tea United States Environmental Protection Agency Municipal Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-81-023 Mar 1981 Project Summary Field Test of Corrosion Control to Protect Asbestos-Cement Pipe Gary S. Logsdon This research program was initiated to determine whether adding zinc orthophosphate to potable water would sufficiently coat an asbestos- cement pipe with zinc to prevent asbestos fibers from entering the water. Storage tanks and chemical and feed pumps were set up at each of the Greenwood, SC, water treatment plants, and zinc orthophosphate was fed into the system at an average rate of 0.3 mg/L. Two sections of new asbestos-cement pipe were installed to represent a low-flow and a high- flow water condition; they were removable for testing. Samples were periodically tested to determine the number of asbestos fibers in the water. The two pipe sections were removed and examined for the amount of zinc deposited on the surface. Although routine tests, such as pH and alkalinity, showed no significant changes during the study period, asbestos fibers in the water decreased substantially. Electron microscope photographs and energy dispersive X- ray spectra analyses showed coatings of zinc products on the two pipe samples. Thus, adding zinc ortho- phosphate under the existing water quality conditions reduced or pre- vented corrosion of asbestos-cement pipe. This Project Summary was devel- oped by the EPA's Municipal Environ- mental Research Laboratory, Cincin- nati, OH 45268, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Asbestos-cement (A/C) pipe has been used in the United States since the 1930's Because this pipe does not rust and cause "red water" or rusty water problems for water users, some water utilities have used A/C pipe as an alternative to cast iron when the treated water has had a history of corroding cast iron water mams. In some instances, using A/C pipe to carry aggressive or corrosive water has deteriorated the A/C pipe. Zinc orthophosphate, developed as a corrosion control additive for water distribution systems, has been used successfully in the 1970's to control problems of corrosion m cast iron mams The Greenwood study was con- ducted to evaluate its use for controlling deterioration of A/C pipe exposed to aggressive water The pipe, much of which had been installed in Greenwood in the late 1940's and 1 950's, had been attacked by the water carried by the pipes During the study, the water leav- ------- \ ing the treatment plant had a pH of 8 2 to 8 3, alkalinity of 20 mg/L as CaCO3, total hardness of 10 mg/L as CaCO3, and an iron content of 0.1 mg/L. As the water passed through the A/C pipes, the pH increased—an indication that constituents of the A/C pipe were being dissolved by the water. Methodology After the equipment was installed, zinc orthophosphate was injected into the system just ahead of the clearwell at each of the two treatment plants, begin- ning on October 11, 1977. The initial feed rate for passivation was 3 0 mg/L. The passivation period was ended after 3 days on October 14, 1977, short of the intended date of October 15, because of problems encountered at one of the system's larger users, a pharmaceutical company. This firm, which processes gauze and surgical supplies, used a cotton-filament, wound filter to remove rust or iron particles as well as other particles in the water. The high concen- trations of zinc orthophosphate clogged the filters sufficiently for the company to change filters every 2 to 3 days during the initial periods, normally, a set of filters would have lasted 6 to 7 months. The feed rate was reduced to 0 5 mg/L in an effort to ease the filter problem When zinc was found at 0.17 mg/L at the low-flow location, it was concluded that zinc was present throughout the system. The clogged filter problem at the phar- maceutical company continued how- ever, and on November 21, the zinc feed rate was lowered to 0.3 mg/L. The concentration of zinc at the low-flow location decreased to less than 0 1 mg/L. This rate was continued until the end of the study, although problems were still encountered with the filters. Water from two test locations (one high-flow, one low-flow) where A/C pipe is used, was routinely sampled for zinc content, pH, alkalinity, and calcium as CaCOs. Water samples werealspfor- warded to the EPA laboratory in Cincinnati to determine the number of asbestos fibers present. The high-flow test site (a 20-cm (8- inch) A/C pipe servicing other mains in a subdivision) was selected because it represented a flow-through situation This location was about 1.7 km (1 mile) from one of the two treatment plants where zinc was added. The low-flow sampling location (a 15-cm(6-mch) A/C main) was on a looped dead end line about 5 km (3 miles) from the same treatment plant At each of thetwosampling locations, a section of new A/C pipe was installed so that it could be removed at the end of the experiment. Throughout the study period, water quality was monitored at both locations. When the water had been tested on March 2, 1976, no asbestos fibers were found in the well water but 022 