Corrosion rates/resistance chemicals

A fresh lead surface slowly oxidizes into a thin, protective lead oxide (PbO) that stops further oxidation of the metal. Lead gives satisfactory resistance to corrosion in rural, marine, and industrial environments. The corrosion rate data for lead is shown as 0.5-0.7 pm/y in industrial (New York, NY), 1.2-2.2 pm/y in marine (Kure Beach, NC), and 1.05-1.85 pm/y in rural (State College, PA) [6]. Lead corrosion products in such environments, in addition to lead oxide, are sulfate, chloride, and carbonate, with lead chloride being the most soluble of all four products (see Table 1). However, lead in outdoor exposures was found to produce sulfate (PbS04) and/or carbonate (PbC03), and indoor exposures lead carboxylates. The primary atmospheric agents responsible for degradation of lead are SO2, CO2, and carboxylic acid [7]. The corrosion rate of chemical lead in Key West, Florida, and La Jolla, California is 0.58 and 0.53 pm/y (0.023 and 0.021 mpy), respectively [2]. 

Corrosion by Various Chemicals and Environments. In general, the rate of corrosion of magnesium ia aqueous solutions is strongly iafluenced by the hydrogen ion [12408-02-5] concentration or pH. In this respect, magnesium is considered to be opposite ia character to aluminum. Aluminum is resistant to weak acids but attacked by strong alkaUes, while magnesium is resistant to alkaUes but is attacked by acids that do not promote the formation of iasoluble films. 

The titanium oxide film consists of mtile or anatase (31) and is typically 250-A thick. It is insoluble, repairable, and nonporous in many chemical media and provides excellent corrosion resistance. The oxide is fully stable in aqueous environments over a range of pH, from highly oxidizing to mildly reducing. However, when this oxide film is broken, the corrosion rate is very rapid. Usually the presence of a small amount of water is sufficient to repair the damaged oxide film. In a seawater solution, this film is maintained in the passive region from ca 0.2 to 10 V versus the saturated calomel electrode (32,33). 

Carbon steel is easily the most commonly used material in process plants despite its somewhat limited corrosion resistance. It is routinely used for most organic chemicals and neutral or basic aqueous solutions at moderate temperatures. It is also used routinely for the storage of concentrated sulfuric acid and caustic soda [up to 50 percent and 55°C (I30°F)]. Because of its availability, low cost, and ease of fabrication steel is frequently used in services with corrosion rates of 0.13 to 0.5 mm/y (5 to 20 mils/y), with added thickness (corrosion allowance) to assure the achievement of desired service life. Product quahty requirements must be considered in such cases. 

Corrosion resistance of stainless steel is reduced in deaerated solutions. This behavior is opposite to the behavior of iron, low-alloy steel, and most nonferrous metals in oxygenated waters. Stainless steels exhibit very low corrosion rates in oxidizing media until the solution oxidizing power becomes great enough to breach the protective oxide locally. The solution pH alone does not control attack (see Chap. 4, Underdeposit Corrosion ). The presence of chloride and other strong depassivating chemicals deteriorates corrosion resistance. 

Where a large collection of data exists then it may be effectively condensed in the form of diagrams. A popular method is the use of iso-corrosion rates plotted on co-ordinates of temperature and concentration for one material and one chemical. Because of the large amount of data on the common acids there are many examples of this type of diagram, e.g. the work of Berg who has chosen metals and alloys that are readily available. He has excluded many metals and alloys on the grounds that they are either Non-resistant or can be substituted by cheaper materials. ... 

The individual characteristics and uses of the basic grades of the austenitic irons are given in Table 3.55. The major uses for these materials occur in the handling of fluids in the chemical and petroleum industries and also in the power industry and in many marine applications. The austenitic irons are also used in the food, soap and plastics industries where low corrosion rates are essential in order to avoid contamination of the product. Ni-Resist grades Type 2, 3 or 4 are generally used for such applications but the highly alloyed Type 4 Ni-Resist is preferred where low product contamination is of prime importance. 

Aluminium is a very reactive metal with a high affinity for oxygen. The metal is nevertheless highly resistant to most atmospheres and to a great variety of chemical agents. This resistance is due to the inert and protective character of the aluminium oxide film which forms on the metal surface (Section 1.5). In most environments, therefore, the rate of corrosion of aluminium decreases rapidly with time. In only a few cases, e.g. in caustic soda, does the corrosion rate approximate to the linear. A corrosion rate increasing with time is rarely encountered with aluminium, except in aqueous solutions at high temperatures and pressures. 

