neutral or slightly alkaline pH are likely to cause only limited corrosion of zinc and its alloys. Zinc coatings will prevent pitting of steel in the soil and, even where the zinc coating is destroyed, the coated steel corrodes much less than do bare specimens. Control of backfill in earth reinforcement ensures that zinc or its alloys can be used satisfactorily. 

Studies on samples exposed underground have shown that tough pitch coppers, deoxidized coppers, silicon bronzes, and low-zinc brasses behave essentially alike. Soils containing cinders with high concentrations of sulfides, chlorides, or hydrogen ions corrode these materials. In this type of contaminated soil, alloys containing more than 22 % zinc experience dezincification. In soils that contain only sulfides, corrosion rates of the brasses decrease with increasing zinc content and no dezincification occurs. 

Almost all types of engineering materials have been reported to experience MIC by SRB copper, nickel, zinc, aluminium, titanium and their alloys [96, 97, 98], mild steel [72, 99, 100], and stainless steels [68, 80, 101, 28] are just some examples. Among duplex stainless steels, SAF 2205 has been reported for its vulnerability to MIC [44, 102, 103]. According to these studies, SAF 2205 can corrode and have pitting initiated due to the presence of SRB after immersion in seawater for more than one year (18 months) [102]. Corrosion rates of lOmm/year [5] in oil treatment plants and 0.7 mm/year to 7.4mm ear due to the action of SRB and/or acid-producing bacteria in soil environments [8] have been reported. 

In practice. Mg alloys are much more popular than pure Mg in industrial applications. One of the well-known uses of Mg alloys is for cathodic protection, and some Mg alloys are used as sacrificial anodes due to their negative potential. Although their rapid rate of corrosion is a disadvantage. Mg alloys are superior to aluminum and zinc anodes in some environments such as in soil and water. The most important application of Mg alloys is for aerospace and military purposes, and some high-strength and creep-resistant... 

All structural metals corrode to some extent in natural environments (e.g., the atmosphere, soil, or waters). Bronze, brass, most stainless steels, zinc, and pure aluminum corrode so slowly in service conditions that long service life is expected without protective coatings. Corrosion of structural grades of cast iron and steel, the 400 series stainless steels, and some aluminum alloys, however, proceeds rapidly unless the metal is protected against corrosion. As described in Chapter 1, corrosion of metals is of particular concern because annual losses in the United States attributed to corrosion amount to hundreds of billions of dollars. 

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