Topside Axial Bearing Wear Under the Eccentric Load of a Single-Anchor Leg Mooring System in Bohai Bay

Abstract

Because the applications of single-anchor leg mooring yoke systems (SYSs) are rarely studied in the offshore industry, the design of such systems features some uncertainties. This paper investigated the effect of eccentricity on the wear of the topside axial bearing of a SYS. The eccentricity of the topside was verified by on-site inspection, and the axial bearing wear was found to be far more serious than the original design. The contact status between the axial bearing and flange surface was studied on the basis of the actual topside load by using nonlinear finite element analysis. Wear tests of the topside bearing under uniform and eccentric loads were also performed to study the effect of eccentric loads on the wear rate. The key parameters obtained from numerical simulations and experimentation were used to calculate the wear depth via a simplified linear wear model based on the product of the pressure and sliding distance. Results showed that eccentric loads are the main factor responsible for the excessive wear of topside axial bearings.

Keywords

Single-anchor leg mooring / Yoke system / Nonlinear finite element analysis / Wear test / Topside axial bearing

References

[1] ABS (1996) Rules for building and classing single point moorings. American Bureau of Shipping

[2] APL Norway AS Staff (2003a) SAL yoke system - bearing design report. APL Norway AS Inc., Oslo, 5, 29

[3] APL Norway AS Staff (2003b) SAL yoke system - topside axial bearing wear. APL Norway AS Inc., Oslo, 3, 40

[4] Largura L, Piana L, Craidy P (2011) Evaluation of premature failure of links in the docking system of a FPSO. OMAE, Rotterdam, OMAE 49350, 257–262. https://doi.org/10.1115/OMAE2011-49350

[5] Lotsberg I, Kristian L. Developments in fatigue design standards for offshore structures, 2001, Stavanger: ISOPE, 102-117

[6] Lyu B, Guo C, Wu W, Feng J, Yue Q. Hinge joint damage identification method of soft yoke mooring system based on multibody dynamic modeling and structural monitoring data. Mar Struct, 2020, 74: 102808

[7] Ma KT, Duggal A, Smedley P, Hostis DL, Su HB (2013a) A historical review on integrity issues of permanent mooring systems. Offshore Technology Conference, Houston, OTC24025. https://doi.org/10.4043/24025-MS

[8] Ma Y, Hu Z, Qu Y, Lu G (2013b) Research on the characteristics and fundamental mechanism of a newly discovered phenomenon of a single moored FPSO in the South China Sea. Ocean Eng 59(2):274–284. https://doi.org/10.1016/j.oceaneng.2012.12.020

[9] Maersk L (2011) Gryphon alpha loss of heading, mooring system failure and subsequent loss of position. Safety Alert issued by Maersk L

[10] Melis C, Jean P, Vargas P (2005) Out-of-plane bending testing of chain links. OMAE, Halkidike, OMAE 67353.https://doi.org/10.1115/OMAE2005-67353

[11] Moan T, Amdahl J, Wang X. Risk assessment of FPSOs with emphasis on collision. Transactions, 2002, 110: 307-339

[12] Moxnes S (2011) Multiple steel wire rope failures on Volve FSU mooring. Statoil, Norway, Safety Alert Report. Synergy No. 1231190

[13] Sun LP, Sun H. Risk management of key issues of FPSO. J Mar Sci Appl, 2012, 11(4): 11-15

[14] Tang D, Zeng X, Wang D, Wu W, Wang Y, Yue Q. The research of soft yoke single point mooring tower system damage identification based on long-term monitoring data. Appl Ocean Res, 2018, 76: 139-147

[15] Teekay Petrojarl Production Sulphate reducing Bacteria – Erfaring med SRB angrep pa kjetting, 2012, Trondlheim: Tekna

[16] Vargas P, Jean P (2005) FEA of out-of-plane fatigue mechanism of Chain links. OMAE, Halkidike, OMAE 67354. https://doi.org/10.1115/OMAE2005-67354

[17] Wang J (2012) To build a reliability SPM. 2nd Annual Summit – Excellence in FPSO Design, Construction and Operation, Tianjin, China, 56–57

[18] Wang A, Pingsheng R, Shaohua Z (2009) Recovery and Re-Hook-up of Liu Hua 11–1 FPSO Mooring System. Proc. Offshore Technology Conference, OTC 19922. https://doi.org/10.4043/19922-MS

[19] Wenhua W, Xiaoning Di, Hongbo C, Yi H, Shuo Y (2018) Effect of transient tidal current on rotational performance of SAL yoke system. China Offshore Platform 33(5):75–80 (in Chinese)

[20] Xia H. Research on single point mooring of underwater soft Yoke. Ship Ocean Eng, 2014, 43(3): 166-171 in Chinese