nickel base superalloys for next generation coal fired ausc … · 2017. 1. 23. · oxidation on...

Procedia Engineering 55 ( 2013 ) 246 – 252

1877-7058 © 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.Selection and peer-review under responsibility of the Indira Gandhi Centre for Atomic Research.doi: 10.1016/j.proeng.2013.03.250

6th International Conference on Cree

Nickel Base Superalloys foPo

Shailesh J. Patel∗, John J. deBarb

Special Metals Corporation, 3

Abstract

Utilities worldwide are facing increased demand for To meet this challenge will require increasing boiler tof boiler construction of future coal-fired boilers. Thand 740H™, aimed at meeting this challenge. The ev740’s mechanical properties, coal-ash and steam cemphasis will be given to recent data on alloy 740H and its subsequent weldability and mechanical proper

© 2013 The Authors. Published by Elsevier LtdGandhi Centre for Atomic Research.

Keywords: Nickel-base alloys; AUSC boilers; creep-rupture

1. Introduction

While worldwide environmental restrictions emissions, economic pressures are simultaneoucoal-fired plants. Adding to the challenge is iThese pressures on the utilities are spearheadinpower generation capacities to meet these chalefficiency. It has been shown that the efficiencwhen ultra supercritical steam (USC) conditionin these systems, the well-established 9-12% higher creep strength and greater corrosion replanned by the Europeans, Chinese and others f

∗

Corresponding Author: E-mail address: [email protected] ® INCONEL, ®NIMONIC and 740H™ are trademarks of Spe

ep, Fatigue and Creep-Fatigue Interaction [CF-6

r Next Generation Coal Fired AUower Plants

badillo, Brian A. Baker, Ronald D. Gollihue

200 Riverside Drive, Huntington, WV 25705, USA

additional electricity, reduced plant emissions and greater effitemperature, pressure and coal ash corrosion resistance of the m

his paper describes two new nickel-base alloys, INCONEL® allovolution of the early alloy 740 into alloy 740H is discussed. Sinccorrosion resistance have already been extensively reported and particularly its commercial-scale manufacturability to stearties.

. Selection and/or peer-review under responsibility of the

e; coal ash corrosion

are requiring power companies to reduce SOx, NOx anusly necessitating improvements in the thermal efficiencyincreasing demand for more electrical capacity worldwing the renovation of older plants and the construction ollenges. A key component of the solution is increased y of pulverized coal-fired boilers can be increased signif

ns greater than 300 bar and 620°C are adopted [4,5]. HoCr steels must be replaced by austenitic stainless steelesistance. Steam conditions up to 375 bar and 700°C,for Advanced Ultra Supercritical (AUSC) power plants ar

ecial Metals Corporation

6]

SC

e

iciency. materials oys 740 ce alloy [1, 2],

am pipe

nd CO2 y of all de [3]. of new

boiler ficantly wever, ls with being re now

Available online at www.sciencedirect.com

© 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.Selection and peer-review under responsibility of the Indira Gandhi Centre for Atomic Research.

http://creativecommons.org/licenses/by-nc-nd/3.0/http://creativecommons.org/licenses/by-nc-nd/3.0/

247 Shailesh J. Patel et al. / Procedia Engineering 55 ( 2013 ) 246 – 252

pushing operating conditions beyond the capabilities of these materials and into regimes only serviceable by new nickel-base alloys.

2. Alloy development methodology

The requirement of a 100,000 hours stress rupture strength of at least 100 MPa at 750oC and a corrosion resistance, defined as metal loss of less than 2 mm in 200,000 hours was imposed by the THERMIE consortium and therefore chosen as a baseline target for the new alloy. It was determined that the aerospace superalloy, NIMONIC® alloy 263, did have the required strength but lacked the demanding corrosion resistance. From the beginning, the intent of the new alloy was to have this level of corrosion resistance in uncoated thin-wall tubing, to avoid the expense and potential breakdown in service of ceramic coatings. Therefore, a program was initiated using alloy 263 as the reference alloy to which Cr and Nb additions were made for enhancing corrosion resistance whilst eliminating Mo, which is known to be harmful in fuel ash environments [6]. Thereafter, using this readjusted base, Thermo-Calc software was used to define the Al and Ti levels needed to produce the desired minimum ´ volume fraction of 15%.

