Located an hour drive away from Oslo, lies the municipality of Holmestrand. Holmestrand kommune is home to over 26 thousand people and transports millions of liters of drink- and wastewater through their pipelines. The municipality of Holmestrand is the first to implement the Acquarius technology in Norway.
Norwegian pipeline owners face unique challenges related to their underground assets. The pipelines are laid deep underground to protect against frost, and the Norwegian landscape consists mostly of rocks. These factors contribute to high expenses to replace pipelines by using open trenches, making No-Dig methods an interesting solution.
An inspection with Acquaints inline inspection tool: The Acquarius. Equipped with advanced ultrasonic sensors, the Acquarius can determine the condition of a pipeline without the need for excavation.
Located an hour drive away from Oslo, lies the municipality of Holmestrand. Holmestrand kommune is home to over 26 thousand people and transports millions of liters of drink- and wastewater through their pipelines. Norwegian pipeline owners face unique challenges related to their underground assets. The pipelines are laid deep underground to protect against frost, and the Norwegian landscape consists mostly of rocks. These factors contribute to high expenses to replace pipelines by using open trenches, making No-Dig methods an interesting solution. A No-Dig inspection with the Aquarius from Acquaint proved to be a valuable solution.
Holmestrand Kommune wanted to have more reliable insight into the condition of a Cement-lined ductile iron drinking water pipeline. The pipeline has an internal diameter of 300mm and a length of 2300m. The drinking water pipe lies in clay soil near salt water and dates from around 1970, which means it is nearing the end of its theoretical life span. In addition to a full condition assessment, the municipality also wanted an accurate XYZ mapping of the pipeline. The Acquarius from Acquaint proved to be a valuable solution for this. The Acquarius is an advanced tool consisting of a foam PIG (Pipeline Inspection Gauge) at the front, commonly used for cleaning pipelines. Acquaints tool, however, is equipped with a large number of advanced ultrasonic sensors that emit and receive high frequency sound waves to measure wall thickness and detect any anomalies (such as corrosion, leaching, H2S damage, and leaks) in the wall or connections of the pipeline. Additionally, the Acquarius has various other sensors that measure the exact location of the pipeline.
Unexpected material
After the first 20 meters of ductile iron pipeline a, for Holmestrand kommune, unknown material was encountered, which was later identified as asbestos cement (AC). This AC pipeline extended for 705 meters, followed again by a cement-lined ductile iron pipeline continuing to the end of the trajectory. Additionally, cast iron fittings were observed, primarily at the bends.
XYZ deviation
Figures 1 and 2 show the results of the XYZ-mapping of the Acquarius compared to expected location based on the clients GIS-file. Figure 1 shows the seven major deviations. In this project a deviation is classified as major onwards from 8 meters. Figure 2 zooms in on location D, where the original GIS-file (blue line) misaligns with the measurements (dots) up to 21,5 meters.
AC Leaching
First a short introduction into AC leaching; Asbestos cement pipes have been widely utilized in pressurized water distribution and sewage systems due to their inherent strength, durability, and corrosion-resistant properties. However, as these pipes age, exposure to environmental factors, particularly water, can trigger calcium leaching within the cement matrix. The gradual depletion of calcium compounds compromises the structural integrity of asbestos cement pipes, leading to potential failures and water contamination risks.
The AC pipeline within the trajectory is quite heavily leached (figure 3). Overall, the AC has a leaching percentage of at least 12% off the original wall thickness. With, in the last 200 meters of the AC part, up till 50% leaching in relative to the original wall thickness of 28,3mm. Meaning that half of the original wall thickness has lost its structural integrity.
Cement lined ductile iron wall thickness
The remaining wall thickness is measured by the ultrasonic sensors. In addition to measuring the total wall thickness, the ACQUARIUS tool has the globally unique feature to distinguish between the inner layer (cement) and the outer layer (ductile iron) of the pipe. The thickness of the inner layer and the thickness of the outer layer together make up the total remaining wall thickness.
The graph below (Figure 4) shows that the average remaining wall thickness for the DN300 ductile iron pipe sections (the outer layer) ranges between 6 and 9 millimeters, with the majority of sections showing an average remaining wall thickness of about 7 millimeters for the ductile iron layer. These results are considered a stable wall thickness.
