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Development of Materials & Manufacturing Technologies for Advanced Ultra Super Critical

Power Plants

Alok Mathur*, T.Jayakumar, A.K.Bhaduri and S.C.Chetal@

*BHEL, New Delhi IGCAR, Kalpakkam

@Former Director, IGCAR

Materials for Indian AUSC Boilers Selection Criteria

Inclusion in ASME Code / Code Case or equivalent International code Adequate high temperature mechanical strength • Average stress to rupture of 100 MPa for 100,000

hours at design temperature of component High thermal conductivity & Low thermal expansion coefficient to minimize thermal stresses Good Formability & Weldability Satisfactory corrosion resistance in steam & flue gas Adequate resistance to creep-fatigue interaction Industrial availability & feasibility of indigenous development

Materials Selected Grade-23 steel (2.25Cr-1.6W-V-Nb-B; ASME CC 2199) for Water-walls tubing Grade-92 steel (9Cr-2W-V-Nb-N-B; ASME CC 2179) for Superheater & Reheater tubing 304HCu SS (18Cr-9Ni-3Cu-Nb-N; ASME CC 2328 / VdTÜV 550) for Final stage of Superheater tubing Alloy 617M (52Ni-22Cr-13Co-9Mo; ASME SB-167 / VdTÜV 485) for Final stage of Superheater & Reheater tubing at hottest zone • With controlled composition &

Stringent limit on C, B, Cr, Ti, Fe, Si, Mn

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Objectives of Materials Development for Boilers Manufacture of Seamless tubes (with MIDHANI & NFC Hyderabad)

304HCu SS (52 mm OD x 9.5 mm wall thickness) Alloy 617M (52 mm OD x 11.9 mm wall thickness) • Optimization of process flow-sheet based on

Thermo-physical properties Thermo-mechanical processing map Microstructural evaluation

Manufacture of ER617 & ER304HCu welding filler wires (with MIDHANI Hyderabad) Development of welding procedures & Qualification of weld joints for

304HCu SS tubes welded using ER625, ER617 & ER304HCu filler wires Alloy 617M tubes welded using ER617 filler wires 304HCu SS to Alloy 617M dissimilar tubes welded using ER617 filler wires

Testing, Evaluation & Qualification of these tube materials & their weld joints Tensile & Creep Low-Cycle Fatigue & Creep-Fatigue Interaction Impact, Quasi-static fracture, Creep Crack Growth, Fatigue Crack Growth Ageing induced degradation

304HCu SS (UNS S30432) 18Cr-9Ni-3Cu-Nb-N Seamless Tubes

OD = 52 mm WT = 9.5 mm

Solution annealing temperature 1100–1150 ºC

Grain size ASTM grain size no. 4–6

ASME SA-213 & SA-1016 Flattening Test Flaring Test Hydrostatic Test

Non Destructive Examination Surface by Liquid Penetrant inspection Ultrasonic (ASME SE-213)

Tolerance (ASME SA 213) Surface Condition:

Pickled & Passivated

Element, wt% Indian AUSC ASME

Carbon 0.07-0.13 0.07-0.13 Manganese 1.00 max. 1.00 max. Phosphorous 0.030 max. 0.040 max. Sulphur 0.010 max. 0.010 max. Silicon 0.30 max. 0.30 max. Nickel 8.00-10.00 7.50-10.50 Chromium 17.00-19.00 17.00-19.00 Copper 2.50-3.50 2.50-3.50 Niobium 0.30-0.60 0.30-0.60 Nitrogen 0.07-0.12 0.05-0.12 Aluminium 0.003-0.030 0.003-0.030 Boron 0.002-0.006 0.001-0.010 Properties Min. / Max. (Room Temp.) Yield strength 235 MPa (min.) U.T.S. 590 MPa (min.) Elongation 35 % (min.) Hardness 219 BHN / 230 VHN (max.)

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304HCu SS: Optimisation of Processing and Heat Treatment Schedules

Metallurgical Features Strengthening through sub-micron Nb(CN) & nano-metric Cu precipitates Avoid coarse M23C6 precipitates Undissolved Nb(CN) limits grain growth

304HCu Stainless steel

Process Flow-sheet for 304HCu SS Tubes

Processing Map for 304HCu SS

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Characterisation of 304HCu SS Tubes Tensile Properties

UTS: 648 MPa [Spec. ≥ 590 MPa] YS: 299 MPa [Spec. ≥ 235 MPa] %E: 46 % [Spec. ≥ 35%]

Hardness 150 VHN [Spec. ≤ 230 VHN]

Ultrasonic Test – Passed Notch depth: 3% WT

Flattening & Flaring Tests – Passed Microstructure

Homogeneity achieved Grain Size: ASTM No. 4-5 Texture: Random Nb-rich precipitates: • Size: 0.5-1.5 μm • Morphology: Globular • Vol. fraction: 0.3

Tensile & Creep Properties of 304HCu SS

650 ºC

Strain–Life plot

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Charpy Impact Energy for 304HCu SS

Ageing Specimen size (mm)

Notch Orientation

Charpy Energy (Joules) Measured Full-Size Eqv.

