1. 1 Strengthening Study on Supervising of Metal Material to Guarantee Operation Safety of Ultra-supercritical Power Unit Yang Fu The China Elelctric Council October, 2006

2. 2 Abstract Based on partial statistics, the account of ultra-supercritical (USC) power unit constructing and scheming is near to 50 all over our country. These units cover two levels of 600MW and 1000MW with the main steam inlet pressure of 25~26.5MPa and the temperature of main steam & reheating steam of 600 ℃ /600 ℃. It is estimated that these units are going to start to run in 2007. In order to guarantee safely running of ultra-supercritical power units, it is urgent to research the key technology of ultra-supercritical power unit, which concerns that during the course of running the evolution of microstructure and mechanical property of new heat-resistant steels of T92/P92, T122/P122, Super304H and HR3C, as well as the repairing technology of new heat- resistant steel while damaged.

3. 3 It is anticipated that the total installed capacity in China will reach 1 billion kW, in which the fossil fired power still accounts for more than 70%. Developing of ultra-super critical unit is an inevitable trend in order to raise efficiency of fossil-fired power generation, save energy, improve environment and reduce cost of power generation. For boiler steam pressure and steam temperature being increased, the critical technologies for developing ultra-supercritical technology lie on heat-resistant steel with regard to selection, welding during fabrication and erection, study of heat treatment process, study of rules of structure performance change during operation and study of repairing technology when metal parts damaged.

4. 4 1. Brief introduction of new heat-resistant steel applied on ultra-supercritical units overseas Brief information of new heat-resistant steel on ultra-supercritical units in Japan is shown in Table 1 and Table2. Brief information of new heat-resistant steel on ultra-supercritical units in Europe is shown in Table 3. Brief information of new heat-resistant steel on ultra-supercritical units in China is as follows: There are several sets of 600MW and 1000MW ultra-supercritical (Pressure=25~26.5MPa, Temperature=600/600 ℃ ) units under construction in China. According to relevant documents, there are several solutions for selecting new heat-resistant steel, which are summarized in following Table 4 for reference.

5. 5 Table 1 ： Main steam pipe with HCM12A (P122) of ultra- supercritical units in Japan Power station Boiler manufacturer Capacity MW Turbine parameters pressure / temperature MPa/ ℃ / ℃ Main steam pipe Superheater tube (stainless steel) Commercial operation date Tachibanawan ＃ 2 Hitachi BHK 105025/600/610HCM12ASUPER304H2001.07 Maizun ＃ 1 90024.5/595/595HCM12A HR3C SUPER304H 2004.08 Hitachinaka ＃ 1 Hitachi 100024.5/600/600HCM12ASUPER304H2003.12 Isogo （ new unit #1 ） 60025.5/600/610HCM12ASUPER304H2002.04 TSURUGA #2 70024.1/593/593HCM12A HR3C 、 Super304H 2000.10 REIHOKU ＃ 2 70024.1/593/593HCM12A HR3C 、 Super304H 2003.07 HIRONO ＃ 5 70024.5/600/600HCM12A HR3C 、 Super304H 2004.07 Tomatoh-Atsuma Power Station ＃ 4 70025/600/600HCM12ASUPER304H 2002.06

6. 6 Table 2: Application of NF616 (P92) for supercritical units in Japan No. Year of delivery AmountManufacturer Fossil-fired power station Boiler capacity Steam conditions 11996 Small-diameter pipe, 13 t IHI Nippon Steel/Tokai # 7 147MW 566 ℃ / 538 ℃ / 16.6MPa 21997 Small-diameter pipe, 147 t IHI J-POWER /Tachibanawan ＃ 1 1050MW 600 ℃ / 610 ℃ / 25MPa 31998 Large-diameter pipe, 60 t * BHK J-POWER /Tachibanawan ＃ 2 1050MW 600 ℃ / 610 ℃ / 25MPa Total 220 t * ： Size: 00×70t ， Φ596.9×97t ， Φ635×106t

7. 7 Table 3 ： Application of P92 steel on power stations in Europe CountryProject name Tube dimension （ mm ） internal diameter × wall thickness Part Main steam temperature （℃） Main steam pressure （ bar ） Erection time Denmark VESTRAFT unit #3 240×39 Main steam vertical pipe 5602501996 Denmark NORDJYLLANDSET 160×45Header 5822901996 Germany KIEL/GK WESTFALEN 480×28 159×27 Header circulating steam 545 650 53 180 1997 - 1998 Denmark AVEDORE 2/ ELKRAFT 400×25 490×30 Main steam piping 580 （ Main steam ） 600 （ Reheat steam ） 300 1999- 2001