As a result of the data obtained from the preliminary mechanical property and corrosion testing programs, an alloy range for INCONEL alloy 740 was defined and is given in Table 1. However, the original targeted use of the alloy was for superheater boiler tubing at steam temperatures of 700oC, for which it has been thoroughly tested and proved to be more than adequate [7]. Subsequently the alloy has been evaluated for other heavy section components in the boiler and turbine, particularly under a USA program that targets service temperatures as high as 760ºC, and has been modified to meet the service requirements of those components [8, 9].

Table 1. Nominal compositional range of the alloys of this study.

Alloy C Cr Mo Co Al Ti Nb Mn Fe Si 263 0.05 20 5.8 19.5 0.5 2.1 --- 0.35 0.5 0.1

740 0.03 25 0.5 20 0.9 1.8 2.0 0.3 0.7 0.5

740H 0.03 25 0.5 20 1.35 1.35 1.5 0.3 0.7 0.15

617 0.08 22 9.0 12.5 1.0 0.4 --- 0.1 0.5 0.1

Evaluation of alloy 740 in thick-section welds revealed a tendency for heat-affected zone (HAZ) micro-

fissures. It was also noted that the ’ was unstable at higher temperatures. Xie et al, working with Special Metals Corporation, conducted an extensive metallographic analysis of alloy 740 aged for up to 5000hrs at temperatures between 704°C and 850°C [10]. This work revealed that during exposure at 725°C and above, acicular -phase nucleated at grain boundaries and grew into the grains while consuming ’. Xie also documented the coarsening rate of ’ and the presence of the Si-stabilized G-phase. Although long time creep-rupture test results have not shown a loss of strength due to these progressive phase transformations, properties such as residual impact strength could be affected.

The specific adjustments that were proposed were to increase Al -Ti ratio slightly to improve the stability of ’, decrease Ti to retard formation of and restrict Si to prevent G-phase. Lab heats demonstrated that these

ideas did provide the desired microstructure stability [10]. This newly optimized chemistry has been designated as INCONEL alloy 740H, Table 1. Figure 1a shows an SEM photomicrograph of conventional 740-composition bar stock exposed in the SA+A condition at 750°C for 4000 hours. Contrast this with Figure 1b that shows material from an alloy 740H heat exposed in the SA+A condition at 750°C for 5000 hours.


(a)

Fig. 1. SEM micrographs a) conventional al

3. Corrosion resistance

Super heater tubing will be required to resisoxidation on the inside. Numerous plant investithe outside is likely to be Type-II hot corrosionscale of the base metal. The steam side corroINCONEL alloy 740 has been characterized fcorrosion mechanisms.

Literature references make it abundantly cleaterm protection against coal-ash corrosion [11]. dense and adherent Cr2O3 can be expected pdiffusion of Cr to the metal/oxide interface. Alneed to be maintained at low levels. The latter films in contact with sulfate and chloride-rich ahas very high rate of attack compared with allostudies of alloy 740 corrosion in a variety of coCr content that protects alloys 740 and 740H agthe presence of high-temperature steam [7, 13].

Fig. 2. Exposure at 700ºC in N2-15% CO2-3.5%O2-0.25%salt consisting of 5% Na2SO4-5% K2SO4-90% (Fe2O3-A

SiO2) [2].

(b)

lloy 740 and b) modified composition similar to 740H. Xie [10].

st fire-side coal ash corrosion attack on the outside andigations confirm that the more relevant corrosion mechann resulting from molten alkali sulfate fluxing of the proosion mechanism is due to water vapor accelerated oxifor its corrosion performance at relevant temperatures t

ar that Cr contents of at least 25% are necessary to achieveIt is at this level of Cr that the rapid and persistent forma

provided the temperature is high enough to ensure adong with this level of Cr, refractory metals such as Mo have been shown to promote breakdown of protective ch

ash deposits. Therefore alloy 617 with 9% Mo and only 2oy 740 that has only 0.5% Mo and 25% Cr, Fig. 2. Indepoal ash conditions have been conducted [12]. The high legainst fuel ash corrosion also makes them resistant to sca

% SO2 Al2O3-

Fig.3. Creep-rupture properties of selected candidate USC bmaterials [14].

