Fatigue Analysis of Steel Jacket Platform in Shallow Water Depth in the Gulf of Guinea

Abstract

This work investigates the fatigue life of a steel jacket installed at a water depth of 22m in the Gulf of Guinea, both deterministic and spectral analysis was done using the Bentley SACS software. Wave data was collected every 3 hours for seven years resulting in 20440 sea states. The analysis was carried out using industry codes and standards for critical inspectable and non-inspectable members. The result of the analysis was obtained for 50 modal shapes, and the mass participation factors show the highest vibration at the mode shape of 2. The fatigue life of the joint was determined for a life of 50 years and applying the factor of safety of 5; the spectral analysis shows that none of the members investigated to meet the fatigue life of 250 years. However, the deterministic analysis shows some members that meet the fatigue life of 250 years. The analysis was also conducted for the piles both above and below the mud line, and the spectral and deterministic analysis show that the piles meet a fatigue life of 500 years using a factor of safety of 10. It was concluded and recommended that the joints on the jacket that do not meet the fatigue life should be rewelded and inspected for structural integrity. Also, the result shows that the spectral analysis is more detailed than the deterministic analysis.

Keywords: jacket, fatigue analysis, Gulf of Guinea, SACS, spectral analysis, deterministic analysis, fatigue damage.

DOI: 10.7176/ISDE/11-3-01

Publication date: April 30^th 2020