Publications internationales
Résumé: 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.
Résumé: Considering corrosion rate during the remaining life assessment of aging pipelines is fundamental to calculate the interval between two consecutive inspections. A total of 798 internal and external corrosion defects have been detected, using the Magnetic Flux Leakage intelligent inspection tool, over 48 km of a pipeline length located in the west region of Algeria. The statistical analysis has shown that there is a strong correlation between the corrosion defect length and the corrosion defect circumferential width, with a significant correlation coefficient equal to 82.87%. A probabilistic methodology is presented for the assessment of the remaining life of a corroded pipeline transporting gas, and a finite element method (FEM) was used to assess the pipeline failure pressure. The numerical FEM modeling results were compared with the commonly used codes-models for calculating limit pressure to establish a more realistic and accurate engineering model. The reliability analysis of an API 5L X60 steel made Algerian natural gas pipeline, in service for thirty years, and exposed to active corrosion attack, is presented. The sensitivity analysis of the basic random variables within the nonlinear limit state function was carried out to bring out the relative contribution of each variable affecting the remaining life of corroded pipelines. The reliability analysis is carried out by using Breitung's formula, based on the second-order reliability method (SORM). The reliability assessment of the corroded pipeline is based on the usage of the notched failure assessment diagram (NFAD), different codes for the calculation of the failure pressure, and the numerical results using the finite element analyses (FEA) software ANSYS.
Résumé: The microstructure and the mechanical properties of a super martensitic stainless steel (SMSS) were investigated in this study. Test specimens were taken from seamless tube generally used in oil and gas industries. The specimens were plastically deformed by tension from its as-received state to different levels of elongation at 2%, 10%, and 15%, respectively. The focus was to study the influence of plastic deformation on the tribological behavior against alumina balls in dry conditions and the corrosion resistance in 3.5% NaCl solution. Analysis results showed an abrasive wear as the main wear mechanism. Plastic deformation prior to sliding wear test increases wear resistance as the deformation rate increases. Based on the electrochemical experiments, all of the specimens showed an increase in their corrosion resistance i.e., the corrosion potential Ecorr (vs. Ag/AgCl) tends to move toward more noble values with respect to the initial potential. The greatest polarization resistance was displayed by the specimen with 10% of deformation rate.