steam ism on

otective dation. to both

e long-ation of dequate and W hromia

22% Cr pendent evel of

aling in

oiler


4. Mechanical properties

Initial tests show that alloy 740 was indeed target of 100,000hr creep-rupture strength as illua concerted effort in USA and Europe to gener740 stock. This data was summarized recently rupture tests to more than 30,000 hrs confirm t740H are covered by the ASME Code Case 270

5. Weldability

Although not seen in the work on tube-to-tub(HAZ) micro-fissures are often found in restraiThis was shown to be the case by Sanders et al. made in solution annealed and aged plate usinDevelopment work was therefore done to minlikelihood of micro-fissuring, levels of Nb, Sithermal stability by suppressing phase formatito Ti was increased. A typical HAZ micro-fissuof original composition using matching filler woptimized chemistry of alloy 740H which has shown in Figures 4 and 5 were welded in the swere aged (800°C/4h) after welding. Cross-welrequirements, based upon the recently establisheMPa. In a more recent paper Siefert et al. repo740H including strain age cracking and ductilityfor fabrication in heavy section weldments using

Fig. 4. HAZ fissures in alloy weld in alloy 740.

6. Commercial scale manufacture

One of the major challenges facing successfuis commercial scale manufacture of the large corange from melting, where large ingots are pprocessing to avoid catastrophic cracking to hahot work superalloys at temperatures where tknowledge combined with equipment capabilitipipes from alloys 263 and 617 for the Europeaproduction process, microstructure, tensile, har

stronger than the solid solution alloy 617 and met the pustrated in Fig 3 [14]. Over the past several years there harate long-term data for ASME boiler code approval usingby Santella et al [15] and the work shows that ongoing the previously projected rupture strength. Both alloys 742 [16].

be welds with wall thickness less than 10mm, heat-affecteined welds of nickel-base alloys having a wide freezing on alloy 740 when 75mm thick narrow-groove butt weldng hot-wire GTAW to simulate header pipe fabricationnimize the freezing range in alloy 740, and to minimii and B were optimized [18]. In the interest of maintion, while keeping the desired ’ volume fraction, the ratioure in a 75mm joint made using hot-wire GTAW in a 74

wire is shown in Fig. 4. Figure 5, on the other hand, shono such features. Both plates for which microstructur

solution annealed (1120°C) and aged (800°C/4h) conditiold room-temperature tensile results exceeded ASME Sected minimum tensile strength for ASME code case 2702 oort the results of more comprehensive welding studies ony dip cracking. This study confirms that alloy 740H is sg conventional processes [19].

Fig. 5. No fissures in weld in alloy 740H.

ul implementation of the AUSC technology strategy woromponents in both the boiler and the turbine. These chalprone to segregation, to minimizing residual stresses aving the forging and extrusion presses with the capabilitheir strengths are very high. This unique material andies has already led to the successful production of large n AUSC program by Special Metals and Wyman Gordordness and toughness properties for the 617 pipes have

project as been g alloy creep-

40 and

d-zone range.

ds were n [17]. ize the taining o of Al 0 plate

ows the res are on and tion IX of 1034 n alloy uitable

ldwide llenges during ities to d alloy header

on. The e been


described in detail [8, 20]. The larger of the twoExtrusion of this pipe required the full capacity temperature. This extrusion, while a remarkableextrusion.

Earlier this year, the first large-scale comme740H ingot was VIM melted and VAR remeltedshows a transverse slice (b) showing no evidencoarse ’ with no evidence of .

(a)

Fig. 6. (a) 750mm diameter ingot of alloy 740H, (c) micro shows carb

After upsetting and piercing, the machined pshown in Fig. 7. Initial mechanical property daare presented in Fig. 8 and show good tensile anto operating temperatures of 750oC. Figure 9 s800oC and times between 600hr and 1123hr. Th740 data published by Oak Ridge National Ltemperatures according to the ASME code casealloy 740H’s advantages over 617 for use as a 700oC. Hence a pipe of a given diameter in allohas low refractory element content (2.0% Mo+Nrange above the ’ solvus increases with refracttests have shown that alloy 740 has 17-27% lowtranslates to the ability to extrude a larger pipe show that the largest pipe that can be made on times the steam volume as the largest possible al

Fig.7. As extruded pipe of alloy 740H with dimensions 380mm OD x 89mm Wall x 10m length.

