Iron-Containing Coatings on Asbestos-Cement Pipes Exposed to Aggressive Water

1984:101: Millette

Proc. of the 1983 Tech. Conf. Proc., AWWA, Norfolk, VA

Abstract:

Asbestos-cement (A/C) pipes are used in many drinking water distribution systems without problems. However, under certain conditions, A/C pipe will be attacked by the water it is carrying and show signs of deterioration (1). In severe cases the structural integrity of the pipe is adversely affected. On a lesser scale, deterioration of the first few hundred micrometers of the pipe material may expose fibers on the surface which is in contact with the water. Concern over the presence of asbestos fibers in the drinking water has caused some water utility personnel to evaluate their A/C pipe in regard to its potential for releasing fibers to the water. Although AWWA has published an aggressiveness index (AI) to help utilities decide whether or not their water is aggressive to the degree that it would harm the structural integrity of A/C pipe (2), there has been criticism of using the AI as a predictor of potential fiber release (3). The AI (Figure 1) is derived from the Langelier Index (4) based on calcium carbonate saturation considerations. The potential for non-calcium carbonate materials to form protective coatings is not estimated by the AI. That is not to say that the amount of calcium carbonate saturation is not an important factor in the attack on Portland cement materials. After studying the deterioration of Portland cement concrete in natural waters, Muller (5) concluded that if a water was not saturated with calcium carbonate, it was aggressive to concrete. Coatings may help bind fibers to the pipe but not necessarily stop water from attacking the pipe.

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