Method for manufacturing of steel tube from a long steel strip, wherein the steel strip material has the following composition in wt%: C: 0.08-0.3 Mn : 1.0-3.0 Si : 0.01-1.5 P: <0.01 S: <0.01 Cr: 0-0.6 Mo: 0-0.6 V: 0-0.3 Ti : 0 - 0.3 Nb: 0-0.3 B : 0 - 0.005 balance Fe and unavoidable impurities, comprising: - providing a length of steel strip to the process, - forming a tube of the steel strip, - welding the formed tube in longitudinal direction, - giving the tube a heat treatment, characterised in that : - the mentioned steps are performed in one continuous in-line manufacturing line, - the heat treatment comprises a heating regime such that in successive cross-sections of the tube a microstructure is achieved which holds at least 50 vol% austenite and a cooling trajectory to re-introduce ferrite, and/or bainite in desired volume fractions, and in that after the tube is subjected to the heating regime, it is cooled down at a rate in the range of 20-50°C/s to a temperature in the range of 750-550°C and subsequently cooled down at a rate greater than 50°C /s; wherein either 1) the heat treatment is variable in order to manufacture tube having various controlled mechanical properties (i.e. grades) from a singular steel chemistry, or 2) the heat treatment is used to manufacture tube of a singular set of mechanical properties (i.e. grade) from a variety of steel chemistries, wherein the tube comprises sections having: a. a yield strength in a range of 600 - 800 MPa, an ultimate tensile strength of 500 - 900 MPa and an elongation in a range of 15 - 30%. b. a yield strength in a range of 800 - 1000 MPa, an ultimate tensile strength of 750 - 1200 MPa and an elongation in a range of 10 - 25%. c. a yield strength in a range of 1000 - 1200 MPa, an ultimate tensile strength of 950 - 2000 MPa and an elongation in a range of 5 - 25%.. - providing a length of steel strip to the process, - forming a tube of the steel strip, - welding the formed tube in longitudinal direction, - giving the tube a heat treatment, - the mentioned steps are performed in one continuous in-line manufacturing line, - the heat treatment comprises a heating regime such that in successive cross-sections of the tube a microstructure is achieved which holds at least 50 vol% austenite and a cooling trajectory to re-introduce ferrite, and/or bainite in desired volume fractions, and in that after the tube is subjected to the heating regime, it is cooled down at a rate in the range of 20-50°C/s to a temperature in the range of 750-550°C and subsequently cooled down at a rate greater than 50°C /s; wherein either 1) the heat treatment is variable in order to manufacture tube having various controlled mechanical properties (i.e. grades) from a singular steel chemistry, or 2) the heat treatment is used to manufacture tube of a singular set of mechanical properties (i.e. grade) from a variety of steel chemistries, wherein the tube comprises sections having: a. a yield strength in a range of 600 - 800 MPa, an ultimate tensile strength of 500 - 900 MPa and an elongation in a range of 15 - 30%. b. a yield strength in a range of 800 - 1000 MPa, an ultimate tensile strength of 750 - 1200 MPa and an elongation in a range of 10 - 25%. c. a yield strength in a range of 1000 - 1200 MPa, an ultimate tensile strength of 950 - 2000 MPa and an elongation in a range of 5 - 25%.. a. a yield strength in a range of 600 - 800 MPa, an ultimate tensile strength of 500 - 900 MPa and an elongation in a range of 15 - 30%. b. a yield strength in a range of 800 - 1000 MPa, an ultimate tensile strength of 750 - 1200 MPa and an elongation in a range of 10 - 25%. c. a yield strength in a range of 1000 - 1200 MPa, an ultimate tensile strength of 950 - 2000 MPa and an elongation in a range of 5 - 25%.. <EOS>