Probability-based strength reassessment of corroded FPSOs using monitored loads

Probability-based strength reassessment of corroded FPSOs using monitored loads

Petillo, F.

Hageman, R. (mentor)
Kaminski, L.M. (mentor)

Mechanical, Maritime and Materials Engineering

Maritime Technology

Ship and Offshore Structures

2015-02-25

FPSOs are nowadays a common practice in the production of oil at sea. These ship-type offshore units, however, cannot have regular dry-docking as they have to be on field sometimes even for their entire lifetime. This is the reason why structural monitoring systems may play an important role in the safety of these units. The MONITAS JIP was started in 2005 in order to continuously monitor the fatigue lifetime consumption of FPSO. However, these extensive measurements can be used for other purposes as well. In this work, the strength reassessment of a corroded FPSO tank has been addressed. For this purpose, thickness measurements coming from the inspections and the loads measured by the MONITAS system have been combined in a new probability-based model, which is able to calculate a probability of failure for the inspected structure. Different failure criteria (yielding, elasto-plastic buckling, brittle fracture) have been identified, and for any of them a closed-form limit state function has been written down. To write down the limit state functions, analytical models (simple beam theory, large deflection analysis, membrane stress-based method and others) and empirical formulae (Johnson-Ostenfeld formula) have been used. The structural reliability analysis has been run using the Monte Carlo simulation method. The results is a reassessment tool which can be used by FPSO operators in order to avoid unnecessary maintenance of a corroded plate, to optimize repair intervention or to justify extra-maintenance.

FPSO
structural reliability
corrosion

http://resolver.tudelft.nl/uuid:44c0cca2-67a5-41cd-bd36-f7e06244049f

2015-02-25

Student theses

master thesis

(c) 2015 Petillo, F.