Steels factors affecting corrosion

Environmental Factors Affecting Corrosion of Weathering Steel... 

Under dissolution-controlled conditions, corrosion by liquid metals should increase with increasing temp)erature. For example, assuming all other factors affecting corrosion are fixed, the corrosion rate-temperature relationship can be expected to follow the classical Arrhenius expression, log k exp(-0/RT), where k is corrosion rate, Q is the activation energy, R is the gas constant, and T is the absolute temperature. This is shown graphically in Fig. 4 for type 316 stainless steel in sodium. In this case, the corrosion rate can be related directly to mass loss, which can be expressed m terms of wall thinning. 

The coefficients in Table 3 provide a better theoretical understanding of how the different factors affect the corrosion of weathering steel. The 3 coefficients affect the solubility of the protective oxide layer and the a coefficients affect the diffu-sivity through the layer. The large ratio of a/3 confirms the relative insolubility of the rust on weathering steel in most environments. Sulfur dioxide increases the solubility of the film while NO2 and rain decrease the solubility. Rain apparently washes away acidic components (deposited during dew formation) that increase the solubility. 

Haynie, F.H. Environmental Factors Affecting the Corrosion of Weathering Steel. To be published in Proceedings of ACS Meeting, Degradation of Materials Due to Acid Rain, Arlington, Va., June 1985. 

G. K. Glass, C, L Page, N. R. Short, Factors affecting the corrosion of steel in carbonated mortars . Corrosion Science, 1991, 32, 1283. 

Factors affecting pitting corrosion in austenitic chromium-nickel-molybdenum steels are listed in Table 20.2. 

Various factors affecting the Cr/OH ratio in the paste and eontrolling the period of time, after whieh the threshold value 0.6 is exceeded and the corrosion process begins are searching. It has been known for a long time that the chloride ions which react with calcium aluminate to form the FriedeTs salt CjA- CaCl2 10H2O, do not accelerate the corrosion of steel [209, 214, 344], However, it is difficult to find a relation between the total chloride content in concrete and the amount of free chloride... 

Metallurgical factors affect metal loss and tend to corrode at a lower rate with higher alloy content. Atmospheric corrosion resistance of steel was improved by alloying with Cu, P or Cr to form passive oxide layer [50]. Studies have shown that these steels show superior corrosion resistance in particular during atmospheric exposure but not so much for immersed exposure as in seawater and close to the coastline in the presence of high chloride concentrations. Alloying elements like... 

Aromaa J, Ronkainen H, Mahiout A, Hannula SP (1999) Identification of factors affecting the aqueous corrosion properties of (Ti, Al) N-coated steel. Surf Coating Technol 49 353-358... 

Sulfur oxides and other corrosive species are brought to react with the zinc surface in two ways dry deposition and wet deposition. Sulfur dioxide has been observed to deposit on a dry surface of galvanized steel panels until a monolayer of SO2 formed (Maato, 1982). In either case, the sulfur dioxide that deposits on the surface of the zinc forms sulfurous or other strong acids, which react with the film of zinc oxide, hydroxide, or basic carbonate to form zinc sulfate. The conversion of sulfur dioxide to sulfur-based acids may be catalyzed by nitrogen compounds in the air—usually referred to collectively as NQt compounds—and it is believed that this factor may affect corrosion rates in practice. The acids partially destroy the Film of corrosion products, which will then re-form from the underlying metal, so causing continuous corrosion by an amount equivalent to the film dissolved, hence to the amount of sulfur dioxide absorbed. Above about 85% RH, corrosion rates increase further—probably as a result of the formation of basic zinc sulfates. 

Haynie, F. H., Spence, J. W., and Upham, J. B. (1976 and 1978). Effects of air pollutants on weathering steel and galvanized steel A chamber study. Atmospheric Factors Affecting the Corrosion cf Engineering Metals. ASTM STP 646, Proc. Golden Anniversary Symposium. ASTM, Philadelphia, pp. 30-47. Also report EPA-600/3-76-015 (1976), 85 pp. 

German, G., Behavior of Zinc-Coated Steel in Highway Environments, Atmospheric Factors Affecting the Corrosion of Engineering Metals, ASTM STP 646, S. K. Cobum, Ed., ASTM International, West Conshohocken, PA, 1978, pp. 74-82. 

Maahn, E, Jensen, S. K., Larsen, R. M., and Mathiesen, T, "Factors Affecting the Corrosion Resistance of Sintered Stainless Steel," Advances in Powder Metallurgy and Particulate Materials, 1994, MPIF, Princeton, NJ, Vol. 7, pp. 253-271. 

The deterioration of metals, commonly referred to as corrosion, is a critical factor affecting the useful life of metals in facilities. Most importantly, the rate of corrosion affects how long a particular metal component wiU function in its intended use. Some metals corrode at a very slow rate, which makes them good candidates for certain applications. For example, aluminum has been found to be an excellent material for hatch covers in atmospheric exposures. On the other hand, the use of 304 stainless steel for pipe hangers in piers over salt water has resulted in failures within a year. The application, the environment, and the intended service are critical to proper material selection. 

MIC and the way it affects corrosion have always been a matter of debate. For example, while acid production by bacteria is presumed to be one of the ways by which corrosion can be enhanced, some researchers [2f in their experience with aerobic Pseudomonas sp. have reported that acid production was not a major cause of corrosion, and others [3] have pointed out that the presence of bacteria was not an important factor in the deterioration of steels . It seems that it is not always easy to come up with a clear, once-forever-true explanation of the inpact of bacteria on corrosion. As a matter of fact, such relatively confusing outcomes have helped make MIC a puzzle to some and to others an industrial joke that is used when there is no other explanation for the failure. 

The major fermentation method used to produce lactic acid on an industrial scale is the batch fermentation process. The factors affecting the batch process have been reviewed (Litchfield 1996 Vick Roy 1985). Because of the very corrosive properties of lactic acid, construction materials used for the fermenter and downstream processing equipment are a major cost item. Copper, copper alloys, steel, chrome steel, and high-nickel steels are all unsatisfactory. High-molybdenum stainless steel like SS316 is satisfactory. Plastic linings of fermentation tanks have been used successfiilly, and new developments in ceramics and plastics may provide future choices (Vick Roy 1985). 

---