ABSTRACT

Failure of water/wastewater mains incurs heavy repair and replacement costs, in addition to customer’s inconvenience. Taking preventive measures such as condition assessment for early determination of corrosion in aging infrastructures is crucial for agencies from both a safety and an economic standpoint. Direct assessment techniques provide valuable insight on the existing condition of any buried structures. In an ideal case, agencies would have enough time, budget, and resources to reveal, excavate, and conduct direct assessment of their entire aging assets (e.g., miles of pipelines). In practice, such extensive assessments seldom occur and are not necessary. Indirect techniques (special over-the-line potential and soil corrosivity surveys) for external condition assessment of water/wastewater lines can be conducted to determine the high risk corrosion areas for further direct evaluation. This paper presents a case study where such indirect assessment techniques were successfully applied on an electrically discontinuous effluent sewer land outfall. Additionally critical areas were identified for excavation and direct assessment was performed. The results of direct assessment were in agreement with the over-the-line survey findings. The 40-year old sewer pipeline was located in environmentally sensitive areas (no tolerance for breaks) and may have become affected by nearby construction loads due to a road widening project. After the existing condition of the pipeline was determined mitigation methods for in-situ protection of the pipeline was recommended.

INTRODUCTION

In the United States the annual number of water main breaks mainly due to corrosion was estimated as 240,000 breaks per year. The cost of replacing over one million miles of corroded water and wastewater pipelines was estimated at US $2.1 trillion if all pipelines were to be replaced at once1. It is reported that 35 to 50 percent of this cost could have been avoided through proper design, operation, and corrosion prevention2. Therefore, condition assessment and maintaining effective corrosion control programs are essential keys for service life extension of pipeline assets. Condition assessment in particular provides useful information to determine the current pipeline condition to make recommendations for repair, renewal, or monitoring. In an ideal case, agencies would have enough time, budget, and resources to excavate and conduct direct assessment of their entire aging assets (e.g., miles of pipelines). In practice, such extensive assessments seldom occur and are not necessary.

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