Corrosion oxygen

Any chemical treatment that reduces general corrosion rates associated with oxygen corrosion will decrease tuberculation. The exact treatment that is best is system dependent. Water chemistries and operating practices may differ widely even among similar industries... 

See Chap. 5, Oxygen Corrosion Chap. 6, Biologically Influenced Corrosion and Chap. 17, Graphitic Corrosion. ... 

The corrosion-product layer that forms due to oxygen corrosion is discussed in Chap. 3, Tuherculation. However, the initial corrosion product is ferrous hydroxide [Fe (OH)2l (Reaction 5.4) ... 

Oxygen corrosion of steel doubles for every 35-55°F (20-30°C) rise in temperature, beginning near room temperature. Corrosion is nearly proportional to temperature up to about 180°F (80°C) in systems open to the air. Although reaction rates increase with temperature, dissolved oxygen is driven from solution as temperatures increase. As temperatures approach boiling, corrosion rates fall to very low values, since dissolved-oxygen concentration also decreases as water temperature rises (Fig. 5.4). 

Oxygen corrosion only occurs on metal surfaces exposed to oxygenated waters. Many commonly used industrial alloys react with dissolved oxygen in water, forming a variety of oxides and hydroxides. However, alloys most seriously affected are cast irons, galvanized steel, and non-stainless steels. Attack occurs in locations where tuberculation also occurs (see Chap. 3). Often, oxygen corrosion is a precursor to tubercle development. 

Oxygen corrosion involves many accelerating factors such as the concentration of aggressive anions beneath deposits, intermittent operation, and variable water chemistry. How each factor contributes to attack is often difficult to assess by visual inspection alone. Chemical analysis of corrosion products and deposits is often beneficial, as is more detailed microscopic examination of corrosion products and wasted regions. 

Table 5-3 Permeation coefficients and rate of oxygen corrosion according to Eq. (5-21).

On the other hand, it can be assumed for the oxygen corrosion of steel in aqueous solutions and soils that there is a constant minimum protection current density, 4, in the protective range, U limiting current density for oxygen reduction according to Eq. (4-5) (see Section 2.2.3.2). Then it follows, with V = +1,1 = 2nr, S = 27crs and d = dU from Eq. (24-54), instead of Eq. (24-58) [12-14] ... 

The simplest form of pressurization uses the expansion of the water content of the system to create a sufficient pressure in an expansion vessel to provide an anti-flash margin of, say, 17°C at the lowest pressure (highest point) of the system. The main disadvantage of a naturally pressurized expansion vessel is the ability of water to absorb air and the consequent risk of oxygen corrosion. 

Grubitsch, H., The Area of Capture Principle with Oxygen Corrosion in Electrolytes , Werkstoffe Korrosion, 17, 679 (1966) C.A., 19674f... 

A specific waterside problem that affects many economizers is normally one of oxygen corrosion. This affects the internal, carbon steel tube header, first-pass tubes, and primary tube bend areas because these areas first receive cold FW. This form of corrosion commonly results in red oxides, economizer pitting and tuberculation, and potentially premature tube failure. 

If dry lay-up procedures are not carried out entirely satisfactorily (e.g., if a nitrogen blanket is not permanently provided to the superheaters during the lay-up period), atmospheric moisture may condense and oxygen corrosion will ultimately occur. 

Corrosion may be associated with fouling. For example, oxygen corrosion of a steam-water separator typically results in corrosion debris that builds up and fouls the separator device, thus preventing the effective separation of steam from BW. 

Hot water heating boilers almost never require softeners (oxygen corrosion and sludge buildup are the most common problems) because MU generally is minimal. 

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