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IntroductionIntroductionSuperheaters and Reheaters
– Corrosion and Erosion Problems– Benefits of Chromium in Ni-Base Materials– Filler Metal 72: High Chromium and Weldable– Corrosion Examples– Application Successes
Corrosion Test Simulating Low-NOx Corrosion Test Simulating Low-NOx Corrosion ConditionsCorrosion Conditions
• The test environment consisted of the following gas mixtures at 1000°F:– Reducing Cycle: N2-16%CO2-10%H2O-5%CO-2%H2S
(flow rate 500 sccm).
– Oxidizing Cycle: N2-17.2%CO2-10.75%H2O (CO and H2S turned off).
Corrosion Test Simulating Low-NOx Corrosion Test Simulating Low-NOx Corrosion ConditionsCorrosion Conditions
• The test consisted of alternating cycles consisting of 4 days reducing and 3 days oxidizing.
• The test was conducted in a horizontal electrically heated muffle furnace having a 100mm diameter mullite tube with sealed end caps and a sealed pushrod mechanism for inserting and removing samples to and from the hot zone.
• Samples were cycled to room temperature and weighed at 500h, 1000h, 3000h and 4940h.
Inlet and Calculated Equilibrium Outlet Compositions for Inlet and Calculated Equilibrium Outlet Compositions for Laboratory Simulation of Low-NOx Boiler Environment at Laboratory Simulation of Low-NOx Boiler Environment at
1000°F1000°F
Inlet Outlet Inlet Outlet
N2 67 67.2 72 72
CO2 16 19.4 17.2 17.2
H2O 10 6.8 10.75 10.75
CO 5 1.45H2S 2 1.97
SO2
H2 3
pS2 2.07E-08pO2 1.64E-28 3.10E-10
Oxidizing-Sulfidizing Oxidizing
Corrosion Test Simulating Low-NOx Corrosion Test Simulating Low-NOx Corrosion ConditionsCorrosion Conditions
• Wrought samples for alloy 625 were produced from cold-rolled and annealed sheet. The machined test samples measured ~3mm X 10mm X 20mm.
• Wrought samples of alloys 622 and filler metal 72 were produced from hot-rolled and solution annealed wire rod; machined test samples measured ~6mm diameter X 20mm.
• Weld overlay samples of filler metals 53MD and 72 were fabricated by first applying two layers of overlay onto carbon steel using the p-GMAW process followed by removal of the top layer and machining samples. The machined test sample size was ~3mm X 10mm X 20mm.
Mass change results after exposure at 1000°F (538°C) Under the Described Simulated Low-NOx Test Conditions
1
10
100
100 1000 10000
Exposure Time, Hours
Mas
s C
han
ge,
mg
/cm
2
Wrought 625
Wrought 622
Wrought FM72(ERNiCr-4)
FM72 Overlay(ERNiCr-4)
FM 53MD Overlay(ERNiCrFeAl-1)
Reducing to Neutral AtmosphereReducing to Neutral Atmosphere
Low Grade Coals
Sulfates
H2S
Cross Section of Superheater tube .250 inches per year
wastage. (Save 25) Actual Tube Cut out - Facing Gas Flow
Cross Section of Superheater Tubes from Cross Section of Superheater Tubes from DOE – McDonald StudyDOE – McDonald Study
Numbering of Specimens Within Test Loop Exposed in a Subcritical Coal Fired Boiler
Firing 3-3.5% Sulfur Ohio Coal
Identification key for INCONEL weld Identification key for INCONEL weld overlays and alloysoverlays and alloys
Name Material %Cr Method of Sample Preparation52WO FM 52 30 WSI weld overlay over 800HT72WO FM 72 43 WSI weld overlay over 800HT671 Clad 671 46 Co-extruded over 800HTThermie 740 25 Solid tubular alloy
Wastage as a Function of Time for Superheater tube Materials
Metal Loss As a Function of Position in Test Loop Exposed for 21,200 Hours in Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal - Results Reported by
McDonald
0
1
2
3
4
5
6
7
540 560 580 600 620 640 660
Exposure Temperature, °C
Meta
l L
oss, m
m/y
r
Save 25
800 Mod
347 HFG
Fe3Al
NF 709
310 Ta
310 HCbN
HR-120
FM52 WO
740-5
FM72 WO
671 Clad
Wastage rate of samples exposed to 560-650°C for Wastage rate of samples exposed to 560-650°C for 21,200 Hours21,200 Hours
0
1
2
3
4
5
6
7
Save 2
5
740-5
FM
52 W
O
FM
72 W
O
671 C
lad
347 H
FG
NF
709
HR
120
310 H
CbN
Save 2
5
800 M
od
310 T
a
310 H
CbN
HR
120
671 C
lad
347 H
FG
Fe3A
l
NF
709
Save 2
5
800 M
od
310 T
a
310 H
CbN
740-5
347 H
FG
NF
709
Save 2
5
800 M
od
310 T
a
310 H
CbN
HR
120
671 C
lad
FM
72 W
O
FM
52 W
O
Me
tal L
os
s, (
mm
/yr)
650°C 565°C
Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - AusteniticsGas Corrosion Upon Temperature - Austenitics
0
20
40
60
80
100
120
140
160
550 750
Temperature, °C
Weig
ht
Lo
ss, m
g/c
m2/1
00 h
ou
rs
304H
310
800H
617
671
Gas composition = 1%SO2-5% O2-15%CO2-Bal. N2 Synthetic ash = 34%Na2SO441%K2SO4-25%Fe2O3
Reference: M. Tamura, N. Yamanouchi, M Tanimura, S. Murase, "Promising Alloys for theHeat Exchangers of Advanced Coal Fired Boilers," Proceedings : Exposition and Symposium on Industrial Heat Exchanger Technology (Materials Park, Ohio: ASM International 1985), p. 273.
