Fracture Toughness and Fatigue Properties of Pipeline Base Steels and Welds in High-Pressure Hydrogen and Technologies for Improving Weld HE and IGSCC Resistance for Alternative Fuel Pipelines

Two types of pipeline steels, Alloy B [Fe-0.05C-1.52Mn-0.12Si-0.092Nb, weight percent (wt.%)] and Alloy C [Fe-0.04C-1.61Mn-0.14Si-0.096Nb, wt.%)], were tested to understand the relationship among composition, microstructure, and fatigue resistance. Vickers hardness and nanoindentation tests were used to obtain the hardness and elastic modulus. Compact-tension (CT) specimens were employed for fatigue experiments. Different frequencies (10 Hz, 1 Hz, and 0.1 Hz) and different stress ratios [0.1 and 0.5, the stress ratio (R) is defined as the ratio between Pmin. (minimum applied load) and Pmax. (maximum applied load). R = Pmin./Pmax.] were used, and the tests were conducted in air, at room temperature. The effects of frequencies and different R ratios on crack-growth rates were compared. It is concluded that a higher R ratio leads to a greater fatigue-crack-growth rate (FCGR), while frequency does not have much influence on FCGRs. Moreover, Alloy B tends to have a better fatigue resistance than Alloy C under various test conditions. The microstructures of two alloys were investigated by optical microscopy (OM), scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). Fracture surfaces show transgranular patterns, and fatigue striations were observed under SEM. Another type of pipeline steel, X70 [Fe-0.053C-1.52Mn-0.25Cr-0.19Si-0.089Nb, weight percent (wt.%)], was also studied. Fatigue tests were performed at different load levels, and comparisons were made between different parts of weld and base metals. Fracture surfaces were observed by SEM to identify fatigue and fracture mechanisms. X-ray and Neutron-scattering-diffraction experiments were performed to study the deformation behavior around the crack tip of X52 [Fe-0.071C-1.06Mn-0.24Si-0.026Nb, weight percent (wt.%)] and X70 pipeline steel. Both the hydrogen-charged sample and as-received sample were used to detect the influence of hydrogen. High-energy X-ray diffraction experiments were performed to detect the plastic-zone information during the deformation. Results are presented in this report.

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  • Corporate Authors:

    University of Tennessee, Knoxville

    Department of Materials Science and Engineering
    Knoxville, TN  United States 

    Oak Ridge National Laboratory

    Oak Ridge, TN  United States  37831

    Pipeline and Hazardous Materials Safety Administration

    Office of Hazardous Materials Safety
    Washington, DC  United States 
  • Authors:
    • Liaw, Peter K
    • Muralidharan, Govindarajan
    • Chen, Bilin
  • Publication Date: 2014-12-31


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report: Part 1
  • Features: Figures; Photos; References; Tables;
  • Pagination: 92p

Subject/Index Terms

Filing Info

  • Accession Number: 01640784
  • Record Type: Publication
  • Report/Paper Numbers: 323
  • Contract Numbers: DTPH56-10-000001
  • Files: TRIS, ATRI, USDOT
  • Created Date: Jun 20 2017 9:33AM