Design Code Considerations for Pipeline Overbends

Abstract Pipeline overbends have significant design challenges and require additional consideration. The significant initial out-of-straightness created by an overbend increases the risk for upheaval buckling. Upheaval buckling can be combated during the design phase using wall thickness, burial depths and backfill specifications. The design requirements may vary depending on the design guidelines and methodologies applied. The soil uplift boundary condition drives a considerable amount of the cost. Better defining the uplift response can aid designers in selecting the appropriate methodology to implement. Potentially reducing pipe stresses and the need for additional mitigations. As allowable pipeline upward deformation limits generally exceed the yield displacement of the backfill the residual soil uplift resistance should be considered in overbend design including upheaval buckling. This becomes a large strain problem that many analyses do not consider. The use of DnV backfill resistance guidelines provides more uplift resistance in drained soils than those provided by the currently applied ALA & PRCI guidelines. These DnV guidelines have been extensively validated for low cover to pipeline diameter ratios, and properly account for both soil weight and its shear resistance. These equations can then be utilized to provide a more accurate representation of actual response conditions, resulting in a more economical design.