In 2005, Sulzer Hickham Indonesia received one unit of a 25 MW steam turbine from a local company. The last stage blades of the turbine were found to have severe erosion on the leading edges. Sulzer Hickham Indonesia repaired the blades by dressing the erosion area and applying chrome carbide coating using the HVOF method.
The rotor came with light to medium corrosion on the entire rotor body and erosion on the blades. The most severe erosion occurred at the last stage blades. Sleave rubbing on both journals was also found.
Observing the damage on the last stage blades, they were considered for replacement. However, due to the budget and time constraint, the customer wanted to reuse the blades with the quickest possible repair option on the eroded areas with a very tight schedule.
The Sulzer Hickham Indonesia Engineering department came up with an alternative solution for temporary repair. It was proposed that the last stage blades would be dressed at the eroded leading edges, and in order to extend their lifetime, chrome carbide coating would be applied as the substitute for the stellite erosion shield.
Sulzer Hickham Indonesia also recommended applying chrome carbide to L-1 blades. Since both the journals also had heavy rubbing, they were also to be restored by HVOF coating. The rotor was set up on the lathe for undercutting the journals for coating preparation.
After the undercutting process of the journals, the rotor was then set on the rollers. The qualified HVOF coating operators made the preparation: degreasing and grit blasting prior to coating for the journals and the last stage blades.
The uncoated areas were masked as a final touch of the preparation and the rotor was then taken to the HVOF coating booth for the coating process.
The coating process was applied to both journals first, and the last two stage blades afterwards. Based on our long term experiences of the HVOF coating, the process was performed successfully.
The average coating thickness on the blades was about 0.25 mm, and they were fully inspected prior to moving to the next repair processes.
After completing the whole workscope, the rotor was shipped back to the customer for installation and an immediate return to operation. The rotor is now running well and producing the specified power output. Sulzer Hickham Indonesia, as one of the Sulzer Turbo Services members, has always pushed the repair boundaries and will continue to do so.
Hepy Hanipa
Sulzer Hickham Indonesia |