Brief Research On The Pipe Scales And The Mechanical State Of Cast Iron Pipes Corrosion In Water Distribution Systems

Gray cast iron pipes were widely in China’s urban water supply network as the first choice. Up to2012, the gray cast iron pipes are banned in the water supply system, but according to the statistics, these pipes are still about51%of the total. Because of the material, there will be corrosion holes in the pipe after being using for some time. Meanwhile the sedimentation results in the pipe scales. Due to the corrosion, the pipe all become thinner, the corrosion substance solute in the water and the pipe scales reduce the cross section. The problems of the water quality, the system safety and the reliability of the water distribution result from the pipe scales have been threat to the users.Considering the frequent problems resulted from the gray cast iron pipes, this paper studied the corrosion scales and tubercles with the method of chemical analysis; With the help of3D scanning modeling techniques, morphology of gray cast iron pipe inner wall was built; through the measurements of the corrosion holes, we get the distribution and the shape of corrosion holes; finally the flow pattern and the pipe stress distribution were simulated without considering the soil load and restraint. Combining the theory of residual strength, the residual strength was obtained; on the basis of the residual strength and the simulation, the safety of the pipe were evaluated.The result show that the electrochemical corrosion of the metal lead to the pipe scales, the main elements are:Fe, O, Al, Si, S, C. The Ferrum and Oxygen are about90%of the total. The pipe scales resulted from the deposit of the corrosion substance. The irregular geometry results in the turbulent flow in the pipeline which increase the head loss, and energy waste in water supply pipe network. The corrosion scales is a good shelter to the microorganisms in the water. In some situations, the corrosion scale will cause serious pollution in water pipe. The corrosion impact the remaining strength of the pipe and stress concentration will occur when there’s corrosion hole in pipe. According to the result, the equivalent stress is the many times of the water pressure, meanwhile it leads the decrease of the safety factor of the pipe.This thesis was kindly supported by National Major Project of Science&Technology Ministry of China(2008ZX07424.2008ZX07424-001and2008ZX07424-004).