Advanced NDE Systems for Flexible Operation ... - Siemens Energy

Advanced NDE Systems for 

Flexible Operation and 

Maintenance of Gas Turbine 

Components 

POWER-GEN International 2006 – Orlando, FL 

November 28-30, 2006 

Copyright © 2006 Siemens Power Generation, Inc. 

Copyright © Siemens AG 2006. All rights reserved.

ADVANCED NDE SYSTEMS FOR FLEXIBLE OPERATION AND MAINTENANCE OF 

GAS TURBINE COMPONENTS 

Paul J. Zombo, Robert E. Shannon 

Siemens Power Generation, Inc. – 4400 N. Alafaya Trail, Orlando, FL 32826 

ABSTRACT 

Hot section parts in today’s gas turbines have to withstand extreme thermal and 

mechanical loads and management of their inspection and replacement cycles requires 

effective use of advanced nondestructive evaluation (NDE) and monitoring 

technologies. Lower temperature rotating and critical stationary parts, designed for the 

full life of the unit, also require effective use of NDE technologies to provide 

opportunities to extend unit life. To assure long component life and highest quality of 

these parts, a broad spectrum of NDE technologies are used in manufacturing and 

service. Siemens maintains a strong pursuit for the development of new and advanced 

NDE technologies: Examples include fast and full field inspections allow for an 

inspection of performance critical areas of the parts, including coating condition and 

through-coating measurements to speed up inspections. Modern imaging methods are 

being increasingly employed side-by-side with high-accuracy measurements of critical 

material parameters as advanced NDE methods. 

This presentation will provide an overview of advanced NDE systems recently brought 

into production and service operations at Siemens Power Generation with examples 

such as active thermography, advanced optical equipment, and on-line monitoring 

systems. The use of these and other advanced NDE technologies will be summarized 

in a strategy for assessing the condition of critical components and overall improvement 

in flexible gas turbine operations and effective planning for service activities. 

INTRODUCTION 

In addition to the goals described in the abstract, a high priority aspect of our advanced 

nondestructive evaluation (NDE) development strategy is to provide technology-based 

innovations that are environmentally responsible. Our most recent developments 

include NDE solutions which have the potential to reduce the dependence on 

hazardous chemical processes for stripping coatings just to provide for inspectable 

surface conditions required by traditional NDE methods. Also, by fully developing some 

of these advanced NDE methods, there is the potential to replace the need for surface 

NDE techniques which require the use and proper disposal of consumable materials. 

The overall goal is to provide the most responsive source of technology-based solutions 

to enable our customers to improve operating plant competitiveness and profitability. 

Our strategy involves a multi-pronged approach in terms of local focus and range of 

NDE technology innovations. The multi-pronged focus includes continued improvement 

of classical NDE methods, such as ultrasonics, eddy current, radiography and others. 

Copyright © 2006 Siemens Power Generation, Inc.

These technologies are well-established in our supply network, in-house manufacturing 

factories, and repair network as an integral part of commitment to provide high quality 

components and systems for our gas turbine, steam turbine and generator products. 

Some of our most advanced applications in these classical NDE methods are integrated 

with highly engineered portable and remote tooling serving as a backbone of all field 

service operations. These include continually developing new NDE probing 

techniques and advanced signal processing methods in support of advancing the use of 

NDE technologies for component life-assessment. 

This paper concentrates on another strategic focus, where we go beyond NDE probe 

improvements and are pioneering the next generation of life-assessment technologies. 

We draw upon a global network of Siemens engineers and scientists, and draw from 

other industries where Siemens has best-in-class technologies. These include 

emerging sensor technologies, visible light and infrared imaging technologies, threedimensional 

digital radiography, advanced optics, automated image processing and 

pattern recognition techniques, and global electronic network expertise. This strategy 

has led to the recent development of three new advanced NDE systems recently 

brought into production and service operations: SIEMAT® acoustic thermography, the 

Global Inspection System, an advanced optical blade and vane scanning systems for 

automated visual inspection, and the On-Line Monitoring System, an infrared blade 

imaging system. 

INTEGRATED NDE STRATEGY 

Our approach is designed to go well beyond the end of the twentieth century notion of 

advancing NDE technologies by focusing on new probe development and transforming 

analog display techniques into digital formats. Analysis of market trends, technology 

trends, and most especially customer needs in the context of NDE and power 

generation component monitoring leads to a number of important conclusions. 

