• Maraetai II Penstock Internal Repaint

    Maraetai II Penstock Internal Repaint

  • Maraetai II Penstock Internal Repaint

  • Maraetai II Penstock Internal Repaint


Lake Maraetai


Mighty River Power


3 months


May 2012



The Project

This project was for the internal painting of the Unit 7 penstock of the Maraetai II powerstation located on the Waikato River.

The penstock is 4.57m in diameter with a total length of approximately 100m and a slope of 60º. Specifically the works included:

  • The full removal of existing internal penstock coatings including the draft tube, scroll-case and head-gate guides via automated ultra high pressure (UHP) water jetting at 2500 bar.
  • Manual abrasive blast of the steel surface off a purpose built self levelling hydraulic stage. The stage was lowered into the penstock via a custom built man riding winch.
  • Spray application of the new coating system to the internal walls of the penstock off the hydraulic stage.

Like all penstock painting, this job presented a number of access challenges and health and safety risks which made it a demanding project to execute. This was largely due to the steepness of the pipe and the restricted number of points of entry.

These challenges were largely overcome through the use of automated UHP water jetting equipment and the custom made self levelling access stage. The automated UHP water jetting significantly reduced the number of operators required at the work front. The custom made self levelling stage enabled workers to get access to the pipe and work safely within the confines of the handrails on the platform.

In addition to the stage, a custom built man riding winch was also used which was built specifically for penstock work. It allowed the stage and the UHP water jetting plant to be safely lowered into the penstock and the speed to be adjusted depending on the requirements.

All work was carried out in accordance with TBS’ strict operating procedures and management plan and met all Mighty River Power requirements as demonstrated by fully compliant audits carried out by independent consultants.

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