In support of using high strength steels for strain-based design of pipeline, curved wide plate (CWP) tests in tension are being performed on API 5L X100 pipes of 36-inch (916-mm) diameter and 0.75-inch (19-mm) wall thickness. The CWP tests are being used to optimize and validate welding procedures and to determine the defect tolerance of the girth welds. A method of fatigue pre-cracking CWP specimens for final notch preparation in bending was developed to follow ASTM guidelines for final flaw preparation by fatigue pre-cracking. In order to achieve sufficient stress levels for fatigue crack growth in the curved plate, a strain field analysis was performed to optimize the loading support design as well as the inner and outer span dimensions for four-point bending. In addition to the stress field analysis, a 3-D finite element model of the CWP specimen was generated to analyze the CWP specimen in four-point bending. The stress-intensity factor required for fatigue pre-cracking under the applied loads was predicted and compared to the experimental data. Finite Element Analysis (FEA) results and experimental data were used to confirm the hypothesis that, under the proposed loading arrangement, the closed form solutions for stress-intensity (K) for flat plates in bending can be used to approximate the K for CWP specimens in bending. The identification of an appropriate K equation allowed the determination of force amplitude levels for fatigue crack growth and the introduction of fatigue marker bands. Force and crack mouth opening displacement (CMOD) data were analyzed to correlate compliance with crack depth measurements taken from the fatigue marker bands measured on liberated crack surfaces. Based on experimental results, a methodology was developed to accurately extend surface flaws in curved wide plate specimens in bending.
Proceedings Title: Proceedings of the 8th International Pipeline Conference IPC2010 September 27-October 1, 2010, Calgary, Alberta, Canada
Conference Dates: September 27-October 1, 2010
Conference Location: Calgary, -1
Pub Type: Conferences
Curved Wide Plate, Fatigue Pre-Crack, Compliance Intercept, X100, Strain Based Design