Abstract: An alloy steel, includes 0.12 to 0.25 wt. % C, 0.40 wt. % or less Si, 1.20 to 1.80 wt. % Mn, 0.025 wt. % or less P, 0.010 wt. % or less S, 0.01 to 0.06 wt. % Al, 0.20 to 0.50 wt. % Cr, 0.20 to 0.50 wt. % Mo, 0.03 to 0.10 wt. % V, 0.20 wt. % or less Cu, 0.02 wt. % or less N, 0.30 to 1.00 wt. % W, and the balance iron and incidental impurities, for making high-strength, weldable seamless steel tubes for structural application, through a hot rolling process and subsequent quenching and tempering.

Abstract: The invention relates to a process for producing seamless line pipes within the quality grade range X 52 to X 90, with a stable yield strength up to a temperature of use of 200° C., and with an essentially constant stress-strain characteristic, by hot-rolling a pipe blank made from a steel which contains the following alloying elements (% by weight): 1 C 0.06-0.18% Si max. 0.40% Mn 0.80-1.40% P max. 0.025% S max. 0.010% Al 0.010-0.060% Mo max. 0.50% V max. 0.10% Nb max. 0.10% N max. 0.015% W >0.30-1.

Abstract: Markings are placed alongside the gap of a split tube and their distance is measured downstream from the point of welding; the measuring result is used to control upsetting pressure in the weld print.