Standard

API TR 5DCB

Revised

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Abstract

To help establish the technical basis for accurately using the double cantilever beam (DCB) test, API sponsored research on the methodology of continuous DCB testing. This work established the testing conditions of specimen design, arm displacement, chemical makeup of the aqueous test solution (composition and pH), time, and temperature. This has brought the state of the art to the point where the proper arm displacements can be selected for both NACE standard conditions and for fit-for-purpose conditions, thereby minimizing the number of invalid tests. The rapidly expanding use of C-110 casing in the search for new supplies of oil and gas in sour formations has made it crucial to accurately characterize the resistance of such tubulars to sulfide stress cracking (SSC). This is best done by the DCB test, the only test that gives a numeric value from each specimen (other tests rely on the statistical analysis of fail/no-fail results, a process that does not give such rapid and precise ratings as does the DCB test). For this reason, the DCB test has gained wide acceptance since it was standardized by NACE in 1990. The fracture toughness calculated by NACE TM0177-2016 [1], Method D, is evaluated by cracks that grow vertically with respect to the direction of opening stress due to wedge insertion. edge cracks that prevent the progress of sulfide stress cracking (SSC) occur in high-strength low-alloy oil country tubular goods such as API 5CT, Grade C110 material (specified minimum yield strength is 760 MP), which affects the evaluation. When the test specimen specified in NACE TM0177-2016 is used, it has been reported that one of the causes is excessive stress concentration at the bottom of the V-shaped side groove with root (R) 0.25 mm, which helps to initiate an edge crack. If edge cracks occur, there is a risk that the results will be judged as invalid by NACE TM0177-2016, which wastes time for testing due to the retest.

Document information

  • Standard from API_AC
  • Published:
  • Version: 0
  • Document type: IS
  • Additional information
    • FIRST EDITION