The disclosure presents processes for improving the design phase of plastic material lined tubular structures used downhole of a borehole. A plastic material lined tubular structure model is utilized for tubular structures that have a metal layer, a grout layer, and a plastic material layer. The model can use a modified wall thickness for the metal layer. A strength model can be applied to the modified critical dimensions, e.g., wall thickness parameters. A thermal model can be applied to the tubular structure to determine pressure and temperature parameters. The strength model and the thermal model outputs can be utilized by a stress analyzer to determine loads, safety factors, and design limit parameters. The plastic material lined tubular structure model can enable more efficient use of tubular structures, designing a longer operational lifetime, such as in acidic environments, or the use of thinner structures while maintaining a satisfactory operational lifetime.