Session: 25-02 Component Assessment

Paper Number: 153402

Cyclic Life Assessment of the Gas Turbine Rotor With Variable Fast Start Using Operational Data 

This paper develops an innovative method to assess the cyclic life of a gas turbine rotor undergoing a variable load gradient start and shut down according to operational data from remote diagnostic and control system. The method also enables a prediction of the cyclic life for variable starts with specified load ramp cycles.

The Simens Energy small industrial gas turbine rotor consists of the inlet and exit stub shafts, compressor discs, and turbine discs. All these components are bolted together and connected with Hirth couplings for alignment and torque transmission. The transient thermal stress induced by the temperature gradient in the compressor discs during start up and shut down is a main damage mechanism for the low cycle fatigue (LCF) life of the gas turbine rotor. The gas turbine is originally designed running baseload and start and shut down with a fixed load ramp.  This approach enables the OEM to provide end users with a fixed service interval or accumulated cycles limit for inspection and life limited parts replacement. However recent market requirements for applications such as combine cycle power generation and backup power demand more operational flexibility.  This requires more frequent starts and faster start-up to provide quick response to transient electricity demand. The approach described within this paper is to assess and manage gas turbine rotor cyclic life dynamically according to the actual load gradient and accumulation of cyclic damage.  This will provide a customised service interval and parts replacement according to the real cyclic life usage.

In this paper an innovative simplified thermal model is developed according to the heat transfer physics. With the input of compressor inlet and discharge temperature during the gas turbine operation cycle, including start and shutdown, the transient response of metal temperature gradient in the life limited compressor discs can be derived by the simplified thermal model.  

The response surface functions for the thermal and mechanical stress relating to the thermal gradient and rotor speed respectively are created based on the transient FE stress analysis. The elastic stress range for the cycle defined by operational data including compressor gas temperature and speed can be achieved by the response surface.  The cyclic life of gas turbine rotor is dynamically assessed based on the stress-strain relationship with Neuber correction and S-N curve derived by material test.

Presenting Author: Zhiqiang (David) Meng Siemens Energy

Presenting Author Biography: Zhiqing (David) Meng received his Ph.D (2002) from the Xi'an Jiaotong University, China in mechanical engineering. After 3 years post-doc research at Manchester University and Shanghai Jiaotong University, Dr. Meng has worked in the compressor for the commercial air conditioning and turbomachinery industry for last seventeen years. Since 2012, He has been working in Siemens Energy in Lincoln, UK. He is currently holding a position of Senior Specialist. He has been working in the area of rotor-dynamics, stress and lifing, probabilistic design for the gas turbine.

Dr. Meng is a CEng and a member of IMechE.

Authors:

Zhiqiang (David) Meng Siemens Energy
Richard Bluck Siemens Energy