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Gas turbine off-line diagnostics
Condition assessment of coatings (COCOM), endoscopy, in situ crack lenght detection, non-destructive testing, optical strain measurements with SPICA, gas turbine lubrication
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Off-line diagnostics
You want to be kept informed of the technical state of your installation in order to minimise the chances of breakdown. As for gas turbines, the hot gas path-components are very critical parts. It is not always possible to monitor the condition of these components during operation. It is of major importance to you to be able to picture the condition of, for example, the gas turbine blades with a minimal operational disruption, i.e., during short stops only. KEMA has many years of experience with inspecting technical installations and can supply the following tools and services concerning gas turbine inspections: - coating condition determination
- boroscopy
- VINSPEC, in-situ crack length measurement and verification
- SPICA, a system for optical strain measurement
- lubricating oil diagnostics
- non-destructive inspection techniques.
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Condition assessment of coatings
How about coating condition in your gas
turbines?
Challenge
Sophisticated coatings protect the superalloys in your turbines
against oxidation, corrosion and environment unfriendly
components.
Solution
Non-destructive evaluation of both new and in-service high
temperature coatings on gas turbine blades is an important factor
to achieve a high level of structural integrity in advanced gas
turbines. Frequency scanning eddy current techniques are capable to
determine the coating thickness as well as the aluminium content of
the coating. Therefore, they can be used as a quality assurance
tool upon acceptance of the blades.
KEMA offers this technique as COCOM (COating COndition
Measurement), a system to assess the condition of gas turbine blade
coatings. Experimentally, the method relies on eddy current
measurements. A multi-frequency approach is required, as it is
necessary to test the material at different depths. Experiments
have shown that using this technique it is possible to measure
coating thickness of a new coating to an accuracy of about 10 %.
This has been verified by thorough destructive evaluation.
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Endoscopy
First aid in gas turbine inspection
Challenge
Many problems can be solved easily by visual inspection;
considering gas turbines, this usually means
looking inside the gas turbine without the
necessity to open the gas turbine housing.
Solution
A range of endoscopy and TV-camera's renders all flexibility as
to visual inspection. If cracking is found the VINSPEC option is
available too.
Practical implementation
To support non-destructive inspections, KEMA employs a range of
endoscopes and CCTV systems. Video endoscopes enable us to record
images on photograph as well as on video tape.
One system is suited to inspect boilers and gasifiers during
operation up to 1,500 °C. This system can be used in connection to
a pyrometric system.
A small diameter endoscope (Ć 1 mm) is available to inspect, for
example, hollow-structured blades and vanes of gas turbines.
Customer benefits
Using video endoscope apllications to support non-destructive
inspections will benefit in:- quality images of inspected areas to support management
decisions
- equipment available in a wide range of lengths and diameters:
flexibility
- broad experience with larger structures as well as with smaller
objects, ensuring quality advice by KEMA
- rapid deployment around the world.
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In-situ crack length detection
Examination and measurements inside the gas turbine: "VINSPEC"
will tell if opening of the gas turbine is necessary
Challenge
Gas turbines can be opened fully for inspections. However, it is
often possible to save the expense of disassembling the housing as
well as of power failure time. Therefore, inspection holes are
mostly integrated into the gas turbine-housing. Many gas turbine
owners have their own endoscope nowadays, specifically for this
reason. To establish a complete blade failure, missing parts, major
damages of blades, vanes and shrouds and colouring of the blade
surface, this is usually an adequate method. Once,
smaller linear crack indications are found this may
be different.
Solution
‘VINSPEC’ developed by KEMA, combines the advantage of rapid
inspection with an endoscope through an inspection opening and
defect (crack) depth measurement.
Practical implementation
The VINSPEC inspection is conducted through inspection holes
(> 6 mm), much the same way as an ordinary endoscopic
inspection. In addition, a measuring probe integrated into the
endoscope provides the possibility to evaluate detected crack like
defect indications. The instrumentation and the specialists can be
available at the required location within 24 hours.
