Lifetime Extension for SIEMENS Gas Turbines

Transcription

1 Lifetime Extension for SIEMENS Gas Turbines VX 4.2 VX 4.3 VX 4.3A Authors: Guido Lipiak Susanne Bussmann Co-Authors: Christopher Steinwachs Andreas Lüttenberg Power-Gen Europe May 1 June 2006, Cologne, Germany

2 Introduction Table of Contents 1 Introduction Objectives of SIEMENS Lifetime Extension Why SIEMENS Lifetime Extension? The Maintenance Concept Maintenance Intervals SIEMENS Lifetime Extension (LTE) The SIEMENS Lifetime Extension Program Gas Turbine Frame-Specific LTE Analyses Unit-Specific LTE Analyses Modernizations and Upgrades (MODs & UPs) LTE Planning Implementation of SIEMENS Lifetime Extension Measures Summary...20 Literature 2

3 Introduction Lifetime Extension for SIEMENS Gas Turbines Dipl.-Ing. Guido Lipiak, Siemens Power Generation, Gas Turbine Field Service Engineering, Mülheim a.d. Ruhr/Germany Susanne Bussmann, Student of Communication Science, University of Applied Sciences, Gelsenkirchen/Germany Dipl.-Ing. Christopher Steinwachs, Siemens Power Generation, Gas Turbine Field Service Engineering, Mülheim a.d. Ruhr /Germany Dipl.-Ing. Andreas Lüttenberg, Siemens Power Generation, Gas Turbine Field Service Engineering, Mülheim a.d. Ruhr /Germany 1 Introduction The worldwide demand for power grows faster than the world population. SIEMENS Power Generation develops and builds combined cycle (gas and steam) power plants and power plant components for all energy resources. SIEMENS gas turbines are renowned for their high availability and reliability as well as high power output at low emissions. With a lifetime expectancy of a combined cycle power station of 30 to 40 years, the gas turbine by far exceeds the design lifetime. Essential components of the SIEMENS VX4.2, VX4.3 and VX4.3A gas turbines - especially the components of the hot gas path and rotor are designed for an operating time of 100,000 equivalent operating hours (EOH, for short) or 3,000 starts. Well founded and realistic lifetime concepts are required to keep the costs over the entire lifetime to a minimum. Figure 1 SIEMENS Power Station Ambarli, Turkey, 6 x V94.2 (Source : Siemens PG) 3

4 Objectives of SIEMENS Lifetime Extension To assure reliable and safe operation of the gas turbine even beyond the design lifetime of the components, SIEMENS has developed the "Lifetime Extension" program (LTE program, for short). Within the LTE program recommendations are made to the gas turbine operator; the recommendations are developed based on the original design of gas turbine frames VX4.2, VX4.3, VX4.3A, the Original Equipment Manufacturer (OEM) fleet operating experience and the specific characteristics of the gas turbine, such as operating mode and unit history. This paper will explain how SIEMENS arrives at the recommendations for lifetime extension measures, and how these measures are subsequently planned and implemented. 2 Objectives of SIEMENS Lifetime Extension The objective of the LTE program is to give the operators of SIEMENS VX4.2, VX4.3 and VX4.3A gas turbines an opportunity to operate the gas turbine beyond the limited design lifetime of the gas turbine components. The LTE measures are to assure high availability, reliability and safety for another lifetime of 100,000 EOH or 3,000 starts. Figure 2 Trend of Siemens Gas Turbine Frames with Respect to EOH (Source: Siemens PG) The EOH a combination of fired hours and start/stop cycles and additional influencing factors like fuel composition or water/steam injection are only one criterion to estimate the life- 4

5 Why SIEMENS Lifetime Extension? time consumption of the gas turbine components. Operated at base load, a gas turbine reaches 100,000 EOH after approximately 12 years. A systematic and uniform course of action for cost-effective evaluation of the SIEMENS gas turbines is required because the number of VX4.2, VX4.3, and VX4.3A machines that will exceed 100,000 EOH in the near future increases steadily (refer to Figure 2). The benefits of the measures derived from the SIEMENS Lifetime Extension by far outweigh the relatively small expenditure for the LTE study. Implementation of the LTE measures does not only significantly reduce the operating risk of the unit, but also significantly decreases potential downtimes due to unscheduled outages or additional maintenance activities. Significant portions of power and efficiency, which had experienced a reduction during the first 100,000 EOH due to wear and aging, can be regained. The maintenance concept itself will not be modified; future maintenance costs can be predicted. The lower operating risk may also have a positive effect on the insurability of the machine. 3 Why SIEMENS Lifetime Extension? The lifetime of SIEMENS gas turbines is limited, and primarily depends on the type of operating regime (base load, medium load or peak load), utilized fuel, firing temperature and ambient conditions. The gas turbine frame specific design of wear parts in the hot gas path as well as maintenance intervals and quality play a key role. Gas turbine components are exposed to stress caused by temperature or static and dynamic loading like creep, low-cycle fatigue (LCF) and high-cycle fatigue (HCF), erosion, oxidation and high temperature corrosion as well as mechanical stress and wear. The limitations for useful service life are in the majority of cases based on the load capability of the components exposed to the highest stress or temperatures. Each type of stress causes characteristic damage which may occur individually or in a combination (refer to Figure 3). The main components of SIEMENS gas turbines specifically the components of the hot gas path and the rotor are designed for 100,000 EOH or 3,000 starts based on the stress they are subjected to (refer to Table 1). 5

