The city of St. Petersburg is located on Florida's gulf coast, part of the Tampa Bay area. Recognizing the importance of proactive asset management, the City of St. Petersburg launched an initiative to inspect, assess, and address its buried pipeline assets.
The city’s water and sewer systems are critical to its residents, businesses, and thriving tourism industry. However, these systems, some of which were installed decades ago, are increasingly vulnerable to corrosion, leaks, and failures due to environmental conditions and the demands of a growing population.
Through its partnership with V&A Consulting Engineers, the city selected CPM Pipelines to deploy Acquaints Acquarius in-line inspection technology for the inspection of a 4-mile, 24-inch ductile iron (DI) force main.
St. Petersburg, Florida, a city with rich history and rapid growth, faces mounting challenges managing its aging buried pipeline infrastructure. The city’s water and sewer systems are critical to its residents, businesses, and thriving tourism industry. However, these systems, some of which were installed decades ago, are increasingly vulnerable to corrosion, leaks, and failures due to environmental conditions and the demands of a growing population.
Recognizing the importance of proactive asset management, the City of St. Petersburg launched an initiative to inspect, assess, and address its buried pipeline assets. The goal: to prioritize rehabilitation and extend the lifespan of critical infrastructure while avoiding unnecessary replacement costs. The city completed a preliminary desktop assessment of twenty-six force mains, categorized as very high, high, and medium risk. V&A was contracted by the city to assess the condition of all 26 force mains and develop a screening assessment ranking. Through its partnership with V&A Consulting Engineers, the city selected CPM Pipelines to deploy the Acquarius in-line inspection technology for the inspection of a 4-mile, 24-inch ductile iron (DI) force main. Based on the screening, the lift station force main was ranked as ”Very High Risk,” with recommendations for further investigation.
The targeted force main transports wastewater from Lift Station 63, traversing neighborhoods, waterway crossings, and major roadways before terminating at the city’s wastewater treatment plant (WWTP). Lift Station 63 pumps wastewater directly to the headworks of the Northeast Water Reclamation Facility through approximately 19,000 feet of 24-inch ductile iron force main, with a peak flow rate of 8.2 million gallons per day.
Historically, this pipeline experienced failures, prompting concerns about its reliability and potential environmental impact. Initially, replacement was considered, with cost estimates exceeding $40 million. Instead, the city opted for a proactive approach to evaluate the pipe’s condition and identify actionable rehabilitation strategies.
The modifications required in preparation for the inspection were:
Installation of a launch assembly with a Wye fitting (Y-piece) and valve near the lift station. And the replacement of a plug valve with a gate valve at a downstream discharge manhole.
These modifications were completed during planned repairs to minimize service disruption. Notably, the inspection was conducted with the pipeline in service, eliminating the need for an expensive bypass system.
Inspections with Acquaints Acquarius technology deliver myriad results and insights. Starting with the location deviation of the pipeline.
Location deviation
Comparing the XYZ mapping of the Acquarius to the client’s GIS file, it showed discrepancies over the complete trajectory. Eight spots of location deviation have been detected. The eight spots highlighted in Figure 2 show a deviation of at least 6 feet (1.8 m) compared to the original files.
Figure 3 shows spot B where the original GIS file (blue line) misaligns with the measurements (dots). This spot contains the biggest deviation of all, with a distance of 45 ft (13,7m). This deviation stood out because in the provided shapefile, the pipeline was depicted on the left side of San Martin Blvd NE. It was expected that the pipeline would return to the side of Lift Station LS63 shortly after the initial crossing. However, in reality, it continues along the opposite side of San Martin Blvd NE. The color scale on the right of Figure 3 represents the distance of the deviation. Green indicates the GIS file runs identical to the Acquarius mapping, red indicates a deviation of 6 ft or higher.
Angular joint displacement
Angular displacements of joints are calculated based on the IMU sensor on board of the inspection tool. Figure 4 shows the horizontal angular displacement of the joints in relation to the American Water Works Association (AWWA) C600 standard for 24” ductile iron pipes, which is 3 degrees.
