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Research Papers: Structures and Safety Reliability

Fatigue Design Recommendations for Conical Connections in Tubular Structures

[+] Author and Article Information
Inge Lotsberg

DNV GL,
Veritasveien 1,
Høvik 1322, Norway
e-mail: Inge.Lotsberg@dnvgl.com

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received December 25, 2017; final manuscript received July 2, 2018; published online August 13, 2018. Assoc. Editor: Kazuhiro Iijima.

J. Offshore Mech. Arct. Eng 141(1), 011604 (Aug 13, 2018) (7 pages) Paper No: OMAE-17-1225; doi: 10.1115/1.4040800 History: Received December 25, 2017; Revised July 02, 2018

Conical connections are important structural members for the integrity of most types of welded tubular structures. They are for example used in traditional jacket structures for oil and gas production and in monopiles for support of wind turbines where an optimal design is aimed for. From contact with the industry, it is noted that there is uncertainty about the basis for the stress concentration factors (SCF) for conical connections in design standards for fatigue assessment. This is related to how fabrication tolerances are accounted for and how a transition in thickness from the cone to the tubular or the cylinder should be made to minimize stresses due to thickness transitions and fabrication tolerances. Analytical expressions for stress concentrations at conical transitions are outlined in this paper to get a better understanding of the effect of thickness of the cone and the cylinder. By a proper basis for fatigue design, it is possible to control additional stresses from thickness transitions and fabrication tolerances at these connections.

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References

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Figures

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Fig. 2

Circular cylindrical shell loaded symmetrically with respect to its axis

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Fig. 1

Conical connection

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Fig. 3

Geometry and forces at conical connection

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Fig. 4

Comparison of SCFs derived from classical shell theory and Eq. (1) for a cone at the larger diameter junction in a large diameter monopile

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Fig. 5

Moment distribution at the larger diameter junction in a large diameter monopile with thickness of the tubular equal 75 mm and the thickness of the cone equal 85 mm

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Fig. 6

Comparison of SCFs derived from classical theory and Eq. (1) for a large diameter junction at a cone in a typical jacket structure

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Fig. 7

Illustration of asymptotic behavior of SCF at the large diameter junction as function of cone thickness

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Fig. 10

Geometry with shift in neutral axis that results in local bending at the thickness transition due to axial force

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Fig. 11

Bending stress along the tubular section 1 in Fig. 3

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Fig. 12

Preferred thickness transition at the large diameter junction in conical connections

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Fig. 8

Moment distribution at the larger diameter junction in a jacket with thickness of the tubular equal 30 mm and the thickness of the cone equal 40 mm, outer diameter 1430 mm and cone angle 8 deg

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Fig. 9

Stress concentrations at larger diameter cone junction in a jacket with thickness of the tubular equal 30 mm and the thickness of the cone equal 40 mm, outer diameter 1430 mm and cone angle 8 deg

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