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762 CHAPTER 55 1960 Guide over ft large area, and accelerate corrosion where they leave the pipe line. Certain bacteria that thrive in the absence of oxygen have the power to obtain hydrogen and dissociate sulfates in the soil, with a resultant production of hydrogen sulfide which attacks iron to form iron sulfide. Stray electric currents from electric power generating stations sometimes find their way into buried steel struc tures, and do damage in proportion to the current density where the current leaves the metal to enter the ground. Pipe Materials Some underground corrosive environments found in the air-conditioning and heating industries require special ma terials. The selecton of such materials must be based upon an economic evaluation, as the use of expensive first cost is not wise if the life of lower cost materials is adequate. On the other hand, a material low in cost and corrosion resistance should be avoided if it leads to costly shut-downs, repairs, and early replacements. Underground piping materials should be selected for their ability to resist exterior as well as interior corrosion, and careful evaluation of the soil and water should be made. Underground corrosion of metals is particularly difficult to predict. There are many different types of soils varying in composition and in ability to corrode both ferrous and non-ferrous metals. Where excessively corrosive soils are encountered, special materials may be necessary, but gener ally the commonly used ferrous materials have proved to be the most economical. Copper and many of its various alloys are also used advantageously, but their use is more restricted to selected localities. It has been found that soils with high content of organic matter or alkaline soils in which the ratio of chlorides and carbonates to sulphates is high, may be corrosive to copper.** Copper or the commonly used ferrous metals should not be embedded directly in cinders or in tidal marshes, as they may be unduly attacked by sulphur com pounds. It is also wise to avoid the embedding of any pipe materials in soils where unusually high salt contents are known to exist. Galvanized wrought-iron pipe and steel will resist under ground corrosion quite satisfactorily, particularly if the gal vanized coating is 3 oz per sq ft or more. The National Bureau -of Standards reports that where an underground piping material contains 3 oz of galvanizing per square foot, or more, the life of the pipe materially increased. The zinc used for galvanized coating is on the electrochemical pro tective side of the iron; and the zinc as it corrodes is changed to zinc compounds before the underlying base metal is at tacked. This fact and the mechanical protection provided by the zinc coating account for the protection afforded by the galvanized coating. Once the galvanized coating has been destroyed, the base metal must then.retard the corrosive attack, so the rate of attack depends upon the composition of such base metals. Lead-coated' pipe*1 has had a limited application for underground service..It corrodes chiefly in 6oils deficient in oxygen or containing cinders. Protective Coating Protective coatings for buried pipe lines are in a class by themselves because of the unusual service conditions, and be cause it is not possible to maintain them by recoating when necessary. Buried steel pipe lines have been protected against corrosion with considerable success by the use of very thick bituminous coatings applied in molten condition. The best results are obtained by applying the bituminous coatings over a standard priming coat such as red lead or a bitumi nous paint, and for long service it has been found that after the bituminous coatings are applied, a wrapping of asbestos fabric saturated with bitumens will prevent movement Mid displacement of the bituminous coatings, and add greatly to the length of time protection will be maintained. Cathodic Protection Protection is obtained by rendering the structure cathodic to the surrounding water or soil by means of a controlled difference of potential. This method, which has proved satis factory and pfflTifimi/'j] on a number of gas and oil pipe lines underground, has also been applied with some success to the protection of the inside of water-storage tanks and other structures that are in contact continuously with water. Pro tective coatings that insulate a large portion of the metal surface will reduce very materially the total amount of pro tective current that must be impressed on bare anodic areas to arrest corrosion. Because of differences in environmental conditions, it is necessary to determine or estimate the minimum current density required for each structure, and design the anode or anodes so that the necessary protection can be obtained most economically. In water having relatively high electrical con ductivity such as in sea water, this is comparatively easy compared with fresh water. In the latter, the composition of the water is a major factor. It is therefore desirable to ob tain an accurate estimate of the minimum current density required. The current is then controlled by the potential be tween the anode and the structure to be protected. Rectifiers have generally proved to be the most practical means for supplying the necessary current for protection of surfaces in contact with neutral waters.*1 HANDLING WATER TREATING CHEMICALS Virtually all the chemicals used in water conditioning are injurious if taken internally in large doses. Many also cause severe skin irritation and should be handled with cautioD. Caustic soda, lime, and concentrated sulfuric acid will burn the flesh. In addition, if mixed with small amounts of water, sufficient heat may be generated so that spattering occurs or the container becomes too hot to handle. The chlorophenol compounds, even in the low concentra tions used in water conditioning, have been reported** to produce dermatitis. Chrom-itch is not uncommon among workers handling chromates. The amines are said to be ab sorbed through the skin.