Fabrication, Construction, and Operation Problems for Grade 91 Fossil Power Components

[+] Author and Article Information
Marvin J. Cohn

 Aptech Engineering Services, Inc., Sunnyvale, CA 94089

Jeffrey F. Henry

 Alstom Power Inc., Chattanooga, TN 37402

Dan Nass

 Arizona Public Service Company, Phoenix, AZ 85004

J. Pressure Vessel Technol 127(2), 197-203 (Nov 22, 2004) (7 pages) doi:10.1115/1.1904054 History: Received November 03, 2004; Revised November 22, 2004

The use of creep strength enhanced ferritic alloys, such as Grade 91, in fossil power plants has become popular for high temperature applications. Since Grade 91 has higher stress allowables than Grade 22, a designer can specify thinner component wall thicknesses, resulting in lower throughwall thermal stresses during transient events and lower material and pipe support costs. During the past two decades, Grade 91 has been used successfully in fossil power plants. However, this alloy has had some incidents of premature failures. Case histories discuss such factors as excessively hard material, extremely soft material, overheating failures, and improper mill processing. This compilation also discusses likely root causes and solutions to avoid these potential Grade 91 problems.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Main steam pipe-wall thickness requirements for Grades P11, P22, and P91

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Figure 2

Hot reheat pipe-wall thickness requirements for Grades P11, P22, and P91

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Figure 3

Log t versus T for Q&T 2-1∕4Cr-1Mo Steel Plates at 78MPa

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Figure 4

Accelerated life consumption for +10°C of 2-1∕4Cr-1Mo steel

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Figure 5

Accelerated life consumption for +10°C of 9Cr-1Mo-V-Nb steel

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Figure 6

Creep or creep∕fatigue failures of superheat outlet tube

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Figure 7

Short-term overheating of finned HRSG tube

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Figure 8

Isometric of main steam piping system

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Figure 9

Creep rupture of F91 wye block to F91 transition spool weldment



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