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ISSN 1018-5593
European Commission
physical sciences
New steels and manufacturing
processes for critical components
in advanced steam power plants
1996 EUR 16858 EN European Commission
physical sciences
New steels and manufacturing
processes for critical components
in advanced steam power plants
K. H. Mayer, C. Berger, R. B. Scarlin
MAN Energy
Edited by
P. J-L Mériguet
DG XII/B.1 COST materials
Rue de la Loi 200
B-1049 Brussels
Supported by the
European Commission through Contract No COST 92-0049DE
Directorate-General XII
Science, Research and Development
1996 EUR 16858 EN Published by the
Directorate-General XII
Science, Research and Development
B-1049 Brussels
Neither the European Commission nor any person acting
on behalf of the Commission is responsible for the use which
might be made of the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1996
ISBN 92-827-6578-4
© ECSC-EC-EAEC, Brussels · Luxembourg, 1996
Printed in Belgium New Steels and Manufacturing Processes for Critical
Components in Advanced Steam Power Plant
R.B. Scarlin, ABB Power Generation Ltd., Baden
K.H. Mayer, MAN Energy, Nürnberg
C. Berger, Siemens Power Generation KWU, Mülheim
An increase in the operating temperature and pressure of a steam power plant leads to an in­
crease in the system efficiency. Although the use of austenitic steels would permit such an in­e these materials suffer from the disadvantage of high price and susceptibility to thermal
fatigue, caused by the higher coefficient of thermal expansion and low thermal conductivity.
For this reason improved ferritic steels were required to minimise turbine and boiler costs and
provide high flexibility of operation (2 shift operation, frequent start­up/shut down). Such steels
are also the subject of extensive research programmes in Japan and the USA.
The long­term aim of the COST programme was to develop and evaluate improved creep re­
sistant 9 ­12% Cr steels and to manufacture, test and seek service operation of critical com­
ponents required for an advanced steam power plant (steam temperature of 600'C and at su­
percritical pressure). Critical components are:
• High­pressure and intermediate­pressure rotors
• Turbine and valve casings
• Turbine and valve bolting
• Main steam pipes and header sections
• Waterwalls
For each of the critical components a working group was constituted comprising:
• steel companies (forgemasters or casting foundries)
• turbine and boiler manufacturers
• utilities and other users
• testing institutes and universities.
The participants are listed in Table 1.
The development goals in terms of required materials properties, fabrication techniques
(forging, casting, welding) and nondestructive examination had been defined by the turbine
and boiler manufacturers.
ι -Within the programme alloy development work was firstly performed on small batches of mate­
rial (150 ­ 500 kg), some of which had been begun within the first round of COST 501. Subse­
quently for the best steels representative components were manufactured to demonstrate the
feasibility of up­scaling. These components were subjected to nondestructive and destructive
Steels were developed which were able to satisfy the targets set for large components, so that
steam power plant can now be built with operating temperatures up to 600'C; i.e. about 35'C
hotter than was previously possible, with a corresponding relative increase in operating effi­
ciency of ca. 2%.
Organisation ΡΜ Header Waterwalls Forgings Castings Bolts Steam Pipes
ABB­Sweden X
ABB Powdermet χ
ABB­Swiizerland X X
AEG­Kanis X X
Ahlström χ
Ansaldo χ
Austrian Research Centre X
Bôhler X
Dalmine χ
Energie und Verfahrenstechnik (EVT) χ
ETH­Zúrich X X
Forgemasters Engineering Ltd. X
Fraunhofer Institute χ
GEC Alsthom X X X
Georg Fischer X
(with Schweissindustrie, Oerlikon)
MAN Energie X X X
(with MW, Darmstadt)
Mannesmann χ
National Power X X X
NEI­Parsons X X X
Royal Scheide χ
Saarstahl, Völklingen X
Siemens­KWU X X X
Stork Boilers χ
Sulzer Bros. X χ χ χ
Techn. Ueberwachungsvereinigung χ
Vallourec χ χ
Vereinigte Schmiedewerke GmbH X
Voest Alpine X
Table 1: List of Participants Contents
Preface - ! -
1. Introduction 5 -
2. International Development for Advanced Steam Power Plant - 5 -
3. Critical Components in Advanced Steam Power Plant - 7 -
4. Materials Development - 8 -
5. New Ferritic-Martensitic Rotor Steels 10 -
6. Newc Cast Steels 19 -
7. Creep-Resistant Bolting Material - 24 -
8. Improved Steels for Steam Pipes and Headers 30 -
9. Conclusions and Future Trends 48 -
10. Acknowledgements - 49 -
11. References 49 -1. INTRODUCTION
Increasing fuel costs, the pressure to reduce environmental pollution and the need to
reduce C02-emissions have lead worldwide to the development of power plants with
higher efficiency, greater operating flexibility, improved availability and longer lifetime
[1]. A key role in the further development of power plant technology has been played by
the materials for highly-loaded turbine components, since basically the aims can only
be achieved through using materials with improved strength and toughness [2 - 4]. This
is particularly clear in Fig. 1 [5] which shows schematically the reduction in heat rate for
a steam turbine of up to 10% achieved by increasing the steam temperature from about
540 to 650'C with a simultaneous increase in steam pressure from about 180 to 300
bar, with double reheat.
