Effect of Time on Pipe Roughness

Abstract

This paper presents the results of laboratory measurements conducted on pipes of different materials to investigate the increase of pipe roughness with the age of pipe. The pipe roughness after time t years would be simply defined as half the average decrease in the effective pipe diameter, 0.5(D0-Dt), where D0 is the pipe original diameter at time t equal to zero and Dt is its diameter at time t. The samples of pipes tested varied in age from zero to 50 years. Pipe samples included lined and unlined Cast Iron, Steel, Reinforced Concrete, Asbestos Cement, and Plastic. Two sets of samples were tested. The first set was for pipes used for filtered water and the second included those used for raw water. It was found that the pipe roughness increased with time in a parabolic trend. The effect of time on pipe roughness was found to be larger in case of pipes prone to rust like Cast Iron and Steel pipes. Plastic pipes showed minimum response to time due to the plastic mixture nature, plastic smoothness, and plastic resistance to rust. After fifty years, the absolute roughness of the PVC pipes was only about 1.5 times its original value while that of steel pipes was about forty times its original value. Also, pipes of the same material were affected more if used to carry raw water than the case of filtered water. The value of the absolute roughness in raw water relative to that in filtered water was found to change with pipe type and time. After fifty years this value was equal to 10 for PVC pipes while for other types was in the range of 2 to 3. Curves and statistical equations were introduced for design purposes.