COMPARISON BETWEEN CONDITIONAL AND UN-CONDITIONAL FAILURE PROBABILITY OF CORRODED GAS TRANSMISSION PIPELINES CONSIDERING STOCHASTIC PROCESS FOR INTERNAL PROSSURE AND CRACK GROWTH RATE

Pipelines are the safest and most economical form of natural gas transmission which are remarkable for their efficiency and low cost [1]. Generally, subsea pipelinescarry oil and gas products from wellhead to the riser base [2]. According to study of Shabani [3], corrosion is the most deteriorative factor on pipeline health and safety. Soidentifying and recognizing corrosion and it’s resultant are essential and necessary for pipeline integrity management [4]. Shabani et. al present a Stochastic-Based Approach fordetermining risk of corroded pipelines considering unconditional form of corrosion attacks. This paper deals with RA of corroded gas transmissionpipelines considering all probable failure modes of corrosion attacks. Reliability level of pipeline is evaluated in three different modes. All pipeline geometricalparameters are modeled as inherent uncertain parameters. Relationship between crack dimension is modeled using correlations. Crack growth rate and internal pressure aremodeled using Poisson Square Wave Process and Ferry orges- Castanheta, respectively, using In-Line Inspection (ILI) and pipe pressure data. Distribution of holes isassessed through pipeline using ILI data. Also, both conditional and un-conditional form of failure modes of corrosion attacks are discussed. Finally, Probability ofFailure (POF) for both conditional and un-conditional is determined using importance sampling technique.