Development of Guideline Documents for the Inspection and Condition Assessment of Pressure Mains

Pressure mains, including both potable water mains and wastewater force mains, rarely receive the levels of inspection and maintenance routinely accorded gravity sewer mains. This is due to the difficulties in taking these critical assets out of service, the lack of redundancy and the lack of adequate access to the pipe interior. In effect, most pressure mains are designed and operated in the ‘run-to-failure’ mode. Utilities are being rudely awakened to the impacts of this approach as pressure main failures become more frequent. The last two years have seen several significant and highly publicized pipeline failures, including major water mains, wastewater force mains, steam lines and gas transmission mains.This paper will describe the work being undertaken to meet the challenges of inspecting and assessing the condition of pressure mains. A case study will be used to present an example of the decision tools used in the development of a custom program for the inspection and condition assessment of pressure mains. The tools include inspection technology selection diagrams, inspection program work flow diagrams and decision trees, pressure main observation and defect coding lists and condition assessment logics and decision trees for selecting the next steps, that is whether to Re-inspect, Repair, Rehabilitate or Replace the asset (the ‘Four R’s’).