The following graph (figure 5) shows the thickness of the inner cement liner attached to the DN300 ductile iron pipeline. Between 750 meters and 1375 meters from the start of the trajectory the cement liner averages a wall thickness of approximately 10 mm. A sudden change in thickness of the cement liner is visible at the 1375 meter point, since the cement liner for the rest of the section has a stable thickness of about 6 mm this sudden change seems to be because a thinner liner or difference pipe manufacturer was used from that point on. The lining appears to be well-adhered to the ductile iron throughout the trajectory.
The healthy remaining wall thickness (ductile iron combined with the liner) is approximately 17 mm for the section up to 1375 meters along the route and about 13 mm for the subsequent section with the thinner cement liner.
Critical joint angles at four positions
All joints are reported on an excel sheet and on Acquaints unique cloud-based dashboard and the critical ones are highlighted in the report. In the table below (figure 6) the norms are displayed for the different pipe types detected in this project. Considering the Acquarius tool has a measurement accuracy of 0.25°, the threshold (safety factor) is set at 0.25° below the norm. All joint angles exceeding this threshold are considered critical.
Two types of displacement are reported, vertical angular displacements and horizontal angular displacements. In the following table (figure 7) four critical angles have been reported. Within the AC DN300 section, one joint (ID31) has been found with a critical vertical angular displacement. The other three critical angular displacements are found in the ductile iron section of the pipeline.
In figure 7 the gap widths of these joints have also been displayed. The norm for gap widths is set at 32mm, no joints within the whole trajectory exceeded this norm.
In September the results were presented to Holmestrand Komunne, following this presentation the results were also publicly presented to the Norwegian water sector during an online webinar. Kjeldaas and Acquaint collaborated to deliver an information-packed webinar that covered all aspects of the Holmestrand project, including preparations, inspections, results, and more.
Click here to watch de webinar.
Rehabilitation of Asbestos Cement
First of all, Holmestrand was surprised with the findings of AC within the trajectory. Holmestrand kommune and Norway as a whole strive to replace all the underground AC pipelines. Besides that, the AC pipeline inspected in this project has been leached up to 50%. These findings combine to the decision to replace the 705 meters of AC.
New XYZ-coordinates
Holmestrand kommune took over the new GIS-Files of the XYZ-mapping conducted by the Acquarius inspection. With seven major location deviations up to a staggering 22,3 meters Holmestrand kommune finds it important to have these new coordinates within their system.
Monitoring critical joint angles
Based on the observations, Holmestrand kommune will monitor the joint angles reported as critical.
Cement lined ductile iron in a good state
Opposing to the AC part of the trajectory, the cement liner as well as the ductile iron are in a good state. Holmestrand kommune can comfortably monitor this segment for the upcoming years.
Kjeldaas is our brand-new partner in Norway and Iceland. Kjeldaas is a civil work company, specialized in road, water and sewer systems for over 50 years. The collaboration between Kjeldaas and Acquaint started of strong with a successful project in Holmestrand.
During the inspection on Wednesday the 12th of June 2024; Kjeldaas, Acquaint and the SSTT organized an eventful demo-day where the Acquarius inspection was the highlight activity. With a live Acquarius demonstration and presentations regarding motivation, preparation and data-usage everything around the inspection was covered.
Click here to watch the demo-day after movie
During the demo-day more than fifty interested experts from the water-pipeline sector were there to see the Acquarius inspection being launched, tracked and received.
As a pilot project we could not wish for much more, with among others; unknown material, change in dimensions, 90 degrees bends, leached asbestos pipes and different thickness of cement liners. It shows the variety of information you can get out of one inspection. A well-attended theme day and over 100 registered participants in the webinar made everything even better. It was great to cooperate with the professional employees of Acquaint who know how to plan and execute the project in detail at the right time. Condition based maintenance is the future and I am really looking forward to getting this into the Norwegian market.
We were very impressed with the results and the accuracy of each joint and pipe segment and how this is shown in the dashboard. With this tool we can plan our investments and know that our limited investment funds are used at the right time and in the right place.
