# US 8,568,901 B2 · Filler metal composition and method for overlaying low NOx power boiler tubes

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- Number: US 8,568,901 B2
- Document ID: US8568901B2
- Status: Granted
- Kind: B2
- Application number: 11/942,252
- Filed: 2007-11-19
- Published: 2008-10-02
- Granted: 2013-10-29
- Earliest claimed: 2006-11-21
- Assignees: Huntington Alloys, Inc.
- Applicants: Samuel D. Kiser; Brian A. Baker
- Inventors: Samuel D. Kiser; Brian A. Baker
- Web page: https://patentgrep.com/patent/US8568901B2

## CPC

- C22C 19/053: {with the maximum Cr content being at least 30% but less than 40%}
- C22C 19/058: {without Mo and W}
- Y10T 428/1266: O, S, or organic compound in metal component
- Y10T 428/12937: Co- or Ni-base component next to Fe-base component
- Y10T 428/12944: Ni-base component
- Y10T 428/13: Hollow or container type article [e.g., tube, vase, etc.]
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An alloy for use as a welding overlay for boiler tubes in a low NOx coal-fired boiler comprising in % by weight: 36 to 43% Cr, 0.2 to 5.0% Fe, 0-2.0% Nb, 0-1% Mo, 0.3 to 1% Ti, 0.5 to 2% Al, 0.005 to 0.05% C, 0.005 to 0.020% (Mg+Ca), 0-1% Mn, 0-0.5% Si, less than 0.01% S, balance substantially Ni and trace additions and impurities. The alloy provides exceptional coal ash corrosion resistance in low partial pressures of oxygen. The alloy also increases in hardness and in thermal conductivity at service temperature over time. The increased hardness improves erosion resistance of the tubes while the increased thermal conductivity improves the thermal efficiency of the boiler and its power generation capabilities.

## Claims

### Claim 1

An alloy suitable for use as a welding overlay for boiler tubes in a low NOx coal-fired boiler comprising in % by weight: 36 to less than 42% Cr, 0.2 to 5.0% Fe, 0.06 to 2.0% Nb, 0-1% Mo, 0.3 to 1% Ti, 0.5 to 2% Al, 0.005 to 0.05% C, 0.005 to 0.020% (Mg+Ca), 0-1% Mn, 0-0.5% Si, less than 0.01% S, balance substantially Ni and trace additions and impurities.

### Claim 2 (depends on 1)

The alloy of claim 1 providing exceptional coal ash corrosion resistance in low partial pressures of oxygen.

### Claim 3 (depends on 1)

The alloy of claim 1 in an after-welded state providing increased thermal conductivity at service temperature over time.

### Claim 4 (depends on 1)

The alloy of claim 1 in an after-welded state providing increased hardness at service temperature over time.

### Claim 5 (depends on 1)

The alloy of claim 1, wherein the alloy comprises in % by weight: 37 to less than 42% Cr, 0.2-4.0% Fe, 0.06-2.0% Nb, 0-1% Mo, 0.3-1.0% Ti, 0.8-1.5% Al, 0.005-0.05% C, 0.1-0.3% Si, 0-0.5% Mn, 0.005-0.020% (Mg+Ca), and balance substantially Ni and incidental impurities.

### Claim 6 (depends on 5)

The alloy of claim 5 nominally containing about 0.02% C, 57% Ni, 37% Cr, 3% Fe, 0.3% Mo, 0.6% Nb, 1% Al, 0.6% Ti, 0.007% (Mg+Ca), 0.06% Mn and 0.08% Si.

### Claim 7

A boiler tube for a coal-fired low NOx boiler having a weld overlay, wherein the overlay is made from an alloy consisting essentially of, in % by weight: 36 to less than 42% Cr, 0.2 to 5.0% Fe, 0.06-2.0% Nb, 0-1% Mo, 0.3 to 1% Ti, 0.5 to 2% Al, 0.005 to 0.05% C, 0.005 to 0.020% (Mg+Ca), 0-1% Mn, 0-0.5% Si, less than 0.01% S, balance substantially Ni and trace additions and impurities.

### Claim 8 (depends on 7)

The boiler tube of claim 7, wherein the weld overlay alloy consists essentially of, in % by weight: 37-41.6% Cr, 0.2-4.0% Fe, 0.6-2.0% Nb, 0-1% Mo, 0.3-1.0% Ti, 0.8-1.5% Al, 0.005-0.05% C, 0.1-0.3% Si, 0-0.5% Mn, 0.005-0.020% (Mg+Ca), and balance substantially Ni and incidental impurities.

### Claim 9

A welding electrode for depositing as a welding overlay for boiler tubes in a low NOx coal-fired boiler comprising in % by weight: 36 to 42% Cr, 0.2 to 5.0% Fe, 0.06 to 2.0% Nb, 0-1% Mo, 0.3 to 1% Ti, 0.5 to 2% Al, 0.005 to 0.05% C, 0.005 to 0.020% (Mg+Ca), 0-1% Mn, 0-0.5% Si, less than 0.01% S, balance substantially Ni and trace additions and impurities.

### Claim 10 (depends on 9)

The welding electrode of claim 9 comprising in % by weight: 37 to less than 42% Cr, 0.2-4.0% Fe, 0.06-2.0% Nb, 0-1% Mo, 0.3-1.0% Ti, 0.8-1.5% Al, 0.005-0.05% C, 0.1-0.3% Si, 0-0.5% Mn, 0.005-0.020% (Mg+Ca), and balance substantially Ni and incidental impurities.

### Claim 11

A method for making a weld overlay boiler tube comprising the steps of:
(a) providing a tube;
(b) providing a weld alloy comprising in % by weight: 36 to less than 42% Cr, 0.2 to 5.0% Fe, 0.06 to 2.0% Nb, 0-1% Mo, 0.3 to 1% Ti, 0.5 to 2% Al, 0.005 to 0.05% C, 0.005 to 0.020% (Mg+Ca), 0-1% Mn, 0-0.5% Si, less than 0.01% S, balance substantially Ni and trace additions and impurities;
(c) applying the weld alloy to the surface of the tube by welding to provide an overlaid tube; and
(d) bending the overlaid tube to a desired configuration suitable for installation in the boiler.