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Inspection tools for pressure pipes tested: Results of the Arnhem field study 

As many pressure pipes in the Netherlands are reaching the theoretical end of their service life, the need to objectively assess their actual condition is increasing. Inline inspections make it possible to evaluate pipes from the inside without taking them out of service. 

Comparison of three inline inspection techniques for asbestos cement pressure pipes. Based on: Stichting RIONED/STOWA report RIONED44_R_250610, june 2025 

To examine how reliable these inspections are in practice, Stichting RIONED and STOWA, in collaboration with the Municipality of Arnhem and three suppliers, conducted a comparative field study. The three techniques involved were SmartBall (Xylem), Acquarius (Acquaint), and 500-UT-V1.0 (Rosenxt). The goal: To gain insight into the accuracy, reproducibility, and practical applicability of inline inspections in a real-world setting. 

Figure 1. The Smartball (l) wrapped in a foam sleeve (r) as inserted into the pressure pipe. 
Figure 2. The Acquarius after extraction.  
Figure 3. The 500-UT-V1.0 on a stand before the inspection. 

The test site: A challenging case in arnhem 

The test pipe was a 500 mm diameter asbestos cement pressure main, 1,245 meters long, with connections made of different materials (AC, GRP, and cast iron). To enable the inspections, a launch unit was constructed next to Pumping Station Vredenburg, a temporary pump installation was set up to control flow, and artificial defects were introduced, including leaks and thickened pipe wall sections. 

Figure 4. Launching device at the Vredenburg pumping station and temporary pumping installation. 

Tested techniques 

Although all three instruments move with the flow, their measurement principles differ significantly. 

Table 1. Overview of measured parameters per technique.   

Execution and field experience 

Each supplier performed two inspection runs under challenging conditions, varying material transitions, limited workspace, and low operating pressure (≤ 0.7 bar). 

  • SmartBall was easy to insert and completed the route without issues. 
  • Acquarius inspections were preceded by thorough pipe cleaning. After optimizing the settings during a test phase, the inspection runs proceeded smoothly and produced stable results. 
  • Rosenxt carried out its inspection several weeks later. The pipe did not need to be cleaned again, and both runs went without incident. 

Results 

Pipe Alignment: Alignment was verified at six points. Acquarius results mostly met the WIBON standard (≤ 0.5 m), Rosenxt showed larger deviations, and SmartBall provided reasonable but combined data. 

Figure 5. Difference between the measured pipe location and the inspection results. *Xylem only reported a single combined result, which may lead to an overestimation of accuracy. 

Leak detection: None of the technologies detected leaks due to the low pressure. Reliable acoustic detection requires at least 1 bar of pressure. 

Wall thickness and leaching: Acquarius and Rosenxt results corresponded well with CT scan data when the correct reference wall thickness was used. For the second verification, three pipe sections were externally coated to simulate thicker walls. Only Acquarius correctly detected and reported these artificially thickened sections in detail. 

Figure 6. Acquaint inspection results for the healthy remaining wall thickness of pipe sections 133 (top) and 135 (bottom) at a distance of 581.81 m (top) and 592.14 m (bottom) from the pumping station, together with the CT scan results. 
Figure 7. Effect of the original wall thickness used on the results for the healthy remaining wall thickness for pipe section 137 at 597.64 m. On the left, an original wall thickness of 30.4 mm was used, and on the right, a wall thickness of 39 mm, which is the wall thickness that also followed from the CT scan results. 
Figure 8. Relationship between the original wall thickness applied to pipe section 137 and the percentage of healthy remaining wall thickness. 
Figure 9. Smeared section of the pipe that can be seen as external leaching in the Acquaint inspection results. 
Figure 10. Thickness of the coated sections per clock position, calculated by taking the difference in healthy remaining wall thickness before and on the thickened section from the inline inspection results of Acquaint. 
Figure 11. Rosenxt inspection results for the healthy remaining wall thickness of pipe section 137 (top) at a distance of 594.11 m from the pumping station, and 139 (bottom) at a distance of 603.25 m from the pumping station, together with the CT scan results. 

Reproducibility: Acquarius demonstrated the highest reproducibility across all measurements. Rosenxt provided one usable run, while SmartBall combined runs into one dataset. 

Summary comparison 

Table 2. Summary of key results. 

Main Conclusions 

  • Measured pipe alignment does not always meet the minimum WIBON accuracy requirement, intended to prevent excavation damage. The issue lies not in the inspection technology itself, but in the calibration of reference points for XY positioning. 
  • As a side effect, the recorded position of a pipe section can shift along the pressure main, making it difficult to compare new inspections with older ones to determine condition changes. 
  • Measured wall thickness values generally match CT scan results. For pipe sections with significantly deviating original wall thicknesses, discrepancies in residual wall thickness may occur. All three artificially thickened locations were successfully detected by Acquaint. 
  • At low pressures (≤ 0.7 bar), leaks of up to 1.8 l/min were not detected. This may also occur near discharge points of long pressure mains. 
  • For pipe joints, Acquaint’s measurements of angular deflection and joint width corresponded with measurements on a decommissioned pipe section. However, since all joints were relatively narrow, it cannot be confirmed whether the same holds for wider joints. Rosenxt did not supply coupling data. 

Acquaint’s Response 

“We would like to compliment Stichting RIONED, STOWA, and especially Partners4UrbanWater for the thorough design and execution of this study,” says Erik Driessen, Managing Director of Acquaint. “We are, of course, very proud of this independent confirmation of our latest generation Acquarius inspection tool.” 

Driessen also expressed his appreciation for Erik Laurentzen from the Municipality of Arnhem: “His commitment, the availability of the network, and his infectious enthusiasm for pipeline management and innovation made this study possible. Erik is a true leader in the field of pressure main management.” 

Acquaint now collaborates with 20 of the 23 Dutch water authorities and an increasing number of municipalities. “It’s encouraging to see how asset managers in the Netherlands are integrating pipeline inspections into their management strategies and that the Netherlands is leading the world in active inspection and management of underground assets. This is exactly the direction we want to grow together as a sector.” 

Click here for the full report (in Dutch).

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