Market trends show global access to knowledge-based solutions is the over-riding 

business need. NDE technologies provide an essential lead role because their quick 

and highly product-specific assessment of service-exposed conditions are absolutely 

necessary for maintenance, repair and replacement planning, supply network 

coordination, and as feedback to life-cycle design engineering and forward-looking 

system performance strategies. 

Technology trends in the areas of sensors and monitoring show a number of simple, but 

important points to consider in finding new direction for NDE development First it is 

important to remember that visual inspection is the most effective overall NDE method 

and forms the basis for all other NDE and monitoring methods. It is what we as humans 

rely on the most to gain a quick, accurate, and most-reliable assessment of conditions 

important to predicting what will happen next. We all know that “seeing is believing” and 

“a picture is worth a thousand words.” This last point is fortunate, because looking 

closely at technologies trends it is evident that digital imaging technology is in a period 

of explosive growth. Digital imaging devices and system are becoming more and more 


available for use in virtually all ranges of the electromagnetic spectrum, and the 

processing of digital images are commonly used not just in two-dimensional formats, but 

increasingly in three-dimensional formats – at least in the entertainment and video 

game business and in military applications. And for now it looks like we can rely on 

Moore’s Law to continue to provide the advantage of speeding up process times and 

lowering costs for digital processing and storage. 

Most importantly is to recognize that engineering departments have fully integrated 

three-dimensional modeling, process analysis and fabrication control, but not NDE 

processes, into a well-integrated set of electronic design and manufacturing tools. That 

is, the integration of modern engineering tools is moving along well, all except for NDE 

processes. As a result, in the area where NDE is of greatest benefit – providing real-life 

feedback of component conditions – there is a significant technology gap. 

Siemens Power Generation has implemented a strategy to fill this gap and to provide for 

the integration of advanced NDE and monitoring technologies into the modern 

engineering toolbox. This involves a number of elements: 

• Implement image-based NDE applications 

• Develop a platform for 3D NDE data fusion 

• Make the link between NDE and design models 

• Implement digital image-based service platforms 

• Invest in technologies that provide rapid design validation 

• Emphasize sensors that are model-based 

A strategy for development of advanced NDE technologies must go beyond NDE probe 

improvement and meet strategy elements important to power generation industry. 

Figure 1 shows a table where these strategic elements are listed to compare with a 

number of advanced NDE-related technologies. The table’s matrix shows an analysis 

of which technologies we are currently developing and have plans to accelerated 

development in the future to address the strategic need elements. 

ADVANCED NDE TECHNOLOGY SOLUTIONS 

As a result of development activities in Siemens Power Generation, three advanced 

NDE technologies are highlighted because they are currently being integrated into our 

gas turbine products and services. They are: 

1. Global Inspection System – using combined 2-D and 3D digital imaging of blades 

and vanes; 

2. SIEMAT® sonic infrared – using ultrasonic vibrations and infrared imaging for 

imaging for crack on coated and uncoated parts; 

3. On-Line Monitor – using high-speed infrared for imaging blades during at power, 

full speed operation. 


Figure 1 – Value assessment and development priorities of advanced NDE 

technologies to meet power generation industry strategic needs. 

Global Inspections System 

The Global Inspection System is a new NDE technology concept, illustrated in Figure 2, 

developed by expanding upon known dimensional and visual inspection techniques and 

integrating nondestructive inspection information with a three-dimensional model of a 

component to provide a novel capability for true virtual space inspection. 

We have recently developed a hardware/software system, shown in Figure 3, that 

combines two dimensional visual inspection data with three dimensional surface 

position inspection data to map acquired 2D optical images onto viewed surfaces of a 

3D digital model of gas turbine blades and some vanes at this time. The result is a true 

virtual 3D image of the real component, including optical images of degradations, 

defects, distortion and other conditions observable during a visual inspection. Once the 

virtual component is created in virtual space, a human inspector can manipulate the 

virtual component to perform a visual inspection of the virtual component. The results 

of such an inspection can be recorded in the virtual space, including marking directly 

onto the virtual part. The inspector can perform the virtual inspection to include 

manipulations that are commonly accomplished during a manual visual inspection of the 

real component. In addition, the system permits the inspector to enhance the 

inspection, such as with zoom imaging, hue, saturation and/or luminance manipulation. 

