Strain-based Design – Advances in Prediction Methods of Tensile Strain Capacity

摘要

In recent years, ExxonMobil has undertaken a comprehensivernexperimental and numerical program to characterize tensile strainrncapacity of welded pipelines under different operational, geometric andrnmaterial property conditions. Key parameters affecting tensile strainrncapacity have been identified through sensitivity studies and used in arnlarge scale FEA-based parametric study to develop closed-form tensilernstrain capacity equations for different limit states. A key parameterrnaffecting tensile strain capacity of welded pipelines is the tearingrnresistance (CTOD R-curve). Small-scale testing techniques have beenrndeveloped to characterize the tearing resistance (R-curve) of full-scalernpipelines using single edge notched tension (SENT) specimens.rnExperimental and numerical results have shown that the SENT Rcurvesrnclosely match the full-scale test R-curves. The generalizedrntensile strain capacity equations have been validated against 20 fullscalerntest data for X65-X80 grades. The equations correctly predict thernobserved failure mode in the full-scale tests and also the tensile strainrncapacity. Simplified, conservative tensile strain capacity equations withrnfewer parameters have been developed by making reasonablernassumptions for several key parameters. The generalized and simplifiedrntensile strain capacity equations can form the basis of a multi-tierrnengineering critical assessment (ECA) procedure for strain-basedrndesign of welded pipelines.