Method for making high-strength steel pipe, and pipe made by that method

Abstract

A method is provided for manufacturing a high-strength, as-welded steel pipe product, with a minimum yield strength in excess of 80 ksi (552 MPa), suitable for use in oil and gas well casings, without the need for a post-weld heat treatment which would otherwise be required to obtain an as-welded pipe having that level of strength.

1 . A method for making an as-welded steel pipe, comprising the steps of:
 forming a cast steel slab, the steel having as components   (i) less than about 0.10% by weight of carbon,   (ii) an Mn content in the range of about 1.5% to about 2.5% by weight,   (iii) at least one of Mo, Cr, Ni, and B, and   (iv) at least one of Nb, V, and Ti;   heating the steel slab to a temperature in excess of about 2000° F.;   rolling the heated steel slab in a rolling mill at a temperature in excess of the Ar 3  transformation start temperature, to obtain a skelp having a desired thickness;   cooling the skelp to a coiling temperature in the range of about 850° F. to about 950° F., to obtain a largely bainitic microstructure in the skelp;   coiling the skelp into a hot-rolled coil;   forming the skelp into a tube such that the two side edges of the skelp are positioned into contact with one another; and   welding the two side edges of the skelp together so as to form the as-welded pipe.   
   
   
       2 . The method according to  claim 1 , wherein the steel contains carbon in an amount of from about 0.040% to about 0.060% by weight. 
   
   
       3 . The method according to  claim 2 , wherein the steel contains carbon in an amount of from about 0.040% to about 0.055% by weight. 
   
   
       4 . The method according to  claim 2 , wherein the steel contains carbon in an amount of from about 0.045% to about 0.060% by weight. 
   
   
       5 . The method according to  claim 1 , wherein the steel contains Mn in an amount of from about 1.5% to about 2.5% by weight. 
   
   
       6 . The method according to  claim 5 , wherein the steel contains Mn in an amount of from about 1.65% to about 1.75% by weight. 
   
   
       7 . The method according to  claim 5 , wherein the steel contains Mn in an amount of from about 1.80% to about 1.90% by weight. 
   
   
       8 . The method according to  claim 1 , wherein the steel contains at least one of Mo in an amount of from about 0.10% to about 0.50% by weight, Cr in an amount of about 0.50% or less by weight, Ni in an amount of about 0.50% or less by weight and B in an amount of from about 0.0005% to about 0.0030% by weight. 
   
   
       9 . The method according to  claim 8 , wherein the steel contains Mo in an amount of from about 0.28% to about 0.32% by weight. 
   
   
       10 . The method according to  claim 8 , wherein the steel contains Cr in an amount of from about 0.15% to about 0.20% by weight. 
   
   
       11 . The method according to  claim 1 , wherein the steel contains Nb in an amount of from about 0.040% to about 0.050% by weight. 
   
   
       12 . The method according to  claim 1 , wherein the steel contains Nb in an amount of from about 0.075% to about 0.085% by weight. 
   
   
       13 . The method according to  claim 1 , wherein the steel contains Ti in an amount of from about 0.008% to about 0.015% by weight. 
   
   
       14 . The method according to  claim 1 , wherein the steel contains Ti in an amount of from about 0.015% to about 0.025% by weight. 
   
   
       15 . The method according to  claim 1 , wherein the steel contains V in an amount of from about 0.05% to about 0.06% by weight. 
   
   
       16 . The method according to  claim 1 , wherein the steel contains
 carbon in an amount of from about 0.040% to about 0.055% by weight;   Mn in an amount of from about 1.82% to about 1.90% by weight;   Si in an amount of from about 0.26% to about 0.34% by weight;   Al in an amount of from about 0.022% to about 0.035% by weight;   Cr in an amount of from about 0.15% to about 0.20% by weight;   Mo in an amount of from about 0.29% to about 0.32% by weight;   Nb in an amount of from about 0.075% to about 0.085% by weight; and   Ti in an amount of from about 0.015% to about 0.025% by weight.   
   
   
       17 . The method according to  claim 1 , wherein the steel contains carbon in an amount of from about 0.045% to about 0.060% by weight;
 Mn in an amount of from about 1.65% to about 1.75% by weight;   Si in an amount of from about 0.12% to about 0.18% by weight;   Al in an amount of from about 0.015% to about 0.025% by weight;   Cr in an amount of from about 0.15% to about 0.20% by weight;   Mo in an amount of from about 0.28% to about 0.32% by weight;   Nb in an amount of from about 0.040% to about 0.050% by weight;   Ti in an amount of from about 0.008% to about 0.015% by weight; and   V in an amount of from about 0.05% to about 0.06% by weight.   
   
   
       18 . The method according to  claim 1 , wherein the steel contains carbon in an amount of from about 0.075% to about 0.080% by weight;
 Mn in an amount of from about 1.82% to about 1.90% by weight;   Si in an amount of from about 0.26% to about 0.34% by weight;   Al in an amount of from about 0.019% to about 0.025% by weight;   Cr in an amount of from about 0.15% to about 0.20% by weight;   Mo in an amount of from about 0.29% to about 0.32% by weight;   Nb in an amount of from about 0.075% to about 0.085% by weight; and   Ti in an amount of from about 0.015% to about 0.025% by weight.   
   
   
       19 . The method according to  claim 1 , wherein the steel slab is heated to a temperature of about 2300° F. 
   
   
       20 . The method according to  claim 1 , wherein the heated steel slab is rolled at a temperature of about 1500° F. 
   
   
       21 . The method according to  claim 1 , wherein the skelp is slit longitudinally to form a plurality of slit strips, each of said strips then being formed into a tube. 
   
   
       22 . The method according to  claim 1 , wherein the welding method comprises electric resistance welding. 
   
   
       23 . A steel pipe formed by the method of any of  claims 1 ,  16 ,  17  or  18 . 
   
   
       24 . The steel pipe of  claim 23 , wherein the pipe has a minimum yield strength in excess of about 80 ksi (552 MPa). 
   
   
       25 . The steel pipe of  claim 23 , wherein the pipe has a minimum yield strength in the range of from about 80 ksi (552 MPa) to about 125 ksi (862 MPa). 
   
   
       26 . The steel pipe of  claim 23 , wherein the pipe has a minimum yield strength in excess of about 100 ksi (689 MPa). 
   
   
       27 . The steel pipe of  claim 23 , wherein the diameter of the pipe is at least about 4.5 inches. 
   
   
       28 . The steel pipe of  claim 23 , wherein the wall thickness of the pipe is at least about 0.25 inches. 
   
   
       29 . An as-welded steel pipe having a minimum yield strength in excess of about 80 ksi (552 MPa), wherein said minimum yield strength is obtained without the use of a post-formation quench and temper heat treatment. 
   
   
       30 . The steel pipe of  claim 29 , wherein the pipe has a minimum yield strength in the range of from about 80 ksi (552 MPa) to about 125 ksi (862 MPa). 
   
   
       31 . The steel pipe of  claim 29 , wherein the pipe has a minimum yield strength in excess of about 100 ksi (689 MPa). 
   
   
       32 . The steel pipe of  claim 29 , wherein the diameter of the pipe is at least about 4.5 inches. 
   
   
       33 . The steel pipe of  claim 29 , wherein the wall thickness of the pipe is at least about 0.25 inches.