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Research Papers: Design and Analysis

# A Combination Rule for Circumferential Surface Cracks on Pipe Under Tension Based on Limit Load Analysis

[+] Author and Article Information
Masayuki Kamaya

Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Fukui 919-1205, Japankamaya@inss.co.jp

J. Pressure Vessel Technol 133(2), 021205 (Feb 11, 2011) (6 pages) doi:10.1115/1.4000353 History: Received December 22, 2008; Revised June 26, 2009; Published February 11, 2011; Online February 11, 2011

## Abstract

The influence of the interaction between two surface cracks on the limit load (LL) was examined by finite element analysis. Circumferential surface cracks were assumed to be on a straight pipe that was subjected to a uniform tensile load. The change in LL due to the relative spacing of cracks and the geometries of the cracks and pipe was investigated. The evaluated LL was equivalent to that of the coalesced crack when the cracks were on the same plane or their offset and horizontal distance were the same, although LL decreased as the offset distance increased in the other cases. It was also revealed that the magnitude of LL depends on the offset distance of the cracks and ratio $Rm/t$, where $Rm$ is the mean radius of the pipe and $t$ is the thickness of the pipe. Based on these results, combination rules for LL were proposed for integrity assessment of cracked pipes.

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## Figures

Figure 1

Recharacterization of parallel cracks (2-3)

Figure 2

Geometry of the pipe with two circumferential surface cracks

Figure 3

Schematic drawing representing the procedure of mesh generation for parallel cracks

Figure 4

Finite element mesh for the cracked portion

Figure 5

An example of finite element mesh for pipe containing two surface cracks

Figure 6

LL for coplanar cracks (H=0, Do=114.3 mm, and t=6.0 mm)

Figure 7

LL for various relative positions (Do=114.3 mm and t=6.0 mm)

Figure 8

LL for parallel cracks at position of S=0(Do=114.3 mm)

Figure 9

LL for parallel cracks at the opposite position (Do=114.3 mm)

Figure 10

LL for parallel cracks at the opposite position under various combinations of pipe diameter and thickness (2c=πR/3, a=0.5t)

Figure 11

Change in normalized LL at the opposite position with distance H/S

Figure 12

Schematic drawing for combination criteria for LL analysis of the interacting cracks

Figure 13

Combinations of Rm/t and H/a under the same normalized limit load of α=1.3

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