Optimisation methodology for composite repair systems of transmission pipelines with volumetric surface defects is presented. Due to large dimension of the numerical tasks to be solved, this methodology is developed employing the method of experimental design and response surface technique. To bring an efficiency of damaged section up to the level of undamaged pipeline, two optimisation problems based on equivalently resistant (equiresistant) and minimum weight designs are formulated and solved in the present study. Features, advantages and limitations of both approaches are discussed in their applicability for the optimal design of composite repair systems of transmission pipelines.