Dependence of Corrosion Behavior in Synthetic Coal Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - FerriticsAsh/flue Gas Corrosion Upon Temperature - Ferritics
Reference: H. Teranishi, et al, presented at the International Conference on HighTemperature Alloys, Preprint Paper No. 21, Petten, The Netherlands, Oct 15-17, 1985.
Chromium content vs. wastage rateChromium content vs. wastage rate
Cross Section Loss (Depth of Attack) for High Temperature Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (1% SOAlloys Exposed at 700°C in Laboratory Flue Gases (1% SO22) )
1
10
100
1000
10000
0 10 20 30 40 50% Cr
Av
era
ge
T
hic
kn
es
s L
os
s
(Mic
ron
s/1
00
0 H
ou
rs)
Blough andStankoCastello, et al
Current Work
Blough and Stanko: N2-14%CO2-10%H2O-3.6%O2-1%SO2, 10% alkali sulfatesCastello, et al: N2-15%CO2-3.5%O2 -1%SO2, 10% alkali sulfatesBaker and Smith: N2-15%CO2-4%O2 -1%SO2, 5% alkali sulfates
Baker and Smith
Cross Section Loss (Depth of Attack) for High Temperature Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (0.25% SOAlloys Exposed at 700°C in Laboratory Flue Gases (0.25% SO22))
1
10
100
1000
0 10 20 30 40 50
% Cr
Ave
rage
Thi
ckne
ss L
oss
(Mic
rons
/100
0 H
ours
)
Blough andStankoCastello, et al
Current Work
Blough and Stanko: N2-14%CO2-10%H2O-3.6%O2-0.25%SO2, , 10% alkali sulfates
Castello, et al.: N2-15%CO2-3.5%O2 -0.25%SO2, 10% alkali sulfates
Baker and Smith: N2-15%CO2-3.5%O2 -0.25%SO2, 10% alkali sulfates
Baker and Smith
Chromium + Nickel Content Versus Metal LossChromium + Nickel Content Versus Metal LossNi Cr Fe Ni+Cr
671 Clad 51.5 48 - 99.5FM72 Weld Overlay 51 41 7 99FM52 Weld Overlay 58.3 30 88.3
Sulfidation-Oxidation at 816°CSulfidation-Oxidation at 816°C
H2 - 45% CO2 - 1% H2S at 816°C
-60
-50
-40
-30
-20
-10
0
10
20
100 1000 10000
Exposure Time, h
Ma
ss
Ch
an
ge
, m
g/c
m2 188
740
671
FM72
690
FILLER METAL 72FILLER METAL 72 FILLER METAL 72
Minimum Tensile Strength: 106,000 psi
Yield Strength (0.2% offset): 73,000 psi
Elongation 30%
AWS A5.14, ERNiCr-4
ASME IX, F-No. 43
ASME II, SFA-5.14, ERNiCr-4
ISO S.Ni6072
Europe NiCr44TiUNS N06072
Available for GMAW or GTAW welding.
FILLER METAL 72FILLER METAL 72
Super heater tube removed after in service testing.
