Solution & Implementation
Furmanite, the specialty services company, was called in to undertake the necessary repairs due to their machining capabilities, and ability to undertake the work within a restricted time window. The challenges were multiple – not least being restricted access and the high level of accuracy required to achieve the necessary tolerances. The work was undertaken on the Snowy Hydro Tumut 1 and Murray 1 and 2 generating units, as part of on-going refurbishment plans, in some cases using updated materials to minimise further degradation. Eighteen turbine units at three Snowy Hydro power stations have been successfully refurbished over the past seven years.
Using sophisticated technology, including the unique circular self-levelling milling (CSLM) technology – developed jointly by Furmanite/SLM and capable of machining circular structures up to 24 metres diameter to highly accurate workshop tolerances – and a purpose-designed four inch blind hole borer, Furmanite undertook the extensive and technically demanding repair work to the turbine cheek plate, throat ring, guide vane inserts and spiral casing mounting.
At Murray 1 Power Station the work included weld repairs undertaken to stainless steel cheek plates with a 14 inch wide face and approx 2.8 metre internal diameter, and the plate machined to size using the CSLM milling machine. This enabled the plate to be milled to a demanding flatness tolerance with a polished surface finish.
The machine can use either a scanning laser source or independent datum reference, which is interfaced into the electronically-controlled hydraulic levelling system. The central pivot supports the CSLM and the hydraulic levelling system travels on the surface to be machined (the unique rigid support design eliminating any distortion of the equipment and surface being machined).
The existing 2.8 metre peripheral ring had to be machined out and a replacement welded in and machined to size. Again, the CSLM machine was used here, to rim cut the 100mm vertical face for the new peripheral ring insert. New guide vane inserts also had to be supplied, installed and machined to size (224mm to a depth of 63mm). For this the blind hole borer was used, purpose-designed by Furmanite to meet the customer’s high tolerance expectations.