© Siemens AG 2005. All rights reserved.

Dr. Vladimir Navrotsky, Per Johansson, Bengt Svensson
Siemens Industrial Turbomachinery AB
Finspong, Sweden, SE-61283
Summary
It follows from Power Generation and Oil & Gas market analyses that there are a number of distinctive trends and changed customer requirements and preferences that point out the need for development in the field of maintenance and operation optimization.
To meet the challenges of the market and to improve our customer’s operating plant competitiveness and to ensure mutual profitability, new and innovative maintenance concepts and appropriate technology have to be developed and employed.
The driving forces behind this development are the industry's relentless demand for profitability through optimized production and cost control. A new condition-based maintenance concept will precisely fit these new market demands, while today’s time based maintenance concepts do not match these demands. This is why at present Siemens allocates considerable R&D resources to develop the technology and tools in order to support a new condition based maintenance concept.
The condition-based maintenance will support customer demands in flexible plant operation, high requirements on availability, maintenance optimization including extended maintenance intervals and reduced spares consumption and, finally, total maintenance cost.
In order to employ the Condition Based Maintenance the following technologies, technique and tools should be developed:
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Rotating equipment (RE) remote monitoring and diagnostic,
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RE component lifetime prediction methods and technique,
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Advanced non-destructive inspection methods and tools,
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RE component condition monitoring technique and tools,
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Reliability and risk analysis tools,
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RE component data base,
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RE operation optimization tool.
This paper presents an overview of the current technology development in Siemens in these respects.
Introduction
Today, the most common maintenance programs for Industrial Gas Turbines (GT) are timebased programs, which means that the GT is maintained after a certain period of time. But at the same time it is well known that the operation profile, operation cycle and operation environments are very different for different GT installations and thus the lifetime consumption of different GTs will be different. If the GT is running smoothly, not only on full load but also on part-load, and does not accumulate many start-stop cycles, the maintenance interval for this GT can be extended. The capabilities to follow up each GT installation individually will allow OEM and operator to move from time-based to condition-based maintenance programs.
Condition based maintenance is a key to support operator demands in flexible plant operation, high requirements on availability, maintenance optimization and, finally, life cycle cost reduction.
In order to employ Condition Based Maintenance, certain technologies, techniques and tools should be developed. To access cutting edge technology for Condition Based Maintenance and Reliability Centered Maintenance, operators have to involve the OEM to play a more important role in the process of determining the extent and timing of inspections and overhauls as well as the daily operation and plant condition monitoring.
The current status of Siemens’ development in this area, which is already utilized in part in
Siemens’s Condition Monitoring System (CMS) is presented below.
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Siemens’ Condition Monitoring System
A project group with experts in design, performance, emission, lifetime analysis, vibration and service has been and is involved in the Condition Monitoring System development utilizing
Siemens’ design processes, knowledge and know-how for Medium Gas turbines (MGT) SGT-
500 – SGT-800. CMS is a part of Siemens’ future service concept Condition Based
Maintenance.
Siemens’ CMS will enable the following capabilities – (1) remote monitoring and diagnostic,
(2) condition monitoring, (3) component lifetime prediction and also (4) operation optimization.
Siemens believes that the operator will have the most benefit from this system as the system shares a lot of OEM knowledge and GT experience with the operator. The recent development of the Siemens’ MGT CMS provides a powerful tool for the operator to follow up their GT, predict the future and thus gain a better method of optimizing the GT and the whole plant operation.
CMS has a modular configuration (see Fig. 1) and can support not only the GT but a complete plant. The operator can start with basic module 0 (remote monitoring) and add on the functionalities he needs from other 4 modules – performance (1), emission (2), vibration (3) and operation support (4).
CMS modularity, current and future release
Module 1
Thermodynamic
Performance module
Module 2
Emission module
Module 0
PC & DB,
Long-term Data storage & trending, reports etc.
Module 6
Operation
Optimisation
Module
Module 5
Condition monitoring,
To support CBM,
Module 3
Vibration module
Module 4
(A module of support)
Analyses, reports operations support etc.
