Development of a Successful Un-Tethered Wastewater Force Main Acoustical Inspection Technology

Inspection of wastewater force mains has historically proven difficult for operators of collection systems. Unlike potable water transmission mains, wastewater force mains generally lack redundancy and therefore, the ability to shut down the pipeline for a comprehensive inspection. Thorough inspections often require significant expenditures in order to bypass the wastewater flow via temporary pumping or installation of an additional pipeline. Desktop force main condition assessment programs are able to identify pipelines with a high likelihood and consequence of failure based on several criteria including flow transmitted, failure history, age, etc. While a desktop assessment may provide an initial screening to identify high risk force mains, it does not provide full pipeline condition data.Technologies that detect anomalous acoustic activity associated with leaks or pockets of trapped gas offer an inspection technique allowing for force main assessments to occur during full operation of the pipeline. Identification of leaks along the pipeline allows the collection system owner to find and repair defects that cause detrimental environmental impacts as well as locate and repair leaks before they become pipe failures. Detection of trapped gas pockets in force mains is especially important since at these locations hydrogen sulfide gas may be converted to sulfuric acid by bacteria in the slime layer on the pipe wall causing corrosion and eventual breakdown of the pipe's exposed surface. If not found and remediated, pipe failure may occur.The SmartBall® acoustical inspection technology allows for a unique, un-tethered inspection deployment able to successfully detect leaks and pockets of trapped gas identifying their location along the length of the force main. After a research and development program, the device began regular use in 2007, initially in potable water transmission mains in order to locate leaks. Inspection of wastewater force mains was not initiated until April 2008 as these pipelines pose challenges not often found in potable water transmission mains including lower flow rates, lower pressures, and higher levels of sediment, solids, and/or debris.This paper will discuss these challenges and solutions employed in order to successfully deploy, retrieve, and analyze data for un-tethered devices in force mains for several inspections. Results of over fifteen deployments will be briefly discussed along with the confirmation of SmartBall®'s ability to identify air pockets and leaks.