A major increase in operating efficiency is possible. A temperature increase to 600'C
constituted the first step in the European COST501 Programme on Critical Compo­
nents for Advanced Steam Cycles. It is considered possible to make a further increase
to about 620"C, through the use of improved creep resistant ferritic steels. The further
step to about 650'C can only be achieved through the use of highly creep resistant
austenitic steels, i.e. through the use of more expensive steels. In addition to the costs
it is also necessary to consider the effect of the different properties such as higher
coefficient of thermal expansion, lower thermal conductivity and higher susceptibility to
stress corrosion cracking.
Since there are no fuel reserves in Japan a programme was initiated in 1979 under the
leadership of the power plant operating organisation EPDC (Electric Power Develop­
ment Corporation) and with financial support from the government (MITI). The aim of
this common initiative of operators, manufacturers and thet has been the
development of a 1000 MW plant with a maximum steam temperature of 593'C in the
first phase and of 649'C in the second phase, with single or double reheat and super­
critical pressure, see Fig. 2 [6, 7]. The figure shows how the live steam and reheat
steam temperatures are increased in steps, whereby the reheat steam temperature
(where the pressure is lower) in generally raised first. All plant named on this figure are
either commissioned or under construction.
In Fig. 3 the materials for this development project are shown for the various compo­
nents. The investigation of materials and components in the laboratory and power plant
continued until 1988. At the beginning of the 80's a start was made with the manufac­
ture of a 50 MW demonstration plant, Wakamatsu. Subsequently test operation was
successfully performed over a period of several years, in the first stage at 593'C [8].
The start of test operation for the second phase (up to 649'C) was planned for August
1990. The satisfactory progress of the research programme led already in 1989 to the
order for a 700 MW steam power plant by a Japanese operator, with the steam condi­
tions 241 bar 538'C/593'C. Commissioning of the plant was in June 1993 [9]. A
1000 MW plant with "ultrasupercritical" steam conditions and both live steam and single
reheat steam temperature of 593'C was ordered for commissioning in 1997.
In addition EPDC plans to manufacture a demonstration combi power plant with a pres­
surised fluidised bed boiler, a gas turbine and supercritical steam conditions. The de­
monstration of this concept is also planned to be made in the Wakamatsu power plant,
subsequent to the test operation of stage two (649"C). 2.2 USA
In 1978 the American power plant operator company EPRI (Electric Power Research
Institute) initiated two feasibility studies for the following steam conditions:
Phase 0 double reheat 316 bar, 566'C
Phase 1 double reheat 316 bar, 593'C
Phase 2 double reheat 352 bar, 649'C.
Both studies led to recommendations for further development to 316 bar and 593'C
with double reheat, since with these parameters it is possible to achieve the maximum
improvement in heat rate without a loss of reliability, at relatively low research and de­
velopment costs [10]. These studies led in 1986 to the initiation of a five year EPRI Re­
search Programme in which certain Japanese and European power plant manufac­
turers also participated. The essential aims of the research programme are summarised
in Fig. 4. In addition to these aims further requirements were also specified for the
• short start-up times (cold start 10 - 12h, warm start-up 4h and hot start-up 2h),
• suitability for peak load operation,
• improved reliability,
• improved efficiency,
•d control and monitoring devices.
The progress of the development work was reported in 1986 [11], 1988 [12] and
April 1991 [13]. No plant with temperatures above 566'C have as yet been ordered in
the USA.
There is already extensive operating experience with smaller plant which was built in
the 50's particularly for the chemical industry e.g. [14 - 16], The plant built in Europe in
the 50's and early 60's is summarised in Fig. 5. The steam temperatures lie between
600 and 650'C and pressures between 180 and 330 bar. The power rating of the
plants, which were mostly built for the chemical industry, is comparatively low (3 to 125
MW). For the highly loaded components austenitic steels and creep resistant ferritic
steels such as X21CrMoV121 or G- X22CrMoV121 were mostly used, sometimes with
cooling, see Fig. 6.
So far recent plans for power plant with advanced steam inlet temperatures are known
from English [17], Danish [18 - 20] and German power plant operators. A particular in­
terest in pulverised coal fired plant with higher steam temperatures is present in Den-
marie. In a study by ELSAM [18] the development potential for pulverised coal fired
power plant is shown, which according to Fig. 7 is only exceeded by oil or gas fired
combined cycle processes with respect to overall efficiency. A power plant with a steam
temperature of 580'C and overall efficiency of 47.5% has been ordered [19]. The pro­
cess 3 with an efficiency of well over 50% and a steam temperature of about 640'C
could be achieved after the year 2000, if new highe materials become
Planning by the German Power Plant Operators for higher steam inlet temperatures
and large power plants is also gaining momentum. In a recent paper [21] it is stated
that coal and lignite will be used increasingly in Europe for the generation of electrical

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