A system comprising: • a joint, wherein the joint comprises at least one position suitable for drilling a conical hole or position where a conical hole has been drilled, the joint being adapted for connecting district heating or cooling insulated pipes, wherein the joint is one of the following types: ∘ a shrink sleeve having a tubular shape for connecting two insulated pipes; ∘ a T-shaped sleeve for connecting three insulated pipes; ∘ a T-shaped shrink sleeve for connecting three insulated pipes; ∘ an open joint, which is connected to an end of two insulated pipes by wrapping the joint around the ends of the two insulated pipes such that the joint obtains a tubular shape, and • at least one plug for closing at least one conical hole in the joint, wherein the at least one plug comprises: - a plug body having round cross-sectional diameters decreasing in size from a first end of the plug body to a second end of the plug body, and - a plug collar with a proximal surface and a distal surface opposite the proximal surface, wherein the plug body extends from the distal surface of the collar and has the largest cross-sectional diameter nearest the plug collar, and wherein the at least one plug is made from a material being directly weldable in at least one conical hole in the joint when the at least one plug and the walls of at least one conical hole are heated to a pre-determined temperature. • a joint, wherein the joint comprises at least one position suitable for drilling a conical hole or position where a conical hole has been drilled, the joint being adapted for connecting district heating or cooling insulated pipes, wherein the joint is one of the following types: ∘ a shrink sleeve having a tubular shape for connecting two insulated pipes; ∘ a T-shaped sleeve for connecting three insulated pipes; ∘ a T-shaped shrink sleeve for connecting three insulated pipes; ∘ an open joint, which is connected to an end of two insulated pipes by wrapping the joint around the ends of the two insulated pipes such that the joint obtains a tubular shape, and ∘ a shrink sleeve having a tubular shape for connecting two insulated pipes; ∘ a T-shaped sleeve for connecting three insulated pipes; ∘ a T-shaped shrink sleeve for connecting three insulated pipes; ∘ an open joint, which is connected to an end of two insulated pipes by wrapping the joint around the ends of the two insulated pipes such that the joint obtains a tubular shape, and • at least one plug for closing at least one conical hole in the joint, wherein the at least one plug comprises: - a plug body having round cross-sectional diameters decreasing in size from a first end of the plug body to a second end of the plug body, and - a plug collar with a proximal surface and a distal surface opposite the proximal surface, wherein the plug body extends from the distal surface of the collar and has the largest cross-sectional diameter nearest the plug collar, and wherein the at least one plug is made from a material being directly weldable in at least one conical hole in the joint when the at least one plug and the walls of at least one conical hole are heated to a pre-determined temperature. - a plug body having round cross-sectional diameters decreasing in size from a first end of the plug body to a second end of the plug body, and - a plug collar with a proximal surface and a distal surface opposite the proximal surface, wherein the plug body extends from the distal surface of the collar and has the largest cross-sectional diameter nearest the plug collar, and