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Research Papers: Fluid-Structure Interaction

J-Resistance Properties of Narrow Gap GTAW Welds for Ferritic Primary Loop Piping

[+] Author and Article Information
One Yoo, Ki-Seok Yoon, Tack-Sang Choi

 Korea Power Engineering Company, Inc., 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353, Korea

Bong-Sang Lee, Min-Chul Kim

 Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353, Korea

J. Pressure Vessel Technol 130(4), 041301 (Aug 15, 2008) (8 pages) doi:10.1115/1.2967810 History: Received March 10, 2006; Revised March 28, 2007; Published August 15, 2008

J-resistance properties of automatic narrow gap gas tungsten arc welds (NGGTAWs) for ferritic primary loop piping were investigated. The piping diameter is 1066mm, and its thickness is 76mm. The tensile, microhardness, and J-R tests were performed, and microstructures of the welds were examined. Tensile and J-R tests were conducted at 316°C and 177°C for temperature effect, and at 1mmmin and 1000mmmin for strain rate effect. The results were compared with other welds, which are fabricated by the conventional shielded metal arc weld (SMAW) process. The NGGTAW welds investigated in this paper have lower J-R curves than the SMAW welds. Fracture surfaces of the NGGTAW welds showed deep ditches and holes due to inclusions and pores. It is believed that the high density of the inclusions and the pores, which exist in the NGGTAW welds, is responsible for this lower toughness and the fracture surface appearances. Therefore, to improve the NGGTAW weld toughness, it is recommended that sulfur content should be limited to a considerably low level, and the pores should be eliminated by modifying the welding procedure specification.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Stress-strain curves of NGGTAW (G1, G2, and G3) and SMAW (S1, S2, and S3) welds. The only lowest data curves from three replicate tensile tests are shown. The test temperature is 316°C if unidentified in the figure.

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Figure 2

J-R curves of NGGTAW (G1, G2, and G3) and SMAW (S1, S2, and S3) welds tested at 316°C under the quasistatic condition. Solid and dotted lines indicate the higher and lower bound J-R curves of the SMAW welds identified from the KOPEC database, respectively.

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Figure 3

J-R curves of NGGTAW welds tested at 316°C and 177°C in the quasistatic condition

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Figure 4

J-R curves of NGGTAW welds tested at 316°C under the dynamic condition (1000mm∕min). Solid and dotted lines indicate the higher and lower bound J-R curves of the SMAW welds identified from the KOPEC database, respectively.

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Figure 5

J-R curves of NGGTAW welds tested at 316°C and 177°C in the dynamic condition (1000mm∕min)

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Figure 6

Microstructures of SMAW and NGGTAW: (a) reheated region of S1(SMAW), (b) reheated region of G3(NGGTAW), (c) as-deposited region of S1, and (d) as-deposited region of G3

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Figure 7

Crack jump behavior of the S1(SMAW) specimen. The other case is taken from the KOPEC database (2) and is shown for comparison.

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Figure 8

Cracked surface of the S1(SMAW) specimen: P: as-deposited region and S: reheated region. The arrow indicates the crack propagating direction

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Figure 9

Bead shape of NGGTAW and SMAW welds: (a) G2, (b) G3, (c) S2, and (d) S3. The weld fusion area is identified as a marker of W.

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Figure 10

Microhardness measured perpendicular to the welding direction. The high hardness regions are identified in the figure.

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Figure 11

Fracture surfaces of SMAW and NGGTAW welds: (a) S2, (b) G1, (c) S3, and (d) G3. The arrow indicates the direction of crack propagation.

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Figure 12

The optical micrographs of the S1 and G3 specimens: (a) S1 and (b) G3. Arrows indicate pores.

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Figure 13

EDX spectrum of an inclusion in the G3 weld. Inclusion is identified by the arrow in the micrograph.

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