Interference effect of a bridge concrete foundation structure on buried pipeline
Christophe Baeté, Elsyca NV.
CP is an effective method for protecting coating defects on buried pipelines if sufficient current reaches the pipeline surface. In the presence of nearby foundations structures shielding effects may jeopardize the effectiveness of CP and coating surveys.
A case is discussed of a 57 km long 30 inch 3L-PE coated high pressure natural pipeline section with very low CP current demand. Halfway the trajectory a new 420 m long motorway bridge structure is built above the pipeline. In total 498 reinforced concrete foundation piles are aligned along the pipeline causing a potential risk of shielding the low cathodic current. In addition, the pipeline is connected to the bridge structure by an anchoring system for stabilization purposes during settlement of the bridge structure after construction. The anchor positions are susceptible locations where significant coating damage may occur on the short or longer term. The reliability of DCVG survey was therefor questioned as well.
The degree of shielding effect was validated with FEM based computer modeling. The protection level of the pipeline and the DCVG sensitivity was computed for various scenarios. Modeling visualizes the CP current path to the pipeline and through the foundation piles. A local CP design was elaborated for anticipating on the possible coating damages in the future.