Fatigue Life Analysis of FSO Mooring Chain by Considering the Effects of Offloading Load

Hafizh Muhammad Naufal Shidqi, Nur Syahroni, Daniel Mohammad Rosyid, Dewinta Putri Cahyaningtyas

Abstract


mooring chains are critical components in the maritime industry used to secure ships and floating oil and gas platforms such as FSOs to stay in their designated positions. The loads exerted on mooring chains during routine operations and additional loads during offloading operations can cause structural fatigue. Therefore, fatigue life analysis of mooring chains is essential to ensure safety and optimal performance. This study aims to conduct fatigue analysis of mooring chains by considering an important factor, namely the influence of offloading. Offloading load refers to the additional load exerted on the mooring chain during loading and unloading operations. The mooring system configuration uses a spread mooring system of 8 chains (4x2), 87 mm in diameter, with 20% pretension. In the fatigue analysis, the "Palmgren-Miner" method was used to evaluate the accumulated damage caused by cyclic loads. Then, the "Rainflow Counting" method is used to identify and count the number of load cycles that occur so that later the fatigue life can be calculated and known. From the research results, it was found that the mooring system configuration design still meets the safety factor requirements recommended by API RP 2 SK both during SLS, ULS, and FLS analysis. In SLS and ULS conditions, the greatest tension value is when the FSO is in the Ballast load condition, with the maximum value of tension that occurs is 2207.4 kN in SLS conditions, and 4151.6 kN in extreme conditions. In the FLS condition analysis, it was found that with an offloading frequency of 24 times per year (1271.89 hours), in the design configuration, the influence of the offloading system can increase up to 7% of the fatigue damage that occurs, and the lowest fatigue life, reduced by 3 years. The least fatigue life occurs in Chain 1.2 at the splash zone segment, which is 67 years.

Keywords


Fatigue; FLS; Mooring Chain; Rainflow Counting; SLS; Spread Mooring; Tandem Offloading; Tension; ULS

Full Text:

PDF

References


S. K. Chakrabarti, “Handbook of Offshore Engineering,” Elsevier Ltd, 2005.

K.-T. Ma, “Mooring System Engineering for Offshore Structures,” In European University Institute (Issue 2), Gulf Professional Publishing, 2018.

I. DKPU, “Zulu Terminal Marine Conceptual Study,” Project Report, 2023.

E. B. Djatmiko, “Seakeeping: Perilaku Bangunan Apung di Atas Gelombang,” ITS Press, 2003.

A. Aldi, “Analisis Resiko Fatigue Mooring Lines pada Spread Mooring Line System FSO Federal II dengan Mempertimbangkan Beban Operasi,” 2018.

J. R. Thalita, “The Study of Tandem Offloading Performance and Operability on The Cylindrical Hull FPSO Sevan Stabilized Platform with Variation in Mooring System Configuration,” International Journal of Offshore and Coastal Engineeing, 1(2), 70, 2017, https://doi.org/10.12962/j2580- 0914.v1i2.705

M. S. Hasan, “A simplified method for analyzing the fatigue life of a FPSO mooring system,” Procedia Engineering, 194, 502–508, 2017, https://doi.org/10.1016/j.proeng.2017.08.177.

J. Du, H. Wang, S. Wang, X. Song, J. Wang, & A. Chang, “Fatigue damage assessment of mooring lines under the effect of wave climate change and marine corrosion,” Ocean Engineering, 206(April), 107303, 2020, https://doi.org/10.1016/j.oceaneng.2020.107303.

American Bureau of Shipping “Rules for Building and Classing Mobile Offshore Drilling Units,” Houston: American Bureau of Shipping, 2018.

S. K. Chakrabarti, “Hydrodynamics of offshore structures,” 1, Offshore structures - Hydrodynamics I, (p. 435), 1987.

BKI, “Guidelines for Floating Production Installations.” 3, 2021.

O. M. Faltinsen, “Sea Loads On Ships and Offshore Structures,” Cambridge University Press, 1990.

Murdjito, M. P. Rosari, and E. B. Djatmiko, “Analysis on the Critical Conditions of Side-by-Side Offloading Operation between SSP Type-FPSO and Shuttle Tanker,” Appl. Mech. Mater. 874 53–63, 2018.

X. Chen, “Offshore hydrodynamics and applications” IES J. Part A Civ. Struct. Eng. 4 124–42, 2011.

W. F. Van, and H. J. J. Van den Boom, “Wind, Wave, and Current Loads on Semisubmersibles Offshore Technol,” Conf. OTC-6521-MS, 1991.

DNVGL-OS-E301, “Position Mooring,” July, 114, 2015.

API RP 2SK, “Design and Analysis of Stationkeeping Systems for Floating Structures,” API, 2005.




DOI: http://dx.doi.org/10.12962/j25481479.v8i2.16941

Refbacks

  • There are currently no refbacks.


Abstracted / Indexed by:
      
  

 

 

 

 

 

P-ISSN: 2541-5972   

E-ISSN: 2548-1479

 

Lisensi Creative Commons

IJMEIR journal published by  Department of Marine Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember Surabaya Indonesia under licenced Creative Commons Attribution-ShareAlike 4.0 International Licence. Based on https://iptek.its.ac.id/index.php/ijmeir/