Other alloys of molybdenum which have been investigated for their corrosion resistance contain 10-50% Ta and were found to have excellent resistance to hydrochloric acid. Ti-Mo alloys were found to resist chemicals that attack titanium and Ti-Pd alloys, notably strong reducing acids such as hot concentrated hydrochloric, sulphuric, phosphoric, oxalic, formic and trichloroacetic. For example, a Ti-30Mo alloy has the following corrosion rates in boiling 20% hydrochloric acid, 0-127-0-254 mm/y in 10% oxalic acid at 100°C, 0-038 mm/y, which compares favourably with the respective rates of 19-5 and 122 mm/y for the Ti-0-2Pd alloy. 

Neufeld, P. and Queenan, E. D., Frequency Dependence of Polarisation Resistance Measured with Square Wave Alternating Potential , Br. Corros. J., 5, 72-75, March (1970) Fontana, M. G., Corrosion Engineering, 3rd edn., McGraw-Hill, pp 194-8 (1986) Dawson, J. L., Callow, L. M., Hlady, K. and Richardson, J. A., Corrosion Rate Determination By Electrochemical Impedance Measurement , Conf. On-Line Surveillance and Monitoring of Process Plant, London, Society of Chemical Industry (1977)... 

Measurements of corrosion rates and other parameters connected with corrosion processes are important, first as indicators of the corrosion resistance of metallic materials and second because such measurements are based on general and fundamental physical, chemical, and electrochemical relations. Hence improvements and innovations in methods applied in corrosion research are likely to benefit basic disciplines as well. A method for corrosion measurements can only provide reliable data if the background of the method is fully understood. Failure of a method to give correct data indicates a need to revise assumptions regarding the basis of the method, which sometimes leads to the discovery of as-yet unnoticed phenomena. 

Corrosion resistant material is a key issue for success of sulphuric thermochemical cycle. Silicon carbide, hastelloy, gold and Fe-Si alloys have a good corrosion rate less than 1 mm per year. However, long-term behaviour is different from that of short-term behaviour due to a protective layer (Kim, H.P., 2008). A long-term corrosion in realistic environment is required for selecting suitable material for large scale SI chemical plant. 

Chemical and physical analysis of the soils where the failures of pipe were observed showed the soils to be either corrosive or very corrosive. The soils consisted of wet salty clay containing irons with resistivity in the range of 820 1200 Ocm. A strong relationship between the corrosion rate of buried cast and ductile iron pipes and soil resistivity was found. 

To identify suitable materials for an acid complex such as Hl, one can begin by surveying materials applicable to the individual acid/chemical. Table 4.5 to table 4.7 list the corrosion properties of various materials in I2, HI acid, and H2SO4.12 is a strong oxidizer, especially in liquid form at high temperature. The corrosion rates of a number of corrosion-resistant materials in I2 at 300 and 450°C are listed in table 4.5. Even though the data show that gold and platinum are stable in an I2 environment, they have been found to dissolve in HI. Refractory metals such as Ta and Nb alloys are probably the best candidates within the l2-rich environment in Section 1. 

SiC-based materials have also shown very good corrosion resistance in HI. Both sintered and chemical vapor deposition (CVD) SiC have very low corrosion rates when tested in HI at elevated temperatures. In addition, Si-infiltrated C-based materials (Si-SiC) also have good potential. This method of manufacturing may become an attractive option in the future, as it promises an extremely low-cost alternative to manufacture SiC-based corrosion-resistant materials and reduce the potential joining problems. Effort is continuing to resolve the manufacturing techniques and improve the inherent mechanical properties of these SiC-based materials. 

A global mean for the rate of net chemical denudation of the continental surface is about 14 mm 1000 yr-1 or 14 pm yr k In comparison to the corrosion rates of metals exposed to a range of environmental conditions, the global continental surface is less resistant to corrosion than zinc and copper, but it is considerably more resistant than iron exposed to coastal oceanic and industrial-area atmospheric conditions. 

Corrosion rates and those of mechanochemical wear of stainless steels and alloys widely applied in friction joints of chemical equipment are presented in Table 4.2 [30]. Owing to the formation of passivating protective films on contact with hostile media, these materials display high corrosion resistance. As can be seen from the table, corrosion rates grow during friction by a factor of thousand. Under such conditions, the material wears largely due to corrosion even in a weak solution of sulfuric acid for both sliding friction over a softer material (PE) and under abrasive action (ceramics). 

Valve Metals Titanium is extensively used in the chemical process industry owing to its excellent corrosion resistance. However, anodic protection of titanium is required for certain environments. For example, anodic protection has been recommended widely for application of titanium in sulfuric acid applications. Experiments indicated that anodic protection considerably increased the corrosion resistance of titanium. In sulfuric acid up to 65% concentration at 65 C, the corrosion rate of anodically protected titanium was found to be 0.025 mmyr . Even at a higher temperature of 90 °C, for sulfuric acid concentration of 57%, the corrosion rate under anodic protection was found to be only 0.13 mm yr [18,19]. A... 

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