o fabricated pipes measured 378mm OD x 88mm AW x 8of Wyman-Gordon’s 35kt press at the highest feasible ext

e achievement, defines the limiting size for making 617 pi

ercial heat of Alloy 740H was made. A 750mm diameted at the Special Metals Huntington WV plant, Fig. 6., whicce of macro segregation and (c), a micro showing carbid

(b) (c)

, (b) transverse slice showing no evidence of macro segregation and bides and coarse ’ with no evidence of .

preform was extruded to 380mm OD x 89mm Wall x 10 mata on this pipe and superheater tubing also made from thnd yield strengths for both alloys 740 and 740H tube and pshows a Larson Miller plot of Stress Rupture data at 70he alloy 740H data fits closely with the summary curve foLabs [15]. Fig. 10 shows the allowable stresses at die, comparing alloys 740H and 617. The figure clearly illu

header pipe. It has almost twice the allowable stress of oy 740H can have a much thinner wall. At the same timeNb for 740H vs. 9% Mo for 617). Flow stress in the hot wtory element content [21]. Hot-compression and Gleeble wer flow stress at extrusion temperatures. This lower flow

diameter or one with a greater wall thickness. Our calcuthe Wyman-Gordon press from alloy 740 can carry at lelloy 617 pipe.

of Fig. 8. Tensile data for alloy 740H tube and pipe.

0

200

400

600

800

1000

1200

20 650 700 750 800

Temperature, °C

Str

eng

th, M

Pa

0

10

20

30

40

50

60

70

80

Elo

ngat

ion

, %

740H Pipe YS

740H Tube YS

740 Tube YS

740H Pipe UTS

740H Tube UTS

740 Tube UTS

740H Pipe Elong

740H Tube Elong

740 Tube Elong.

.9m L. trusion ipes by

er alloy ch also

des and

m L as his heat pipe up 00oC to or alloy ifferent ustrates 617 at , 740H

working tensile

w stress ulations east 2.2

g.

g.


Fig. 9. Larson Miller plot for stress rupture life of alloy 7700oC to 800.

Finally, Fig. 11 (a) shows the joint configuraGTAW with a narrow groove joint design (5° bewall (79 mm actual) alloy 740H header pipe, wcondition, using 0.9mm diameter matching fillerno indications of fissuring or welds metal dfabricability of alloy 740H in thick sections. Fconducted on this and other similar and dissimil

(a)

Fig. 11. Configuration and fina

7. Summary

INCONEL alloys 740 and 740H meet desiAmerican AUSC power plants. Alloy 740H apiping for temperatures up to and including 76approval has been granted. Boiler tubes have bheader pipe in alloy 740H has also been succeswithout any cracking or fissures. An intensive ef

References

[1] B.A.Baker and G.D.Smith, Corrosion Resistance of APaper 04526, presented at the NACE Annual Confere

[2] INCONEL alloy 740 Bulletin, Special Metals Corpor[3] R.Viswanathan, R.Purgert, U.Rao, Materials for Ultr

Power Engineering 2002, Proceedings Part II. Forsch

100

1000

21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5

Larson-Miller Parameter, C=20, T in °K

Str

ess,

MP

a

740H at Fig. 10. ASME Code allowable stresses for alloys 617 and 7

ation and 11 (b) the finished weld performed utilizing hoevel) to complete a butt joint in 380mm OD x 72 mm min

welded in the solution annealed (1120 °C) and aged (800r wire. Visual examination during the welding process rediscontinuities. This is an important demonstration Further detailed metallographic and mechanical testing war welds of 740H.

(b)

al GTA weld in annealed & aged alloy 740H pipe.

ign property requirements for boiler tubes for Europeaalso meets requirements for use as steam header and tr0oC. Creep-rupture testing exceeds 30,000hrs and ASMEeen successfully manufactured and met property targets.sfully made and initial GTA welds have been made of thffort to characterize the weld and its properties is underwa

Alloy 740 as Superheater Tubing in Coal-Fired Ultra-Supercritical Boilence 2004, New Orleans, LA, March 28-April 1, (2004). ration, Huntington, WV (2004). ra-Supercritical Coal-Fired Power Plant Boilers, Materials for Advancehungszentrum Julich GmbH, (2002)pp.1109-1129.

