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RESEARCH PAPERS

# Time-Dependent Fracture and Defect Assessment of Welded Structures at High Temperature

[+] Author and Article Information
Fu-Zhen Xuan1

School of Mechanical Engineering, East China University of Science and Technology, Mail Box 402, 130 Meilong Street, Shanghai 200237, P.R.C.fzxuan@ecust.edu.cn

Shan-Tung Tu, Zhengdong Wang

School of Mechanical Engineering, East China University of Science and Technology, Mail Box 402, 130 Meilong Street, Shanghai 200237, P.R.C.

1

Corresponding author.

J. Pressure Vessel Technol 128(4), 556-565 (Nov 30, 2005) (10 pages) doi:10.1115/1.2349567 History: Received January 03, 2005; Accepted November 30, 2005

## Abstract

The present work reports several new insights into creep crack growth performance and defect assessment of welded structures at elevated temperature. First of all, an equivalent homogeneous model based on the limit load analysis is proposed to reflect the mismatch effects of the base and weld metals, the geometrical dimension of weldment constituents and the location of the pre-existing defects. Secondly, using the proposed equivalent homogeneous model, an estimation methodology for the time-dependent fracture mechanics parameter $C*$ is developed in conjunction with the reference stress (RS) method and the GE/EPRI scheme. Such an estimation method was validated by using nonlinear finite element analysis of 48 compact tension (CT) specimens with various degrees of mismatch in creep behavior and different width of the welding seam. After that, the applicability of $C*$ measurement recommended in ASTM E 1457 is re-examined for the CT specimen with a mismatched cross-weld. From the limit load analysis, a series of modifications for experimental $C*$ estimation equation from ASTM E 1457 is introduced based on the proposed equivalent homogeneous model. Finally, a failure assessment diagram (FAD)-based method is presented for the welded structures at high temperatures. The application of such an approach to a welded cylinder with an internal circumference crack under axial tension is also reported in this paper.

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## Figures

Figure 1

The cracked mismatched idealized bimaterial weld joints and fictitious equivalent material model

Figure 2

Finite element models for CT specimens with a mismatched cross-weld

Figure 3

The comparison between the estimated C* and that of FEM results

Figure 4

Comparison of the predicted ηw factor and the FE solutions for CT specimens with different weld widths

Figure 5

Comparison of the predicted ηw factor and the FE solutions for CT specimens with weld width W∕h=10 and different mismatch ratios

Figure 6

Comparison of the predicted ηw factor and the FE solutions for CT specimens with weld width W∕h=10 and different crack locations in weld line

Figure 7

Thin-walled cylinder with fully circumferential crack in the weld center under tension

Figure 8

Comparison of TDFADs for cylinder with different cracks in the weld center and for the cylinder made of homogeneous metals (t=1000h)

Figure 9

Variation of TDFAD with service time for the cylinder with a∕T=0.5, 2h=0.5T (for M<1, base metal: Mt1 and weld metal: Mt3)

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