8. 8 Table 4: Application of new heat-resistant steel on 1000MW class ultra-supercritical unit in China PartScheme IScheme II Scheme III Waterwall Tube Coil TypeSpiralVertical Pipe TypeRifledSmooth Rifled /smooth MaterialT2 T12 、 T2 T12 T12 、 T23 Superheater Low temperature T12 、 T22 T12 、 T22 、 TP347H Enclosed T12 、 T 1a Pedant HR3C 、 Super304H T22 、 T91 、 Super304H 、 HR 3C Rear T91 、 HR 3C Final stage HR3C 、 Super304H T91 、 Super304H 、 HR 3C Platen T12 、 T91 Final stage T91 、 Super304H 、 HR 3C Reheater Low temperature T2 、 T 1a High temperature HR3C 、 Super304H Horizontal section of low temperature heater T22 、 T12 、 T1 、 SA 210A1SA210C 、 T12 、 T91 V ertical section of low temperature heater TP347HT91 Final reheater T91 、 Super304H HR3C 、 TP347H Main steam piping P92 P92 、 P122 P92 Hot reheaterP91 Cold reheaterA672B70CL32A691Cr1-1/4CL22A672B70CL32 HP feedwater pipe WB36

9. 9 It can be drawn from comparison of above data that P122 produced by Sumitomo Co. is used on main steam piping for ultra-supercritical units in Japan, P92 produced by Vallourec & Mannesmann is used on main steam piping for ultra-supercritical units in Europe. As for the parameters of ultra-supercritical units in China, the pressure is higher that that in Japan, while the temperature is higher than their counterparts in Europe. There is not an identical unit can be referred in the world. Therefore, the metal material supervising must be strengthened after the ultra-supercritical units in operation in China.

10. 10 2 ． Research of metal supervising, critical technology for safe operation of ultra-supercritical unit It is worthy of mentioning that the structure made of P92 has been used experimentally on some electric power projects, though, it has not been widely used in building power station. The main reason is that material and welding specialists are not yet fully convinced without practice. The knowledge is needed for rules of change of steel microstructure, and the resulted impact on creep rupture strength and plastic ductility after long period of real operation under high temperature and high pressure in power station.

11. 11 2.1 Research on main steam pipe made of P92 steel for 1000MW ultra-supercritical unit according to data provided in ASME specification When designing Main steam piping, the high temperature creep rupture strength of steel shall be considered. It must meet the thermal stress requirement due to thermal expansion of piping. Generally, the steel suitable for high temperature pipe shall have a creep rupture strength up to 90~100 MPa under working temperature for 10 5 h. In order to meet the requirements of unit start-up and shutdown, it is required that the pipe steel shall have relatively low thermal expansion coefficient and thermal conductivity so as to reduce thermal stress level inside pipes.

12. 12 The data in ASME specification has been extrapolated by Nippon Steel based on creep rupture in short period. The value is σ105600 =132 MPa. The allowable stress is 88 MPa for P92 steel at 600 ℃ according to its creep rupture strength. Furthermore, the wall thickness of main steam pipe of P92 steel can be calculated for 1000MW ultra-supercritical unit. Europe is however suspicious of the extrapolation method by Japan. The extrapolation result from European Creep Collaborative Committee (ECCC) indicates that the creep rupture strength of P92 steel is only 113 MPa at 600 ℃ and 105h. The resulted allowable stress is 75.3 MPa at 600 ℃ and 66.6MPa at 610 ℃ for P92 steel. For the main steam pipe of P92 steel of 1000MW ultra-supercritical unit, the calculated wall thickness based on this allowable stress is bigger than that according to ASME specification. The metal supervision on main steam pipe of P92 steel with thinner wall calculated by data from ASME specification should be strengthened during operation. The creep rupture test under working temperature of 600~610 ℃ and period of 10 5 h on P92 steel applied on main steam pipe for ultra-supercritical unit in China should be done as soon as possilbe

13. 13 2.2 Research on rules of steel microstructure and performance change after long period of operation under high temperature and high pressure 2.2.1 The P92 and P122 are selected as materials for main steam pipe and header for ultra-supercritical unit in China The microstructure change of these two kinds of steel after long period of operation under high temperature and high pressure are mainly decrease of dislocation density and formation of Laves phase due to solid-state precipitation of W. The Laves phase will not only reduce stress under high temperature but also reduce impact toughness. For containing 0.30~1.70% Cu, the P122 steel will promote precipitation and formation of Laves phase, which has worst stability during long period operation.

14. 14 2.2.2 Super304H and HR3C being used on high temperature superheater of ultra-supercritical boiler in China at present The Super304H obtains relatively high stress-rupture strength for fabricated by adding 3 ％ Cu and 0.5% Nb in the conventional 18-8 austenitic stainless steel (TP304H), of which allowable stress at 650 ℃ is higher than TP304H by 40%. It has stable structure and performance after running of 2.5 years, which is give priority as material used on fire-side of ultra-supercritical unit.

15. 15 HR3C is of 25Cr-20Ni steel, and added with Nb to form precipitation strengthening, through which extreme high creep rupture strength. Though the allowable stress at 650 ℃ is slightly lower than that of Super304H, HR3C has superior performance in terms of high temperature flue gas corrosion resistance and steam oxidation resistance due to high Cr content. Hence, the HR3C is preferably selected as the high temperature parts for superheater and reheater. According to present research, the drop of toughness of these two kinds of steel are found subject to certain temperature range. The rules of structure change of these two kinds of steel are still need to be studied further after long period operation.