Customer benefits- in case of doubt, upon finding flaws, with endoscopic
inspection through limited access inspection holes, the character
and size of the indication can be established instantly
- a clear decision can be made by the owner to further open the
gas turbine to repair/replace a blade or to leave it in place and
postpone repair/replacement to a better moment in time or even
forget about it altogether
- after leaving the blade unrepaired / unreplaced there will be a
trending possibility (crack progression monitoring)
- before opening the gas turbine housing for further inspection,
you will be sure that the flaw indication is not just a trivial,
superficial crack
- the possibility of rapid deployment around the
world.
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Non-destructive testing
NDT avoids crashes/postpones replacement of gas turbine
parts.
Challenge
During planned gas turbine stops non-destrcutive testing (NDT)
of hot gas parts (HGP), in particular blades and vanes, as well as
non-HGP parts will lead towards improved reliability, avoiding
crashes and postponing replacement/repair.
A special challenge is the application of NDT at restricted
access site situations (for example: through inspection openings
only).
Solution
Clearly, conventional techniques are not always sufficient tools
to tackle all problems. Therefore, KEMA developed several "special
applications".
Practical implementation
KEMA has been performing many dedicated NDT-methods on gas
turbine blades and disks, both at mounted and dismounted blades.
World wide over 200,000 compressor and turbine blades have been
inspected with eddy current and ultrasonic methods in addition to
magnetic and dye penetrant testing. In addition, these methods have
been made available for application in limited access situations.
One of the examples is "VINSPEC" , to size crack indications. KEMA
(together with daughter company NRG) employs a 3D-tomography system
for off line testing (in particular) of hollow structured turbine
blades.
Customer benefits- accurate and reliable data; whenever requested: recordable
data
- specialist solutions to "new" type of customers requests
- in situ possibilities
- non-destructive blade coating metallurgy (COCOM).
- crack depth monitoring in housing parts (trending in stead of
replacement/repair)
- rotor remnant life analysis support: cracking and surface
structure analyses - life extension.
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Gas turbine lubrication
KEMA has significant experience in oil business. For more than 30 years the Dutch electricity companies discuss their oil problems with KEMA. This leads to a specific and unique knowledge of using oil in the steam and gas turbines. In 1980 KEMA has introduced their independent recommendations for lubricating oil for steam turbines.
In the past, several problems were encountered in the Netherlands with respect to lube oils for gas turbines. These included rapid degradation of the oil, flocculation of degradation products and remarkable analytic results. For some years the same problems have been observed in Denmark. For reasons of common interest, ELSAM and KEMA decided to join efforts and do a common research project.
In this project a total of 16 gas turbines were involved including ones built by GE, ABB, Rolls Royce, KWU, Dresser Rand and Solar. These gas turbines have been selected on criteria such as age, abundance and future applications. Also operation mode and the brand of lubricating oil used were considered. 12 different types of oil of 4 different suppliers have been evaluated for the aforementioned gas turbines.
Our monitoring programme consists of a wide range of classical chemical analyses, such as TAN, RBOT, colour etc. Suppliers usually present their own recommendations concerning the proper use of their type of oil. Because of their double part as supplier as well as adviser, the end-users had a need for independent advice on the use of lubricants. KEMA recommendations cover a broad range of relevant aspects of the lubrication of (gas and) steam turbines and also selection criteria for which oil to use. Contrary to the commonly used ASTM D 4378 92 standard, KEMA’s recommendations provide the user with a list of warning- and discard criteria (e.g. colour development based on years of operational experience with steam turbines.
KEMA also evaluates the application of phosphate esters (synthetic) as control oil and as lube oil. Besides excellent lubrication one of the key properties of this fluid is its fire resistance. In general KEMA can support you in the oil business with knowledge on the application of additives, inhibitors and filtration techniques leading to the best performance of your gas turbine.
For more information please contact us.
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