25.00

50

100

150

200

250

300

600 650 700 750 800 850

Temperature, °C

All

ow

able

Str

ess,

MP

a

N07

N06

Maximum Use temp. = 800°C

40H.

ot-wire nimum

0°C/4h) evealed of the will be

an and ransfer E code Large

he pipe ay.

lers,

ed

900

7740

6617

C.


[4] R.Blum, Preliminary Considerations for the Design of a Pulverized Coal Fired Steam Boiler with Ultra Supercritical Advanced Steam Parameters, Advanced (700°C) PF Power Plant, EC Contract No. SF/1001/97/DK (1997).

[5] R.Vanstone, Advanced 700°C Pulverized Fuel Power Plant, Proc. 5th International Charles Parsons Turbine Conference: Parsons 2000 Advanced Materials For 21st Century Turbine and Power Plants, A.Strang, W.M.Banks, R.D.Conroy, G.M.McColvin, J.C.Neal and S.Simpson, Eds., IOM Communications, Ltd., London, Book 736(2000)pp. 91-97

[6] G.D.Smith and H.W.Sizek, Introduction of an Advanced Superheater Alloy for Coal-Fired Boilers, Paper 00256, presented at the NACE Annual Conference Corrosion 2000, Orlando FL, March 26-31, (2000).

[7] R.J.Smith, B.A.Baker and G.D.Smith, Nickel Alloys for the Next Generation of Advanced Steam Boilers, VGB Materials and Quality Assurance Conference, March 10-11, Dortmund, Germany (2004).

[8] J.de Barbadillo, B.A.Baker, L.Klingensmith and S.J.Patel, Nickel alloy development and use in USC boilers, Symposium on Advanced Power Plant Heat Resistant Alloys, SPERI, Shanghai, (2009).

[9] B.A.Baker and R.D.Gollihue Optimization of INCONEL alloy 740 for advanced ultra-supercritical boilers, 6th Intl Conf on Advances in Materials Technology for Fossil Power Plants, EPRI, Santa Fe NM, (2010).

[10] Xie X, S.Zhao, J.Dong, G.D.Smith and S.J.Patel, A new improvement of INCONEL alloy 740 for USC power plants, Materials Science Forum, Vols. 475-479, (2005), pp 613-618

[11] G.D.Smith, S.J.Patel, N.C.Farr and M.Hoffmann, The Corrosion Resistance of Nickel-Containing Alloys in Coal-Fired Boiler Environments, Paper 55 at the NACE Annual Conference 99, San Antonio, TX, (1999).

[12] M.S.Gagliano, H.Hack and G.Stanko; Fireside corrosion resistance of proposed USC superheater and reheater materials, Proc. of 34th Intl Technical Conf on Clean Coal and Fuel Systems, Coal Technology Assoc., Clearwater, FL, (2009).

[13] J.M.Sarver and J.Tanzosh. An evaluation of the steamside oxidation of USC materials at 650ºC and 800ºC, Advances in Materials Technology for Fossil Plants, Viswanathan ed. ASM International, (2005).

[14] R.Viswanathan, J.P.Shingledecker, J.Hawk and M.Santella; Materials for advanced ultra supercritical fossil plant, ibid. [15] M.Santella, J.Shingledecker and R.Swindeman. Materials for advanced ultra-supercritical steam boilers, 24th Annual Conf on

Fossil Energy Materials, DOE, Pittsburgh, PA, (2010). [16] ASME Code Case 2702, ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, Three Park Avenue,

New York, New York 10016-5990, USA [17] J.M.Sanders, J.Ramirez and B.Baker, Proc of Fifth Intl Conf on Advances in Materials Technology for Fossil Power Plants, EPRI,

DOE and OCDO, Marco Is, FL, (2007). [18] J.M.Sanders, B.A.Baker, J.Siefert and R.D.Gollihue, Proc of 34th Intl Technical Conf on clean Coal and Fuel Systems, Coal

Technology Assoc, Clearwater FL, (2009). [19] J.A.Siefert, J.M.Tanzosh, and J.E.Ramirez, Weldability of INCONEL alloy 740, Proc 6th Intl Conf on Advances in Mat Tech for

Fossil Power Plants; EPRI, Santa Fe, (2010). [20] L.Klingensmith, Process development of heavy-wall large diameter nickel-base alloy piping, ibid. [21] J.de.Barbadillo, Special Metals unpublished data.

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