Cylindrical tube for industrial chemical installations

Abstract

The invention provides a tube for use in furnaces where gas and liquid media are being passed through the tube from one end to the other while being subjected to substantial heating and decomposition resulting therefrom. The tube is made of a stainless iron-nickel-chromium-base alloy comprising in weight-% max 0.08% C, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15% rare earth metals, and Fe and usual impurities. The cylindrical tube has a smooth outer surface and an inner surface provided with valleys or recesses extending longitudinally with a smoothly curved bottom profile.

What is claimed is:  
     
         1 . A metal tube for use in furnaces where gas and liquid formed media is being pressed through such tube from its inlet end to its opposite end while being subjected to substantial heating and decomposition therefrom, the metal tube comprising: 
 a body;    a smooth outer surface; and an inner surface with a profile; wherein the body is made of a stainless iron-nickel-chromium base alloy comprising, in weight %:    max 0.08% C,    23-27% Cr,    33-37% Ni,    1.3-1.8% Mn,    1.2-2% Si,    0.08-0.25% N,    0.01-0.15% rare earth metals,    and normal impurities; and    the profile comprises a plurality of valleys or recesses, said valleys or recesses extending longitudinally along the tube, and having a smoothly curved bottom.    
     
     
         2 . The tube according to  claim 1 , wherein each of the plurality of valleys or recesses are straight whilst extending longitudinally along the tube.  
     
     
         3 . The tube according to  claim 1 , wherein each of the plurality of valleys or recesses and each of the plurality of peaks extend helically from an inlet end to an opposite end of said tube.  
     
     
         4 . The tube of  claim 1 , further comprising a chromium oxide layer on the inner surface.  
     
     
         5 . The tube according to  claim 1 , wherein the amount of rare earth metals is 0.03-0.10%.  
     
     
         6 . The tube according to  claim 1 , wherein the amount of silicon is 1.3-1.8%.  
     
     
         7 . The metal tube according to  claim 1 , wherein the amount of nitrogen is 0.13-0.18%.  
     
     
         8 . A hydrocarbon cracking furnace comprising a tube according to  claim 1 .  
     
     
         9 . A method of using a metal tube comprising: 
 forming a tube according to claim  1 ;    placing the tube in a hydrocarbon cracking furnace; and    passing gas and liquid reactants through the tube while heating the tube to a temperature above 800° C.