Owner/operators attending the annual meeting of the 501F and 501G Users Groups who did not attend one of the five presentations offered in each of the 10 sessions that comprised the 2012 Vendorama program passed on a valuable learning experience. Vendorama is the name used to describe the lineup of vendor presentations that supplement the user exchange at these two annual conferences.
The steering committees of both groups expended significant effort to ensure that the presentations would be technical in nature and not the sales pitch attendees would likely get in the exhibition hall. Not every presentation was worthy of an “A” grade, of course. But there were many of commercial value to users—such as the 501F rotor upgrades described by Scott Cloyd, director of gas turbine engineering for Mitsubishi Power Systems Americas in the first session. Cloyd followed that later in the day with a 30-min review of 501FD2 upgrades possible with Mitsubishi’s F4 technology derived from its most advanced engines. A summary of the first presentation is below; the second will be covered in the next edition of CCJ ONsite.
Belly bands (or baffle plates if you prefer) seal against air leaks between turbine rotor disks. You don’t have to attend many 501F or 501G meetings to realize belly-band issues strike a nerve in many users. Cloyd suggested that users consider replacing their original belly band with Mitsubishi’s two-layer baffle plate and bolted locking piece as several users already have done. He said this mod could be made any time the turbine casing is lifted. Some machining is involved, he added, because the existing slot must be enlarged. A benefit of the design was said to be easy removal when leaks occur.
Blade root springs. Disk serration wear caused by long-term operation on turning gear now can be mitigated with a patented blade root spring that is slipped between the wheel and the bottom serration of the blade. The spring forces the blade out into the running position and eliminates turning-gear wear. It also tightens the vibration profile of the machine making vibration more repeatable from start to start. At the present time, the spring is only designed for R4. A typical row can be equipped with springs during a 48-hr outage. Access is via the exhaust duct with removal of the locking plates. A cover lift is not required.
Bolted air separator is designed to replace goose-neck air separators still in use on FC and FD machines. In the latter, the seal of the air separator to the R1 turbine disk is provided by the spring force of the goose neck against the air separator. The force at this point is critical to the rotor:
- Too low a force leads to fretting at the disk interface.
- Too much force reduces the preload at the spacer disk and increases wear at the curvic coupling.
- Startup and shutdown thermal transients adversely impacts the preload and results in high rotor vibrations.
Cloyd said the bolted air separator decouples the seal portions of the device from the rotor core. New components required are the air separator, seal ring, dummy rings, and bolts. Modifications are required to the torque-tube seal housing and R1 turbine disk. The retrofit requires de-stacking of the rotor and makes most sense to conduct during a comprehensive rotor inspection.
For history buffs, the bolted air separator has been used in Mitsubishi gas turbines since 1996. Siemens stayed with the original air-separator design developed by Westinghouse and Mitsubishi when the latter went to the bolted design.
For more information, contact todd.baker@mpshq.com.
