Full Content is available to subscribers

Subscribe/Learn More  >

Mooring Line Components With Semi-Brittle Behavior: Verification of Fitness for Purpose

[+] Author Affiliations
Tom Lassen

University of Agder, Grimstad; Advanced Production and Loading, Arendal, Norway

Paper No. OMAE2011-49231, pp. 155-164; 10 pages
  • ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 3: Materials Technology; Jan Vugts Symposium on Design Methodology of Offshore Structures; Jo Pinkster Symposium on Second Order Wave Drift Forces on Floating Structures; Johan Wichers Symposium on Mooring of Floating Structures in Waves
  • Rotterdam, The Netherlands, June 19–24, 2011
  • ISBN: 978-0-7918-4435-9
  • Copyright © 2011 by ASME


Low impact energy for Charpy V Notch (CVN) specimens and associated low Crack Tip Opening Displacement (CTOD) values have occurred on several occasions in high strength steel offshore mooring components. In the present work an Engineering Critical Assessment (ECA) for shackles has been carried out to demonstrate fitness for purpose. Typical values for CVN and CTOD are 17 Joules and 0.01 mm respectively at design temperature. The purpose of the present work is to demonstrate that even in the case where normal quality requirements are not met, the shackles may still have enough structural integrity and fatigue durability to withstand the load spectrum in the field during the planned target service life of typically 20 years. The ECA is based on applied fracture mechanics as outlined in the BS7910 document. Shackles made of QR4 high strength steel with different geometries and loading modes are analyzed. Extreme load cases and fatigue load spectra are treated and fracture mechanics modelling is discussed. A CTOD value as low as 0.01 mm may give critical surface crack depth close to 1% of the diameter in an ultimate limit state condition. For normal ductile steel behaviour the critical crack depth is usually close to 15% of the diameter. However, under the assumption that the pre-existing crack depth is 0.25 mm, the predicted fatigue life based on fracture mechanics analysis is still over 100 years. For a target service life of 20 years this corresponds to a Design Factor Fatigue (DFF) of 5. This is close to the requirement given by DNV for mooring chains. Based on the present analysis it can be concluded that the shackles are fit for purpose as manufactured even under unfavourable and unlikely assumptions.

Copyright © 2011 by ASME
Topics: Brittleness , Mooring



Interactive Graphics


Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature

Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In