STEAM TURBINE REPAIRS | BALANCE OF PLANT
Z lock shroud was CNC machined to reproduce the correct profi le. This was critical to ensure the blades can interlock during installation
Fully repaired leading edge incorporating Stellite bar-nose for enhanced erosion protection
Above left, figure 5: Blade furnace Above right, figure 6: Repaired blade
repair zone. The final heat treatment procedure was documented and followed to ensure repeatability throughout the repair cycle. After all blades had been successfully stress relieved, they were polished and inspected to ensure the repair had been completed. First, blades were hardness checked across various locations to ensure the material was within the required hardness range. Using the sample data taken prior to the repair in conjunction with the relevant Welder Performance Qualification Record (WPQR) we could determine that the heat treatment processes had not adversely affected the microstructure of the base material. The final inspection methods were dye penetrant to
ensure no surface defects had propagated during stress relieving and then a full set of dimensional data was captured and cross referenced against the ‘goods-in’ figures. This data covers axial and radial position of each blade and chord widths & maximum thicknesses at various section points throughout the repair length. Finally, the shroud was machined to reinstate the correct
geometry and achieve the required tolerances. Figure 6, above right, shows the repaired blade.
Success achieved Once the blades had been repaired, the power plant installed all six blades into one of their units to test the
repair performance over a prolonged period. They also had a small quantity of new blades coated and induction hardened by other sub-suppliers to establish which option offered the greatest level of erosion protection. Figure 7 shows the condition of an EthosEnergy repaired blade after 60 months in operation. There is very light erosion on the leading edge. In contrast, the other repaired blades were severely eroded. In 2016, EthosEnergy repaired another four blades to enable the plant to undertake a second performance test in one of their other units. This time only very light erosion was found to be present on the leading edges after three years of operation. Reflecting this success, in 2020 the power plant placed
an order with EthosEnergy for the repair of 860 blades, the company’s largest ever order for blade repairs. Whereas the OEM’s blades had been lasting, at most,
eight years the blades repaired by EthosEnergy have comfortably surpassed that. Indeed, the blades repaired in 2014 are still in operation. Repairing the blades is estimated to achieve a saving of about 70% relative to new blades. Also, the longer life of the EthosEnergy repaired blades increases periods between outages, boosting power plant output, and reduces expenditure on repairs. Overall, the result is improved power plant profitability. ■
Above, figure 7: Condition of repaired blade after 60 months operation with very light erosion on leading edge
www.neimagazine.com | September 2022 | 29
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