Siemens Industrial Turbomachinery AB 4
Fig.1. Siemens’ MGT Condition Monitoring System configuration.
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Modules 0-4 are already in use, modules number 5 – condition monitoring and 6 – operation optimization are under development.
Module 0 – remote monitoring.
The following GT parameters and their trends are followed up by Module 0 of CMS:
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Ambient conditions,
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Number of start-stop cycles and operating hours,
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Vibration trends (bearing, combustion chamber),
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Speed of Gas Generator and Power turbine trends,
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Compressor air and exhaust gas temperature and pressure,
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Lubrication oil parameters,
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Fuel (gas and liquid) parameters,
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Ventilation system parameters,
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Generator parameter,
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Grid parameters,
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Auxiliary system parameters,
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GT governor parameters.
The system supports a lot of interesting and valuable plots, trends, X-Y and polar diagrams.
Performance of the various main parts in the turbine is shown with expected and actual values.
These data are stored in the system and can be used for further analysis of the GT operation, troubleshooting, root cause analysis or GT operation optimization.
Performance module.
Allows calculation of expected and actual GT performance at actual ambient conditions.
Provides normalized performance comparison for detection of degradation (compares with
“new and clean”). Generates performance reports and indicates:
∆
-Power, efficiency, heat rate, filter and compressor fouling etc.
The Performance module enables the operator to control GT performance and optimize planned maintenance, for example to optimize the compressor washing.
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Emission module.
The emission module requires a Continuous Emission Monitoring System (CEMS) to measure the actual emissions.
The emission module allows emission monitoring (NOX, O2, CO2, CO), trending and data storage, generates an emission report with totalized values over a selectable time, hourly, daily, monthly and indicates and informs when operation is outside normal values.
The emission module supports the operator in monitoring and controlling emission in order to satisfy the growing legislative demands for environmental safety.
Vibration module.
With the vibration module OEM and operator are able to study vibration patterns in depth. By help of this module Siemens or the operator can detect and handle the following events and phenomena: - unbalance (1), misalignment in flexible coupling (2), cracks in rotor (3), rubbing in seals (4), rubbing between rotor and stator (5), blade failure (6), bearing damage
(7), housing and foundation resonance (8), cooling problems in generator (9), different kinds of gearbox-problems (10), problems related to combustion (11).
The vibration module can be used for remote balancing, which makes this procedure very fast and efficient, and results in maintenance cost reduction.
Siemens has built up knowledge and experience which is very valuable during the vibration analysis of GTs. For example, knowledge of correlation between vibration and - IGV position,
- speed, - bleed off position, - fuel PFR and etc., in some cases is a key for fast and efficient operating support or troubleshooting.
Operation support module (4).
The Operation support module is not a software itself, but the work processes for information assessment and analysis established in order to provide and simplify analysis of stored operation data (1), reporting of RE status/condition, recommendations for maintenance activities or improvement possibilities (2), documentation exchange (3), operation support from operator service team and Siemens support group (4).
The level of OEM support obtainable is dependent on what CMS module (0-3) the operator has chosen to add to his system.
© Siemens AG 2005. All rights reserved.

Process support
Maintenance
Management
Plant Operation
Guidance
SERVICE
Module 4
The support module!
Analyses, reports, op. support
G G
Analysis of data
Condition Monitoring
Siemens Industrial Turbomachinery AB 21
Fig.2. Siemens’ MGT Process support module (4).
Condition monitoring module (5).
Module 5 is at present under development. In this module we intend to incorporate additional diagnostic tools with built-in expert knowledge, for example diagnostics of vibration patterns, combustion patterns, air and hot gas patterns.
Module 5 will enable OEM and operator to perform prognoses of remaining lifetime prediction for GT components. Furthermore the processes and tools for FMECA-analysis are utilized to build a platform for enhanced reliability and maintainability of the basic turbine designs. This module will support GT component condition monitoring and as a next step
Condition Based maintenance.
We are now rapidly improving our ability to assess consumed lifetime of critical components through the development of advanced computer models, which are calibrated and supported by innovative and precise component tests.
