GROWTH – DEDICATED CALL – 10/00
TOPIC IV.1
Cyclic oxidation testing - development of guidelines for high
temperature materials
1. CONFORMITY WITH THE WORK PROGRAMME
This topic falls under the Competitive and Sustainable Growth Programme, generic
activity Measurement and Testing. Specifically, it is related to Objective GROW-20006.2.1 Methodologies to Support Standardisation and Community Policies for which
expressions of interest have been called.
The topic is also relevant to:
- Generic Activity Materials and Their Technologies for Production and
Transformation.
- Key Action 1 : Innovative Products, Processes and Organisation.
2. KEYWORDS
High temperature materials, performance quantification, reliability, safety, economical
use, testing, guidelines development
3. SUMMARY OF OBJECTIVES AND JUSTIFICATION
The performance of materials at high temperatures is depending on their behaviour
under the complex interaction of temperature changes, corrosive attack, oxidative
attack, and in some cases mechanical loads. Life time and probability of unexpected
failure for materials and components under these conditions can be characterised in a
laboratory by cyclic oxidation testing. Although it is generally agreed that this test is the
most valuable one for performance assessment of high temperature materials, no general
guidelines or standards exist so far neither nationally, Europe wide nor internationally.
Results from measurements existing today can actually not be compared with each other
nor can their significance for performance assessment really be quantified. Thus, a
strong need exists to close this critical gap by pre-normative research and the
development of reliable and useful guidelines or standards for cyclic oxidation testing.
4. BACKGROUND
In modern high temperature technology materials play a key role with respect to
performance, reliability, safety, economical profit and ecological compatibility. The
advances in the development of energy conversion systems (low CO2 emission power
stations, solid oxide fuel cells, waste and bio-mass combustion or gasification, coal
conversion, etc.) and in engines for transportation (car engines, catalytic converters,
advanced jet engines, etc.) are to a largest extent based on high temperature materials
issues. In most cases these materials are subjected to a complex interaction of
temperature changes, oxidative high temperature attack, corrosive high temperature
DC 10/00/Topic IV.1/ Pg 2
attack and mechanical stresses. This interaction determines whether components exhibit
premature failure or show reliable long-term performance and also limits the upper
service temperature which decides the degree of efficiency and hence the economical
and ecological performance. This complex interaction can not be simulated in the
laboratory on a one-to-one basis without extremely high cost and unjustified man-hours.
Therefore, a number of tests have been developed which are used to characterize the
high temperature materials behaviour under somewhat simplified conditions.
With regard to high temperature oxidation resistance, isothermal exposure tests at the
potential operation temperatures, are performed either continuously (usually
accompanied by weight gain measurements in a thermobalance) or discontinuously
(weight change of the specimen is measured in a balance after cooling). These tests
provide information about the high temperature oxidation/corrosion kinetics, and the
first steps towards the development of guidelines1,2,3 have been undertaken. Such
guidelines or standards have not existed although these tests have been used for more
than half a century. The drawback of the isothermal test, from an industrial point of
view, is that during operation components almost never experience isothermal
conditions. Additionally, isothermal oxidation behavior usually reflects a better
oxidation resistance of the materials than the more near-service conditions of cyclic
oxidation (i.e. oxidation under superimposed temperature changes). Therefore, for years
the cyclic oxidation test has been the major test for the assessment of high temperature
materials performance under such complex conditions in all industrial laboratories and
also in some academic laboratories.
Of course it can be argued that cyclic oxidation testing does not include mechanical
loading of the substrate. Following this argumentation the thermo-mechanical fatigue
test was developed which is, however, sophisticated, requires expensive testing
equipment and highly skilled operation personal, and only one specimen can usually be
tested in one testing machine at a time. Especially for industry, the fatigue test excludes
the testing of a large number of specimens or different materials in particular for the
assessment of long term behaviour since the test is very expensive. As a consequence
often „accelerated“ tests with loads clearly above the operation stresses and short testing
times are performed which, however, do not take into consideration the role of
oxidation or high temperature corrosion in a realistic manner. It should furthermore be
mentioned that especially under high temperature corrosion conditions component lifetime will predominantly be determined by corrosion processes in the surface region of
the component rather than by mechanical failure mechanisms in the substrate.
The cyclic oxidation test has been developed because industry needed a relatively
simple and cost-effective test for the assessment of materials behaviour under high
temperature oxidation or corrosion conditions which, at the same time is relatively close
to the situation in operation of components in high temperature plants and engines.
