Fatigue Design Data Derived From Full Scale Tests on 6”OD Pipe Girth Welds

A literature survey of high quality girth welds intended for pipelines risers was carried out and the results are compared with full scale resonance fatigue test data on 6” pipes. The samples were made from 168.3×9.9mm (OD×WT) seamless pipes, each having two welds. Axial misalignments (hi-lo’s) and lack of penetration (LOP) defects were introduced in the test pipes to study the effects on the mean minus 2 stand, deviation design S-N curve that was calculated. Post failure examination of the welds was performed to determine the type and size of defects in the failure initiation area. Fracture mechanics calculations were carried out to determine the effect of defects on fatigue life. The test results were compared with published data on 6” pipes with high quality welds. The scatter in the fatigue test data was reduced when comparisons were based on the local stress at the point of fracture initiation. The implications for design rules of the findings in this work are discussed.