Reliability assessment of pipeline steel under corrosion defect

Abstract

The assessment of the reliability index and /or the failure probability of the corroded pipeline was estimated. By comparing the results of the different standards and using the probabilistic approach, this paper provides a more accurate assessment of the reliability of the pipeline under corrosion defects. The probabilistic approach is carried out by confronting the results of the commonly used standards such as B31G, modified B31G, Batelle, DNV RP F101 and Shell, in order to know the more conservative technique and determine the reliability in which the burst pressure of the pipeline is controlled. The commonly used standards are coupled with the Rackwitz optimization algorithm, and the deterministic failure assessment diagram is coupled with the Monte Carlo simulation. The degradation models are used to assess the probability expressed by the index of reliability (β) through the dimensions of the defects based on the operating pressures. For instance, for a target reliability index value of 5.2, the pipeline API 5L X 52 work within safe condition for ASME B31G and modified ASME B31G models. In addition, at an operating pressure equal to 9 MPa, the safety defect depth is equal to 55% and 49% for the two codes respectively. When the operating pressure reach 13 MPa, the safety defect depth is equal to 39% and 38% for the two codes respectively. When the assessment is based on DNV RP F101 and Battelle methods, for a target reliability index value of 5.2, the two codes indicate that any value of the reliability index is higher than the target index up to the ratio d/t of 44% for a working pressure of 13 MPa. For the relative defect depth d/t = 60%, all the different pressures fall into the domain of failures (β < 3.72). The important reliability assessment results can manage maintenance and inspection strategies to ensure the safe and efficient operation of pipelines in the oil and gas industry.