Depending on the size of the test equipment, a large number of different specimens and
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1
2
3
H.J. Grabke et al.
Points to be considered in Thermogravimetry, Materials and Corrosion 44 (1993) 345 - 350
Guidelines for Methods of Testing and Research in High Temperature Corrosion,
Eds. H.J. Grabke, D.B. Meadowcroft, EFC-Publications No. 14, IoM Communications, London 1995
Discontinuous Corrosion Testing in High Temperature Gaseons Atmospheres - First Draft Code of
Practice ERA Technology, Leatherhead 1996
DC 10/00/Topic IV.1/ Pg 3
materials can be tested without high costs at the same time in industrially relevant
atmospheres and at temperature cycles oriented at operational conditions. This type of
test also allows long-term testing with testing times close to operational times since,
costs are in a reasonable order of magnitude in particular for industrial laboratories. The
importance of this test is reflected by the fact that a two day workshop organised by the
European Federation of Corrosion took place in February 1999 which was solely
devoted to this topic4. An alarming result of this workshop was, however, that despite of
the ample use and importance of this test no general or binding rules, guidelines or
standards exist. Therefore, neither can the results from different laboratories be
compared and evaluated reliably nor can the results be assessed with respect to their
significance for service performance. In particular industry complained, during
workshop discussions, about the unsatisfactory situation and demanded a rapid solution
which would close this critical gap. This message of the workshop even went as far as
to stimulate an initiative on this topic in the United States where it is planned to begin
guideline development in the year 2000. Furthermore, Japanese industry has indicated
their interest at a meeting after the workshop to join initiatives on this topic by
supplying their test experience. Since, parallelity of the initiatives can duplicate the
work and can finally end up in different recommendations for guidelines or standards it
is strongly recommended to perform such an initiative in co-operation with the activities
outside Europe. Leaving this important topic to industries and research laboratories
outside Europe would presumably bring Europe into a position where one would have
to adapt guidelines without having any chance of an influence favouring European
industries.
5. ECONOMIC AND SOCIAL BENEFITS
The main groups of industry confronted with the problem of characterizing the high
temperature oxidation resistance of materials are gas turbine and jet engine
manufacturers, car manufacturers (e.g. mufflers, metallic catalyst carriers and
turbocharger components), power generation equipment manufacturers and operators
(boilers, heat-exchangers, etc.), high temperature process industries (petrochemical and
chemical plants) and their equipment manufacturers (mostly SMEs), and last but not
least the materials manufacturers for these areas. The latter are in strong international
competition in particular with the US and to some extent with Japan but still have a
front position in this business. The materials supplied by European industry are different
grades of steel (usually special high alloy steels) and nickel base alloys either developed
for use under process plant conditions or for use in gas turbines. The annual turnover of
the largest companies of this group of materials manufacturers in Europe is about 2.8
billion EURO. The turnover of the 3 largest engineering companies in the field of high
temperature plant design and construction in Europe is about 1.5 billion EURO while
that of the gas turbine and jet engine manufacturers lies around 24 billion EURO.
If European industries are the first or among the first who can offer their high
temperature materials and components with certificates identifying that their products
were tested following reliable guidelines allowing a clear assessment of their
performance this would definitely put these companies into a particularly competitive
position. Investments in high temperature technologies are always expensive and all
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4
Cyclic Oxidation at High Temperature Materials - Mechanisms, Testing Methods, Characterisation and
Life Time Estimation, Eds. M. Schütze and W.J. Quadakkers, EFC-Publications No. 27, IoM
Communications, London 1999
DC 10/00/Topic IV.1/ Pg 4
data proving increased reliability, life-time, safety and temperature capability will cause
strong arguments in investment decisions. Today, as already mentioned, European
industry has a very high international standard in the field of high temperature
technology which has, however, to be actively defended against competitors, in
particular in the US. General guidelines for testing and the qualification of materials and
components performance would allow a fair comparison of products and would show
the high standard of European industries in this field.
The development of such guidelines or standards will furthermore contribute to much
better defined data for assessment of the upper service temperature limit and, thus, a
better use of the temperature potential of the materials. Besides the aspects mentioned
so far, ecological aspects come into play since increased temperatures in thermal plants
and engines allow a reduction of CO2 emissions and of energy consumption as a
consequence of increased efficiency. Increasing the material temperature in
steamturbines from the present 565°C to the desired 600°C increases efficiency by
about 2 %5 which, is feasible for 9 - 12 % Cr steels if reliable oxidation data existed.
