RELIABILITY BASED PREVENTIVE MAINTENANCE FOR CORRODED PIPELINES

Resumo

Pipeline’s infrastructure grows every year, worldwide. Although pipelines are one of the
safest ways of transporting oil and gas, corrosion is a major concern in the petroleum industry. Due to
corrosive environment (underground or undersea), defects can be generated and increased through
time, reducing pipe’s resistance. In order to evaluate effectively pipeline’s integrity during its service
life, understanding uncertainties involved in corrosion is necessary; therefore, reliability assessment is
necessary. With reliability predictions, maintenances plans can be developed. Maintenance means that
a segment of pipe is excavated and the corrosion defects are “fixed”, which restores the pipeline
segment to its pristine condition, without defects. Whenever reliability coefficient falls to a predefined
threshold, maintenance takes place, this approach is called Reliability Based Preventive Maintenance
(RBPM), and it is used in this paper, according to industry’s practice. There are two main
contributions in this paper: first, a parametric study is conducted, using RBPM strategy, and the
parameters are 3 design variables: wall thickness of the pipe, type of steel used (tensile strength) and
also operation (internal) pressure, which is the load considered in all examples. In addition to that, the
second contribution is to evaluate how different ways of modeling growth of defects influence
maintenance planning; preliminary results indicate that the way of modeling growth can cause
significant changes in the reliability coefficient against time. The parameters will be considered as
random variables, with distributions, means and standard deviations considered as indicated in
literature. The internal pressure will be considered as a stochastic process.