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Evaluation of Welding Flaws Under Ratcheting Fatigue

[+] Author Affiliations
Paulo Gioielli, Jaime Buitrago

ExxonMobil Upstream Research Company, Houston, TX

Wan Kan, Michael Weir

ExxonMobil Development Company, Houston, TX

Graham Chell, Steve Hudak

Southwest Research Institute, San Antonio, TX

Paper No. OMAE2008-57165, pp. 141-151; 11 pages
doi:10.1115/OMAE2008-57165
From:
  • ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering
  • Volume 3: Pipeline and Riser Technology; Ocean Space Utilization
  • Estoril, Portugal, June 15–20, 2008
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4820-3 | eISBN: 0-7918-3821-8
  • Copyright © 2008 by ASME and Southwest Research Institute

abstract

Hydrocarbon-carrying lines can be subjected to cyclic loads superimposed on monotonically increasing mean strains well into the plastic domain, resulting in tearing and tearing fatigue of initial welding flaws. This combined demand is referred to here as ratcheting fatigue. Examples of these loads are frost-heave in pipelines and thermal cycling of flowlines. This paper presents the experimental verification of a fracture mechanics model of monotonic and cyclic crack extension under ratcheting fatigue loads and its calibration to small-scale tests. The model is an extension of one currently used to predict tearing and tear-fatigue due to reeling. Crack driving forces (J-solutions) under load- and displacement-control conditions were derived and used with the model to predict test results. A total of 24 single-edge notched bend (SEN-B) specimens, taken from a welded riser, were tested for crack extension under combined monotonic and cyclic loads. Comparisons of predicted to measured fatigue crack-growth rates, and alternatively cyclic J-R curves, provide quantitative and qualitative validation of the model. However, calibration to large–scale tests are needed before the model can be used for design. ExxonMobil has already completed the first set of large-scale pipe tests under ratcheting fatigue loading, including internal pressure.

Copyright © 2008 by ASME and Southwest Research Institute
Topics: Fatigue , Welding

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