Research Papers: Design and Analysis

The Influence of Imperfections and Nonlinearities on the Failure and B2 Stress Index of Thin-Walled Pipes

[+] Author and Article Information
Henry Schau

TÜV SÜD Energietechnik GmbH,
Dudenstrasse 28,
Mannheim 68617, Germany
e-mail: henry.schau@tuev-sued.de

Lilit Mkrtchyan

Cooperative State University Baden-Wuerttemberg,
Coblitzallee 1-9,
Mannheim 68163, Germany
e-mail: lilit.mkrtchyan@dhbw-mannheim.de

Michael Geier

TÜV SÜD Energietechnik GmbH,
Dudenstrasse 28,
Mannheim 68617, Germany
e-mail: michael.geier@tuev-sued.de

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 28, 2014; final manuscript received April 8, 2015; published online May 20, 2015. Assoc. Editor: Spyros A. Karamanos.

J. Pressure Vessel Technol 137(6), 061205 (Dec 01, 2015) (7 pages) Paper No: PVT-14-1072; doi: 10.1115/1.4030366 History: Received April 28, 2014; Revised April 08, 2015; Online May 20, 2015

The effects of imperfections and nonlinearities on the failure mode and the B2 stress index of thin-walled straight pipes are investigated with finite element (FE) analyses. The analyses were performed for pipes made of an ideal elastic–plastic material and the austenitic steel X6CrNiNb18-10. The B2 index is calculated from the instability bending moments obtained by limit load analyses. The effects of initial imperfections as well as the D/t-ratio and the yield stress on the B2 stress index are studied. As a first result, it is noted that thin-walled straight pipes and imperfections fail due to local plastic buckling. Further analyses show that the type of imperfections, the ovality, the D/t-ratio, and the yield stress have significant influences on the B2 index. The obtained B2 indices for thin-walled straight pipes with D/t > 40 and possible technical imperfections are considerably higher than 1.0. The results have been compared with those of other investigations.

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Fig. 1

Definition of the collapse and instability moment for exemplary curves

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Fig. 2

Normalized moments for ideal elastic–plastic material for different D/t-ratios without buckling

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Fig. 3

B2 index for an ideal elastic–plastic material as a function of the D/t-ratio without buckling

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Fig. 4

Ratio Mpl/MIL for austenitic steel X6CrNiNb18-10 for different D/t-ratios without imperfection

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Fig. 5

Two examples of buckling modes used as imperfections in the analyses

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Fig. 7

Normalized moments as functions of the rotation angle for an ideal elastic–plastic material with D/t = 100 and σY = 200 MPa

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Fig. 8

B2 index for an ideal elastic–plastic material with D/t = 100 and σY = 200 MPa as a function of the ovality

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Fig. 9

B2 index for an ideal elastic–plastic material with D/t = 100 as a function of the yield stress

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Fig. 10

B2 index for an ideal elastic–plastic material with σY = 200 MPa as a function of the D/t-ratio

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Fig. 11

Normalized moments for a pipe of austenitic steel X6CrNiNb18-10 with D/t = 100 as a function of the rotation angle

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Fig. 6

Two examples of numerically obtained failure modes by local buckling



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