High performance material for coiled tubing applications and the method of producing the same

Abstract

Embodiments of the present disclosure are directed to coiled steel tubes and methods of manufacturing coiled steel tubes. In some embodiments, the final microstructures of the coiled steel tubes across all base metal regions, weld joints, and heat affected zones can be homogeneous. Further, the final microstructure of the coiled steel tube can be a mixture of tempered martensite and bainite.

1 .  22 . (canceled) 
     
     
         23 . A coiled steel tube having improved yield strength and fatigue life at weld joints of the coiled steel tube, the coiled steel tube comprising:
 a plurality of strips welded together end to end by a bias weld to form a plurality of bias welded strips and formed into a coiled steel tube, each of the plurality of bias welded strips having base metal regions, bias weld joints, and heat affected zones surrounding the bias weld joints, each of the plurality of bias welded strips having a yield strength greater than about 80ksi;   an equivalent carbon content (CE) in the range of 0.237 to 0.733;
   where CE=%C+((%Mn+%Si)/6)+((%Cr+%Mo+%V)/5)+((%Cu+%Ni)/15); 
   wherein the coiled steel tube has a final microstructure formed from a full body heat treatment applied to the coiled steel tube;   wherein the final microstructure comprises a mixture of tempered martensite and bainite;   wherein the final microstructure of the coiled steel tube comprises more than 90 volume % tempered martensite in the base metal regions, the bias weld joints, and the heat affected zones;   wherein the final microstructure across all base metal regions, bias weld joints, and heat affected zones is homogeneous; and   wherein the final microstructure comprises a uniform distribution of fine carbides across the base metal regions, the bias weld joints, and the heat affected zones.   
     
     
         24 . The coiled steel tube of  claim 23 , wherein the tube has a minimum yield strength of 125 ksi. 
     
     
         25 . The coiled steel tube of  claim 23 , wherein the tube has a minimum yield strength of 140 ksi. 
     
     
         26 . The coiled steel tube of  claim 23 , wherein the tube has a minimum yield strength of between 125 ksi and 140 ksi. 
     
     
         27 . The coiled steel tube of  claim 23 , wherein the final microstructure comprises at least 95 volume % tempered martensite in the base metal regions, the bias weld joints, and the heat affected zones. 
     
     
         28 . The coiled steel tube of  claim 23 , wherein the tube has a final grain size of below 20 μm in the base metal regions, the bias weld joints, and the heat affected zones. 
     
     
         29 . The coiled steel tube of  claim 28 , wherein the tube has a final grain size of below 15 μm in the base metal regions, the bias weld joints, and the heat affected zones. 
     
     
         30 . The coiled steel tube of  claim 23 , wherein the fatigue life at the bias weld joints is at least about 80% of the base metal regions. 
     
     
         31 . The coiled steel tube of  claim 23 , wherein a percent hardness of each of the bias weld joints, including its heat affected zone, is 110% or less than a hardness of the base metal region. 
     
     
         32 . The coiled steel tube of  claim 23 , wherein the coiled steel tube passes method C of NACE TM0177 for resistance to SSC cracking. 
     
     
         33 . The coiled steel tube of  claim 23 , wherein a final length of the coiled steel tube is between 10,000 feet and 40,000 feet. 
     
     
         34 . The coiled steel tube of  claim 23 , wherein the fatigue life is at least 100% greater than an equivalent grade steel which has not undergone the fully body heat treatment; 
     
     
         35 . The coiled steel tube of  claim 23 , wherein the coiled steel tube has a reduced segregation band as compared to an equivalent grade steel which has not undergone the full body heat treatment. 
     
     
         36 . The coiled steel tube of  claim 23 , wherein the coiled steel tube has an equivalent carbon content (CE) in the range of 0.35 to 0.733. 
     
     
         37 . The coiled steel tube of  claim 23 , wherein the coiled steel tube comprises 0.0005% to 0.0025% (by weight) boron. 
     
     
         38 . A method of forming a steel tube having improved yield strength and fatigue life at weld joints of the tube comprising:
 providing strips of steel having an equivalent carbon content (CE) in the range of 0.237 to 0.733 (where CE=%C+((%Mn+%Si)/6)+((%Cr+%Mo+%V)/5)+((%Cu+%Ni)/15));   bias welding the strips of steel together end to end to form bias welded strips with longitudinal sides;   welding the longitudinal sides of the bias welded strips to form a welded tube from the bias welded strips, wherein the welded tube comprises base metal regions, weld joints, and heat affected zones surrounding the weld joints;   austenitizing the welded tube using a full body heat treatment at greater than 900 degrees C. to form an austenitized tube;   quenching the austenitized tube to form a final as quenched microstructure of martensite and bainitine in a quenched tube;   tempering the quenched tube to form a quenched and tempered tube;   wherein the final as quenched and tempered microstructure comprises more than 90 volume % tempered martensite in the base metal regions, the bias weld joints, and the heat affected zones;   wherein tempering of the quenched tube results in a yield strength greater than about 80 ksi; and   wherein the microstructure of the quenched and tempered tube across all base metal regions, bias weld joints, and the heat affected zones is homogeneous; and wherein the microstructure of the quenched and tempered tube comprises a uniform distribution of fine carbides across the base metal regions, the bias weld joints, and the heat affected zones.   
     
     
         39 . The method of  claim 38  wherein the steps of welding, austenitizing, quenching and tempering are done in a continuous process. 
     
     
         40 . The method of  claim 38 , comprising;
 coiling the welded tube on a spool; and   uncoiling the welded tube off the spool and then austenitizing the uncoiled tube, quenching the uncoiled tube, and tempering the uncoiled tube.   
     
     
         41 . The method of  claim 40 , further comprising coiling the quenched and tempered tube on a spool. 
     
     
         42 . The method of  claim 38 , wherein the step of austenitizing forms a grain size below 20 μm in the base metal regions, the bias weld joints, and the heat affected zones. 
     
     
         43 . The method of  claim 38 , wherein the step of providing strips of steel comprises providing strips comprising:
 0.17 to 0.30 wt. % carbon;   0.30 to 1.60 wt. % manganese;   0.10 to 0.20 wt. % silicon;   up to 0.7 wt. % chromium;   up to 0.5 wt. % molybdenum;   0.0005 to 0.0025 wt. % boron;   0.010 to 0.025 wt. % titanium;   0.25 to 0.35 wt. % copper;   0.20 to 0.35 wt. % nickel;   up to 0.04 wt. % niobium;   up to 0.10 wt. % vanadium;   up to 0.00015 wt. % oxygen;   up to 0.03 wt. % calcium;   up to 0.003 wt. % sulfur; and   up to 0.010 wt. % phosphorus.   
     
     
         44 . The method of  claim 38 , wherein the step of providing strip of steels further comprises providing strips comprising:
 up to 1.0 wt. % chromium;   up to 0.5 wt. % molybdenum;   up to 0.0030 wt. % boron;   up to 0.030 wt. % titanium;   up to 0.50 wt. % copper;   up to 0.50 wt. % nickel;   up to 0.1 wt. % niobium;   up to 0.15 wt. % vanadium;   up to 0.0050 wt. % oxygen; and   up to 0.05 wt. % calcium.   
     
     
         45 . The method of  claim 38 , wherein the quenched and tempered tube has a yield strength greater than or equal to 125 ksi. 
     
     
         46 . The method of  claim 38 , wherein the quenched and tempered tube has a minimum yield strength of 140 ksi. 
     
     
         47 . The method of  claim 38 , wherein the quenched and tempered tube has a minimum yield strength between 125 and 140 ksi.