Research Papers: Materials Technology

Sensitivity of Plastic Response of Defective Pipeline Girth Welds to the Stress-Strain Behavior of Base and Weld Metal

[+] Author and Article Information
Stijn Hertelé

FWO Flanders Aspirant,
Laboratory Soete,
Ghent University,
Technologiepark Zwijnaarde 903,
9052 Zwijnaarde, Belgium
e-mail: Stijn.Hertele@UGent.be

Wim De Waele

e-mail: Wim.DeWaele@UGent.be

Rudi Denys

e-mail: Rudi.Denys@UGent.be

Matthias Verstraete

e-mail: Matthias.Verstraete@UGent.be
Laboratory Soete,
Ghent University,
Technologiepark Zwijnaarde 903,
9052 Zwijnaarde, Belgium

Contributed by the Ocean Offshore and Arctic Engineering Division of ASME for publication in the JOURNALOF OFFSHORE MECHANICSAND ARCTIC ENGINEERING. Manuscript received March 8, 2011; final manuscript received April 16, 2012; published online February 22, 2013. Assoc. Editor: Pingsha Dong.

J. Offshore Mech. Arct. Eng 135(1), 011402 (Feb 22, 2013) (8 pages) Paper No: OMAE-11-1027; doi: 10.1115/1.4007049 History: Received March 08, 2011; Revised April 16, 2012

One of the key parameters influencing the acceptability of a pipeline girth weld defect subjected to remote plastic deformation is the strength mismatch between weld and base metal. However, no single definition exists for weld strength mismatch, as it can be defined either on the basis of yield stress, ultimate tensile stress or any intermediate flow stress. To investigate the relevance of such definitions, the authors have performed a series of analyses of curved wide plate tests, using a validated parametric finite element model. The results indicate that, whereas yield stress overmatch determines crack driving force for small plastic strains, ultimate tensile stress overmatch is the more important parameter for advanced plastic strains and determines the eventual failure mode. Further, the strain capacity and exact crack driving force curve are additionally determined by uniform elongation and crack growth resistance.

Copyright © 2013 by ASME
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Fig. 1

CWP specimen (Laboratory Soete)

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Fig. 2

The Ramberg-Osgood equation predicts a unique relation between Y/T and em, which is not respected by experimental data [13]

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Fig. 3

Example finite-element model of a half CWP specimen, with a focus on the spiderweb mesh near the defect tip

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Fig. 4

Geometry of the CWP specimen's body, as recommended in the UGent guidelines [7]

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Fig. 5

A cross section of the semielliptical weld root surface defect

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Fig. 6

The girth weld is V-shaped and has excessive weld cap material

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Fig. 7

CMOD, CTOD and J have been calculated (figure not to scale)

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Fig. 8

Four LVDTs are used to deduce pipe strains [7]

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Fig. 9

Example stress-strain relations used for the base metal (Y/T = 0.85)

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Fig. 10

OMYS determines the CMOD response for limited (plastic) strains

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Fig. 11

Weldments with an identical yield stress overmatch OMYS can fail differently

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Fig. 12

As compared to OMYS (Fig. 10), OMTS is less suited to characterize the CMOD response of weldments for small plastic strains

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Fig. 13

Ultimate tensile stress overmatch OMTS is a key factor governing the failure mode in absence of ductile crack growth

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Fig. 14

In absence of stable or unstable crack growth, failure strain can be related to the uniform elongation of the base metal, em

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Fig. 15

CMOD is not related to eo/em, for a fixed OMYS and OMTS

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Fig. 16

Graphical representation of the UGent stress-strain model




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