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Research Papers: Design and Analysis

# The Effect of the Distance From the Center of a Weld to the Fixed End on the Residual Stress and Stress Intensity Factor of a Piping Weld

[+] Author and Article Information
Katsumasa Miyazaki

Materials Research Laboratory, Hitachi, Ltd., Hitachi, Ibaraki 317-8511, Japan

Masanori Numata

Consulting Engineering Department, Hitachi Engineering Co., Ltd., Hitachi, Ibaraki 317-0073, Japan

Koichi Saito

Hitachi Works, Hitachi, Ltd., Hitachi, Ibaraki 317-8511, Japan

Masahito Mochizuki

Department of Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

J. Pressure Vessel Technol 131(2), 021205 (Dec 30, 2008) (9 pages) doi:10.1115/1.3007428 History: Received April 16, 2007; Revised July 22, 2008; Published December 30, 2008

## Abstract

The fixed conditions of butt welds between straight pipe and the valves or pump in an actual piping system are different from those of straight pipes. However, the effect of the fixed condition on the residual stress and the stress intensity factor for the evaluation of the structural integrity of cracked piping is not clear. In this study, finite element analyses were conducted by considering the differences in the distance from the center of weld to the fixed end $L$, to clarify the effect of the fixed condition on the residual stress and the stress intensity factor. For 600A piping, the residual stress distribution was not affected by $L$. Furthermore, the stress intensity factors of circumferential cracks under the residual stress field can be estimated by using an existing simplified solution for piping.

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## Figures

Figure 1

Schematic of the piping system

Figure 4

Residual stress distributions with L=0.2(Rt)0.5: (a) axial stress and (b) hoop stress

Figure 2

Geometry of the piping model with distance from weld center to the fixed end L: (a) piping model; (b) detail in A, configuration of weld

Figure 3

Residual stress distributions with L=2.5(Rt)0.5: (a) axial stress and (b) hoop stress

Figure 15

Redistributions of axial residual stress due to the crack propagation (L=0.2(Rt)0.5, z=5.0mm, fixed end)

Figure 16

Changes in stress intensity factor due to crack propagation estimated by the nodal release method with FEA and the simplified method (L=0.2(Rt)0.5)

Figure 5

Axial residual stress distributions at the fixed end: (a) distance from the center of weld to fixed end, L=2.5(Rt)0.5; (b) distance from the center of weld to fixed end, L=0.2(Rt)0.5

Figure 6

Hoop residual stress distributions at the fixed end: (a) distance from the center of weld to fixed end, L=2.5(Rt)0.5; (b) distance from the center of weld to fixed end, L=0.2(Rt)0.5

Figure 7

Comparison of axial residual stress distributions at the fixed end and free end (distance from the center of weld, z=5.0mm): (a) distance from the center of weld to fixed end, L=2.5(Rt)0.5; (b) distance from the center of weld to fixed end, L=0.2(Rt)0.5

Figure 8

Comparison of hoop residual stress distributions at the fixed end and free end (distance from the center of weld, z=5.0mm): (a) distance from the center of weld to fixed end, L=2.5(Rt)0.5; (b) distance from the center of weld to fixed end, L=0.2(Rt)0.5

Figure 9

Effect of distance from the center of weld to the fixed end, L on the axial residual stress distribution: (a) distance from the center of weld, z=0.0mm (the center of weld); (b) distance from the center of weld, z=3.0mm; (c) distance from the center of weld, z=5.0mm; (d) distance from the center of weld, z=10.0mm

Figure 10

Effect of distance from the center of weld to the fixed end, L on the hoop residual stress distribution: (a) distance from the center of weld, z=0.0mm (the center of weld); (b) distance from the center of weld, z=3.0mm; (c) distance from the center of weld, z=5.0mm; (d) distance from the center of weld, z=10.0mm

Figure 11

Procedure for estimation of stress intensity factors

Figure 14

Example of changes in axial residual stress distribution (a∕t=0.2): (a) after welding; (b) after initiation of crack, a∕t=0.2

Figure 12

Mesh division of the finite element model for estimation of stress intensity factors by the nodal release method (a∕t=0.2): (a) mesh division of finite element model of piping; (b) detail in A; (c) detail in B

Figure 13

Approximation of axial residual stress distribution for estimation of stress intensity factors by the simplified method (L=0.2(Rt)0.5, z=5.0mm, side of fixed end)

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