An Experimental Determination of Fracture Toughness of API X46 Steel Pipeline Using Single Edge Bend and Crack Assessments by Failure Assessment Diagrams

For the first time, the fracture toughness of pipeline with outer diameter of 168.3mm (thickness: 6.9mm; grade: API X46) was determined using the J-integral (according to ASTM standard E1820), single edge bend [SE(B)], and single-specimen method. The pre-crack was created using fatigue and the crack propagation was measured using the unloading compliance method. In each stage of crack propagation, the J-integral parameter was calculated and JQ was obtained using the J-R curve. The results indicated that satisfied the test’s validity criteria, and was equated to JQ. Subsequently, KIC was gained from the relationship between JIC and KIC. For the given pipeline, JIC and KIC were equal to 51 kJ/m2 and 105.4MPa√m, respectively. In addition, assessment of longitudinal cracks with different depths and lengths on the pipes body was conducted using fracture toughness and Failure Assessment Diagrams (FADs) for levels one and two of BS7910 standard. Results showed that a longitudinal crack with a depth of 5mm and a length of 220mm lies in the safe zone.