DNV GL has recently carried out a JIP to propose rational design criteria for clad and lined pipes. Attention has been paid to pressure containment, local bucking/wrinkle, fracture and fatigue limit states. In DNV GL JIP design guideline, a strain criterion for the liner wrinkle limit state is proposed. The criterion is based on experimental test results and it does not include any safety factor. Advanced FE Model, purposely calibrated through dedicated experimental tests, can be developed to quantify the strength and deformation capacity of lined pipes considering installation and operational loads, pipeline geometry and fabrication technology and tolerances.
The FEM analyses well reproduced the behavior of clad/lined pipelines subject to combined loads. The presence of liner contributes to the overall pipeline strength and deformation capacity, although introduces an issue due to the risk of wrinkling and detachment from the baking steel. For lined pipes with no or low internal pressure, the liner will normally separate, i.e. wrinkle, from the backing steel prior to reaching the local buckling capacity of the backing steel alone.
Advanced FEM analysis approach can be very helpful for lined pipe strength and deformation capacity assessment, aiding engineer during the design process. The accurate reproduction of failure modes under combined loads can drive engineers through a proper design of clad/lined pipe in offshore extreme environment/loading conditions.