Overview

The Harania Culvert Upgrade formed part of critical wastewater infrastructure works in Māngere, supporting increased flow capacity through the Eastern Interceptor network. 

As part of the upgrade, a new 2850mm steel pipe bridge required internal corrosion protection before entering service. Contech was engaged to install a Sewpercoat PG25 liner, providing a purpose-designed protective system for the pipe’s future operating environment. 

The project demonstrates the value of protecting wastewater assets at the point of construction, rather than waiting for corrosion to become a maintenance or remediation problem later. 

The Problem 

Wastewater infrastructure can be exposed to biogenic corrosion when hydrogen sulphide gas is converted into sulphuric acid by bacteria on the internal surface of a pipe. Over time, this can attack unprotected materials and reduce the service life of an asset. 

For a new steel pipe bridge, the challenge was not to repair damage that had already occurred. It was to prevent corrosion from becoming an issue in the first place. 

This required a lining system that could perform in a wastewater environment, be installed to a controlled thickness, and provide long-term asset protection from day one. 

The Challenge 

The internal surface of the pipe needed to be prepared and lined within a large circular steel structure, while maintaining consistent quality across the full internal surface. 

That meant the installation process had to control three things: surface preparation, material application and final liner thickness. 

In a project like this, the material specification is only part of the answer. Long-term performance also depends on how accurately the liner is installed, checked and finished. 

The Solution 

Traditionally, epoxy coatings have often been used as the primary biogenic corrosion protection system for steel and concrete wastewater assets. In corrosive and abrasive wastewater environments however, epoxy coating failures often lead to costly remedial works, asset disruption and repeat maintenance.  

For the Harania Culvert Upgrade, Sewpercoat PG25 was selected as the primary corrosion protection system. As a calcium aluminate mortar specifically designed for wastewater environments where biogenic corrosion is a risk, Sewpercoat provided a purpose-fit alternative for protecting the new steel pipe bridge before it entered service. 

The liner was wet-sprayed onto the prepared steel surface, creating a continuous internal protective layer. Thickness was controlled to 30mm using guidance rails, helping ensure the lining remained consistent across the internal surface of the pipe. 

The application process required careful staging, skilled installation and continuous monitoring. This ensured the final lining was not just applied, but installed to the required standard. 

The result was a continuous, controlled lining designed to protect the pipe from biogenic corrosion over its service life. 

The Outcome 

Contech completed the Sewpercoat PG25 installation inside the new steel pipe bridge, providing long-term protection against biogenic corrosion before the asset entered service. 

By installing the protective lining during construction, the project helped reduce future corrosion risk, extend asset life and support more resilient wastewater infrastructure. 

For wastewater assets exposed to biogenic corrosion, the best time to protect the structure is before the problem begins. 

Delivering quality in challenging conditions

The project was delivered under a comprehensive quality, health and safety, and environmental management framework.

Inspection and test plans guided each stage of the repair process, while environmental controls and stakeholder management measures were maintained throughout construction.

Contech worked collaboratively with NZTA, Beca and other stakeholders to ensure the repairs were delivered safely, efficiently, cost-effectively, and in accordance with project requirements.

Project Details 

Project: Harania Culvert Upgrade 

Location: Māngere, Auckland 

Client: Watercare 

Asset type: New 2850mm steel pipe bridge 

Contech solution: Sewpercoat PG25 corrosion protection lining 

Application method: Wet-spray installation 

Lining thickness: 30mm 

Design intent: Minimum 50-year service life 

Primary risk addressed: Biogenic corrosion in wastewater infrastructure