Reliability and Risk-Based Assessment of Offshore Jacket Structures in the Niger Delta, Nigeria.
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Date
2014
Authors
Omotoso, M.F
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Abstract
In Nigeria, a large number of jacket platforms installed in the Niger Delta have been
operating beyond design life of 25 years due to the exorbitant cost of replacement
with new ones. These Jacket structures often undergo corrosion and fatigue
damages due to hostile offshore conditions and accidental release of corrosive agents
from crude oil production activities. Therefore, there is a growing need to closely
monitor the structures to protect unexpected failures. Applications of appropriate
assessment methods for corrosion and fatigue hazard mitigation measures can assist
to check mate or prevent the jacket structure premature failures. The available
basic design techniques and the standards in the petroleum industry standards for the new structures are somehow inappropriate for the assessment of the existing
jacket structures. The ambiguity in the characteristics of corrosion and fatigue
hazard has made the deterministic approach unsuitable for the risk-based
assessment of jacket structures. The above mentioned reasons have made it
imperative to search for a new structural assessment technique for the jacket
structures.
This study established the appropriate relationship between chloride accumulation
and diffusion process within the offshore jacket structures. Marine steel structure
corrosion damage model was developed for corrosion damage monitoring and
mitigation. The study also evaluated the existing jacket platform integrity in the
Niger Delta with special reference to the jacket structure system reliability and
operational safety. Relevant engineering standards for offshore structures, new
design and assessment with special reference to API RP 2A WSD which are widely used in the petroleum industry were appraised. Several jacket component damage
scenarios were evaluated and simulated with due consideration to corrosion and
fatigue hazard. Reliability method for the assessment of corroded jacket structures
was developed. A ratio between reliability of an intact and a corrosion damaged
jacket structure known as reliability factor (RF) was also derived to establish when
the jacket platform with associated corroded jacket structure would be due for
abandonment.
The study revealed that jacket structure reliability (Rsj) and RF for three jacket
structures investigated in the study are 85.8% and 1.166 respectively. It
demonstrated that components with localized corrosion and fatigue damage exhibited an unacceptable risk level that urgently required revamp works
Description
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
Keywords
Jacket Structures , Risk-Based Assessment of Offshore , Offshore , Research Subject Categories::TECHNOLOGY::Civil engineering and architecture::Water engineering
Citation
Omotoso, M.F (2014), Reliability and Risk-Based Assessment of Offshore Jacket Structures in the Niger Delta, Nigeria. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 146pp.