High tides among the obstacles faced during Vancouver Island force main inspection

By Mark Fodchuk and Justin Hebner

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 because of 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, British Columbia.

The pipeline was installed in the early 1980s and consists of an 8.75 km large-diameter force main that connects Courtenay, Comox and K’ómoks First Nation Community to the Comox Valley Water Pollution Control Centre. This includes a 5-km 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.

A new concept was developed that would utilize a portion of the existing force main within the foreshore, but remove from service the exposed portion. 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 remaining service life and overall condition. The project timeline was tight as CVRD needed quick results to proceed with corrective action immediately should it be required.

The inspected portion of the pipeline was built of two different materials, prestressed concrete cylinder pipe and barwrapped pipe, and three different pipe diameters: 450 mm, 750 mm and 820 mm. As well, the critical line could not be taken out of service. Associated Engineering, CVRD’s consultant, assisted in developing the request for proposal process. Pure Technologies, part of Xylem Inc., was selected to conduct the condition assessment. This included an electromagnetic inspection, structural curves, leak and gas pocket detection, and transient pressure monitoring.

Pure Technologies proposed using its acoustic-based SmartBall® tool for the leak and gas pocket detection, and its free-swimming PipeDiver® inspection platform for the electromagnetic inspection of the line.

Transient pressure monitors were installed at the Courtney Pump Station. For more than four weeks, recorded pressure data was used to understand the operational and surge pressures within the force main and their impact on structural integrity.

While transient pressure data was being collected, Pure Technologies deployed SmartBall, 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 it is deployed, the pipeline remains in service, limiting disruption to customers.

Analyzing data gathered by the SmartBall.

Pure Technologies also deployed the PipeDiver platform, a free-swimming condition assessment tool that collects electromagnetic data about the pipe wall. It also operates while the pipeline remains in service. The tool travels with the flow and utilizes flexible petals to navigate plug valves, tees and bends in the pipeline.

Tight time frame for tool insertion

Due to the critical nature of the line, and a small capacity wet well at the Courtney Pump Station, inspection teams had only 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. The solution was to first use the SmartBall inspection tool to test flows in order to optimize the inspection approach for the PipeDiver run.

Retrieving the PipeDiver inspection system.

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 the extra flows expected. 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 problems. Inspection crews needed to monitor tidal forecasts in order to access the tracking sensors during the tide ebb, which meant a short window to retrieve sensor data.

In spite of the challenges and risk, the four-day inspection proved successful and went off without a hitch.

Inspection results

Based on the inspection data, Pure Technologies’ analysts identified zero leaks, one acoustic anomaly associated with trapped gas, five acoustic anomalies characteristic of transient gas, and two acoustic anomalies associated with entrained gas. 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.

“This project had a lot of challenges, especially since the asset was so critical to the region. However, Pure Technologies 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,” says Kris La Rose, Senior Manager Water/ Wastewater Services, Comox Valley Regional District.

Mark Fodchuk and Justin Hebner are with Pure Technologies, a Xylem brand. For more information, email: mark.fodchuk@puretechltd.com