AWWA WQTC65842

Malcolm Pirnie has been involved in conducting several pipe loop studies to understandthe impacts of distribution system water quality on red water occurrences. The pipeswere retrieved from several areas of the distribution system from cities in Texas andArizona. The retrieved pipes were of different diameter and different types of materialsfound in the distribution system. Care was taken to retrieve pipes with varying levelsof internal corrosion. Pipe segments with different degrees of internal corrosion werecoupled to form loops. The arrangement of various pipe segments is referred as "pipeloops".Pipe loops were exposed to simulated distribution system water qualities. The extent ofof corrosion was measured by measuring changes (increase or decrease) in concentrationof corrosion byproducts (Fe, Zn, Ca) and water quality parameters (pH, alkalinity,turbidity, dissolved oxygen).Performance of corrosion inhibitors (polyp and orthophosphates, sodium silicate, andstannous chloride) were evaluated as a part of red water control strategies. Corrosioninhibitors interact with pipe scale and form a surface complex or a passive layer on thepipe scale surface. Spectroscopic analysis was performed to understand the pipe scalecomposition. Multiple phases of iron oxide/hydroxides were present in the pipe scale.Composition of pipe scale is related to its potential to release the corrosion byproducts.Based on findings from the study conducted in Arizona and Texas, recommendationswere developed inline with maintaining finished water quality goals at the treatmentplants, exploring the possibility of adding a corrosion inhibitor at the treatment plant,managing flow velocities, pressure zones and, exploring the possibilities of long termchanges in treatment strategies to increase the chemical stability of finished water. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2007

Number of Pages:

6

File Size:

1 file , 180 KB