** Morpholine is said to cause kidney and lung trouble when so absorbed. Chlorine gas irritates the skin, eyes, and mucous mem branes. Concentrations as low as 0.004 percent by volume in air cause dangerous illness in one-half to one hour. When relatively large amounts of the non-gaseous chemi cals are to be handled, protective clothing, including goggles, should always be provided, and a shower head or its equiv alent provided at or very near the point where the chemicals are mixed. Chemicals should always be washed from the skin with large volumes of water. For the handling of chlorine and chlorin&tors, the U. S. Public Health Service" stipulates the following safety re quirements: I. Suitable gas masks and a small bottle of ammonia for testing for leaks should be kept at convenient points ixnme- Corrosion and Water-Formed Deposits, Causes qnd Prevention 763 Table 7------Recommended Maximum Allowable ' Content in Water Supply* Sohdonn Max. Cancanfrafion, ppm The U. S. Public Health Service stipulates: "Salta of barium, hexavalent chromium, heavy-metal glucosidea, ot other substances with deleterious physiological effects, shall not be allowed in the water supply system." Iron & Manganese (Total)...................... Magnesium........................................... Fluorine................ .......................... Selenium.................................... Phenols (Total)................................... Polyphosphate of Sodium................. pH Value @ 25C.................................. * U. 8. Public Health Servjco- 0.3 125.0 1.0 0.05 0.001 10.0 10.6 The same agency recommends that the concentration of the substances listed be held below the values cited in Table 7. The Board of Directors of the American Water Works Association has accepted these values as standard for all public water supplies in the United States." While their action is net binding, prudence dictates that no form of treatment should be used that will result in raising the con centration of the substances listed above the value cited. Since virtually all of the permissible chemicals used for scale, slime, and corrosion control have deleterious physio logical effects if taken internally in relatively large doses, they should alwayB be carefully proportioned. To insure this, the Detroit ordinance stipulates that the chemical feeding device must have the following major characteristics: - diateiy outside the room or enclosure in which chlorine is being stored or is in use. Gas masks should be inspected at regular intervals and kept is serviceable condition. Note:--All purpose offer adequate protection only when the concen tration of acid gases does not exceed two percent--see Safe Practices Pamphlet #64 National Safety Council. 2. Chlorinating equipment and cylinders of chlorine should be housed preferably in separate buildings above the ground level. 3. The room or building housing chlorinators in service should be maintained at a temperature above 60 F, but never in excess of the normal summer temperature. The cylinders of chlorine should be shielded, where necessary, from excessive heat or cold. Direct heat should not be applied to cylinders of chlorine, nor should hot water be poured over them or come in contact with the cylinder valve. 4. Adequate ventilation should be provided for all enclosures in which chlorine is being fed or stored. 5. All joints of tubing connecting chlorine cylinder and chlorinators should be kept absolutely tight and inspected frequently to insure tightness. Tubing should dope upward from,the cylinder. LEGAL REGULATIONS In a number of states, the water used for humidification, even in industrial plants, is required to meet drinking water standards insofar as bacteriological quality is concerned. A ruling of the U- S. Department of Agriculture, Meat Inspec tion Division, prohibits the use of chromate in water used for air washing when the air later contacts foodstuffs." There is an ever growing consciousness on the part of public health officials, of the necessity for regulations to protect potable water supplies. Attesting this is an ordi nance" now in effect in Detroit, Michigan, which stipulates in part: y pumps, or tanks supplied from any other source. Where dual supplies are necessary or desired rrf .water must b? protected against back flow PUutecl wtr by an atmospheric gap. Secondary supplies `"'"ie: surface waters from rivers, raKM, ponds, lagoous, and reservoirs; well waters both deep and raSS LW,'U'-r Jhid* " been stored, held, or usswved after being used for industrial purposes; cooling water bLTmhSS wsy h*TM `mated, processed, or hu tariff contamination of a bacterio- Etoec$`Sk?`Ure: "d ,rom "V Other source n wdvci metering aevice, seaie shall be installed to measure the flow of water being treated. 3. The device shall be constructed back-flow or vacuums, the maximum may be possibly hack-sipboned from attachments or parts shall not exceed so that in the event of amount of material that the device or any of its one fluid ounce, 4. Should there the water supply, operating," be a failure the feeding of the device water metering device or shall automatically cease REFERENCES `Committee D-19: Annual Report (American Society for Testing Materials, 1947). *H. H. Uhlig (ed.); Corrosion Handbook (John Wiley & Sons, New York, p. 27). * Discufflion (.Corrosion and Material Protection, May 1945, P- 2). 4 W. C. Schroeder: Round-table discussion on organizing the classification of industrial waters (American Society for Testing Materials Proceedings, Vol. 44,1944, p. 1057). * W- D. Collins: Typical water analyses for classification with reference to industrial use (American Society for Testing Ma terials Proceedings, Vol. 44, 1944, p. 1057). * ASTM Standard D-636-41 (American Society for Testing Materials). 1E. W. Guernsey: Discussion on preventing solution of CO* in condensates (A8HVE Transactiohs, Vol. 51,1945, p. 69). 1L. F. Collins: Studies of the mechanism of solution of CO* in condensates formed in steam heating systems of buildings (ASHVE Tbassactidns, Vol. 51,1945, p. 39). *W. F. Langelier: The analytical control of anti-corrosion water treatment (American Water Works Association Journal, Vol. 28, 1936, p. 1500). " G- B. Hatch and Owen Rice: Surface-active properties of hexametaphosphate (Industrial and Engineering Chemistry, VoL 31,1939, p. 51). " G. B. Hatch and Owen Rice: Threshold treatment of water systems (Industrial and Engineering Chemistry, Vol. 37, 1954, p. 710). u Beit Handbook of Industrial Water Conditioning (W. H. A L. D. Betz Co., 4th ed.). "S. Sussmsn: Cooling water problems in the New York metropolitan area (Industrial and Engineering Chemistry, August 1952, p. 1740). UJ. A. Holmes: Slime control in cooling equipment with phenol derivatives (Annual Water Conference Proceedings, Engineers* Society of Western Pennsylvania, 1944, p. 61). UH. G. Reddick and S. E. Linderman: Tuberculation of 1! i