Steel limitations from corrosion

Only Continental and Inner-Tite offered protective sleeves to their customers as an option. None of these manufacturers has published installation recommendations to limit shear and bending forces on the plastic pipe that connects to their steel tapping tees. On another issue related to protective sleeves. Safety Board examination of a protective sleeve offered by Continental to its customers revealed that the sleeve that did not have sufficient clearance to allow the application of field wrap (intended to protect the steel tee from corrosion after it is in the gronnd) to that portion of the steel tee under the sleeve. This observation was confirmed by a Continental representative. 

High tin concentrations in food may cause short-term acute health effects in some people, including stomach upsets, abdominal cramps, nausea and/or diarrhoea. These short-term effects may occur in some individuals at concentrations above 200 mg/kg.33 The UK Tin in Food Regulations 1992 limit the maximum amount of tin in food sold in the UK to 200 mg/kg.34 Fortunately, concentrations of tin in most foods are well below 10 mg/kg, although canned foods may contain higher concentrations as a result of slow dissolution of the tin coating used on some cans to protect the steel body of the can from corrosion. Tomato-based products tend to have high levels of tin as nitrate in the food accelerates corrosion of the tin. A survey of canned tomato products sold in the UK in 1998/1999 found that 98% of the products tested were below the 200 mg/kg limit.35... 

Scrubber liquid can be recycled to obtain a salt solution of any desired concentration prior to regeneration of ammonia from the solution. The upper limit on solution concentration presumably will be controlled by the vapor pressures of the components, ammonia and sulfur dioxide. At high pH, ammonia vapor predominates at low pH, sulfur dioxide is the dominant vapor. Therefore, optimum recycle of the scrubber liquid will be controlled at low pH and dilute solution concentration concurrent with and relative to equipment (capital) and operating costs. A solution having low pH (e.g., < 6.0) requires stainless steel or protected carbon steel to prevent corrosion. 

To limit arid corrosion and avoid the u of.high-ailoy steels, the effluents must be neutralized upon leaving the reactor. The addition of caustic soda, sodium carbonate, lime etc, in the form of aqueous solutions or directly in solid form, presents many drawbacks (gelatinous or colloidal precipitates difficult to separate, handling of solids, slow reaction rates, etc.). It is preferable to use aqueous sodium pheoate,. which acts rapidly in stoichiometric quantities and yields sodium sulfate in solution, (hat is easy to remove. This phenate can also be obtained in die unit itself from the phenol produced. 

Deaeration is accompanied by some reduction of carbon dioxide content, particularly if the water is acidified before the deaeration process to liberate carbonic acid from the dissolved carbonates. Carbonic acid is corrosive to steel in the absence of dissolved oxygen and more so in its presence [18], but addition of alkali to boiler water limits any corrosion caused by carbon dioxide to the boiler itself by converting dissolved carbon dioxide to carbonates. At prevailing boiler temperatures, however, carbonates dissociate as follows ... 

The corrosion mechanism for weathering steels is similar to that of unalloyed carbon steels. The rust forms a more dense and compact layer on the weathering steels than on unalloyed carbon steels. The rust layer more effectively screens the steel surface from the corrosive envirorunents of the atmosphere. The corrosion process may be affected in several ways by this rust layer. The cathodic reaction may be affected by the low diffusion rate of oxygen, whereas the anodic reduction may be retarded by limiting the supply of water and corrosion-stimulating ions that can reach the surface of the steel. In addition, the increased electrolyte resistance may also decrease the corrosion rate. 

Stainless Steels. Stainless steels are more resistant to msting and staining than plain carbon and low ahoy steels (47—50). This superior corrosion resistance results from the presence of chromium. Although other elements, such as copper, aluminum, shicon, nickel, and molybdenum, also increase corrosion resistance these are limited in their usefiilness. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

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