Lifetime prediction module
The following lifetime and damage models were developed and will be utilized in the module:
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Creep/oxidation power laws calibrated to experience,
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Cyclic life model with ageing calibrated to experience (accounts for reduction of low temperature yield strength with time, accounts for decreased ductility with time),
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Creep/oxidation power laws calibrated to experience.
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Based on the main GT parameters which are recorded and stored by CMS continued thermal and stress analysis will be done. Thermal and stress analysis of GT components takes into account loading rate, load levels and their duration, unloading rate, trip/no trip, ambient temperature, ambient pressure. The results of thermal and stress analysis of GT components will be used for the assessment of accumulated damage and remaining lifetime of the components.
Power Stress Stress/
Starin time
Life time, Hours/Cycles time
Fig. 3. Thermal, stress and lifetime analysis of GT components.
In order to increase the reliability of the lifetime prediction of GT components, Siemens’ material properties database and special test are used, and the data are continually being updated. The analysis of the degradation in material properties of GT hot path components after different operating times gives us some important correlations that are very valuable during condition assessment and remaining lifetime prediction of GT components.
It is important to mention that an on-line system to keep the track of the GT component life time is already installed on two fast ferries which are equipped with SGT-500 (GT35) GT.
GT component database. Accurate life prediction requires well known operating history – component’s version number, where the components were installed (Site, position of site), detailed loading and operation history (detailed log of operating parameters - TIT/TET, rpm, ambient conditions, …), repair history (whether the repair was carried out, if yes, when it was carried out, what the repair changed). In order to ensure that all these requirements are satisfied, it is necessary to build up a Component Database. In Siemens the component data base is built up in SAP. The component database stores the information about individual components, their installation and repair history. CMS is used to trace load history, site and time of operation, consumed and remaining lifetime of GT components.
Advanced non-destructive inspection technique and tools.
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Inspections are part of the maintenance program and have an influence on maintenance program duration and reliability of GT component operation after the inspection and maintenance. So this is why the further development and employment of a new advanced nondestructive technology and tools is very important in order to reduce the duration of the maintenance program and to improve the quality of the inspections.
Recently a new advanced non-destructive inspection tool Acoustic Thermography was developed and is in use in Siemens Power Generation (PG). This is a patented technology and is licensed for use only by Siemens PG. The technique provides the capability to ‘see through’ coatings and into hidden passages of such complicated components as GT cooled blades and vanes.
The principle of this technique is the following: Specimen vibrates due to ultrasound pulse.
Cracks (also sub-surface), generates heat by rubbing and can be seen in recorded infrared sequences.
Acoustic thermography, SIEMAT™ z Patented technology, licensed for use only by Siemens Power
Generation. Developed by Siemens CT for PG G z
Sees through coatings and into hidden passages
Specimen
IR camera
Ultrasound welder
2
Fig.4. Acoustic thermography – Non-destructive and very effective inspection tool.
The acoustic thermography technology has already been successfully used for examination of gas turbine cooled blades. It was confirmed that this is a very powerful tool allowing us to significantly improve the quality of inspection.
Siemens will continue the development of this technology and tool for site application.
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Acoustic thermography, SIEMAT™
3
Fig.5. Acoustic thermography. Non-destructive examination of Turbine blades.
Operation optimization module (6)
At present this module is under development. The elements and tools supporting the technical and commercial risk assessment, logistic handling, technical and commercial issues optimization will be employed in this module.
Conclusion
Siemens believes that by storing data and having easy access to the data, OEM and operator can learn and understand a lot about their RE. By analyzing the data in cases of disturbance or an unusual operation situation normally gives us a better understanding of what happened and what was the reason for it. The employment of CMS and other technologies and tools described above will utilize these opportunities and Condition Based Maintenance.
Condition based maintenance, supported by advanced on-line monitoring and component test, is a key to support operator demands in flexible plant operation, high requirements on availability, maintenance optimization and, finally, life cycle cost reduction.
© Siemens AG 2005. All rights reserved.