Stainless steel tubes and method for production thereof

Abstract

A method for producing a tube of a stainless steel alloy tube which comprises the steps of hot working a stainless steel casting into a pretubular shaped workpiece or into a cylindrical bar, trepanning the cylindrical bar or machining an inner diameter of the pretubular shaped workpiece to obtain a tubular workpiece, and cold working the workpiece. The hot working comprises one of: rolling, forging, and a combination thereof. The cold working comprises flow forming or pilgering. The stainless steel tube produced with the method comprises an outer diameter greater than or equal to 152 mm, an average wall thickness greater than or equal to 2.8 mm and less than or equal to 70 mm, and a length greater than 5 m.

1 . A method for producing a tube of a stainless steel alloy, the method comprising:
 (a) hot working a stainless steel casting into a pretubular shaped workpiece or into a cylindrical bar;   (b) trepanning the cylindrical bar or machining the inner diameter of the pretubular shaped workpiece to obtain a tubular workpiece; and   (c) cold working the tubular workpiece.   
     
     
         2 . The method of  claim 1 , wherein:
 the method further comprises (d) quenching the pretubular shaped workpiece or cylindrical bar; and   (d) is performed after (a).   
     
     
         3 . The method of  claim 1 , wherein:
 the method further comprises (e) casting the stainless steel casting; and   (e) is performed prior to (a).   
     
     
         4 . The method of  claim 1 , wherein the stainless steel alloy is an austenitic-ferritic stainless steel alloy. 
     
     
         5 . The method of  claim 4 , wherein the stainless steel alloy is duplex stainless steel or super-duplex stainless steel. 
     
     
         6 . The method of  claim 1 , wherein the hot working comprises one of: rolling, forging, and a combination thereof. 
     
     
         7 . The method of  claim 1 , further comprising (f) solution annealing the pretubular shaped workpiece or cylindrical bar, at a temperature between 1030° C. and 1120° C. 
     
     
         8 . The method of  claim 1 , further comprising (f) solution annealing the tubular workpiece, and wherein (f) is performed in at least one of the following: after (b) and prior to (c), and after (c). 
     
     
         9 . The method of  claim 1 , wherein:
 the method further comprises (g) heating the stainless steel casting to a temperature higher than 1000° C., and preferably higher than 1200° C.; and   (g) is performed prior to (a).   
     
     
         10 . The method of  claim 2 , wherein quenching the pretubular shaped workpiece or cylindrical bar is performed with water at a temperature not higher than 50° C., and preferably not higher than 35° C. 
     
     
         11 . The method of  claim 1 , wherein the cold working comprises one of: flow forming and pilgering. 
     
     
         12 . The method of  claim 11 , wherein the cold working comprises flow forming, and the flow forming at least reduces thickness of walls of the workpiece by 70% in one pass. 
     
     
         13 . A stainless steel tube produced with the method of  claim 1 , characterized by:
 an outer diameter greater than or equal to 152 mm;   an average wall thickness greater than or equal to 2.8 mm, and less than or equal to 70 mm; and   a length greater than 5 m.   
     
     
         14 . The stainless steel tube of  claim 13 , wherein:
 the outer diameter is greater than or equal to 200 mm;   the average wall thickness is greater than 12 mm; and   the length is greater than 10 m.   
     
     
         15 . The stainless steel tube of  claim 13 , wherein the tube comprises an austenitic-ferritic stainless steel alloy with:
 an average austenite spacing less than or equal to 30 microns; and   a ferrite content greater than or equal to 40%, and less than or equal to 60%.   
     
     
         16 . The stainless steel tube of  claim 13 , wherein the stainless steel tube is seamless.