Abstract: A weldable plastic tube has at least one end designed to be butt welded and designed for the conveyance of a fluid producing a drop in mechanical resistance of the weldable plastic. The tube includes an internal layer for protection of the plastic of the tube from contact with the fluid conveyed and adjoining the welding end has a terminal section permanently covered with an external reinforcing sleeve also of weldable plastic to participate in the butt welding of the tube. The sleeve has a thickness such as to make the mechanical resistance of the tube section nearest the welded end at least equal to the mechanical resistance of the tube not in contact with the fluid when in contact with the fluid in the welding zone which will be without the internal protective layer.

Abstract: A union for tubes having a first external wall and a second internal wall coaxial with the first to define a chamber around a central duct. The union includes at least two seats for reception each of one end of a tube to be connected. Each seat includes a first surface designed to adhere to an end segment of the first wall of a tube inserted in the seat and a second surface coaxial with the first and designed to adhere to an end segment of the second wall of the tube. Between the first and second surfaces of the union there is a connection surface. The union includes in it first ducts which lead into the connection surfaces to provide connection between the chambers of tubes inserted in the seats and second ducts which lead into spaces circumscribed by the second surfaces to provide connection between the central ducts of the tubes.

Abstract: A pipe for fluid transportation is made up of a first layer of material with a first desired critical pressure PC1 and a second layer of material with a critical pressure PC2<0.4PC1. Thickness of the first layer is between 0.1% and 25% of total pipe thickness but not less than 0.3 mm and preferably 0.5-1 mm). Surprising it is observed that a pipe made in this manner has a critical pressure CP near the first desired critical pressure PC1 despite the low thickness of the first layer.

Abstract: A pipe fitting for pipelines comprises at least one seating (12) for receiving the end of a pipe to be coupled. The seating surface which is intended to come into contact with the surface of the pipe end, is made of a material having a chemical adhesion reaction on reaching of a predetermined temperature and, around the seating (12), the pipe fitting incorporates an electric winding (14) for heating of the material when an electric current passes therethrough in order that said predetermined temperature can be reached. Advantageously, the seating (12) is formed in a sleeve (17) incorporating the electric winding (14) which in turn is incorporated into the pipe fitting body.