Unaged 5 × 5 × 55

(notch: 1mm)

Type-A (circumferential) 33 ± 1 272 ± 6

Type-B (radial) 34 ± 1 276 ± 4 700°C / 1000 h

Type-A (circumferential) 21 ± 0 168 ± 2

Type-B (radial) 22 ± 3 175.5 ± 4.5 Charpy energy of sub-size specimens converted to full-size equivalent using empirical formula: Cv (full-size) = K*Cv (sub), with K=8

Alloy 617M (UNS N06617) 52Ni-22Cr-13Co-9Mo

Seamless Tubes OD = 52 mm WT = 11.9 mm

Vacuum Induction Melted + Vacuum Arc Refined (VAR) Solution annealing temperature

1140-1200 ºC Grain size (ASTM E112)

ASTM 4 – 6 Hydrostatic Test (ASME SB-167) Non Destructive Examination

Surface by Liquid Penetrant Inspection Ultrasonic (ASME SE-213)

Tolerance (ASTM B 829-04a)

Element (wt%) Adv USC(617M) ASME (617) Chromium 21.0-23.0 20.0-24.0 Iron 1.5 max. 3.0 max Manganese 0.3 max. 1.0 max Molybdenum 8.0-10.0 8.0-10.0 Cobalt 11.0-13.0 10.0-15.0 Aluminium 0.8-1.3 0.8-1.5 Carbon 0.05-0.08 0.05-0.15 Copper 0.5 max. 0.5 max Boron 0.002-0.005 0.006 max Silicon 0.3 max. 1.0 max Sulphur 0.008 max. 0.015 max Titanium 0.3-0.5 0.6 max Nitrogen 0.05 max. – Nickel Balance 44.5 min. Nb & V For record – Properties Min. (Room Temperature) Yield strength 240 MPa U.T.S. 665 MPa Elongation 35 %

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Alloy 617M: Optimisation of process flow-sheet and Heat Treatment Schedule

Optimisation of the flow-sheet • Grain size • Uniformity of grain size -

Avoid bimodal distribution • Precipitate size & distribution

Dissolve / reduce size of Cr- & Mo- rich precipitates Dissolve intergranular carbides

Optimisation of solution annealing temperature after

Forging Extrusion First stage pilgering Final pilgering

Process Flow-sheet for Alloy 617M Tubes

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Tensile, Creep Fatigue and Impact Properties of Alloy 617M

Strain–Life plot Ageing Specimen size (mm)

Notch Orientation

Charpy Energy (Joules)

Unaged

10 × 10 × 55 (notch: 2 mm)

Type-A (circumferential) 327.5 ± 0.5

Type-B (radial) 269.5 ± 4.5

750°C / 1000 h

Type-A (circumferential) 133.0 ± 3.0

Type-B (radial) 121.5 ± 1.5

Development of Welding Procedure TIG welding process employed for

Weld Procedure Specifications (WPS) Weld Procedure Qualification (WPQ) Record Production weld-joints for metallurgical characterisation & evaluation of mechanical properties

Filler wires used 304HCu SS tube joints • ER304HCu • ER625 (AWS ERNiCrMo-3) • ER617 (AWS ERNiCrCoMo-1)

Alloy 617M / Alloy 617M similar joints and 304HCu SS / Alloy 617M dissimilar joints

• ER617 (AWS ERNiCrCoMo-1)

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Joint No. Tube Material Filler Material Radio

graphy Bend Tests YS

(MPa) UTS

(MPa) Failure

Location Root Face 304HCu SS Tube – – – 311 635 –

1 304HCu SS ER625 (Imported) Passed Passed Passed 479 688 Base metal 2 304HCu SS ER617M Passed Passed Passed 436 762 Base metal 3 304HCu SS ER304HCu Passed Passed Passed 435 670 Weld metal

Alloy 617M Tube – – – 420 850 – 4 Alloy 617M ER617M Passed Passed Passed 418 747 BM / WM

5 Alloy 617M/ 304H Cu SS ER617M Passed Passed Passed 455 706 Base metal

304HCu SS Joint with ER625 filler wire

Root Bend

Face Bend

Welding Procedure Qualification

Creep Properties for 304HCu SS Base Metal & Weld Joint (ER625)

Base Metal

650°C/200 MPa/1250 h

Weld Joint

650°C/200 MPa/610 h

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Conclusion Development of process route for production of 304HCu SS and Alloy 617M boiler tubes

Development of filler wires for welding

Evaluation of mechanical properties of base metal and weld joints