PSM destacks, begins repairing its first F-class rotor in Alstom’s Midlothian shop

PSM continues to reinvent itself and add new services. The company’s field engineers and craftsmen recently removed a damaged rotor from a 7FA in base-load service and shipped it to parent Alstom’s turbine and generator repair facility near Richmond where PSM destacked its first compressor. The Jupiter (Fla) firm, known best for its capabilities in the manufacture and repair of critical industrial gas-turbine components, also is developing a rotor life extension program.

Alstom hosted a shop tour and dinner for GT owner/operators attending CTOTF’s Spring Turbine Forum. The group had the opportunity to inspect the debladed wheels before reassembly begins. CTOTF attendees were told that the unit started commercial operation in 2004 and had accumulated about 56,000 operating hours before the 6 o’clock S1 vane failed and its tip went downstream, damaging a significant number of rotating and stationary airfoils. Risks associated with S1 vanes were covered in a recent Heads Up for 7FA users.

Shortly after the rotor was received at the shop (photo), the marriage coupling was broken and the turbine section moved aside for cleaning and the repair of one bucket without destacking. Compressor blades were difficult to remove, the tour guide said, requiring cooling and old-fashioned persuasion to accomplish the task.

PSM will re-equip the entire compressor with blades and vanes of its manufacture and having the most advanced features available. For example, all vanes have attachment undercuts to prevent fretting wear and no shims will be used in the unit. In addition, the undamaged R0 stage will be rebladed with PSM airfoils that permit unrestricted water washing and fogging without the need for periodic ultrasonic inspections and dental molds. The blades and vanes are designed to serve out the expected remaining life of the unit. The rotor will be reassembled using tie and marriage bolts manufactured by PSM. A high-speed balance in the Alstom shop’s pit will confirm work quality.

PSM enhancements include the following, moving from the front of the compressor aft:

• Rows S0-S4 will have 10 vane segments each with vane carriers made of high-grade stainless steel. Recall that users are generally critical of the OEM’s design which has only six vane segments that often become locked in place and cannot be removed without destroying them. PSM says experience shows its vane segments are relatively easy to remove. Also, S0 will have one more vane in the lower half of the casing than it does in the top half and S1 one more vane in the top half than the bottom—this to decrease stresses on R1 and R2 blades.

• Rows S5-S12 are assembled using individual vanes with radial hooks to provide smooth contact between the airfoils and the casing.

• Rows S13 through the exit guide vanes (EGV) are comprised of so-called vane packs—groups of four or five airfoils attached together. Number of vanes in a pack depends on the stage. Packs help stabilize vanes in the case and reduce fretting found in many units with individual vanes.

 

 

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