Figure 5 shows the vertical angular displacement of the joints in relation to the American Water Works Association (AWWA) C600 standard. A total number 154 joints (horizontal and vertical combined) exceed the AWWA C600 standard of 3 degrees.
The angular displacement norm for ductile iron pipelines based of Saint-Gobain is set at 4 degrees. By subtracting the 0.25 measurement accuracy of the Acquarius tool, the threshold for angular displacements is set at 3.75 degrees (Figure 6). A total of 45 joints exceeded this threshold, these are labeled as critical.
A common failure as a consequence of angular displacements is gap width. However, no extreme gap widths (larger than 1 inch) have been found.
Acquaints interactive online dashboard covers all collected data in a visual overview. Figure 7 showcases all 45 critical joints, visualized as a red dot.
The 45 critical joints are distributed throughout the entire trajectory. However, as illustrated in Figure 8, multiple spots with displacement are clustered in the submerged pipeline at the river crossing section.
Depth profile
Figure 9 shows the depth profile of the pipeline. The depth is measured to the center of the pipeline. The zero-value on the profile equals the zero-value in the used ESSG:2778 coordinate system.
From 3,080 feet to 3,247 feet along the trajectory, an elevation rise is visible in the depth profile. This corresponds to the section where the pipeline runs above ground, adjacent to the bridge along San Martin Blvd NE. Following this, there is a gradual decline in the depth profile until Tallahassee Dr NE. Between 6,840 feet and 7,000 feet along the route. Another decline is observed in the depth profile, where the pipeline runs from Macoma Dr NE beneath the water toward 79th Ave NE. Additionally, around 11,500 feet, a drop in the depth profile can be seen where the pipeline crosses under the waterway along 1st St NE, near the intersection with 70th Ave NE.
Wall thickness
The inspected pipeline was assumed to be an AWWA Class 52 pipe based on the wall thickness measurements of the excavated pipe at the beginning and end of the force main. The average remaining wall thickness of the ductile iron (Figure 10) is just below 0.4 inch (10mm). The wall thickness is stable over the whole trajectory, except for one section.
The exception is at the submerged river crossing (Figure 8), where the average remaining wall thickness is 0.8 inches (20 mm). Based on the as-built plans, these pipe segments are assumed to be Class 56 ductile iron pipes with ball-and-socket joints.
Unknown material
In the section after the bridge, a non-metallic material (reported as unknown) was detected (red line in Figure 11). This is unexpected, as the pipe was previously documented as ductile iron (DI), and the customer was unaware of this discrepancy.
Gas pockets
A significant number of gas pockets have been detected along the entire pipeline trajectory. Figure 12 provides an overview of the interactive dashboard, highlighting the locations (in purple) where gas pockets have been identified. Gas pockets have been observed over a total length of 6,286 feet and may consist of either air or H2S.
The results show a stable wall thickness indicating a healthy status of the pipe segments.
The municipality of St. Petersburg decided to excavate the pipe segment where the non-metallic material has been detected after the bridge (Figure 11). This part of the trajectory will be replaced.
The joints that have been found critical due to angular displacement will be monitored to assess deterioration over time.
St. Petersburg’s decision to utilize innovative inspection technology has reshaped its approach to pipeline management.
For less than 1% of the reserved replacement budget, the city gained critical insights that enabled it to:
– Defer Replacement Costs: Avoiding a $40 million pipeline replacement.
– Prioritize Investments: Addressing only critical segments for repair or replacement.
– Enhance Decision-Making: Using data to plan future maintenance strategies.
By transitioning from reactive to proactive management, St. Petersburg has set a precedent for other municipalities facing similar challenges. The use of field data ensures more informed decisions, reliability of service, and financial prudence. All critical for a city committed to sustainability and resilience.
“The City and V&A conducted a condition assessment of Lift Station 63 Force Main (LS 63 FM). Based on an internal risk screening, the force main was classified as “Very High Risk,” with recommendations for further investigation focusing on both external and internal corrosion. Thanks to the results of this inline inspection, we avoided a $40 million investment that would have been required to replace the entire pipeline. Instead, we can now concentrate on repairing only the weakened sections, preserving the intact portions of the pipeline.”
