STP700: Development of Some Analytical Fracture Mechanics Models for Pipeline Girth Welds

    de Wit, R
    Physicist and metallurgist, Fracture and Deformation Division, Center for Materials Science, National Measurement Laboratory, National Bureau of Standards, Washington, D.C.,

    Smith, JH
    Physicist and metallurgist, Fracture and Deformation Division, Center for Materials Science, National Measurement Laboratory, National Bureau of Standards, Washington, D.C.,

    Pages: 16    Published: Jan 1980


    Abstract

    Analytical models based on fracture mechanics technology are developed to establish predicted critical defect sizes for sharp, circumferential defects in pressurized pipe. These models are only intended to provide a theoretical basis for establishing predicted critical defect sizes. The general problem considered here is that of a surface-defect in a plate; that is, the flat plate analogy is used here for a pipeline. Failure is considered to occur when the ligament ruptures and provides a leakage path. The fracture mechanics model used, called the collapsed ligament model, is based on the work of Erdogan and Bakioglu, which is in turn based on the Dugdale model. The collapsed ligament model assumes plastic collapse in the depth direction but any fracture mechanics model in the length direction. To illustrate the use of these theoretical models for defects in pressurized pipes, curves are derived that show the predicted critical defect sizes. In these curves, the defect depth is plotted versus the defect length for a given set of material properties and applied stress. Defects having sizes that fall below this curve are not expected to extend. On the other hand, it is assumed that defects with sizes which fall above the curve will extend.

    Keywords:

    collapse, cracks, defects, failure, fracture mechanics, girth welds, pipeline, plasticity, strength, stress, toughness, fractures (materials), crack propagation


    Paper ID: STP36989S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP36989S


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