When much of your critical sewer pipeline lies buried under a bay of shimmering ocean water, the challenges required to assess its condition may seem daunting. That task faced the Town of Longboat Key, an affluent retirement community located on the barrier island of the same name off the west coast of Florida.
Sensitive to environmental, health and safety issues, the Town has been concerned about their 20-inch ductile iron pipe (DIP) force main installed in 1973. Inspections have been conducted in 1996, 2007 and 2011 with ultrasonic and visual methodologies for assessment.
With talks of constructing a redundant pipeline, an island resident inquired about the condition of the existing force main and so the Town’s familiar engineering consultant, Greeley and Hansen, contracted Pure Technologies (Pure) as part of the comprehensive condition assessment project.
One of the challenges in assessing DIP is determining if the pipe has undergone any loss of wall thickness due to internal or external corrosion, which are the primary causes of failure.
SmartBall® platform provides a variety of condition data in a single deployment
To maximize the amount of actionable information to be gleaned from the force main project, Pure proposed leak and gas pocket detection services coupled with a pipe wall assessment (PWA) utilizing the SmartBall technology platform.
SmartBall is a multi-sensor inspection platform that provides utilities with a variety of pipeline condition data in a single deployment. Because the tool doesn’t disrupt service, it integrates easily into a management strategy to help pipeline owners reduce water loss, screen their network for problem areas and gain a better understanding of the condition of their assets.
SmartBall PWA technology is a screening tool that provides an indication of pipe wall stress on metallic pipes. The technology can be used as a first stage of pipeline condition assessment to help make informed decisions to focus higher resolution investigations, inspections, data collection and subsequent management of the pipeline.
SmartBall was also used to locate leaks and gas pockets in the line. Pipeline leaks are of concern for all pipe materials as they are often found to be the precursor of major failures. A pipeline failure can begin with weakening of the joint or barrel that may include a small leak.
Project challenges include underwater tracking throughout inspection
From inception, the biggest challenge was tracking the SmartBall over the 12,000-feet (2.27 miles) subaqueous portion of the pipeline. The Town was very concerned about sedimentation in that section under the bay, and insisted on Pure tracking the SmartBall PWA sensor tool throughout the inspection.
To accommodate the Town’s tracking request, 11 surface-mounted acoustic sensors (SMS) were placed along the pipeline to track the progress of the SmartBall tool during the inspection. SmartBall receivers (SBRs) were connected to the sensors on the pipeline to track the tool during the inspection based on information and drawings supplied by the Town.
Results from acoustic and electromagnetic anomalies
From the data collected and analyzed, SmartBall detected zero (0) acoustic anomalies characteristic of leaks and zero (0) gas pockets during the inspection. This indicated no leaks within the detection limits of the detection technology.
At the same time, of the 1,133 identified pipe segments, 95 (8.4 percent) showed signals not attributed to known features. The anomalies identified from the SmartBall PWA analysis included one large anomaly, 18 medium-sized anomalies and 76 small -sized anomalies. The electomagnetic signals associated with 28 of the 76 small anomalies appeared to be similar or repeatable, leading to the likelihood that a manufactured difference in pipe design exists between these 28 pipe sections.
More accurate GIS data revealed
Based on the PWA results, Pure recommended choosing a diversity of pit locations and assessing these with external verification techniques (e.g. high resolution magnetic flux leakage, pulsed eddy current, ultrasonic thickness testing, etc.) to further evaluate the probability of pipeline failure.
As well, Greely and Hansen (and the Town) now have a better handle on the spatial data of the system (GIS) and by statistically analyzing the data, can now develop pipe management strategies for the short-term management and long-term renewal strategies for the force main. By its proactive approach to asset management, the Town sets itself apart as a great example of how a community can plan for its long-term infrastructure needs.