Method for producing a steel underwater pipe that is able to carry a corrosive fluid

A pipe element that is able to carry corrosive fluids, an internal wall of which is partially lined by a protective coating of plastic material of a liner type wherein an assembly by welding directly together ends of at least two pipe elements is provided for, wherein a method for making the pipe element comprises successive steps:

• a) applying a layer of corrosion-resistant steel alloy on a terminal part of length L1 of the internal wall of each pipe element from a first end to be welded;
• b) machining on the pressure side surface of the layer of corrosion-resistant steel alloy,
• c) applying a protective coating of plastic material directly on the internal wall of each pipe element;
• and covering a first part of length L2 of said layer of corrosion-resistant steel alloy, a second, adjacent part of length L3 of said layer of corrosion-resistant steel alloy on a side of the first end to be welded of each pipe element not being covered by said protective coating of plastic material,
• d) coaxially inserting of a compression ring of corrosion-resistant steel alloy inside said terminal part of each pipe element and the crimping of a first annular part of length L4 of said compression ring against the pressure side face of the terminal part of said protective coating of plastic material covering a first part of said layer of corrosion-resistant steel alloy, and the welding of a free end of a second annular part of said compression ring against a second part of said layer of corrosion-resistant steel alloy not covered by said protective coating of plastic material, said first annular part of the compression ring comprising an outer side face which is corrugated, over a part at least of its length said second annular part of said compression ring continuing said first annular part, said second annular part being applied against a part of said second part of the layer of corrosion-resistant steel alloy not covered by said coating of plastic material and extending over a length L5 less than L3, from and against the end of said coating of plastic material until said free end of said compression ring closest to the first end to be welded of the pipe element, and
• e) assembling by welding directly together the ends to be welded of two pipe elements by a corrosion-resistant steel alloy weld;
• wherein, before step e), finish machining is also carried out of the end of the pipe to form a chamfer allowing receiving a weld bead during step e) of end-to-end assembly by welding;
• wherein the pipe element obtained in step 1) and useful in step 2) comprises:
• a layer of corrosion-resistant steel alloy on a terminal part of length L1 of the internal wall of said pipe element from the first end to be welded;
• a protective coating of plastic material applied directly on the internal wall of said pipe element;
• and covering a first part of length L2 of said layer of corrosion-resistant steel alloy, a second part of length L3 of said layer of corrosion-resistant steel alloy on the side of said first end to be welded of said pipe element not being covered by said protective coating of plastic material,
• a compression ring of corrosion-resistant steel alloy inserted inside the pipe element comprising:
• (i) a first annular part of length L4 comprising an outer side face which is corrugated, over a part at least of its length L4, said first annular part being crimped against the pressure side face of at least one terminal part of said protective coating of plastic material covering said first part of said layer of corrosion-resistant steel alloy, and
• (ii) a second annular part of length L5 less than L3, continuing said first annular part, applied against a part of said second part of the layer of corrosion-resistant steel alloy not covered by said coating of plastic material, said second annular part of said compression ring extending from and against the end of said coating of plastic material until said free end of said compression ring closest to the end to be welded of the pipe element, welded against said second part of said layer of corrosion-resistant steel alloy not covered by said protective coating of plastic material;
• wherein a second end of said pipe element is arranged not to be welded and is provided without said compression ring, the second end comprises a rigid tubular junction sleeve of thermoplastic material, a first longitudinal end of said sleeve being in sealed contact or being formed in a continuous piece with the other end of said coating of plastic material inside said pipe element, a second end of said sleeve protruding by a length L0 outside the other end of said pipe element.