Very few studies have been conducted concerning fatigue in steel line pipe and fewer using full-scale testing. Further, at the time of this study, no research based on full-scale testing was available in open literature regarding longitudinal fatigue cracks, despite being considered more critical. In the current research work, fatigue crack growth was investigated in NPS 20, API 5L X 70 grade, ERW straight-seam steel line pipes in the base metal and at the weld seam for various orientations. It was found that there was no significant difference between fatigue crack growth in the base metal and at the weld seam for the tested stress ratio. Increasing the angle of inclination of the crack with respect to the weld line was found to decrease the rate of fatigue crack growth due to a decrease in the Mode I stress component. Finally, it was observed that despite the difference in fatigue crack growth rates, the crack aspect ratios were nearly identical for all cracks at the same crack depth.