6 Why SIEMENS Lifetime Extension? Erosion & Contamination Corrosion Corrosion & Oxidation Creep Fatigue Mechan. Stress Low Cycle Fatigue Figure 3 Examples of Effects Causing Aging in Turbines Exceptions are components that are refurbished earlier during scheduled maintenance outages or because they are considered wear parts (e.g. 1st stage blades or ceramic heat shields). Table 1 Design Criteria and Life Expenditure Effects 6

7 The Maintenance Concept 4 The Maintenance Concept Wear is the price paid for the use of a device or a unit. The objective of maintenance therefore is not only to recognize the wear, but to influence it and create new reserves by repairing the components or unit (refer to DIN ). Reliable operation of the gas turbine is not feasible without inspection and potentially re-establishing these wear reserves at inspections and major overhauls. Inspections are performed to determine the condition of the machine and to define condition-related corrections and repairs to protect the operator against unscheduled outages, secondary damage, and loss of operation. 4.1 Maintenance Intervals Gas turbine components are subjected to a series of inspections and maintenance inspections at specified intervals: Figure 4 Maintenance Intervals of SIEMENS Gas Turbines Components deteriorate as a function of time and temperature (creep processes, corrosion and oxidation) and also due to cyclic processes (high-cycle fatigue HCF, low-cycle fatigue LCF and thermo-mechanic fatigue TMF). SIEMENS determines the inspection intervals of the VX4.2, VX4.3 and VX4.3A gas turbines based on equivalent operating hours (EOH) of the unit. Maintenance inspection intervals are the basis for safe and disturbance-free unit operation. SIEMENS gas turbines are subject to different maintenance intervals over the course of their 7

8 The Maintenance Concept operating time. The intervals, i.e. time between inspections and major overhauls, depend on the specified maintenance concept. The inspections are performed according to a Checklist. Currently, there are two basic maintenance inspection concepts [2]: Figure 5 SIEMENS Maintenance Inspection Concepts MI = Minor Inspection HGPI = Hot Gas Path Inspection MO = Major Overhaul LTE = Lifetime Extension Inspection Minor Inspection (MI) The minor inspection comprises the visual inspection of the accessible regions of the machine, the compressor and turbine inlet, the combustion chamber and the exhaust. Optionally, non-accessible regions may be examined using borescopes. The minor inspection includes the examination of various external gas turbine components. Hot Gas Path Inspection (HGPI) The turbine is opened for the hot gas path inspection. Based on the findings, the vanes and blades of the turbine are inspected, refurbished or replaced based on the maintenance concept. Various non-destructive examinations (NDE) are performed to determine the condition of the essential components. 8

9 The Maintenance Concept Figure 6 HGPI of SIEMENS VX4.3A Gas Turbines Major Overhaul (MO) At a major overhaul, the compressor casing is removed and all compressor blades are inspected, as necessary and according to the checklist. The coated compressor front stages are refurbished. The compressor guide vane carrier and the inlet casing are inspected as well. Non-destructive examinations (NDE) and detailed visual inspections are performed, the rotor is removed from the machine. Figure 7 MO of SIEMENS VX4.3A Gas Turbines 4.2 SIEMENS Lifetime Extension (LTE) The maximum number of EOH reached by a gas turbine in the course of a calendar year essentially depends on the number of starts and the service factor (fired hours) of the unit. Consequently, the time at which a gas turbine should be subjected to an LTE analysis varies between 12 and 25 years. The scope of the LTE inspection exceeds the scope of the major overhaul. The rotor must be destacked in order to re-qualify the forged rotor components. New mechanized non-destructive examination (NDE) methods have been developed and qualified to detect critical defects 9

