Method for producing a high-pressure pipe

Abstract

Method for producing a high-pressure tube with inner tube and outer tube made of metal are drawn together through a first drawing die. The outer diameter of the inner tube is smaller than the inner diameter and drawing forms a very stable frictional connection between the inner tube and the outer tube. The manufactured tube has a large wall thickness and is very robust and pressure-resistant while having a very high quality outer shell surface and in particular a very high quality inner shell surface by virtue of the cold forming process. These two properties allow a sufficiently high protection against bursting when pressures in excess of 12,000 bar are applied to the tube. The produced tube has improved dynamic pressure resistance against high pressures by combining a large wall thickness of the tube to be manufactured with a high quality inner shell surface of the tube to be manufactured.

1 . A method for manufacturing a tube comprising the steps of:
 providing an inner tube made of metal having a first inner diameter and a first outer diameter;   providing an outer tube made of metal with a second inner diameter and a second outer diameter, wherein the first outer diameter is smaller than the second inner diameter, and wherein inserting the inner tube into the outer tube such that the inner tube extends within the outer tube; and   drawing of the inner tube and the outer tube together through a first drawing die, wherein the second inner diameter is reduced such that a frictional connection of the outer tube and the inner tube is established.   
     
     
         2 . The method according to  claim 1 , wherein the tool diameter of the forming inner surface of the first drawing die, the second outer diameter of the outer tube, the second inner diameter of the outer tube, the first outer diameter of the inner tube and the first inner diameter of the inner tube are selected such that the first inner diameter of the inner tube during the drawing of the outer tube and inner tube extending therein together through the first drawing die is reduced by at most 5%. 
     
     
         3 . The method according to  claim 1  wherein the first outer diameter of the inner tube by drawing of the outer tube and the inner tube extending therein together through the first drawing die is reduced by at least 0.01 mm and by at most 0.3 mm. 
     
     
         4 . Method according to  claim 1 , wherein the inner tube after drawing of the outer tube and the inner tube extending therein together through the first drawing die is strain-hardened and has a tensile strength of at least 900 N. 
     
     
         5 . The method according to  claim 1 , wherein the tube to be manufactured after drawing of the inner tube and the outer tube through the first drawing die has a wall thickness, which is defined by half the difference between the second outer diameter of the outer tube and the first inner diameter of the inner tube, at least one third of the outer diameter of the outer tube, wherein the wall thickness is at least one third of the outer diameter of the outer tube. 
     
     
         6 . The method according to  claim 1 , wherein the tool diameter of the forming inner surface of the first drawing die prior to drawing of the inner tube and the outer tube together through the first drawing die is by at least is 5% smaller than the second outer diameter of the outer tube prior to drawing. 
     
     
         7 . The method according to  claim 1 , wherein the inner shell surface of the inner tube has a surface quality such that existing cracks on the surface do not exceed a depth of 50 μm. 
     
     
         8 . The method according to  claim 1 , wherein the inner tube is manufactured by drawing a hollow of metal through a second drawing die and over an inner die tool. 
     
     
         9 . The method according to  claim 1 , wherein the inner tube is manufactured by in a pilger mill by rolling a hollow of metal over a mandrel. 
     
     
         10 . The method according to  claim 2 , wherein the inner die tool or the mandrel is made of steel with a polished surface, such that an inner shell surface of the inner tube is burnished during drawing of the inner tube over the inner die tool or by rolling over the mandrel. 
     
     
         11 . The method according to  claim 1 , wherein a material of at least the inner tube or the outer tube is selected from a group consisting of a carbon steel, a low alloy steel and a high-alloy steel or a combination thereof. 
     
     
         12 . The method according to  claim 1 , wherein the first outer diameter of the inner tube prior to drawing of the outer tube and the inner tube extending therein together through the first drawing die is in a range from 6.25 mm to 6.45 mm, and after the common drawing is in a range from 6.08 mm to 6.28 mm, wherein the first outer diameter of the inner tube is reduced by the common drawing. 
     
     
         13 . The method according to  claim 1 , wherein the inner tube and the outer tube are made of the same material. 
     
     
         14 . The method according to  claim 1 , wherein the inner tube and the outer tube are made of different materials. 
     
     
         15 . The method according to  claim 2 , wherein the first outer diameter of the inner tube by drawing of the outer tube and the inner tube extending therein together through the first drawing die is reduced by at least 0.01 mm and by at most 0.3 mm. 
     
     
         16 . The method according to  claim 3 , wherein the inner die tool or the mandrel is made of steel with a polished surface, such that an inner shell surface of the inner tube is burnished during drawing of the inner tube over the inner die tool or by rolling over the mandrel.