Reheater tuber overlaid with Filler Metal 72 after 2+ years of service at 1000 –
1100oF after simulated repair weld and LP inspection
FILLER METAL 72 Hardness Profile after 2+ FILLER METAL 72 Hardness Profile after 2+ Years at 1000°F-1100°FYears at 1000°F-1100°F
Filler Metal 72 Overlay Hardness Values
0
100
200
300
400
500
600
1 2 3 4 5 6 7 8 9 10 11 12
Hardness Locations
Har
dnes
s V
alue
(H
v)
72 O.D 72/Steel
Corrosion – 209 mpy- Corrosion – 209 mpy- ((Save 25)Save 25)
Protection - 671Protection - 671
Protection from CorrosionProtection from Corrosion
Protection – Filler Metal 72Protection – Filler Metal 72
- 2 year installed
Protection – Protection – Filler Metal 72Filler Metal 72
Wastage – less than 10 mpy
Filler Metal 72Filler Metal 72 Surface Description Surface Description
Area Description Visual Appearance Ni Cr Fe Ti Al Si C O K Na As P S
1 Bulk deposit analysis Rust red deposit with spherical particles.
0.4 11.57 0.39 7.78 13.7 20.7 35.6 1.73 0.63 4.37 1.03 1.07
2 Deposit / scale analysis 0.5 4.7 4.79 16 22.9 36.3 12.5 1.91 0.37
3 Tightly adhering scale. Near interface 0.76 50.7 5.45 0.67 0.51 0.22 39.6 1.47 0.65
4 Scale in grain boundary Near interface 52.5 21.5 2.8 7.43 0.99 5.57 7.17 2.03
5 Scale in grain boundary Near interface 40.3 20.3 1.71 0.75 5.3 6.81 24.3 0.51
6 Partially consumed metal Within interface zone 56.9 20 3.78 0.64 5.7 12.4 0.61
7 Base metal near interface. Near interface 50.5 46.5 1.8 1.21
8 Inclusion and corrosion product at grain boundary
.Near interface 48.1 41.8 1.45 3.02 2.12 3.45
9 Partially consumed metal Within interface zone 53.4 19.8 3.53 0.68 1.14 4.78 15.8 0.83
Bulk overlay analysis Normal etched appearance 52 44.4 2.37 0.73 0.58
Reference bulk analysis 54.8 41.8 1.85 0.59 0.24 0.19 0.03 0.019
Sample Reheater Tube Removed from Low Nox BoilerSample Reheater Tube Removed from Low Nox BoilerActual Service – 6 yearsActual Service – 6 years
Field SuccessField SuccessPhiladelphia Electric Company - 671 Clad Reheater Tubes
– 9 years of service– 1100o F (595o C)– Ave. 2.44% sulfur content– Ave. 10.8% ash content– 671 unaffected by corrosion
Field SuccessField SuccessThe Outlet Leg of a Secondary Superheater.
– 5 ½ years of service– 1000ºF (538°C) Steam – Cyclone coal fired 4.5-5% sulfur, 20% ash– No visible evidence of corrosion
Field SuccessField SuccessThe UK Central Electricity Generating Board
– 1974 – 1980 trouble free service– Testing led to full replacement of reheater tube– Stainless tubes had corroded at 3.5 mm/year
Field SuccessField Success
Large Mid-West Power Provider– Met 20 year design life– Installed Muskingum River OH and
Kammer, W.V.
Field SuccessField Success
Fuel-Ash Corrosion-Resistance in Power Plant Steam Superheaters. – Operating temperature 1055ºF– 32 months and 66 months– High sulfur pulverized coal– 671 Cladding remained uniform and
showed minimal corrosion
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
Filler Metal 72 Overlay on Superheater Tubes
Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in AEP
Rockport Unit I, Spring of 1999.
Unifuse 360 overlay job using Spiral GMAW Followed by a GTAW pass welding process to
deposit a corrosion resistant weld overlay usingAlloy 72 filler metal
- 2200 Tubes were manufactured for use as Reheater Tubing in a coal-fired supercritical boiler
- Base material was SA 213 Tp 304H 2.5” OD x 0.165” mwt.
- Overlay thickness average is 0.070”
- Typical Chemical Analysis:
Ni 52.5%Cr 41.0%Fe 6.0%Ti 0.5%
TESTING and RESULTS
- Longitudinal and transverse cross-sections were cut from 5% of production (approximately 110 tubes)
- Liquid Penetrant, X-Ray Flouresence and thickness measurements were made on the 5% samples and randomly on the balance of the production
- None of the tests conducted revealed the presence of cracking or any major welding discontinuities. Additional to our test plan the customer performed extensive macrographic work on each of the sectioned samples (110 samples) with no evidence of defects when examined at 5X magnification.
SummarySummary
Superheaters and Reheaters- Aggressive Corrosion/Erosion Conditions.
- High Chromium Content Required to Resist Molten Sulfate
Corrosion.
- Enhancement in Strength and Hardness Resulting from
Exposure may Serve to Enhance Erosion Resistance.
- Filler Metal 72 Weld Overlay Proven in the Laboratory and in
the Field to Possess Superior Corrosion Resistance.
- Long-Term Experience with 671 Clad Tubes Reinforces
Confidence in Filler Metal 72.
Thank you for your attention.Thank you for your attention.