Home » Water & Wastewater » Case Studies » Hutt Valley, New Zealand

Case Study

Hutt Valley, New Zealand

Hutt City’s main outfall pipeline (MOP) is one of its most critical assets, taking treated wastewater from the Seaview treatment plant to the outfall at Pencarrow Head. The MOP is 18 kilometres long and has an average flow is about 550 litres per second. It was commissioned in 1962 and has an expected life of about 60 years.

Project Details

Assess and Address®Technology Driven Pipeline Solutions
Electromagnetic Inspection
SmartBall® Leak and Gas Pocket Detection
3D Finite Element Analysis and Structural Modelling
2007- ongoing
Pipe Material
Inspection Length
18 km (11 miles)
1295mm (50-inch)
Transmission Type
Treated Wastewater

Project Highlights

EM inspection showed 354 of 4,662 pipe sections with some distress

92% of Hutt City’s main outfall pipeline had no deterioration at all

Hutt City was able to extend the life of the critical asset through proactive pipeline management


Monitoring the condition of underground assets is a major challenge; much of the New Zealand’s infrastructure was constructed more than 60 years ago and is beginning to reach the end of its design life. While councils search for solutions to manage infrastructure, there is increasing public pressure to minimise rates and improve environmental performance.

Over time, Hutt City’s MOP has showed signs of deterioration, culminating with one pipe section failing catastrophically during normal operation. While replacing the ageing MOP is one solution, it is very difficult and expensive to complete. While the main has a replacement value of $60 million, the costs associated with replacement would likely be much higher due to the logistical challenges associated with constructing a new main.


In May 2013, Hutt City Council and Hutt Valley Water Services contracted MWH Global to assess the possibility of repairing or replacing of the MOP. In order to complete a comprehensive condition assessment of the main, MWH contracted Pure Technologies, a Calgary-based company.

In order to fully understand the condition of an asset, it is important to use a variety of solutions that identify different aspects of deterioration. This approach is called Assess and Address®, which focuses on identifying and locating isolated areas of distress along a pipeline for renewal. Through this approach, Hutt City can avoid replacing the entire MOP – which is challenging and costly – while increasing its reliability and extending its useful life. Pure used multiple solutions for to assess the MOP for leaks, gas pockets, and structural deterioration. The SmartBall® tool was used to identify leaks and pockets of trapped gas, as well as validate the results of the electromagnetic (EM) inspection. The tool is a free-swimming and measures the acoustic activity associated with leaks and gas pockets in pressurized pipelines.

To identify structural deterioration, electromagnetic technology was used on the PipeRider platform in the dewatered pipeline. Once calibrated above the ground using spare pipe sections – with one of the pipes having some wires exposed and cut for the calibration – the bike was disassembled and placed in one end of the pipeline. The inspection was completed by generating an eddy current and measuring the signal as it conducts through the reinforcing steel within the concrete pipe wall as the tool traverses the pipeline. In Prestressed Concrete Pipe (PCP), the reinforcing steel wires are the main structural component. As these wires begin to deteriorate, specific pipe sections become structurally weaker and are more likely to fail.

Upon completion of the inspection, Pure performed 3D Finite Element Analysis and Structural Modelling on specific sections of the MOP. This process determines how the specific pipe material will perform under different operating conditions, which will guide Hutt City on how to safely operate its main to prevent pipe failures.

This analysis also provides an estimated remaining useful life for the asset, which aids in the development of re-inspection and replacement planning.  


By managing the MOP in favour of replacement, Hutt City was able to determine that one of its most critical assets had remaining useful life. This prevented a very expensive and challenging replacement project, allowed for the deferral and redeployment of capital to other projects.

The data collected and subsequent structural analysis provided an understanding of the condition of the pipe’s main structural component while being non-destructive to the pipe itself. In total, 8 percent of pipe sections had some level of deterioration (354 of 4,622), meaning a complete replacement was unnecessary and the asset has remaining useful life.

By managing its critical infrastructure, Hutt City demonstrated its commitment to providing safe, reliable and sustainable service while ensuring that capital works budget is efficiently and responsibly allocated.

It’s fantastic we’re able to use this world-class technology in our city and benefit from the advanced results it can give us to help plan for the future.

Bruce Sherlock

General Manager, Hutt Valley Water Services