The system also permits layering of additional forms of inspection data and evaluation 

results onto the virtual component, addition of automatic evaluation techniques, and 

other data enhancement, data comparison, and statistical analysis techniques. 


Figure 2 – Working principle of the Siemens Global Inspection System using 

combined 2-D and 3D digital imaging of blades and vanes 

Most importantly the system provides for the 3D files of the virtual component to be 

archived for later comparison with similar information for the same component at a point 

in time later in the component's life after the original component condition has been 

changed, or for comparison with similar information for other similar components. This 

allows the results of the inspections (i.e. component condition assessments) that are 

created by the human inspector using the inspector's training and experience, combined 

with graphical user interface (GUI) image processing operations or automated image 

processing operations, to be recorded as additional surface mapping features on the 

virtual 3D image of the real component rather than as a disconnected piece of paper or 

reduced to tablular data points or rough sketch information in disconnected files. 

This allows for inspection results to be archived and recalled for various comparisons, to 

track condition assessment changes through the partial or entire life-cycle of a 

component or a population of components, and for the comparison of various 

components or groups of components with design, operational, service and repair 

history data. 

SIEMAT ® Acoustic Thermography 

The advanced NDE method called SIEMAT ® Acoustic Thermography (or Sonic IR by 

some) involves exciting the object to be inspected with sufficient ultrasonic energy to 

cause the cracks themselves to produce heat, as illustrated in Figure 4. Typically, only 

sufficient energy to produce a short (0.1 to 1.0 second) heat pulse of a few degrees 

centigrade is used, sufficient enough to be detected using available, high-speed, highsensitivity 

infrared (IR) imaging systems, but not so much vibration energy to cause any 

damage to the component. 


Figure 3 – Siemens Global Inspection hardware/software system for blades 

Development of the SIEMAT ® acoustic thermography method has resulted in processes 

that are used on a variety of gas turbine products. Practical processes are available for 

NDE inspections of turbine blades, turbine vanes and transitions. Inspection of the 

entire area of the hot gas exposed surfaces of a blade is accomplished in one shot 

lasting lest than two seconds on one side (suction side) and a second shot lasting less 

than two seconds on the other side (pressure side). Analysis using special thermal 

imaging processing software allows the real-time or later off-lie viewing of any heatpulse 

indications that stand out against the ambient temperature background to indicate 

the presence of cracks. The basic process of vibrating a component with a variety of 

ultrasonic frequencies has been demonstrated to be especially effective at detecting 

very tight cracks. Experience shows in some cases these cracks may not be reliably 

detected by other more traditional NDE techniques. Even the smallest cracks can be 

expected to generate some heat when vibrated sufficiently, so there are a wide variety 

of techniques that can be implemented by selecting the appropriate vibration excitation 

parameters and thermal imaging optics. 

Because the vibrations are supported by the base metal structure of the components, 

they are produced regardless of whether the component is coated or not. The heat 

pulses are very short duration and can diffuse through coatings, such as MCrAlY or 

thermal barrier coatings (TBCs) sufficiently to be recorded discretely by high speed 

infrared imaging systems. In some cases special image processing software designed 

using thermal signal behavior known from physics or discovered during research in the 

SIEMAT® acoustic thermography method is required to aid the NDE operator. The 

application of the various image processing options, playback of the time-varying 

thermal images and highlighting of thermal image indications is implemented with 


specifically designed graphical user interfaces in the SIEMAT® acoustic thermography 

systems. 

Figure 4 – Full-field inspection for cracks using SIEMAT® acoustic thermography 

Siemens Power Generation has extensive experience with Sonic IR techniques. Our 

developments include over six years of research and development, leading to 

implementation of the new NDE tools for inspection and diagnostics of power 

generation components, shown in Figure 5. These new technologies have been 

integrated into Siemens product lines under the SIEMAT ® acoustic thermography label. 

We have developed advanced expertise in the critical Sonic IR process parameters, 

including vibration excitation, infrared imaging and image capture, image processing, 

hardware/software systems integration and evaluation of the results in the context of 

component design, manufacturing condition and degradation from exposure to service 

conditions. 