10 The SIEMENS Lifetime Extension Program in the volume of service-stressed forgings. Potential LTE measures, for example, are additional visual and non-destructive examinations (NDE) like ultrasonic, eddy current and magnetic flux testing. Tailor-made recommendations for implementation of modifications and upgraded products as well as condition based repair and replacement of components are implemented in the course of the LTE inspection. 5 The SIEMENS Lifetime Extension Program The SIEMENS LTE program allows evaluation of gas turbine components with respect to potential remaining lifetime and is therefore the basis for subsequent LTE recommendations. Unit-specific conditions and operator requests are taken into consideration as well. The SIEMENS LTE program comprises the examination of each gas turbine frame and the unitspecific analysis of the individual gas turbine. At the same time, recommendations for potential modifications and upgrades (MODs & UPs) are discussed, specifically with respect to the components that should be replaced in the course of the LTE measures. The gas turbine operator subsequently has the Figure 8 LTE on a V94.2, Source Siemens PG appropriate LTE measures implemented by SIEMENS Field Service Personnel to extend the lifetime of the gas turbine for another 100,000 EOH, or only for another interval. 5.1 Gas Turbine Frame-Specific LTE Analyses SIEMENS implemented frame-specific LTE analyses for the individual gas turbine frames, i.e. VX4.2, VX4.3 and VX4.3A, based on component design lifetime and the fleet operating experience. Design-dependent recommendations for LTE measures applicable for the affected components were determined in gas turbine frame specific LTE programs. As a result, LTE Checklists for Lifetime Extension Inspections and LTE measures have been prepared in addition to the frame-specific Major Overhaul Checklists. 10

11 The SIEMENS Lifetime Extension Program Within the scope of the frame-specific LTE analyses, all essential design groups of the three gas turbine frames were examined and evaluated with respect to further operation of another 100,000 EOH or 3,000 Starts. This examination and evaluation took place in the course of the Component Review and Component Analysis. Component Review Components for which further operation to 200,000 EOH is considered critical are determined on the basis of their design and design data, and the SIEMENS gas turbine fleet operating experience. Example of Component Review on a SIEMENS V94.2 Gas Turbine: The Component Review of a SIEMENS V94.2 gas turbine starts with selecting the components that are subject to lifetime limitation due to creep and LCF/HCF, corrosion/erosion, and others, for example: Figure 9 Selected Components at Component Review 11

12 The SIEMENS Lifetime Extension Program The following decisions must be made for the selected components: Figure 10 Component Review Component Analysis The lifetime limitation of individual components is determined in the scope of the "Component Analysis". Main components such as rotor disks and hollow shafts, compressor and turbine vane carriers, casings and piping, but also compressors and turbine blades are analyzed using different numerical and analytical methods, i.e. finite element method (FEM) and fracture mechanics (FM), ASME Code and AD bulletins (refer to Figure 12). The parts are analyzed with regard to static and dynamic loading as well as start and stop cycles (steady state / transient). The component lifetime limitations were determined taking the calculated variables, i.e. stress cycle number for crack initiation, crack growth and creep deformation, and the long-time fleet operating experience of the gas turbine frame into account. Crucial factors for a meaningful component analysis are the basic design data and a consolidated knowledge of boundary conditions like thermal convection and radiation, mechanical restrains or contacts during the gas turbine operation. Selecting the appropriate analysis type applying suitable and sufficient material data are preconditions for interpretation and validation of the computation results with the OEM fleet experience. The determined component lifetime limitations and critical start numbers always apply for a gas turbine frame (VX4.2/VX4.3/VX4.3A); they do not take individual deviations during op- 12

13 The SIEMENS Lifetime Extension Program eration or configuration of the unit into account. These gas turbine-specific values must be determined by unit-specific LTE analyses. Figure 11 Numerical Analysis of Turbine Rotor Disk and Turbine Exhaust Casing Another result of the component analyses facilitated the definition of critical defect sizes as well as location and orientation of critical defects in the component volume. This knowledge in turn allowed the development of specific NDE processes, such as partially mechanized ultrasonic testing of the rotor wheel disks. The partially mechanized ultrasonic test is used to check internal growth of material defects caused by the forging process in the region of the wheel disk bores (refer to Figure 11). It is possible to evaluate critical indications based on available calculation results. The mechanized test technology and the digital acquisition of the ultrasonic test data allows comparison testing for potential deterioration of previous findings at any time. Recommendations for specific repair measures or safe further operation of the affected component can be made. Figure 12: Mechanized Ultrasonic Testing of Wheel Disk in Hub Area a) Mechanized Test System b) Test Probes and Setup 13

