Study On The Influence Of Inner Corrosion Of Iron Pipe On Water Quality In Distribution Systems

On the basis of reviewing the related references home and abroad, sampling of iron pipes from water ditribution system had been conducted to study the structrues and composition of corrosion scales and tubercles of different iron pipes. It was found that the tubercles had similar morphological structure, with almost 3 layers: the outer layer, the"shell-like"layer and the porous interior. The main chemical composition of the tubercles were iron corrosion byproducts, Fe3O4 andα-FeOOH are the main chemical composition of the outer layer and the"shell-like"layer, Fe3O4,α-FeOOH,γ-FeOOH are the main chemical composition of the the porous interior. The forming of tubercles starts from electrochemical reaction and the growth of tubercles is affected by electrochemical and microorganism reaction together. Fe3O4 is importont to form of tubercles and iron bacteria is an importont force to the corrosion of iron continously. The Cement mortar layer can decrease the corrosion rate effectively and control localized corrosion. The Cement mortar layer will form similar morphological structure as tubercles gradually in long time running and iron corrosion products will become one of the main chemical composition of the cement mortar layer. Another Experimental research on the influence of inner corrosion of iron pipe on water quality had been also conducted using BAR reactor in 60 days. The results shows that iron corrosion increased turbidity, chromaticity, Fe2+, Mn2+, total bacterium, Al3+ and other metal ion concentration remarkablely and cause residue chlorine and DO been massively consumpted, Al3+ concentration reduced because of its adsorption loss in reaction. It was found that the influence of residue chlorine and pH on the corrosion rate of iron pipe was remarkble. The corrosion rate decreased with the rising of pH in the range of pH 7.3~8.0 and the decreasing of residue chlorine in the range of 0.05~0.5mg/L. In the first 30 days, the corrosion rate of iron pipe decreased rapidly and then tend to be a stable value 0.03mm/a and the accumulating and releasing of corrosion products reached a balance status at and after 30th day from the start of the experiment.