Abstract
US EPA reports that there are over 240,000 water main breaks and up to 75,000 sanitary sewer overflows per year in the United States (EPA, 2009). The number of failures has also been increasing as the systems approaching their service life. Effective management is required to extend the lives of the pipelines, and to ensure the public health and safety. An effective assets management plan, in turn, requires proper pipe condition assessment. About two thirds of the installed municipal pipelines consist of various forms of ferrous pipes (EPA, 2005). Methods are very limited to assess the corrosion condition of metal pipelines buried underground without interrupting services or excavating. This paper presents a synergistic non-destructive method to assess the condition of underground metal pipelines by discussing a case study of 140,000 ft of sewer force mains (Cast Iron, Ductile Iron).
This non-destructive method synthesizes the environmental condition with the pipe-to-soil potential data. The environmental information includes soil condition and stray currents. In this method, soil resistivity and soil pH are regarded as surrogate parameters for the corrosivity of the soil environment. High level of stray current is regarded as an indicator of corrosion activities. Environmental information (i.e., the soil and stray current information) is supplemented by the pipe-to-soil potential data. Pipe-to-soil potentials are measured with two Cu-CuSO4 half cells by following a cell-to-cell protocol. By comparing the readings of the two half cells, actively corroding areas (anodic) can be identified.
This synergistic assessment method was shown to accurately locate corroding pipes in 140,000 ft of the subject sewer force mains. Actively corroding areas selected by this method was excavated and it is confirmed that these areas have very high corrosion rate (shown by Tafel curve developed in-situ). Severe wall thinning and even pipe bursts were recorded at these actively corroding areas as well.
