Avaliação de integridade estrutural em dutos e tubulações de alta pressão utilizando metodologias baseadas em deformação plástica.

Abstract

Oil and gas pipelines traverse distances of the order of hundreds and even thousands of kilometers. Along those distances the pipelines may be subject to several accidental loads such as large-scale soil movement, slope slides and seabed movements. The plastic strain resulting from these events can seriously affect the structural integrity of pipelines, compromising its mechanical integrity and fluid containment in an eventual pipeline failure. For this reason, it is important to guarantee the structural integrity of those components in order to avoid their plastic instability or ductile fracture. This work explores the capability of computational cell methodology coupled with the Stress Modified Critical Strain (SMCS) damage criterion to simulate the behavior of ductile fracture in tensile specimens subjected to tension load and pipe specimens subjected to large longitudinal strains. Thus, this work focuses on the development of an engineering procedure to assess the structural integrity of pipelines, in order to predict the critical load (tensile failure load) at onset of ductile fracture in pipelines used to transport oil and gas subjected to large plastic strains. A series of tensile test conducted by Toyoda et al. [1] on tensile specimens with different notch radius, for a structural steel, provides the stress-strain response used to calibrate the SMCS damage criterion. Full scale cyclic bend test also performed by Toyoda et al. [1] on a pipe specimen with 165 mm outer diameter and 11 mm wall thickness evaluates the proposed procedure for predicting ductile fracture behavior in damaged pipelines. This exploratory study predicts the tensile failure load associated with the onset of ductile fracture in the highly damaged area by plastic strains inside buckling zone in good agreement with the experimental measurements.