Abstract: A welded joint for metal pipes provided with an inner lining, which is resistant to damages caused by the fluids flowing through them. The pipes are machined in the inside at the areas next to the ends to be joined, forming an undercut at each end. An spacer ring is inserted in the hollow annular space formed by both undercuts. The outer diameter of this spacer ring is substantially equal to the diameter of the corresponding undercuts, and its axial length is substantially equal or less than the sum of the axial lengths of the undercuts of the pipes to be joined. The spacer ring is made of an outer annular layer of a high thermal conductivity metal and at least one inner annular layer of heat-insulating and heat resistant material. The outer annular layer abuts in heat conducting contact with the metal pipes within said undercuts, and the metal pipes are joined by a weld seam.

Abstract: A composite pipe formed by an outer metallic pipe with plastic material inner lining is described. The pipe presents resistance to internal and external pressure defined by the metallic pipe properties, and resistance to aggressive agents defined by the plastic material. The inner lining is a prefabricated plastic material pipe inserted into the metallic pipe, interposing a means able to transmit the internal pressure within the plastic material pipe to the metallic pipe. Also described is a method of manufacturing said composite pipe, wherein a prefabricated thermoplastic material pipe is inserted into a metallic pipe, also interposing a means able to transmit the internal pressure within the plastic material pipe to the metallic pipe.

Abstract: A composite pipe formed by a metallic pipe with inner lining, in particular of plastic material, resistant to corroding agents, wherein the inner lining is constituted by a prefabricated plastic material sleeve which is expanded inside the metallic pipe to abut its inner surface, interposing an adhesive means capable of transmitting mechanical loads to transmit the internal pressure in the plastic material sleeve to the metallic pipe, preventing collapse of the plastic material sleeve when lacking internal pressure. Also, a method for manufacturing said composite pipe and its use.

Abstract: Composite pipe formed by a metallic pipe with inner lining of plastic material resistant to corroding agents, the inner lining formed by a prefabricated plastic material lamina, curved to tubular shape to adapt it to the inner surface of the metallic pipe, its longitudinal edges abutting or separated by a small width joint. The curved lamina is placed inside the metallic pipe adhered to its inner surface, filling the joint between its longitudinal edges with a filler compatible with the plastic material of the lamina and the material of the metallic pipe, and resistant to the fluids to be conveyed through the composite pipe. Also, a method to manufacture said composite pipe, comprising placing into the metallic pipe a curved plastic material lamina, expanding same until adhering against the inner surface of the metallic pipe, by means of an adhesive, filling the joint between the edges of the curved plastic material lamina with a filler material.

Abstract: A seal for threaded joints of pipelines formed by pipes with outer threads joined by couplings with inner threads, the seal constituted by a substantially cylindrical sleeve of elastomeric material, wherein the outer surface of the sleeve has at least on part of its length a thread engaging the inner thread of the coupling. The sleeve can be enlarged at both ends by sealing lips. Preferably, the seal is used for joints of pipelines to convey fluids, especially corroding fluids, hydrocarbons and its derivates, and the like.