Evaluating In-Service Force Mains with Air Pocket and Leak Detection Technology

Bay County, Florida Utility Services Department initiated a project in Spring 2008 to evaluate several large diameter force mains for the purpose of locating potential air pockets and leaks within the pipelines. This was achieved by releasing an Un-tethered Acoustic Air Pocket and Leak Detection device directly into the pipeline's flow. Four (4) pipes were involved in the leak and air pocket detection survey, the pipes ranged in diameter of 36-inch to 54-inch. Two of the pipes were subaqueous waste force mains, the remaining two were raw water mains. Three of the pipes were prestressed concrete cylinder (PCCP) material and the fourth pipe was high density polyethylene (HDPE). The un-tethered acoustic air pocket and leak detection device was recently introduced to identify and locate air pockets and leaks in large diameter force main pipelines. The device is inserted into a fully operational pipeline and is released into the flow stream to monitor several miles of pipeline during a single deployment. A 4-inch diameter access was required for both insertion and retrieval of the device. Because the device traveled in the flow and passed directly adjacent to the air pocket or leak, it identified the noise signature created by the air pocket and leak. The position of the device was continuously tracked and recorded by a proprietary GPS synchronized acoustic receiver that identified a high frequency timed pulse from an ultrasonic transmitter located inside the device. This recorded data was analyzed to identify locations of air pockets or leaks.