Tuberculation

Povidone—iodine is a brown, water-soluble powder containing approximately 10% iodine. However, the amount of free iodine, which is responsible for the antimicrobial activity, is low in a concentrated solution, but is released as the solution is diluted (41). Concentrated solutions have actually been contaminated with bacteria (42). For use as an antiseptic, povidine—iodine is diluted with water or alcohol to a concentration of 1% iodine. Detergents are added if it is used as a surgical scmb. lodophors are important as broad-spectmm antiseptics for the skin, although they do not have the persistent action of some other antiseptics. They are also used as disinfectants for clinical thermometers that have been used by tuberculous patients, for surface disinfection of tables, etc, and for clean equipment in hospitals, food plants, and dairies, much as chlorine disinfectants are used. 

Methylcytosine (964 X = O) was synthesized in 1901 and its isolation from hydrolyzates of tubercule bacilli was reported in 1925. However, this was later shown to be incorrect and only about 1950 was it isolated by hydrolysis of the deoxyribonucleotide fractions from thymus, wheat germ and other sources (50MI21302). Nucleotides and a nucleoside of 5-methylcytosine are known. 

Asbestos Cement Asbestos-cement pipe is seamless pipe made of sihca and portland cement, compacted under heavy pressure, uniformly reinforced with asbestos fiber, and thoroughly cured. The interior surface is smooth, does not corrode, and does not tuberculate. Under normal conditions of operation, asbestos cement will handle... 

Cement-Lined Steel Cement-hned steel pipe is made by lining steel pipe with special cement. Its use prevents pickup of iron by the fluid handled, corrosion of the metal by brackish water, and growth of tuberculation. Threaded pipe in sizes from to 4 in is stocked however, cement-lined pipe in sizes smaller than in is not considered practical for common use. 

The three major forms of concentration cell corrosion are crevice corrosion, tuberculation, and underdeposit attack. Each form of corrosion is common in cooling systems. Many corrosion-related problems in the cooling water environment are caused by these three forms of wastage. The next three chapters—Chap. 2, Crevice Corrosion, Chap. 3, Tuberculation, and Chap. 4, Underdeposit Corrosion — will discuss cooling water system corrosion problems. 

See Chap. 3, Tuberculation Chap. 7, Acid Corrosion and Chap. 16, Galvanic Corrosion. ... 

Figure 3.1 Utility service water system pipe almost plugged by heavy tuberculation.

Common cooling water components that suffer tuberculation are listed below ... 

Figure 3.12 Heavily tuberculated 3-in. (7.6-cm) outer diameter steel mill water supply line.

Figure 3.13 Emergency supply line shows moderate tuberculation.

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... 

Cathodic protection using sacrificial anodes or applied current can retard or eliminate tuberculation. However, costs can be high and technical installation can be very difficult. Costs are markedly reduced if surfaces are coated (see Material substitution below). 

Internal surfaces were moderately tuberculated (Fig. 3.14). Extremely thick, hard magnetite shells capped large internal cavities (Fig. 3.9). Pipe cross-sectional area was reduced by at least 30% in some places. Tubercles were aligned with flow, indicating that growth occurred during service. No failure occurred, and deepest metal loss was only 0.093 in. (0.033 cm) from the nominal pipe wall thickness of 0.225 in. (0.572 cm). 

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. 

See also Chap. 2, Crevice Corrosion Chap. 3, Tuberculation and Chap. 4, Underdeposit Corrosion. ... 

Internal surfaces were heavily tuberculated. The circumferential weldbacking ring was heavily corroded (Fig. 6.21). The perforation shown in Fig. 6.10 occurred at the ring, which was entirely consumed by corrosion in places. At intact areas the weld was sound, showing adequate penetration and no unusual characteristics. 

Figure 17.10 shows metal loss on the throat of the pump housing. External pump housing surfaces were also affected (Fig. 17.11). Note the large tubercles. (Tubercles are knoblike mounds of corrosion products. They typically have a hard, black outer shell enclosing porous reddish-brown or black iron oxides) (see Chap. 3, Tuberculation ). The metal surface beneath these tubercles had sustained graphitic corrosion, in some cases to a depth of Vi in. (0.6 cm) (Fig. 17.12).

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