Seamless steel pipe for steam injection and method for manufacturing the same

Abstract

There is provided a steel pipe for steam injection having high yield stress even at 350° C. The seamless steel pipe for steam injection according to the present invention has a chemical composition comprising, by mass percent, C: 0.03 to 0.08%, Si: 0.05 to 0.5%, Mn: 1.5 to 3.0%, Mo: more than 0.4 to 1.2%, Al: 0.005 to 0.100%, Ca: 0.001 to 0.005%, N: 0.002 to 0.015%, P: at most 0.03%, S: at most 0.01%, and Cu: at most 1.5%, the balance being Fe and impurities. The seamless steel pipe is manufactured by being water cooled after hot working and by being quenched and tempered.

1 . A seamless steel pipe for steam injection having a chemical composition comprising, by mass percent, C: 0.03 to 0.08%, Si: 0.05 to 0.5%, Mn: 1.5 to 3.0%, Mo: more than 0.4 to 1.2%, Al: 0.005 to 0.100%, Ca: 0.001 to 0.005%, N: 0.002 to 0.015%, P: at most 0.03%, S: at most 0.01%, and Cu: at most 1.5%, the balance being Fe and impurities,
 wherein the seamless steel pipe is manufactured by being water cooled after hot working and further by being quenched and tempered.   
     
     
         2 . The seamless steel pipe according to  claim 1 , wherein the chemical composition comprises, in place of part of Fe, one or more types selected from the group consisting of Cr: at most 1.0%, Nb: at most 0.1%, Ti: at most 0.1%, Ni: at most 1.0%, and V: at most 0.2%. 
     
     
         3 . The seamless steel pipe according to  claim 1 , wherein the seamless steel pipe has yield stress of at least 600 MPa at 350° C. 
     
     
         4 . The seamless steel pipe according to  claim 2 , wherein the seamless steel pipe has yield stresses of at least 600 MPa at 350° C. 
     
     
         5 . A method for manufacturing a seamless steel pipe for steam injection, comprising the steps of:
 heating a round billet having a chemical composition comprising, by mass percent, C: 0.03 to 0.08%, Si: 0.05 to 0.5%, Mn: 1.5 to 3.0%, Mo: more than 0.4 to 1.2%, Al: 0.005 to 0.100%, Ca: 0.001 to 0.005%, N: 0.002 to 0.015%, P: at most 0.03%, S: at most 0.01%, and Cu: at most 1.5%, the balance being Fe and impurities;   piercing the heated round billet to produce a hollow shell;   rolling the hollow shell to produce a seamless steel pipe;   water cooling the seamless steel pipe after rolling;   quenching the water cooled seamless steel pipe; and   tempering the quenched seamless steel pipe.   
     
     
         6 . The method of manufacturing a seamless steel pipe according to  claim 5 , wherein the chemical composition of the round billet comprises, in place of part of Fe, at least one types selected from the group consisting of Cr: at most 1.0%, Nb: at most 0.1%, Ti: at most 0.1%, Ni: at most 1.0%, and V: at most 0.2%.