GE94-02: Repair Flow Testing and Calibration Procedures for ...

Detection of these pressure pulsations and “humming” is accomplished by mounting piezo‐
electric transducers onto the outside of the combustion section of the turbine and monitoring
both the frequency and magnitude of the signals over the load range of the unit. This is done by
both GE and Westinghouse is developing a system that will permit users to monitor their
machines in the future, but there has been no commercial offering as of this report. Very little
information is provided to users as to the allowable magnitude and frequency of these pressure
pulsations and the most common method of control is to reduce load when the “humming”
becomes clearly audible.
HRSG20‐14. Life Extension Techniques for HRSGs in Cycling Service. October
2001.
With the advent of deregulated power generation, more and more combined cycle and
cogeneration plants are being operated in a cycling mode. This can cause accelerated wear and
tear on the heat recovery steam generator (HRSG), especially if it was not originally designed to
accommodate cycling.
This report reviews the negative impacts cycling can have on an HRSG. Those impacts can be
grouped into two main categories: those related to thermal stress and those related to water
chemistry. Thermal stress related problems are principally caused by either ramping at
excessive rates or by thermally shocking metal parts during start‐up or shutdown. Water‐
related problems can ultimately almost all be traced back to poor lay‐up practices. This report
describes techniques that can be employed to mitigate or even eliminate these problems. The
techniques include both changes in operating procedures and modifications or additions to
plant equipment. Recommendations for design changes are provided for both existing plants
and for new, yet to be built, combined cycle plants.
WE20‐06. For Sealing Blade Tips in Industrial Gas Turbine Compressors.
December 2002.
The efficiency of an axial compressor is reduced by loss of air through the gap between tips of
the blades and the wall of the case. This loss can also reduce revenues from industrial gas
turbines. Abradable coatings on the case wall can eliminate these losses by sealing this gap. As
the turbine spins up the full speed, blades stretch and the tips cut a groove into the abradable
material creating the airtight seal.