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RESEARCH PAPERS

10-Year Experience With T23(2.25Cr-1.6W) and T122(12Cr-0.4Mo-2W) in a Power Boiler

[+] Author and Article Information
N. Komai

 Nagasaki R&D Center, Mitsubishi Heavy Industries, Ltd.

F. Masuyama

Graduate School, Kyushu Institute of Technology

M. Igarashi

 Corporate R&D Laboratories, Sumitomo Metal Industries, Ltd

J. Pressure Vessel Technol 127(2), 190-196 (Dec 08, 2004) (7 pages) doi:10.1115/1.1904052 History: Received September 28, 2004; Revised December 08, 2004

Tungsten strengthened ferritic steels, 2.25Cr-1.6W-V-Nb and 12Cr-0.4Mo-2W-V-Nb-Cu have been developed and approved by the ASME Boiler and Pressure Vessels Code Committee for use in Section I construction, designated as T23 and T122, respectively. A field exposure test installing both steel tubes in service along with comparative materials in the tertiary superheater and secondary reheater of a 156MW utility power boiler has been conducted since April 1993. The tubes were removed to confirm their material properties and corrosion/steam oxidation behaviors after 1-year, 3-year, 6-year, and 10-year periods of service. The tensile and creep rupture strengths of both steels showed no remarkable change during service. Examination of steam oxidation scale on the inner surface of the tubes indicated that the scale growth rate of T122 was extremely small following 1-year service. The growth rate and morphology of steam oxidation scale is discussed, as compared with conventional materials.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Installed locations of T23 and T122 tubes

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Figure 2

Tensile properties of T23 used at tertiary superheater

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Figure 3

Tensile properties of T122 used at tertiary superheater and secondary reheater

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Figure 4

Changes in Charpy impact value at 0°C with service duration

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Figure 5

Creep rupture strength of T23 base metal and weldment after 10-year(79,102h) service

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Figure 6

Creep rupture strength of T122 base metal after 10-year(79,102h) service

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Figure 7

Hardness distribution of T23 (3SH) and T122 (2RH) weldments

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Figure 8

Optical microstructures of T23 and T122 at fire side after 10-year(79,102h) service

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Figure 9

Carbon extracted replica microstructures of T23 and T122 used at tertiary superheater after 10-year(79,102h) service

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Figure 10

Inside apperance of tubes after 10-year(79,102h) service

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Figure 11

Cross-sectional microstructure of steam oxidation scale at fire side after 10-year(79,102h) service

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Figure 12

Changes of x-ray intensity from base metal to scale analyzed by EPMA

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Figure 13

Cross-sectional microstructure of scale exfoliated and unexfoliated part

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Figure 14

EPMA analysis results of T122 scale near the scale exfoliated part

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Figure 15

Changes in steam oxidation scale thickness at fire side

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Figure 16

Relationship between steam oxidation scale thickness and serviced time

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Figure 17

Calculated Kp comparing with the data of EPRI

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