Remaining Local Buckling Resistance of Corroded Pipelines

Abstract

This paper describes a multi-year PRCI research program that investigated the local buckling (or wrinkling) of onshore pipelines with metal-loss corrosion. The dependence of local buckling resistance on wall thickness suggests that metal-loss defects will considerably reduce such resistance. Due to the lack of experimental data, overly conservative assumptions such as a uniform wall thickness reduction over the entire pipe circumference based on the defect depth have been used in practice. The objective of this research work was to develop local buckling criteria for pipelines with corrosion defects. The work related to local buckling was carried out in three phases by C-FER and the University of Alberta. The first phase included a comprehensive finite element analysis to evaluate the influence of various corrosion defect features and to rank key parameters. Based on the outcome of Phase 1 work, a test matrix was developed and ten full-scale tests were carried out in Phase 2 to collect data for model verification. In Phase 3, over 150 parametric cases were analyzed using finite element models to develop assessment criteria for maximum moment and compressive strain limit. Each criterion includes a set of partial safety factors that were calibrated to meet target reliabilities selected based on recent research related to pipeline code development. The proposed criteria were applied to in-service pipeline examples with general corrosion features to estimate the remaining load-carrying capacity and to assess the conservatism of current practice.

The Local Buckling Response of Internally Corroded Steel Pipelines under Combined Loads

“…For most steel used in pipelines, the ultimate to yield strength ratio based on the actual yield strength according to testing standards falls within 1.1 to 1.5. This has also been found in test specimens by Dorey et al (2001) and Chen et al (2010). When there is no yield plateau, the actual yield strength is always higher than the proportional limit.…”

“…The average of these end moments is referred to the global moment (M g ). When there is an applied axial load and internal pressure, an additional moment is introduced at the mid-span due to the second order effect, as shown in the schematic of the pipe loads for the tests by Chen et al (2010) in Fig. 2.4.…”

“…Dorey et al (2001) andTan (2008) have been successfully conducted using the finite element software package ABAQUS. Based on the good agreement between the analytical and experimental results shown in the aforementioned studies, ABAQUS (2013) is also used in the current study.The finite element model is validated against a series of plain and corroded pipe tests that have been conducted byChen et al (2010). Therefore, the model similar to that of the test setup is maintained in the numerical model.…”

“…Measured material properties for LB-I specimens byChen et al (2010) Results for materials with the relative strains (ε er ) of 0.07, 0.12 and 0.17 with σ er ratio of 1.65 =0.07 ε er =0.12 ε er =0.17 ε er =0.07 ε er =0.12 ε er =0.17 ε er =0.07 ε er =0.12 ε er =0.Results for materials with the ultimate to yield strength ratios (σ er ) of 1.3, 1.65 and 2.0 with ε er of 0.12 Parameters for the material properties used in the finite element parametric study…”

“…Table A.1 True stress-true plastic strain relationship for specimen LB-I, LB-II and LB-IIIbyChen et al (2010) …”