16. 16 2.3 Research on hot corrosion resistance and high temperature steam oxidation resistance of steel after long term operation under high temperature and high pressure 2.3.1 Research on hot corrosion resistance and high temperature steam oxidation resistance of T92/P92 andT122/P122 Generally speaking, the protective oxide skin must be formed by selective oxidation of one or several alloy elements for high temperature material. That implies that two conditions must be met. The first is that the selective oxidation in base body must have high concentration. The second is that these elements must have diffusion rate higher enough so as to ensure supplement to base body under the developing oxide skin, hence the long term protection is guaranteed. Chrome is one important element for raising oxidation resistance performance. For containing high chrome content, the flue gas corrosion resistance and steam oxidation resistance of T122/P122 are superior to T92/P92. Due to high steam temperature for ultra-supercritical unit, the oxidation on steam side and peel-off of oxidation of ultra-supercritical unit is more severe than those of sub-critical unit. It happened overseas that the ultra-supercritical unit had to run with reduced parameters due to severe steam oxidation problem. This problem should be highly attended during operation.

17. 17 2.3.2 Research on hot corrosion resistance and high temperature steam oxidation resistance of Super304H and HR3C As a kind of fine grain steel, the Super304H steel shows better hot corrosion resistance and high temperature steam oxidation resistance than TP304H and TP321H. The HR3C is not of fine grain steel, the Cr of HR3C is, however, increased to 25 ％， Therefore, the HRC steel is superior to Super304H steel in terms of hot corrosion resistance and high temperature steam oxidation resistance. All these are important issues need to be studied during long term operation.

18. 18 2.4 Research on early failure mechanism of weld joint of heterogeneous steel It was shown by research and operation experience in the past that early failure may happen on heterogeneous steel weld joint of austenitic steel and ferretic steel. It is regarded generally that early failure is caused by creep damage, which is related to special metallurgy and mechanics conditions formed on the interface between two materials of weld joint with different creep strength. As austenitic steel, Super304H and HR3C are mainly used on ultra-supercritical boilers in China, which both have very high creep rupture strength. The study on creep failure mechanism of weld joint of Super304H and HR3C and ferretic steel in operation should be highly attended.

19. 19 2.5 Research on aging rules of new material to ensure safe operation of unit For sub-critical units in operation, the life assessment has been well studied and applied widely, which provides powerful data for unit status maintenance. There still lacks sufficient knowledge of aging rules for the new heat-resistant steel used on ultra-supercritical in operation under higher temperature and pressure, though the performance of new heat-resistant steel has been improved dramatically. Therefore, the material aging mechanism must be researched from the beginning of operation of unit, and grasp material aging rule gradually, in order to guarantee safe operation of ultra-supercritical unit.

20. 20 2.6 Research on welding repair technology of damaged part of new heat-resistant steel after long period of operation under high temperature and high pressure For the ultra-supercritical units under construction in China, there are four kinds of new heat-resistant steel being used for the first time, namely, T92/P92, T122/P122, Super304H and HR3C. T92/P92 and T122/P122 are new ferretic heat-resistant steel, of which problems include low welding toughness, cold cracking tendency, Ⅳ type crack and weld failure tendency.

21. 21 Super304H and HR3C are new austenitic heat-resistant steel, of which problems include high temperature cracking (crystal cracking, high temperature liquid cracking and high temperature brittle crack), weld corrosion and brittle failure of weld metal. In case of damage on the ultra-supercritical boiler part fabricated with abovementioned new heat-resistant steel after long period of operation under high temperature and high pressure, the repair by welding will be much more difficult than fabrication and erection due to very poor welding conditions and complicated stress status. Hence the research on welding repair of new heat-resistant steel parts on ultra- supercritical boilers must be conduced as soon as possible.

22. 22 3. Summary The new heat-resistant steel used on ultra- supercritical boiler is a critical technology for safe operation of ultra-supercritical unit. The owner, designer, manufacturer, constructor, research institute and operator shall join hand in hand, and conduct studying on critical technology for safe operation of ultra-supercritical unit in advance.

23. 23 Strengthening Study on Supervising of Metal Material to Guarantee Safely Running of Ultra-supercritical Power Unit Abstract: Based on partial statistics, the account of ultra-supercritical (USC) power unit constructing and scheming is near to 50 all over our country. These units cover two levels of 600MW and 1000MW with the main steam inlet pressure of 25~26.5MPa and the temperature of main steam & reheating steam of 600 ℃ /600 ℃. It is estimated that these units are going to start to run in 2007. In order to guarantee safely running of ultra-supercritical power units, it is urgent to research the key technology of ultra-supercritical power unit, which concerns that during the course of running the evolution of microstructure and mechanical property of new heat-resistant steels of T92/P92, T122/P122, Super304H and HR3C, as well as the repairing technology of new heat-resistant steel while damaged.

24. 24 谢谢 !