Water-supply systems contact corrosion

Partial what-if analyses for the two example processes described in Section 4.0 are shown in Tables 4.9 and 4.10. Although for actual, more complex analyses, the what-if tables for each line or vessel would be separate, for these examples, a single table was developed. A preliminary hazard analysis (PHA) would identify that the intrinsic hazards associated with HF are its reactivity (including reactivity with water, by solution), corrosivity (including carbon steel, if wet), toxicity via inhalation and skin contact, and environmental toxicity. The N2 supply system pressure is not considered in this example. The specific effects of loss of containment could be explicitly stated in the "loss of HF containment" scenarios identified. Similarly, the effects of loss of chlorine containment, including the reactivity and toxicity of chlorine, could be specified for the second example. 

The treatment of cooling water is a subject for specialists. Requirements are affected by the quality of the water supply the extent of contamination by corrosion products, process leakage, and the use of the water in direct-contact applications and the nature and quantity of solids and gases scrubbed from the air in the cooling tower. There are extreme variations in some of these factors, and each plant will need its own treatment system and program. 

When they choose a corrosion control method, water systems are required to study all of the potential complications and ensure that their actions do not cause the water supply to violate any of the other federal drinking water standards. For technical information on corrosion control, contact your regional EPA office, listed in Appendix A, and the organizations listed in Appendix B under Drinking Water. 

A Clamp on a Plain Piece of Metal. Before the clamp (or some equivalent cover, see Fig. 12.31) is placed on a metal sheet immersed, say, in saline water in contact with air, the pQ is the same everywhere along the surface of the sheet of metal and Ap is zero, so no electrochemical reaction—no corrosion—occurs. However, the clamp prevents access of 02 to the metal under it and therefore Ap becomes finite. Around the clamp there is usually a large area that is excellently aerated and able to supply electrons for the reduction of 02. Of course, the electrons to do this have to come from somewhere in the underlying metal. In such a system, there is no... 

A second generation of phenolic dispersions, patented by J. S. Fry (33). involved the post dispersion of phenolic resins in a mixture of water and water-miscible solvents. To conform with air pollution regulations, the solvent was held to 20 volume %, or less, of the volatiles. A heat-reactive phenolic resin dispersion (34) and a phenolic-epoxy codispersion have become commercially available based on the above technology. Supplied at 40-45% solids, these products, which have a small particle size (0.75-1.0 ym), are better film formers than the earlier dispersions. Used alone or in blends with other waterborne materials, corrosion-resistant baking coatings may be formulated for coil coating primers, dip primers, spray primer-surfacers, and chemically resistant one-coat systems. Products of this type are also tackifiers for acrylic latexes, and such systems have been employed as contact, heat seal, and laminating adhesives for diverse substrates. 

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