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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

First Major Improvements to the Two-Curve Ductile Fracture Model-Part I Main Body

The most commonly used fracture analyses procedure used for the prediction of minimum arrest toughness and fracture speed for axially running cracks in natural gas transmission line pipe materials is the Battelle Two-Curve approach. This analysis procedure incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this model, the effect of backfill on the propagating crack fracture speeds is lumped into one empirically based “backfill coefficient,” which does not distinguish different soil types or strengths. Some modifications to this backfill coefficient have been proposed for frozen soil as a function of moisture content, and for water backfill for offshore applications, but no attempt has been made to quantify the effects of soil type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. This report details the results generated from a program sponsored by the US Department of Transportation and the Pipeline Research Council International aimed at making the first improvement to the treatment of soils in the Battelle Two-Curve approach. A series of small-diameter (6-inch) pipe burst tests were conducted with different well-controlled soil backfill conditions. These experiments were conducted at the Emc2 high-energy pipe experimental facility in Mojave California and thus termed, “Mojave Experiments.” Different soil types ranging from cohesive clays to fine grain sands were used as backfill in the burst tests. The moisture content and compaction level was well controlled and varied between the experiments. In addition soil strength experiments were carried out to determine the changes in strength with moisture and compaction levels. Through an information exchange agreement, the results from a series of large-diameter burst tests conducted by the Japanese Gas Association were combined with the results generated in this program to develop trends relating the depth and cohesiveness of soil to the fracture velocities. These trends are incorporated into a Windows-based computer code called PIPEDFRAC for the calculation of minimum arrest toughness. Also in this program, unique instrumentation was developed for the measurement of the crack-tip-opening-angle (CTOA) in a full-scale burst test. The CTOA has been shown to be a very useful fracture parameter in predicting stable crack propagation for large amounts of crack growth in engineering materials. The development of this instrumentation focused on an electronic device, termed the Hall Effect Sensor, and a mechanical device, termed the WireCTOA. The details of the development of each of these devices and their application to both the Mojave and JGA experiments are presented in this report.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Program Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 300p

Subject/Index Terms

Filing Info

  • Accession Number: 01648527
  • Record Type: Publication
  • Report/Paper Numbers: 03-G78-01
  • Contract Numbers: DTRS56-03-T-0007; PR-276-04505
  • Files: TRIS, ATRI, USDOT
  • Created Date: Oct 17 2017 5:27PM