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Research Papers: Materials and Fabrication

# Evaluation of Creep Crack Growth Rate of P92 Welds Using Fracture Mechanics Parameters

[+] Author and Article Information
Masataka Yatomi, Akio Fuji

IHI Corporation, 1 Shinnakahara-cho, Isogo-ku, Yokohama 235-8501, Japan

Masaaki Tabuchi

National Institute of Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan

Yasushi Hasegawa

Nippon Steel Corporation, 20-1 Shintomi, Huttsu 293-8511, Japan

Ken-ichi I. Kobayashi

Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Toshimitsu Yokobori

Tohoku University, 6-6-1 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

Takeo Yokobori

Teikyo University, 1-1 Toyosatodai, Utsunomiya 320-0003, Japan

J. Pressure Vessel Technol 132(4), 041404 (Jul 23, 2010) (8 pages) doi:10.1115/1.4001522 History: Received June 09, 2009; Revised February 24, 2010; Published July 23, 2010; Online July 23, 2010

## Abstract

High Cr ferritic heat resisting steels have been widely used for boiler components in ultrasupercritical thermal power plants operated at about $600°C$. In the welded joint of these steels, type-IV crack initates in the fine-grained heat affected zone during long-term use at high temperatures and their creep strength decreases. In this paper, creep properties and creep crack growth (CCG) properties of P92 welds are presented. The CCG tests are carried out using cross-welded compact tension $C(T)$ specimens at several temperatures. The crack front was located within the fine-grained HAZ region to simulate type-IV cracking. Finite element analysis was conducted to simulate multiaxiality in welded joints and to compare experimental results. The constitutive behavior for these materials is described by a power-law creep model. $C∗$ and $Q∗$ parameters are used to evaluate CCG rate of P92 welds for comparison. $C∗$ parameters can characterize approximately 20% of the total life of CCG in P92 welds, and $Q∗$ parameters can characterize approximately 80% of the total life. $Q∗$ parameter is one of the useful parameters to predict CCG life in P92 welds.

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## Figures

Figure 1

Simplification of the creep curve using an average creep curve, ε̇A

Figure 2

Derivation method of the Q∗ parameter

Figure 3

Creep rupture data for P92 at 923 k

Figure 4

Specimen geometry of C(t) specimen

Figure 5

Representative creep crack propagation of welded joints

Figure 6

Creep crack growth behavior for C(T) specimens of the welded joint and base metal

Figure 7

Relationship between the creep crack growth and normalized time for the welded joint at different temperatures and loading conditions

Figure 8

Relationship between the creep crack growth rate and C∗: (a) comparison between the base metal and welded joint at 923 K; (b) comparison of the creep crack growth rate at different temperatures

Figure 9

Relationship between the creep crack growth rate and C∗ based on the validity criteria of ASTM E 1457-07 (12)

Figure 10

Relationship between the creep crack growth rate and Q∗ for the base metal and welded joint

Figure 11

Relationship between the life of the creep crack growth and Q∗ for the base metal and welded joint

Figure 12

Validity area of the C∗ and Q∗ parameters in the total life for the welded joints

Figure 13

Finite element mesh for the creep crack growth analysis of a CT specimen for P92 welds

Figure 14

Contour plot of triaxiality h=σm/σe: (a) crack front is located at the center of the HAZ region; (b) crack front is located at the edge between the HAZ and base metal

Figure 15

Contour plot for the equivalent stress: (a) crack front is located at the center of the HAZ region; (b) crack front is located at the edge between the HAZ and base metal

Figure 16

Comparison of the analyzed C∗ line integrals

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