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Fatigue Capacity of Wellhead Housings

[+] Author Affiliations
Sergey Kuzmichev, Kristoffer H. Aronsen, Guttorm Grytøyr

Statoil ASA, Fornebu, Norway

Javier Rodriguez Garcia, Erik Simonsen

Aker Solutions AS, Fornebu, Norway

Finn Kirkemo

Statoil ASA, Tranby, Norway

Paper No. OMAE2017-61421, pp. V03BT02A053; 11 pages
doi:10.1115/OMAE2017-61421
From:
  • ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 3B: Structures, Safety and Reliability
  • Trondheim, Norway, June 25–30, 2017
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-5766-3
  • Copyright © 2017 by ASME

abstract

The issue of wellhead fatigue has been given significant attention during recent years. The complexity of the wellhead system in terms of interactions betwe[en conductor (low pressure) and wellhead (high pressure) housings leads to various analysis methods being proposed to evaluate fatigue damage in the system. Most of the critical base material hotspots are located in the wellhead housing region where the loads start to distribute between the high- and low pressure housing and the load paths are highly complex varying for different input parameters. Due to this, detailed fatigue analyses are typically performed on a project to project basis for the same wellhead geometry. This paper proposes an approach that simplifies the analysis of the base material hotspots in the housings and makes it independent of where the specific type of the wellhead system is used. It is suggested to consider the housings of the wellhead system as one component with a single characteristic M-N curve, or a few M-N curves if complexity requires so. The M-N curve is a specialization of the standard S-N curves provided in rules and standards. They are generated by combining the calculated load-to-stress curve at a given hotspot with the applicable S-N curve. The load used as a reference is typically a cross-sectional moment at the top of high pressure housing.

For these purposes 3D FE models have been developed for two principal wellhead types, rigid lock and non-rigid lock. The models are used to investigate the effect of different boundary conditions and applied loading on M-N curves for each hotspot analysed. Sensitivity studies have been performed for several parameters that are considered important in wellhead fatigue analysis. Based on the sensitivity studies, the effect of each parameter on typical base material hotspots is presented.

This paper provides estimates for the spread in the M-N curves for each individual base material hotspot in the wellhead housings. Results indicate that a single characteristic M-N curve per wellhead system type can be selected to represent the wellhead housings. In addition, based on results from the analyses carried out, recommendations regarding generalized boundary conditions to obtain a characteristic M-N curve for a specific wellhead type have been given.

Copyright © 2017 by ASME
Topics: Fatigue

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