Rising tide among obstacles during this force main inspection
For this Vancouver Island community, tight deadlines, plug valves, and a rising tide were among the challenges faced during this condition assessment project.
Sometimes the catalyst for a pipeline inspection can come from an unexpected source. In this instance, the story began when it was noticed that a sewer pipe was exposed from erosion during low tide along the beach. That observation set the wheels in motion for an eventual inspection of a critical force main that services approximately 41,000 residents in both the Town of Comox and the City of Courtenay on the eastern coast of Vancouver Island.
The pipeline was installed in the early 1980s, and consists of an 8.75 km large-diameter force main that connects the City of Courtenay, Town of Comox and K’ómoks First Nation Community to the Comox Valley Water Pollution Control Centre (CVWPCC). This includes a five-kilometer portion buried in an “intertidal” foreshore section (area between high and low tide).
Over time, a section of beach eroded and exposed the line to coastal wave action (high tide hides the pipe). The Comox Valley Regional District (CVRD) took steps to restore the beach section where pipeline had been exposed, and began developing plans to relocate the exposed force main off the foreshore.
Sensitive location and potential environmental consequences strike nerve with community.
A new concept was developed that would utilize a portion of the existing force main within the foreshore but remove from service the exposed force main. Due to its sensitive location and the environmental consequences of a potential failure, the CVRD elected to complete a highly specialized pipe condition assessment on the entire length of the line to better understand the remaining service life and condition of the force main. As a result, the project timeline was tight, as CVRD needed imminent results to proceed with corrective action immediately should it be required.
The assessment challenges began from the get-go.
The inspected portion of the pipeline was built of two different pipe materials (PCCP and BWP) and three different pipe diameters (450-, 750- and 820-mm). As well, the critical line could not be taken out of service. The CVRD consultant, Associated Engineering, assisted in developing the request for proposal (RFP) process used to select Pure Technologies (Pure) to conduct the condition assessment, which included an electromagnetic inspection, structural curves, leak and gas pocket detection, and transient pressure monitoring.
“This project had a lot of challenges, especially since the asset was so critical to the region. However Pure was able to help us understand the true condition of the line without requiring a shutdown of the critical force main, and has given us defensible information to make informed decisions in the future.”
Transient pressure monitoring used to understand surge pressures within the line.
First, transient pressure monitors were installed at the Courtney Pump Station (CPS). For more than 4 weeks, the recorded pressure data was used to understand the operational and surge pressures within the force main and their impact on the structural integrity of the pipeline.
While transient pressure data was collecting, Pure deployed its proprietary SmartBall technology, a multi-sensor tool used to detect and locate the acoustic signature related to leaks and gas pockets in pressurized pipelines.
The tool has the ability to inspect long distances in a single run, and while the SmartBall is deployed, the pipeline remains in service, limiting disruption to customers.
PipeDiver® electromagnetic technology designed to assess PCCP, BWP and metallic pipes.
In addition to utilizing the SmartBall tool, Pure chose to deploy the PipeDiver platform, a free-swimming condition assessment tool that collects electromagnetic data regarding the pipe wall, and operates while the pipeline remains in service, an important factor for the force main inspection. The tool travels with the product flow and utilizes flexible petals to navigate plug valves, tees and bends in the pipeline.
Tight time-frame for tool insertion and retrieval of sensor data.
Due to the criticality of the line, and a small capacity wet well at the CPS, the inspection teams had a very short time window (20 minutes) to insert the inspection tools. The small capacity wet well also meant that boosting flows was limited – if pumped too hard, the wet well would draw down and empty, and if pumped too slow, the PipeDiver tool could get lodged at the inline plug valves. (Low flow rate is not a significant problem for the SmartBall tool.) The solution was to first use the SmartBall inspection tool to test the flows in order to optimize the inspection approach for the PipeDiver run.
While the low flow rate slowed the SmartBall inspection, a forecast of rain moved up the PipeDiver run a day ahead in order to take advantage of extra flows that could be provided by the wet weather. The tool also had to navigate a series of 90-degree bends and a plug valve with a small port width in the pump station pipe.
Tracking the tools along the beach was fraught with potential for problems. Inspection crews needed to monitor the tidal forecasts in order to access the tracking sensors during the tide ebb, which meant a short window to retrieve the sensor data.
In spite of the challenges and risk, the dynamic four-day inspection proved successful, and went off without a hitch. The Pure Technologies crew and CVRD operators worked very well together, and their collaborative efforts ensured that this important project was successfully completed.
Data analysis indicated no electromagnetic distress on inspected pipes.
Based on the inspection data, Pure analysts identified zero (0) leaks, one (1) acoustic anomaly associated with trapped gas, five (5) acoustic anomalies characteristic of transient gas and two (2) acoustic anomalies associated with entrained gas. In particular, gas pockets are of significant concern in force mains, as concentrations of hydrogen sulfide gas within wastewater may be subsequently converted to sulfuric acid by bacteria in the slime layer on the pipe wall. This may cause corrosion and eventual breakdown of the pipe’s exposed surface.
The results also showed no indication of electromagnetic distress on the inspected pipes, which was good news, in spite of the corrosive salt water environment.
Overall, the CVRD was pleased with the inspection results, as they were able to understand the condition of the pipeline and make an informed decision for capital improvements. The project demonstrates how the region uses actionable data to effectively manage their finances and risk, while continuing to provide the community with a safe and reliable delivery of wastewater.