THICK-WALLED HIGH TENSILE SULPHUROUS-GAS RESISTANT MAIN PIPE AND METHOD FOR ITS MANUFACTURE Russian patent published in 2017 - IPC C21D8/10 C21D9/08 C21D11/00 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: pipe is made of steel containing the chemical composition of C, Si, Mn, P, S, Al, Nb, Ca, N and O, as well as one or more component selected from Cu, Ni, Cr, Mo, V and Ti, as optional components, and the rest is Fe and unavoidable impurities. The microstructure in the pipe thickness direction contains 90% or more in the bainite in the area which extends from position 2 mm from the inner surface to the position 2 mm from the outer surface. The pipe thickness hardness is distributed in such a way that the hardness of the areas other than the center segregation area is 220 or less Hv10, and the hardness of center segregation area is 250 Hv0.05 or less. The length of the major axis of voids, inclusions and inclusion clusters present in the area which extends from the position 1 mm from the inner surface to the position of 3/16 of the pipe thickness, and an area that extends from the position 1 mm from the outer surface to the position of 13/16 of the pipe thickness, in the pipe thickness direction is 1.5 mm or less.

EFFECT: provision of resistance to hydrogen induced cracking of the main pipe surface used for sour gas, having a thickness 20 mm or more and a tensile strength of 560 MPa or more.

6 cl, 3 tbl