14 The SIEMENS Lifetime Extension Program Other examples of NDE utilized in the course of the LTE are manual ultrasonic inspection of all forged turbine components and dye penetrant inspection of the casings. Surface crack detection by magnetic flux inspection will also be used on a number of components. Geometrical measurements, wall thickness measurements and length measurements of components are enhancing the measures for lifetime extension. 5.2 Unit-Specific LTE Analyses Unit-specific analyses allow detailed evaluation of each gas turbine. This means, all influental factors relating to operation and state are gathered on each gas turbine and taken into account in the analyses. Aspects with respect to history as well as previous and future operating mode of the gas turbine must be taken into consideration; the data are compiled and documented using a questionnaire. Unit history The history of the gas turbine plays an important role in the unit-specific evaluation. Of special importance are what inspections were already performed and what the results were, and which components have already been replaced or repaired. Already known damage on the unit must be disclosed. Operating Mode Also included in the evaluation of the lifetime limitation must be the way the machine was operated in the past, how it is operated now, and how it is supposed to be operated in the future. A differentiation is made between base load, intermediate load and peak load. The power plant owner decides whether the gas turbine is to be operated for another 100,000 EOH or only for the next maintenance interval. Decisive in the evaluation of the lifetime are also the extent of fast loading, the utilized fuel and firing temperature and the use of water or steam injection. The results of the gas turbine frame-specific and unit-specific analyses yield the unit-specific LTE recommendations for lifetime extension measures. 14

15 The SIEMENS Lifetime Extension Program 5.3 Modernizations and Upgrades (MODs & UPs) "MODs & UPs" are modernization and upgrade measures that contribute to improved power or efficiency, lower emissions or longer component lifetime or inspection intervals of the gas turbine. The improvement options are investigated in the scope of the unit-specific and framespecific analyses. These options may be selected by the gas turbine operator when the SIEMENS LTE measures are due instead of replacing worn components. SIEMENS, the Original Equipment Manufacturer (OEM), has developed and is continuing to develop a number of modernizations and upgrade packages to keep up with the requirements of utilities to increase output and efficiency, decrease maintenance cost, increase reliability and robustness of the systems as well as availability, and starting reliability. The implementation of these upgrade measures within the extended LTE work scope does not only improve the specific key performance requirements of the owner but also reduces the cost for intermediateterm operation. Examples of these modernizations and upgrades are concepts for increased compressor mass flow, upgrade packages to extend major overhaul intervals of specific hot gas path components, emission reduction packages, e.g. improved low NOx burners and improved NOx control, as well as packages for frequent startup operation or increased firing temperatures, wet compression or evaporation cooling for power augmentation, upgrades to minimize compressor efficiency losses utilizing improved compressor coating and advanced compressor cleaning methods. [3] 5.4 LTE Planning The time-consuming planning of LTE ideally begins in the course of preparing for the last major overhaul or hot gas path inspection before 100,000 EOH are reached (refer to Figure 13). With this approach, pre-investigations for LTE for premature wear on strategic components can already be performed at the last MO or HGPI ahead of the intended LTE inspection. 15

16 The SIEMENS Lifetime Extension Program Figure 13 The Date of Planning LTE It also provides an opportunity to take samples and perform material analyses with respect to creep rupture strength, low-cycle fatigue, or metallographic analyses of microsections. This applies, for example, for taking samples from the inner casing and mixing casing on VX4.2 gas turbines. Consequently, the results of microstructural analyses of stage 3 and stage 4 turbine blades performed in the course of the HGPI after 75,000 EOH will make it easier to estimate the potential remaining lifetime when another analysis is performed on the blades which had remained in operation until 100,000 EOH, for LTE purposes. If the gas turbine operator requests a quote for LTE measures, SIEMENS Service Marketing/Sales and SIEMENS Service Engineering will perform the LTE analyses jointly (refer to Figure 14). Based on the preceding analyses, a unit-specific recommendation is made with respect to future gas turbine operation, component life extension, repair, or replacement of the compo- 16

17 The SIEMENS Lifetime Extension Program nents. These LTE recommendations are presented to the operator in the form of a bid. The measures are subsequently implemented by SIEMENS Field Service Personnel. Figure 14 The Workflow of Planning SIEMENS Lifetime Extension All results are appropriately documented in the course of LTE planning and implementation. To assure on-time delivery of replacement parts, the need of required strategic replacement parts is discussed already after initial operator discussions, and delivery dates are coordinated between Manufacturing and Marketing/Sales. The advantage of early LTE planning and early 17