The on-going objectives for future advancement of SIEMAT® acoustic thermography 

technology are being directed to provide a significant positive impact to the 

environment. As a result of successful demonstrations of the capability of the method to 

detect cracks in all locations of coated components, we believe SIEMAT® acoustic 

thermography will be preferred on components that are currently inspected using dye 

penetrants with the same or greater reliability and sensitivity. This will create a 

significantly positive benefit by replacing the current chemical-intensive inspection 

processes and eliminate the environmental hazards associated with paint stripping by 

utilizing a mechanical inspection capability. 


Figure 5 – SIEMAT ® acoustic thermography systems are available for global 

support of gas turbine products and services 

Because SIEMAT ® acoustic thermography is an image-based inspections technology, 

the inspection “data” and results are ready for direct integration with the Global 

Inspection System 2D-3D archive files. The structure of the Global Inspection System 

2D files mapped as a surface skins or layers on the underlying 3D solid model leads to 

a number of significant advantages. Life assessment analysis strategies rely 

extensively on the integration of all information available about component conditions 

and history. Modern design engineering technologies are based on solid model 

analysis, so the analysis of NDE inspection results directly on the actual, as measured 

solid model of the component is the right approach for integration into design 

engineering processes. Figure 6 shows how SIEMAT® crack indications (on the left) 

are displayed and analyzed along with visual inspection images and dimensional data. 

More complex and clearly more reliable diagnostics of fleet diagnostics and prognostics 

of components classes are being developed by using this standardized inspection data 

archiving and analysis system. Statistical analysis of fleet data and life-cycle inspection 

data will result in more profound technology-based life-assessment engineering 

solutions. 

On-Line Monitor Technology 

The third advanced NDE technology, On-Line Monitor, is a breakthrough in terms of 

pushing inspection of components to a true on-line assessment solution for critical gas 

turbine components. Usually, NDE solutions provide value after unit shut-down or 

disassembly when traditional NDE inspections can be effectively performed. 

Additionally, for most hot-section components in a gas turbine, complete inspection of 

the metallic structure of components, such as blade, vanes and transitions, have to wait 

until the coatings are removed. This presents significant limitations to the task of 

gathering and assessing information needed for life-assessment programs in support of 

flexible operation and maintenance. The process of stripping coatings is timeconsuming, 

expensive and involves the use of aggressive chemicals that are a potential 


threat to the environment, requiring additional costs and risks in proper handling and 

disposal. Also, the stripping process itself is aggressive enough that the condition of 

the underlying metals are significantly altered, especially the size and morphology of the 

very degradations that are the object of the NDE inspections. The previous discussed 

technologies, for example SIEMAT® acoustic thermography, are a solution to these 

reliability and environment issues, but there is a delay in the availability of assessment 

results from off-line NDE inspections and additional information management is required 

to correlate results to the actual operating conditions. The advantages are obvious in 

being able to inspect or monitor critical components, not only in the gas turbine before 

disassembly, but while it is actually operating. And there is an additional advantage to 

be able to directly monitor the effects on critical component performance when actually 

making changes to operation conditions, such as power changes. 

Figure 6 – Images of SIEMAT ® crack indications are ready for fusion with the 

component’s Global Inspection System inspection archives 

The first On-Line Monitor Systems were designed to image row 1 and row 2 blades 

during operation, while they are moving at full-speed, 3600 rpm. The blade sensor 

uses high-speed thermal imaging and computer recognition software to thermally 

examine each blade as it passes a focal plane array sensor. With the use of highspeed 

sensor arrays, the aspects of spatial resolution related to using an array are 

considered, and the full field two-dimensional images provide substantially more robust 

data sets of the blades thermal conditions compared with single-point pyrometer 

readings. Operating conditions that the sensor is subject to in the turbine engine are 

accounted for in the design. A turbine case penetration system is design to place the 

sensor optics in the pressure chamber of the engine turbine section, as illustrated in 

Figure 7. 