x 106 fibers/liter were found in water that had passed through about 2 miles of A/C pipe. The finished water had an Aggressiveness Index (Al) of about 104 to 105 The tendency of a water to deteriorate the structure of asbestos- cement pipe has been described by the Al as tapping' Al = pH + log (AH) where pH = -log a(-T (-log of the hydrogen ion activity) A = total alkalinity in mg/L as CaC03 H = calcium concentration in mg/L as CaCO3 Waters possessing an Al >120 are considered to be "nonaggressive", those where Al < 10.0 are said to be "highly" aggressive," and those with an Al between 10 and 12 are "moderately aggressive." During the study, the Al of the water at the closer, high-flow loca- tion ranged from 10.6 to 11.2, which is somewhat above the Al at the treatment plant. At the more distant, low-flow location, the Al varied from 11 2 to 11 9 during the study—a range considerably higherthanthe 104 to 105AI values at the treatment plant Results After the initial passivation period, zinc concentration at the closer location averaged about 0.2 mg/L; at the distant location, it was generally less than 0.2 mg/L, averaging 0 1 mg/L These con- centrations were not sufficient to prevent a rise in pH and calcium between the two sampling locations. Most of the calcium increase in the distribution system occurred between these sites, where zinc concentration was lowest Two times after A/C pipe had been tapped in the sample location vicinity, high asbestos fiber counts were ob- served. Because pipe operations can temporarily raise the fiber count in the distribution system, the use of tapping machines equipped to flush away drilling and tapping debris is recommended. The scanning electron microscope (SEM) was used to examine the interior pipe wall of pipe samples removed from both sample locations. The interior sur- face of the 20-cm (8-mch) pipe was smooth, and some coating resulting from zinc treatment could be identified. The interior of the 15-cm (6-inch) pipe, with a lower concentration of zinc (0.1 mg/L), had much larger uncoated areas on the pipe surface. Regardless of which portion of the pipe was examined, the 20-cm (8-inch) pipe always showed better coverage than the 15-cm (6-inch) pipe. This indi- cates that the zinc or zinc compounds do adhere to the A/C pipe, and that to be effective, the zinc concentration should be 0 2 mg/L, or higher if possible Energy-dispersive, X-ray spectro- metric elemental analyses were made on the surfaces of the two test pipes, these analyses were compared with that for a new, unused piece of pipe. Orj the unused pipe, the only large peak shown was calcium High peaks were seen for iron and zinc on the 20-cm (8- inch) test pipe and the low peak seen for calcium could indicate that t'ie pipe is well protected and the calcium is masked at this location. High silica and calcium peaks and a low zinc peak were observed for 1 5-cm (6-inch) pipe at the low-flow locatom. This again indicates that the low zinc concentration of 0.1 mg/L in the 1 5-cm (6-inch) A/C pipe is not adequate to provide a protective coating—certainly not as effectively as the higher concentration (10.2 mg/L)a1 the other site. In the energy-dispersive, X-ray spectrornetric analyses, the peak size for zinc and iron varied with location ir the pipe. A comparison of these peakj from the 15-cm (6-inch) and the 20-crr (8-inch) pipes showed, however, tha the highest peaks of the 20-cm (8-mch pipe were always higher than the high est peaks of the 1 5-cm (6-inch) pipe, anc the lowest peaks of the 15-cm (6-mch pipe were always lower than the lowes peaks of the 20-cm (8-inch) pipe Th< results for the iron peaks suggest tha iron in the water provides a partial pro tective coating to the A/C pipe in thi: system. ------- Conclusions The study results of using zinc ortho- phosphate to protect A/C pipe suggest that this treatment will cause A/C pipe to be coated with a protective com- pound. A zinc concentration of 0.2 mg/L was adequate to provide a coating on the pipe wall, but pH and calcium increases occurred at this concentra- tion of zinc The concentration of zinc reaching the end of the distribution system should exceed 0.2 mg/L. Because zinc precipitates in the system, the amount of zinc orthophosphate dosed at the treatment plant to obtain the desired zinc residual would have to be determined for each system. The full report, submitted in fulfill- ment of Grant No R804888-01 by Com- missioners of Public Works, Greenwood, CA, under the sponsorship of the U.S. Environmental Protection Agency, was authored by Clarence E. Grubb Gary S. Logsdon is with the U.S. Environmental Protection Agency (see below). Ralph W. Buelow was the EPA Project Officer. The complete report, entitled "Field Test of Corrosion Control to Protect Asbestos-Cement Pipe." (Order No. PB 81-152 878; Cost: $5.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield. VA 22161 Telephone: 703-487-4650 Gary Logsdon. the present contact, can be reached at: Municipal Environmental Research Laboratory U.S. Environmental Protection Agency Cincinnati. 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