The management of the flow availability in presence of corrosive fluids may considerably impact on CAPEX and OPEX of offshore pipelines. A correct approach starts from the preliminary phases of a project, with the selection of the most appropriate material in relation to the nature of the corrosive fluids and expected degradation mechanisms (i.e. general corrosion, localized or mesa corrosion and pitting). The construction phases include measures that allow meeting welding requirements and safe guarding the integrity of the line-pipe. The operation shall account for the control of process parameters and transported fluid composition.
In the upcoming future offshore pipeline and field development projects, challenging operating conditions in deep/ultra-deep waters means that increasingly careful considerations on the effect of metal loss: corrosion leading to local loss of material may cause a potential pipeline failure under the additional effect of functional and environmental loads, in particular the high external pressure and applied bending moment. The assessment of the structural integrity depends on the type and accuracy of available measurements. In presence of corrosion patterns and accordingly to existing standards (DNV RP-F101, ASME B31G, API 579, BS 7910) the assessment might be unduly conservative; further the presence of important combined loads is not fully covered by standard assessment format.
The use of FEM numerical lab can help the evaluation of the residual strength and deformation capacity of the pipeline affected by corrosion, leading to a quite-deterministic characterization of pipeline strength capacity at design stage and in operation. Several studies (both theoretical and experimental) available in the open literature faced this issue and their findings support the proposed analysis methodology. Recently full scale tests have been conducted by the relevant Oil & Gas industry companies (such as Statoil and ENI) and the obtained results have been used for the FE Model calibration and validation of corroded pipelines. Herein an application is presented in order to understand and appreciate the proposed methodology performance in corroded pipeline assessment.