Introduction Superheaters and Reheaters –Corrosion and Erosion Problems –Benefits of Chromium in...

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).


• 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


• 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


Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.


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.

Introduction Superheaters and Reheaters –Corrosion and Erosion Problems –Benefits of Chromium in...

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