Carbonate Deposits for Pipe Protection

Self Cite

Success attained in work with synthetic recirculated water with a low ME of calcium carbonate and containing colloidal calcium carbonate has suggested that a practical field method might be devised for developing permanent protective coatings in relatively short periods of time. In order to explore this possibility, studies were begun with a continuous flow of Michigan State University tap water. In a series of tests, the tap water flow was divided to feed sodium hydroxide and sodium carbonate to a bypassed portion. The high, 10.5 pH level in the bypassed flow resulted in the development of colloidal calcium carbonate in that line. Data and qualitative observations reported here show that a useful approach to the problem of the formation of protective calcium carbonate coatings in iron water mains has been developed. The experimental data lead to these conclusions: Michigan State University tap water develops hard, dense, calcite coatings on iron nipples within a few hours at velocities of 8.0‐13.5 fps and a momentary calcium carbonate excess of about 5 ppm. Momentary excesses as high as 60 ppm, with a flow velocity of 1.5 fps, develop similar coatings, an uncontrolled momentary excess of more than 30 ppm results in heavy deposits of loose calcite, which vary from fine to coarse grain; the addition of O.5‐1.5 ppm metaphosphate controls calcium carbonate precipitation and permits the use of momentary‐excess values as high as 100 ppm without encrustation of feed lines or piping. With a velocity of 3.0 fps, thin, translucent calcite coatings have been developed which have useful anticorrosion value; calcite coatings have been obtained with metaphosphate concentrations of 2.2 ppm and calcium levels as high as 1,500 ppm (as CaCO3); however, these coatings are not superior to those obtained at lower metaphosphate and calcium levels; the DFI and ME values have proved to be more useful for predicting carbonate deposition than Langelier's or Ryznar's indexes; microscopic examination of the coatings developed on sandblasted metal has shown imperfections and rusting in the translucent calcite coatings, it is believed that imperfections are at points of deep penetration by high‐velocity sand grains during sandblasting; and, better coatings were obtained in 2‐hr experiments at 3.0 fps than at 1.5 fps. In general, better coatings have resulted at high velocity than at low velocity, probably because of the decreased thickness of the laminar boundary film, more rapid mixing rate, and increased velocity distribution.

mentioning

confidence: 99%

Use of Polyphosphates for Developing Protective Calcite Coatings

McCauley¹

1960

Self Cite

New Developments in Deposition of Calcite Linings in Small‐Diameter Pipe

Radziul¹,

Campbell²,

Flentje³

1965

Chemical Control of Corrosion

Larson¹

1966

This article considers chemical control of corrosion as an alternative to a variety of consequences. It is most effective as a supplement to other protective measures. Because of the variety of water qualities and of environments, it is subject to many interesting complications. The application of chemical control may be limited by cost; its effectiveness may be limited by the nature of the distribution system. In the public water utilities, the range of measures for chemical control is limited by the undesirable effects that certain inhibitors have on quality.