N E W S   R E L E A S E   from  FURMANITE  AUSTRALIA

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Spherical machining gets round turbine damage

Specialist expertise from Furmanite, the technical services company geared to maximising asset uptime, enabling spherical surfaces to be precision machined, saw a worn turbine bearing successfully repaired at short notice last month (including design and build of the necessary equipment) at Verve Energy’s Kwinana power station in Western Australia, solving the problem and enabling the shutdown to remain on schedule.

In the course of the unit inspections during the major nine-yearly outage on unit 5 at the power station, it was discovered that fretting on the bearing supporting the intermediate pressure turbine shaft had caused localised wear of the spherical surface at around 0.2mm depth at the lower bearing pad. This would cause problems in achieving an acceptable bedding-in of the bearing’s lower pad, which could result in operational problems and limit bearing life expectancy.

Furmanite was called in for its specialist on-site machining expertise and experience after Verve Energy and outage contractor Siemens UKG Alliance identified the solution: to build up the affected area with weld and re-machine it to conform to the original spherical surface profile. Any base metal removal was to be minimised to enable standard bearing pads to be used and the original shaft plane maintained. Furmanite’s proven expertise in machining of spherical surfaces in-situ – well beyond the capabilities of most machining suppliers – had been demonstrated in meeting similar requirements on turbines at power stations in South and Western Australia (including Verve Energy’s Muja power station).

To undertake the work, Furmanite technicians began by inspecting and measuring the turbine components, and designing and manufacturing an adjustable precision bearing housing assembly that would interface with specific locations on either side of the spherical surface to be machined, to carry the six inch boring shaft and spherical radius generator. The housing assembly and accessories were manufactured over the weekend to allow site work to commence on Monday morning.

With the boring bar and radius generator assembled into the turbine housings and bucked into plane with the original spherical surface, the set-up Dial Test Indicator (DTI) readings were witnessed and recorded, proving the boring bar to be within 0.02mm of the original spherical surface. The weld area was then machined down in 0.25mm increments to remove 2.5mm of green weld material.

“The rigid design and precise manufacture of the boring bar assembly were critical to success, and DTI readings taken at intervals during the work to ensure machining path accuracy showed zero deflection or movement,” Furmanite senior service technician Stan Horton explains.

As target size was approached DTI readings were taken at 0.05mm cut increments. When the spherical surface was matched within 0.03mm the finish was inspected and it was decided to pass a final cut at 0.05mm depth to provide a consistent surface finish which would enable an acceptable bedding in of the lower spherical bearing pad.

“With the final cut completed, inspection and final DTI readings showed the surface finish to be better than 1.6µm and diametrical run out less than 0.03mm,” Horton reports.

The entire project, from initial inspection and measurement to completion of the machining to restore the spherical profile, took just five days.

Commenting on the project Furmanite sales manager David Arnold states: “The combination of Furmanite’s precision-built radius generator and the experience of its technicians resulted in a highly accurate, timely and cost-efficient repair for Verve Energy. We were able not only to provide rare if not unique skills and expertise (the geometries involved put this beyond standard machining capabilities), but to provide them at short notice, enabling the highly specialised work to be undertaken quickly and avoid any delays to the shutdown.”

Kwinana power station, 40km south of Perth, is Verve Energy’s second largest (after Muja) with a total generating capacity of 900MW and can burn three fuels – coal, gas and oil – making it unique in WA. It consists of six generating units and a 20MW capacity gas turbine.

For further press information contact:
Sarah Manwaring-White
Keep in Touch Ltd
Tel: +44 (0)1451 844 488
Email: sarah_mw@keepintouch.co.uk