Research on the toe structure design of FPSO module stools

Abstract

The Nanhai Fenjin floating production storage and offloading (FPSO) vessel has been in service for 20 years, since 2002, and this paper describes a safety assessment for continued service until 2032. In particular, the influences of the toe shape and plate thickness of the module stools on the stress distribution and fatigue life in the toe region were investigated. Initially, four stools located on the port side and in the middle sections were evaluated. The stool with the highest stress levels was then selected for life extension and performance enhancement studies. The investigated factors include panel taper angles, toe shape, soft-toe length, and plate thickness variations; the effects of these factors on stress and fatigue life were determined. A thorough analysis of the stress concentration and weld fatigue in the toe region was performed. Results indicate that altering the toe shape can effectively enhance toe strength and fatigue performance, and extending the toe length within an appropriate range results in large improvements in stool performance. Other factors also exert varying degrees of influence on toe strength and fatigue performance. This study provides valuable insights for designing toes for various marine structures.