When looking at the actually needed amounts of coal or other fuels in power stations,
this means a significant step forward with regard to fuel conservation and environmental
protection. Successes in the development of materials and components with increased
temperature compatibility would furthermore support the technological leadership of
Europe in environmental technologies.
Consequently, the evidence of a leading international position of European industries in
the technological fields mentioned, documented by results from tests based on the
respective guidelines, would lead to an increase in sales in the area of high temperature
materials and components which, can be quantified in a rough estimation to about 5 to
10 %. This increase in sales will be associated with a respective increase of employment
in Europe.
For a large number of high temperature plants component failure means emission of
environmentally harmful atmospheres which can endanger the population living around
these plants as well as the natural habitat. The staff operating the plant will furthermore
be exposed to this danger in an extremely high degree which can result in injuries and
loss of life. Unplanned failure of jet engines may lead to expensive stand-still periods of
aeroplanes and in extreme cases (e.g. during flight) even to high risk of life. High
temperature failures can be avoided by a reliable cyclic oxidation data base since most
failures in high temperature technology involve the effect of oxidation. The increased
reliability of thermal plants and engines minimises the risk of damage and pollution for
the population in the neighbourhood or as passenger.
The European dimension in the development of such guidelines is due to the fact that
only the joint efforts of as many as possible contributors from industry can provide the
necessary broad basis for such an initiative which can help all branches of industry in
high temperature technology. A simply national initiative would fail and as mentioned
above even a European initiative should not ignore similar initiatives worldwide.
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5
W. Schlachter, G.H. Gessinger
Innovation in Power Engineering - Role of Materials
in „High Temperature Materials for Power Engineering“,
Eds. E. Bachelet et.al., pp. 1-24, Kluwer Academic, Dordrecht 1990
DC 10/00/Topic IV.1/ Pg 5
6. SCIENTIFIC AND TECHNOLOGICAL OBJECTIVES
a) Evaluation of test procedures and data existing
As already mentioned cyclic oxidation testing has been used by all industrial
laboratories involved in high temperature technology. However, procedures show
vast differences and the published data has large scatter so, before moving to the
establishment of guidelines it is necessary to analyse procedures and data with
respect to their reliability and significance. In particular test atmospheres,
temperatures, test durations, dwell times, materials tested and data evaluation
methods as well as post-experimental investigations have to be assessed.
Furthermore, the test equipment has to undergo an analysis e.g. with respect to
sources leading to potential data scatter, with respect to investment cost and to the
necessary laboratory environment.
b) Development of guidelines
Based on the results of 6a) a set of guidelines can be developed. This should contain
an exact description of the background and the significance of the test procedure,
specimen shape and preparation, test equipment, test parameters, data to be
measured, data evaluation and interpretation, post-experimental evaluation,
significance of the results and transformability with respect to assessment of service
use. The guidelines have to reflect the different service situations with respect to
temperature histories, environments, materials groups, etc. The test parameters can
be adapted to the service conditions within certain limits with respect to dwell time,
temperature, cooling rate and test atmosphere but all other parameters, in particular
specimen shape and preparation, must be fixed by the guidelines. Variation in dwell
time, temperature and gas atmosphere should be limited to a certain number of fixed
values representing certain ranges of operating conditions.
c) Development and verification of the test procedure
The test procedure to be established from the guidelines should be sufficiently
flexible for adaptation to different parameters representing different practical
applications but rigid enough to deliver reliable data of low scatter and high
significance, i.e. details of the hardware have to be defined as well as all data to be
acquired. The test equipment should be available at reasonable cost, not requiring a
special laboratory environment and provide all data required in the guidelines.
Presently different principles are used with moving furnaces, moving specimens,
opening furnaces, etc. among which the most practicable method should be identified
and developed for recommendations in the guidelines. Verification of the test
procedure should be performed by applying the guidelines to reference materials
with tests in different industrial and non-industrial laboratories in a round robin
action.
7. TIME SCALE
Since there is serious interest in the standardization of cyclic oxidation testing in the US
and Japan where respective initiatives are in the state of being started, it is
recommended that a European initiative should be started without great delay. It is
expected that the time for achieving the objectives described in 6a - c amounts to about
3 years.