In February this year a power utility in Sothern Africa approached Metalplus with an urgent request: Could it perform a complex repair procedure on a 30t 2.9m diameter low pressure steam turbine rotor from one of its coal-fired power stations in just four days?
This extremely daunting challenge was promptly taken on by Metalplus, which quoted to perform the work on the massive CNC lathe located at Marthinusen & Coutts’ Power Generation workshop in Benoni.
The power utility’s own engineering company had already taken the first step towards repairing the rotor by having installed locally manufactured last stage blades to replace all the blades that had been damaged over time during the 200MW turbine’s extended operating lifetime. However, the new blades still needed to be ground down to the correct size and profile, which was where Metalplus’ grinding expertise came into play.
“The tight time limit of four days in which we were required to perform this task was due to the engineering company having booked a slot on the following day for balancing of the rotor in the large balancing machine at its own works. If this time slot had been missed a new slot would not have been available for a number of weeks, which would have resulted in a long delay in completing the job and having the rotor returned to service at the power station” explained Roman Mornau, Metalplus’ Divisional CEO.
Steven Rudd, Metalplus’ Supervisor, was instrumental in setting up the precision grinding wheel on the tool-post of the 40t CNC lathe and thereafter supervised the grinding process to ensure complete accuracy of workmanship in grinding down the tips of the blades to the correct conical geometry, while at the same time correcting the blades’ outer diameters to specifications.
“Verification of the slope was then done with the recently acquired state-of-the-art mobile 3D scanning arm, which digitally records millions of surface points and uses colourful software analysis to project the shapes onto the original design to identify any discrepancies and provides accurate protocol data for the dimensional quality records,” Roman added.
“Everything was done within the stipulated period, with Steven and the team working extended hours to ensure completion in just four days.”