Abstract: Described in the artide are the requirements for design of the chemical composition of the HSL450S submarine linepipe.Detailed are the trial manufacture of the steel and the pipe,the measures as taken for the process control as well as the tests concerning property evaluation thereof.The testing and inspection re-sults show that the newly-developed HSL450S steel billet features low inclusion contents and high cleanness,while the rolled pipe is in possession of all the mechanical properties and corrosion-resistance which are in full compliance with applicable product standard.The HSL450S submarine linepipe of X65 St.Grade are developed so successfully that conditions are ripe for massive production thereof.