2. Introduction Superheaters and Reheaters Corrosion and Erosion Problems
Benefits of Chromium in Ni-Base Materials
Filler Metal 72: High Chromium and Weldable
Corrosion Examples
Application Successes
This is what will we cover in this presentation.

3. Corrosion Test Simulating Low-NOx Corrosion 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%CO %H2O (CO and H2S turned off).

4. Corrosion Test Simulating Low-NOx Corrosion 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.

5. Inlet and Calculated Equilibrium Outlet Compositions for Laboratory Simulation of Low-NOx Boiler Environment at 1000°F

6. Corrosion Test Simulating Low-NOx Corrosion 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.

7. Mass change results after exposure at 1000°F (538°C) Under the Described Simulated Low-NOx Test Conditions

8. Reducing to Neutral Atmosphere
Low Grade Coals
Sulfates
H2S
Thes were taken from the same tube from the DOE-McDonald study. Overlay was done with Save25. We’re not picking on Save 25, they were just a great example of poor performance.
Cross Section of Superheater tube .250 inches per year wastage. (Save 25)
Actual Tube Cut out - Facing Gas Flow

9. Cross Section of Superheater Tubes from DOE – McDonald Study

10. Numbering of Specimens Within Test Loop Exposed in a Subcritical Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal

11. Identification key for INCONEL weld overlays and alloys

12. Wastage as a Function of Time for Superheater tube Materials

13. 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

14. Wastage rate of samples exposed to 560-650°C for 21,200 Hours

15. Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - Austenitics
Reference: M. Tamura, N. Yamanouchi, M Tanimura, S. Murase, "Promising Alloys for the
Heat Exchangers of Advanced Coal Fired Boilers," Proceedings : Exposition and Symposium on Industrial Heat Exchanger Technology (Materials Park, Ohio: ASM International 1985), p. 273.
Gas composition = 1%SO2-5% O2-15%CO2-Bal. N2
Synthetic ash = 34%Na2SO441%K2SO4-25%Fe2O3

16. Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - Ferritics
Reference: H. Teranishi, et al, presented at the International Conference on High
Temperature Alloys, Preprint Paper No. 21, Petten, The Netherlands, Oct 15-17,

17. Chromium content vs. wastage rate

18. Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (1% SO2)
Baker and Smith
Blough and Stanko: N2-14%CO2-10%H2O-3.6%O2-1%SO2, 10% alkali sulfates
Castello, et al: N2-15%CO2-3.5%O2 -1%SO2, 10% alkali sulfates
Baker and Smith: N2-15%CO2-4%O2 -1%SO2, 5% alkali sulfates

19. Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (0.25% SO2)
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%O %SO2, 10% alkali sulfates
Baker and Smith: N2-15%CO2-3.5%O %SO2, 10% alkali sulfates
Baker and Smith

20. Chromium + Nickel Content Versus Metal Loss

21. Sulfidation-Oxidation at 816°C

22. FILLER METAL 72 FILLER METAL 72 Minimum Tensile Strength: 106,000 psi
Yield Strength (0.2% offset): ,000 psi
Elongation %
AWS A5.14, ERNiCr-4
ASME IX, F-No. 43
ASME II, SFA-5.14, ERNiCr-4
ISO S.Ni6072
Europe NiCr44Ti
UNS N06072
Available for GMAW or GTAW welding.

23. FILLER 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

24. FILLER METAL 72 Hardness Profile after 2+ Years at 1000°F-1100°F

25. Corrosion – 209 mpy- (Save 25)

26. Protection - 671

27. Protection from Corrosion

28. Protection – Filler Metal 72
- 2 year installed

29. Protection – Filler Metal 72
Wastage – less than 10 mpy

30. Filler Metal 72 Surface Description

31. Sample Reheater Tube Removed from Low Nox Boiler Actual Service – 6 years

32. Field Success Philadelphia 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

33. Field Success The 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

34. Field Success 1974 – 1980 trouble free service
The 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

35. Field Success Large Mid-West Power Provider Met 20 year design life
Installed Muskingum River OH and Kammer, W.V.

36. Field 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

37. Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.

38. Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.

39. Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.

40. Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213-T2 Superheater tubes installed in AEP Rockport Unit I, Spring of 1999.

41. Unifuse 360 overlay job using Spiral GMAW
Followed by a GTAW pass welding process to
deposit a corrosion resistant weld overlay using
Alloy 72 filler metal
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%

42. 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.

47. Summary 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.

48. Thank you for your attention.