18 Implementation of SIEMENS Lifetime Extension Measures ordering thereby is ruling out logistic problems, and assuring smooth execution of the maintenance measures. The close working relationship between the plant operator and SIEMENS Service Marketing/Sales, SIEMENS Field Service Engineering and SIEMENS Field Service Personnel assures that the appropriate analyses are performed on the individual machines and that the lifeextending measures are implemented optimally. Effective project management is required on both sides, i.e. manufacturer's side and customer's side. 6 Implementation of SIEMENS Lifetime Extension Measures Approaching 100,000 EOH, a series of steps must be taken in preparation of lifetime extension measures. The information gained from gas turbine frame-specific experience and calculation results as well as unit-specific analyses are the basis for developing SIEMENS LTE measures. The first step of implementing the entire SIEMENS Lifetime Extension measures is to contact the plant operator based on the results of the planned outage prior to the 100,000 EOH to inform him of the LTE concept and the associated implications to assure that he is aware of the program. Secondly, the history and operating mode of the gas turbine will be investigated via a questionnaire. Based on the input as well as fleet investigations and recalculations for certain components, a tailor-made concept will be presented to the specific operator. Thirdly, depending on the preparation time for the lifetime extension and the time schedule of the operator, a minor inspection ahead of the LTE inspection will be used for a number of additional investigations in preparation of the unit-specific LTE. Finally, depending on operator s intention to use the plant short-term or over decades, the scope of work, including modernization and upgrade measures, will be defined. All LTE measures are performed in addition to the scope of a normal major overhaul. 18

19 Implementation of SIEMENS Lifetime Extension Measures Examples of LTE Measures Implemented on a SIEMENS V94.2 Gas Turbine: Figure 15 Examples of LTE Measures Implemented on a Siemens V94.2 Gas Turbine Component Potential Test Methods Findings Measures 1 Compressor Blades Magnetic Particle Test/ Eddy Current Test Corrosion and Cracks Replacement 19

20 Summary Component Potential Test Methods Findings Measures 2 Compressor Vanes Ultrasonic Test Cracks on Hooks Replacement 3 Flame Tube/Tile Holders Standard per LTE Program Wear Replacement per LTE Program 4 Burner NDE / Visual Inspection Corrosion/ Cracks Replacement 5 Seal Ring Visual Inspection Wear Replacement 6 Casing Dye Penetrant Test Cracks Repair 7 Turbine Blades Sample Taking/ Metallurgical Analyses Cracks/ Degradation Live Extension for one further interval 8 Inner Casing Sample Taking / Metallurgical Analyses Oxidation Repair and life extension for one further interval 9 Rotor Disk Mechanized Ultrasonic Testing No Findings Re-qualification and life extension for EOH Table 2 Examples of Methods, Findings and LTE Measures on Components 7 Summary The SIEMENS LTE program provides gas turbine-specific recommendations for LTE measures based on gas turbine frame-specific analyses taking unit-specific analyses, machine history and findings into account. Besides SIEMENS LTE measures, modernization and upgrade options are offered to allow the operator to replace components. This approach provides a low risk, reliable and significant advantage to the plant operator. There is also a clear advantage with respect to estimated life cycle cost as well as reliability and availability of the plant; the lower operating risk alone may have a positive effect on the insurability of the power plant. 20

21 Summary The SIEMENS LTE Program is crucial for reliable and safe operation of the SIEMENS gas turbines for another 100,000 EOH or 3,000 starts, thereby assuring business success to the operators of SIEMENS gas turbines beyond the original design lifetime. Literature [1] Wrede, U.; Bohrenkämper, G.; Umlauft, R.: Lebensdauerverlängernde Maßnahmen an Gasturbinen; Allianz Report 2/99. [2] Deblon, B.; Bohrenkämper, G.: Rehabilitation and retrofitting of heavy-duty gas turbine; Power-Gen Europe Conf., Madrid (Spanien) Juni [3] Dibbert, Andreas: Neue Power für Gasturbinen; Energiespektrum 10/2005 Biographical Information Speaker: Company: Country: Guido Lipiak Siemens Power Generation Germany Guido Lipiak is Manager of the Mature Frame Team in Gas Turbine Field Service Engineering Mülheim, Germany. He earned his degree in mechanical engineering at the University of Duisburg, Germany. In 1995 he joined Siemens KWU and initially worked for the gas turbine blade technology and materials engineering departments. For damage clarification and root cause analysis, he started working as a Fact Finding Engineer in 1996 and became Project Manager in the Mülheim Gas Turbine Service Department in 1999 where he initiated the SIEMENS Lifetime Extension Program in Since 2005 Mr. Lipiak has been team manager of the Mature Frame Team for the VX4.2 and VX4.3 Gas Turbines in Field Service Engineering. He is an expert for the fleet operating experience of the SIEMENS V64.3 Gas Turbine. 21