Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Reliability-based Methodology for the Integrity Management of Subsea Oil and Gas Pipelines Subject toCorrosion Degradation
Edilson Gabriel. Veruza; Mateus Mendes. Miguela; Gilberto Francisco Martha. de Souzaa; Marcelo Ramos. Martinsa
Rene Thiago Capelari. Orlowskib; Gustavo Leitão. Vazb; Leonardo Oliveira de. BarrosbaDepartment of Mechatronics and Mechanical Systems, Escola Politécnica - University of São PauloSão Paulo, São Paulo, Brasilb
Centro de Pesquisas, Desenvolvimento e Inovação Leopoldo Américo Miguez de Mello - Cenpes, Petrobras, Rio de Janeiro, Brasil

ABSTRACT.

the sum of the product of the corrosion rates and their respective timeintervals. The failure probability calculation was performed using theAFOSM and MCS method based on the limit state equation for burst
pressure considering the uniform corrosion failure mechanism
referenced by the ASME B31G remaining life determination standard.
Case studies are executed to present the proposed technique as well asverify the findings in the results and compare them with the direct useof corrosion rate estimation by the prediction software in determining
the failure probability. Compared to conventional RBI, the proposed
methodology allows evaluating the uncertainties of variations inoperating conditions in determining the inspection time. The scope of
this research is to introduce an efficient methodology to calculate thefailure probability considering the variations of operating conditions
that will be used in RBI practice, allowing to monitor and guarantee theintegrity of the evaluated pipeline system.

This article proposes a new methodology for evaluating the uniform
corrosion depth growth model in the calculation of failure probabilityof subsea oil and gas pipelines or equipment aiming at supporting theapplication of the risk-based inspection process to control the burst
failure. It was noted that variations in operating conditions caninfluence the corrosion rate, requiring additional analyzes in theevaluation of structural reliability. As a result of the probability of
failure calculation, at low operating pressure levels, the depth of theuniform corrosion does not play a significant role in the probability offailure, limiting the use of the RBI methodology.

KEYWORDS: Risk-based Inspection; Pipelines; Internal Corrosion;
Loss of Thickness.
INTRODUCTION

LITERATURE REVIEW

During the operational life of the pipes used in oil and gas offshore
exploration, different failure mechanisms may arise, including
degradation by corrosion. High inspection costs make it difficult toverify the integrity of these structures considering only the results ofsome sparse inspection reports. Optimizing time between inspections
reduces the accidents risks but this optimization must rely on structuralreliability analysis that shall indicate the evolution of the probability offailure during operational life. Structural integrity management requires
corrosion rate estimates, typically using corrosion prediction software.
In general, corrosion rate estimates do not consider variations inoperating conditions over time, e.g., temperature and pressure. The
present paper deals with a risk-based inspection (RBI) methodology tocertify the structural integrity of offshore pipelines, introducing a newway of estimating the corrosion rate by considering the variations ofoperating conditions over time. To evaluate these variations, the time
discretization was performed according to the shortest interval between
the measurement records of the parameters that affect uniform
corrosion, keeping the other parameters constant until the appearanceof a new record. Thus, the pipeline thickness reduction is composed ofRisk-Based Inspection
The proper operation of equipment used in the oil and gas industry is
intrinsically linked to its structural integrity. Planned inspections andmaintenance have a fundamental role in preventing failures. A large
portion of operating costs is allocated to the inspection andmaintenance of these facilities. Thus, by adopting optimized inspection
and maintenance strategies, it is possible to balance operating costs andthe reliability needed to maintain the structural integrity of the pipelines(Bai & Bai, 2014).
Inspections designed and optimized for components with the greatest
potential for risks, whether economic, environmental, and/or safety, arecalled risk-based inspections (RBI). The characteristics of the RBI
make it a rational decision framework for determining which
equipment to carry out the inspection, when, where, and how to inspect(Bai & Bai, 2014; Marley et al., 2001).
The methodologies developed for RBI differ in terms of risk modeling;
Bai & Bai (2014) indicate that the risk modeling is given by the productof the probability of failure (PoF) and the consequence of failure (CoF)
as shown in Eq. 1, and the differences in methodologies are in the way1643