The sensor selection is based on the best combination of reliability, robustness and 

sensitivity. Infrared instrumentation is selected to operate at some optimum spectral 

response within the infrared band of 0.09 – 12.0 µm. Very short integration times, on 

the order of a millisecond or less are required to get the “snap-shots” of blades moving 


through the viewing window at greater than the speed of sound. Additionally, the 

system includes design considerations for resolution, array size, sensor cooling, power 

dissipation, dynamic range, package size, thermal stability, vibration resistance, and of 

course cost. Infrared camera and support systems have been operated in test-bed and 

operating plant environments and have demonstrated integrity of the system for 8000 

hours of engine operation. 

Figure 7 – Example of penetration for on-line thermal imaging of row 1 turbine 

blades 

The On-Line Monitor supervisory control software, shown in Figure 8, includes the 

ability to control sensor parameters and synchronize the image timing to the rotation of 

the gas turbine shaft, such that individual blades can be selected for instantaneous or 

continuous monitoring. The software operates in a PC environment and can be brought 

to the customer plant site to be connected directly to the installed optical system. 

Alternatively, the control signal and resulting image outputs can be streamed through 

internet connections so that the On-Line Monitor can be operated remotely, from 

Siemens service support locations, such as the Orlando Power Diagnostic Center. 

Figure 8 – On-Line Monitor software controls the real-time, high-speed IR sensor 

to capture turbine images on-site or from Siemens Power Diagnostics Center. 


Extensive testing of the On-Line Monitor System has been completed for imaging 

blades during power operation. The initial component life-assessment target for the 

system was to be able to detect, measure and monitor the growth of TBC defects, 

should they occur in operation. The upper left, bottom left and bottom center images in 

Figure 9 shows some examples images made of test samples that were operated in 

W501F engines for the purpose of qualifying the On-Line Monitor System. In the 

process, the system has proven to be very sensitive to a wide range of turbine blade 

operation conditions. Such changing conditions as cooling hole blockage, platform 

rubs, cooling hole performance, and TBC thickness result in images that change 

dynamically when monitored during plant operation and during load changes. 

Figure 9 – On-Line Monitor images operating features and service conditions of 

row 1 or 2 gas turbine blades while operating at power and 3600 rpm. 

This new class of inspection and monitoring information is leading to new engineering 

methods for validation of component designs. The On-Line Monitoring images, as 

shown in Figure 9 and top left of Figure 10, are two-dimensional radiance maps of the 

blades as they are viewed by the imaging system. Work is ongoing to design additional 

features into the system, including software analysis of the signal contents to calibrate 

the images for analysis as surface temperature maps. Figure 10 shows an example of 

the conversion of the On-Line Monitor images into surface temperature maps. Each 

color in the resulting image constructed from the radiance map data represents a 20°C 

isotherm. 


Figure 10 – On-line imaging of blade surface temperature at 20°C isotherms 

CONCLUSIONS 

A strategy for the integrated development of advanced NDE technologies has 

successfully led to three new technical solutions for effective life-assessment of gas 

turbine components. The combined 2D-3D blade and vane imaging system embodied 

in the Global Inspection system provides a platform for the collection, archiving and 

analysis of inspection data. This platform is a pioneering step towards integrating NDE 

technology with modern design engineering tools. The SIEMAT ® acoustic 

thermography method, with factory, repair depot and field-portable systems, is a key 

technology solution for improved inspection of coated components, and rapid full-field 

inspection of components without waiting for delicate, detailed scanning systems. 

An even more forward-looking NDE technology is now available in the On-Line 

Monitoring System which allow for the direct assessment of critical internal components. 

There simply is no equivalent alternative solution to the advantages of the On-Line 

Monitor for validation of engineering designs and real-time assessment of operational 

factors for hot section components, such as turbine blades and vanes. This technology 

has been fully demonstrated for performing these assessments even while blades are 

running inside the gas turbine at 3600 rpm and full power. 

These global inspection solutions form an integrated approach to developing advanced 

NDE technologies, that rely on multi-mode inspections and data analysis and link 

readily with CAD-based engineering design systems. They provide a new pioneering 

approach to predictive maintenance and extending life in critical gas turbine 

components. 

The content of this paper is copyrighted by Siemens Power Generation, Inc. and is licensed to PennWell 

for publication and distribution only. Any inquiries regarding permission to use the content of this paper, in 

whole or in part, for any purpose must be addressed to Siemens Power Generation, Inc. directly.

Advanced NDE Systems for Flexible Operation ... - Siemens Energy

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