Taking on the Impossible

Design and build of a bespoke mixed metals compact deep hole boring machine for in-situ refurbishment at the Burrinjuck Hydropower Station in Australia.

Located in Burrinjuck National Park approximately a 1 hour and 35 minute drive from Canberra Australia, the Burrinjuck Hydropower Station (then owned by Trustpower, now owned by Meridian) set out to be a challenging project.

Many companies deemed the project to refurbish the Main Inlet Valve (MIV) drive dowels in-situ as too difficult, bordering on impossible. The radial dowels connecting the control arm to the butterfly valve body had become worn with the risk of failure. This was an unacceptable situation for Trustpower.

Several potential solution providers were approached across Australia and NZ with the consensus being it was just too difficult to create an appropriate solution. Farra was approached and were confident in providing a resolution given our extensive experience in hard to do site machining works and our out of the box thinking.

Farra was tasked with the design and build of a bespoke compact high precision boring machine to repair the valve with consideration to the complexities of:

  • A location with restricted access.
  • Working in confined spaces and limited work space to complete the project.
  • Producing a parallel, straight and round borer with a 0.02mm tolerance, that can bore through half 431 stainless steel and the other half low carbon steel.

Location / Access

The first location hurdle was the access to the building housing the MIV. This was accessible by either a two man lift; the approximate size of a telephone box which descended the face of the Burrinjuck station or hundreds of stairs which wound their way down to the bottom of the dam.

Access was reduced further by the 600mm diameter entrance hatch being the only entry to the penstock tube. As the average male’s shoulder width is 465mm, the entry hatch did not leave much room for movement.

The location access and physical valve body construction eliminated the use of any standard OEM supplied equipment as part of the solution.

Borer Design

The Farra team worked hard to create a borer that was small and light enough to fit within the access restrictions of the dam but powerful and precise enough to bore through the low carbon steel of the control arm and valve body, and through the stainless steel of the connecting shaft.

Key Facts

Completion: From design to completion the project took just over six months.

Multipurpose Design: Farra’s design is multipurpose and has been adapted to work on other Trustpower projects.

Creating one piece of equipment to bore 250mm deep through two different types of metals takes a lot of skill.

To guarantee that precision was able to be implemented on site, the team in the machining workshop tested the borer to the accuracy of 0.01mm. This ensured that the boring machine could achieve within the 0.02mm tolerance when it came to on-site implementation.

When on-site and it was time for the borer to be implemented, the team executed it perfectly with the borer performing within 0.015mm.