All OEMs have given component specific recommended life for refurbishment as well as for replacement. As a result of this, IPP has to spend a substantial amount either for refurbishment or for procurement. In most of the cases both refurbishment and procurement are done through OEM. The procurement cost How to reduce the procurement cost can be reduced if the components’ life are extended without sacrificing reliability and efficiency.

We invite all to discuss possible measures for enhancement of Gas Turbine Hot gas path Components’ Life without sacrificing performance and reliability.

Before going for searching specific remedial measure, first we have to know why the Gas Turbine Hot Path Components are required to be refurbished or replaced after a certain interval.Whereas no such activities are recommended by OEM for steam Turbine irrespective of Size and make. To get the answer, first we have to identify the fundamental difference between Gas Turbine Operating parameters and Steam Turbine Operating Parameters. Steam Turbine are operated at a lower Temp with respect to Gas Turbine. This high temperature is the primary cause for metallurgical degradation. Which in turn reduces the Component’s life. A famous metallurgist “Larson Miller” has established an empirical relation between Time (life in Hours) and Temperature (in Deg-F) at a particular stress and this value is popularly known as “LMP”.This value is the main indicator for taking a decision whether the life of this component can be extended further or not. As mentioned above due to prolonged exposure to very high temp ( > 1000 Deg-C to 1350 Deg-C), Gas Turbine Hot Gas Path Components are bound to undergo metallurgical degradation resulting reduction in mechanicalstrength which in turn causes premature failure.

But now knowhow and Technologies are available by which the degraded metallurgical properties of the Gas Turbine Hot Gas Path Components can be regained again owing to which the mechanical strength is also improved. Thus the improved metallurgical properties and mechanical strength enhance the components’ life even beyond OEM recommended life.

The entire process can be broadly divided in to two parts.

Non Destructive Test (NDT) :-  This test is to be conducted on one piece of component identified for refurbishment with life extension at  as received condition and after Rejuvenation Solution Heat Treatment. In this test namely, Hardness measurement and Micro Structure analysis is carried out for assessment of Carbide PPT and Coarsening Grain structure.

Destructive Test ( DT) :-  This test is also conducted on one piece of component identified for refurbishment with life extension at as received condition and after Rejuvenation Solution Heat Treatment. Creep Rupture Test at Elevated temp and in some cases Thermo- Mechanical Fatigue (TMF) are carried out. Destructive test is must for Moving Blades of any stage, but for Vanes, by seeing microstructure decision is to be taken whether destructive test is required or not.

For getting better result, the following activities are must:-

1. Detail History of the component selected for Life Extension.
2. Eq. Operating Hours (EOH)
3. Number of Starts experienced this component after installation.
4. Physical Inspection
5. Inspection by DPT.
6. A comprehensive Scope of Work.
7. Quality Plan along with Customer Holding Point (CHP)

By following this method refurbishment with life extension of both Moving Blades and Stationary Vanes of all 3 Stages for GE make Gas Turbines and all 4 stages of both Moving Blades and Stationary Vanes of MHI make Gas Turbines can be carried out which will reduce the procurement cost and in turn will increase the bottom line of the balance sheet.

Normally OEM does not encourage to do life extension beyond OEM recommended life, but various literatures including EPRI literatures are available on this subject. If OEM does not agree, then the same can be done through alternate source by floating Global Tender.