Patent ID: 11945020
Assignee: JFE STEEL CORPORATION
Field: Machine tools (Mechanical engineering)
Classification: CPC B | IPC B

Claim 0:
1. A method for manufacturing a metal pipe, the method comprising:
a pipe-end-portion expansion step of expanding pipe end portions that are located at both ends of a mother pipe;
an internal pressure application step that is performed after the pipe-end-portion expansion step and includes expanding the mother pipe by applying an internal pressure p to an entire interior of the mother pipe until the internal pressure, p (MPa), that corresponds to changes in an axial compression amount, s (mm), over time, the axial compression amount, s, representing an amount of compression in a pipe axial direction against pipe extreme ends which are the both ends of the mother pipe, becomes a preset maximum internal pressure pmax (MPa); and
a metal pipe formation step of forming the metal pipe having an outer diameter, DX, in a range of 150 mm or larger and 3,000 mm or smaller and a wall thickness, tX, in a range of 2 mm or larger and 50 mm or smaller and in which a maximum outer diameter (mm) and a minimum outer diameter (mm) in an entire length of the metal pipe satisfy Formula (1):, (
              
                
                  maximum
                  ⁢
                  
                    
                  
                  ⁢
                  outer
                  ⁢
                  
                    
                  
                  ⁢
                  diameter
                
                -
                
                  minimum
                  ⁢
                  
                    
                  
                  ⁢
                  outer
                  ⁢
                  
                    
                      
                    
                    ⁢
                    
                      
                    
                  
                  ⁢
                  diameter
                
              
              )
            
            /
            
              [
              
                
              
              ⁢
              
                
                  (
                  
                    
                      maximum
                      ⁢
                      
                        
                      
                      ⁢
                      outer
                      ⁢
                      
                        
                      
                      ⁢
                      diameter
                    
                    +
                    
                      minimum
                      ⁢
                      
                        
                      
                      ⁢
                      outer
                      ⁢
                      
                        
                      
                      ⁢
                      diameter
                    
                  
                  )
                
                /
                2
              
              ]
            
          
          ≤
          0.0015
        
        ,
      
    
    
      
        Formula
        ⁢
        
          
        
        ⁢
        
          (
          1
          )
        
      
    
  

wherein the internal pressure p and the axial compression amount s satisfy Formula (2):, 0.5
          ×
          
            (
            
              
                p
                /
                p
              
              ⁢
              
                
              
              ⁢
              max
            
            )
          
          ×
          
            (
            
              a
              /
              200
            
            )
          
          ×
          
            L
            0
          
        
        ≤
        s
        ≤
        
          
            (
            
              
                p
                /
                p
              
              ⁢
              
                
              
              ⁢
              max
            
            )
          
          ×
          
            (
            
              a
              /
              200
            
            )
          
          ×
          
            L
            0
          
        
      
    
    
      
        (
        2
        )
      
    
  

where a stands for a preset expansion ratio (%) satisfying 0.30≤a≤5.0, and L0 stands for an average length (mm) of the mother pipe before the pipe-end-portion expansion step.