A process for producing a multilayer pipe by expansion, wherein the multilayer pipe comprises at least one external layer made from an outer pipe of metallic material and an internal layer made from an inner pipe of metallic material the inner pipe having an elastic return smaller than the elastic return of the outer pipe when both are deformed and having an external diameter smaller than the internal diameter of the outer pipe; said process comprising the steps of: mounting the pipes, wherein the inner pipe is inserted inside the outer pipe; joining the inner pipe and the outer pipe together in a first mechanical expansion, which comprises providing a relative movement between a mandrel and the mounted pipes in a longitudinal direction, with the mandrel being located internally in the inner pipe, wherein at least part of the mandrel has a greater external diameter than an internal diameter of the inner pipe, wherein in the first mechanical expansion, the mandrel causes plastic deformation of a wall thickness of the inner pipe, said process being characterized in that: the outer pipe of metallic material consists of a carbon manganese steel alloy and the inner pipe of metallic material consists of a corrosion-resistant alloy; in the first mechanical expansion the expansion of the pipe causes only elastic deformation of a wall thickness of the outer pipe, wherein an external diameter deformation of 0.1 to 20% and a wall thickness deformation of 0.1 to 40% is provided to the mounted pipes together when comparing the total deformation values of the final pipe to the initially assembled pipes before the production process. mounting the pipes, wherein the inner pipe is inserted inside the outer pipe; joining the inner pipe and the outer pipe together in a first mechanical expansion, which comprises providing a relative movement between a mandrel and the mounted pipes in a longitudinal direction, with the mandrel being located internally in the inner pipe, wherein at least part of the mandrel has a greater external diameter than an internal diameter of the inner pipe, wherein in the first mechanical expansion, the mandrel causes plastic deformation of a wall thickness of the inner pipe, said process being characterized in that: the outer pipe of metallic material consists of a carbon manganese steel alloy and the inner pipe of metallic material consists of a corrosion-resistant alloy; in the first mechanical expansion the expansion of the pipe causes only elastic deformation of a wall thickness of the outer pipe, wherein an external diameter deformation of 0.1 to 20% and a wall thickness deformation of 0.1 to 40% is provided to the mounted pipes together when comparing the total deformation values of the final pipe to the initially assembled pipes before the production process. the outer pipe of metallic material consists of a carbon manganese steel alloy and the inner pipe of metallic material consists of a corrosion-resistant alloy; in the first mechanical expansion the expansion of the pipe causes only elastic deformation of a wall thickness of the outer pipe, wherein an external diameter deformation of 0.1 to 20% and a wall thickness deformation of 0.1 to 40% is provided to the mounted pipes together when comparing the total deformation values of the final pipe to the initially assembled pipes before the production process.