Method for Producing Seamless Pipe

Abstract

Disclosed is a method for producing a seamless pipe by using a piercing mill which pierces and rolls a round billet heated to 1300° C. or lower, wherein the piercing mill is composed of a pair of skew rolls disposed to face each other around a pass line, a pair of guide devices disposed to face each other around the pass line, and a plug disposed along the pass line, between the pair of the skew rolls and also between the pair of the guide devices, wherein the piercing-rolling is performed under the conditions satisfying the following formulas (1) to (3) to prevent wrinkle flaws of the seamless pipe: −1.0<Δθ  (1) Δθ=θ p −θ r   (2) −0.37×Δθ+1.47≦ R n ≦0.37×Δθ+2.67  (3) wherein the meanings of the individual symbols in the above-described formulas are as follows: θ r : The half angle (°) between the pass line and the main roll face in the condition of the feed angle of the main rolls being zero θ p : The half angle (°) between the pass line and the reeling section of the plug R n : The number of times of the reeling of the plug

1 . A method for producing a seamless pipe by using a piercing mill which pierces and rolls a round billet heated to 1300° C. or lower, wherein the piercing mill is composed of:
 a pair of skew rolls disposed to face each other around a pass line; 
 a pair of guide devices disposed to face each other around the pass line; and 
 a plug disposed along the pass line, between the pair of the skew rolls and also between the pair of the guide devices, 
 wherein the piercing-rolling is performed under the conditions satisfying the following formulas (1) to (3):
   −1.0<Δθ  (1)
 
   Δθ=θ p −θ r   (2)
 
   −0.37×Δθ+1.47 ≦R   n ≦0.37×Δθ+2.67  (3)
 
 
 wherein the meanings of the individual symbols in the above-described formulas are as follows: 
 θ r : The half angle (°) between the pass line and the main roll face in the condition of the feed angle of the main rolls being zero 
 θ p : The half angle (°) between the pass line and the reeling section of the plug 
 R n : The number of times of the reeling of the plug 
 
     
     
         2 . A method for producing a seamless pipe by using a piercing mill which pierces and rolls a round billet heated to 1300° C. or lower, wherein the piercing mill is composed of:
 a pair of skew rolls disposed to face each other around a pass line; 
 a pair of guide devices disposed to face each other around the pass line; and 
 a plug disposed along the pass line, between the pair of the skew rolls and also between the pair of the guide devices, 
 wherein the piercing-rolling is performed under the conditions satisfying the following formulas (1), (2) and (4):
   −1.0<Δθ  (1)
 
   Δθ=θ r −θ r   (2)
 
   −0.24×Δθ+1.73 ≦R   n ≦0.37×Δθ+2.67  (4)
 
 
 wherein the meanings of the individual symbols in the above-described formulas are as follows: 
 θ r : The half angle (°) between the pass line and the main roll face in the condition of the feed angle of the main rolls being zero 
 θ p : The half angle (°) between the pass line and the reeling section of the plug 
 R n : The number of times of the reeling of the plug 
 
     
     
         3 . The method for producing a seamless pipe according to  claim 1 , wherein the piercing-rolling is performed under the conditions further satisfying the following formula (5):
   −1.37 ×D   2   /D   1 +2.74  (5)
   wherein the meanings of the individual symbols in the above-described formula are as follows:   D 1 : The roll diameter (mm) in the gorge portion of the main rolls   D 2 : The main roll outer diameter (mm) at the position of the maximum-diameter portion of the plug   R n : The number of times of the reeling of the plug   
     
     
         4 . The method for producing a seamless pipe according to  claim 1 , wherein the piercing-rolling is performed under the conditions further satisfying the following formula (6):
   −1.25 ×D   2   /D   1 +2.88 ≦R   n   (6)
   wherein the meanings of the individual symbols in the above-described formula are as follows:   D 1 : The roll diameter (mm) in the gorge portion of the main rolls   D 2 : The main roll outer diameter (mm) at the position of the maximum-diameter portion of the plug   R n : The number of times of the reeling of the plug.