51313-02565-A Case Study of Nondestructive Force Main Condition Assessment

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Product Number: 51313-02565-SG

ISBN: 02565 2013 CP

Author: Yaofu Zhang

Publication Date: 2013

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US EPA reports that there are over 240000 water main breaks and up to 75000 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 140000 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 140000 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.

1. EPA 2005. White Paper on Improvement of Structural Integrity Monitoring for Drinking Water Mains. EPA/600/R-05/038.
2. EPA 2009. State of Technology Review Report on Condition Assessment of Ferrous Water Transmission and Distribution Systems. EPA/600/R-09/055.