Oxidation resistant alloy

Abstract

The present invention relates to alloys used to prepare steel pipes i.e. tubes for use in chemical engineering applications. In particular, the invention relates to low carbon aluminium steel alloys and pipes made from such alloys. They may be used in plant such as ethylene cracker furnaces that need to be able to withstand elevated temperatures oxidation and carburisation for extended periods of time, the alloy been able to develop a pure, stable and continuous aluminium oxide layer on it surface when in service which is protective and anti-coking

1 .- 14 . (canceled) 
     
     
         15 . A steel pipe made from an alloy consisting of:
 from 0.15 to 0.35 wt % carbon,   from 2.5 to 5.0 wt % aluminium,   from 40 to 45 wt % nickel,   from 25 to 35 wt % chromium,   from 0.50 to 1.50 wt % niobium and/or vanadium,   from 0.01 wt % to 0.25 wt % yttrium,   from 0.01 wt % to 0.25 wt % tungsten and/or tantalum,   from 0.01 wt % to 0.25 wt % in total of one or more of titanium and zirconium and hafnium,   up to 0.9 wt % manganese,   up to 0.9 wt % silicon, and   up to 0.10 wt % nitrogen,   with the balance of the composition being iron and incidental impurities;   wherein the steel pipe has a substantially continuous layer of alumina on its internal surface.   
     
     
         16 . The steel pipe of  claim 15 , wherein the substantially continuous layer of alumina contains no nickel, no chromium, and no iron. 
     
     
         17 . The steel pipe of  claim 15 , wherein the alloy consists of:
 from 0.15 to 0.35 wt % carbon,   from 2.5 to 5.0 wt % aluminium,   from 40 to 45 wt % nickel,   from 25 to 35 wt % chromium,   from 0.50 to 1.50 wt % niobium, and/or vanadium,   from 0.01 wt % to 0.05 wt % yttrium,   from 0.05 wt % to 0.25 wt % of tungsten and/or tantalum,   from 0.04 wt % to 0.15 wt % in total of one or more of titanium and zirconium and hafnium,   an amount of up to 0.9 wt % manganese,   an amount of up to 0.6 wt % silicon, and   an amount of up to 0.10 wt % nitrogen,   with the balance of the composition being iron and incidental impurities.   
     
     
         18 . The steel pipe of  claim 15 , wherein carbon is present in an amount of from 0.20 wt % to 0.35 wt %. 
     
     
         19 . The steel pipe of  claim 15 , wherein aluminium is present in an amount of from 3.5 wt % to 4.5 wt %. 
     
     
         20 . The steel pipe of  claim 15 , wherein nickel is present in an amount of from 42 wt % to 45 wt %. 
     
     
         21 . The steel pipe of  claim 15 , wherein chromium is present in an amount of from 28 wt % to 30 wt %. 
     
     
         22 . The steel pipe of  claim 15 , wherein niobium is present in an amount of from 0.80 wt % to 1.50 wt %. 
     
     
         23 . The steel pipe of  claim 15 , wherein silicon is present in an amount of from 0.3 wt % to 0.6 wt %. 
     
     
         24 . The steel pipe of  claim 15 , wherein manganese is present in an amount of from 0.4 wt % to 0.8 wt %. 
     
     
         25 . The steel pipe of  claim 15 , wherein tungsten is present in an amount of from 0.05 wt % to 0.15 wt %. 
     
     
         26 . The steel pipe of  claim 15 , wherein titanium is present in an amount of from 0.08 wt % to 0.15 wt %. 
     
     
         27 . The steel pipe of  claim 15 , wherein yttrium is present in an amount of from 0.01 wt % to 0.03 wt %. 
     
     
         28 . The steel pipe of  claim 15 , wherein nitrogen is present in an amount of from 0.03 wt % to 0.06 wt %. 
     
     
         29 . A steel pipe capable of forming a substantially continuous layer of alumina on its internal surface, the steel pipe being made from an alloy consisting of:
 from 0.15 to 0.35 wt % carbon,   from 2.5 to 5.0 wt % aluminium,   from 40 to 45 wt % nickel,   from 25 to 35 wt % chromium,   from 0.50 to 1.50 wt % niobium and/or vanadium,   from 0.01 wt % to 0.25 wt % yttrium,   from 0.01 wt % to 0.25 wt % tungsten and/or tantalum,   from 0.01 wt % to 0.25 wt % in total of one or more of titanium and zirconium and hafnium,   up to 0.9 wt % manganese,   up to 0.9 wt % silicon, and   up to 0.10 wt % nitrogen,   with the balance of the composition being iron and incidental impurities.   
     
     
         30 . The steel pipe of  claim 29 , wherein the steel pipe is capable of forming the substantially continuous layer of alumina on its internal surface when heated to above 900° C. 
     
     
         31 . The steel pipe of  claim 29 , wherein the alloy consists of:
 from 0.15 to 0.35 wt % carbon,   from 2.5 to 5.0 wt % aluminium,   from 40 to 45 wt % nickel,   from 25 to 35 wt % chromium,   from 0.50 to 1.50 wt % niobium, and/or vanadium,   from 0.01 wt % to 0.05 wt % yttrium,   from 0.05 wt % to 0.25 wt % of tungsten and/or tantalum,   from 0.04 wt % to 0.15 wt % in total of one or more of titanium and zirconium and hafnium,   an amount of up to 0.9 wt % manganese,   an amount of up to 0.6 wt % silicon, and   an amount of up to 0.10 wt % nitrogen,   with the balance of the composition being iron and incidental impurities.