Development of Acceptance Criteria for Mild Ripples in Pipeline Field Bends

Field bends in large diameter pipe are routinely used in the construction of oil and gas pipelines. Mild ripples along the intrados are often unavoidable where such bends have a high D/t or high yield strength. Present regulations and industry standards differ in their treatment of mild ripples, consequently, the acceptance of such features has been heretofore inconsistent. A review of prior work on the subject was undertaken. Shell finite element analysis was then used to estimate the effect of ripple magnitude and spacing on stresses due to pressure and bending. Stress concentration effects were used with a suitable fatigue damage rule to estimate the effect of ripple parameters on service life. Results were benchmarked against the available test data.