Calculation of parameters for welding annular joints of high-strength steel Kh80 gas pipelines

Abstract

Parameters are calculated for a welding regime for gas pipeline annular joints made of high-strength steel Kh80. A structural diagram for the most dangerous area, i.e., the zone near the seam (ZNS) of a welded joint, and the dependence of hardness and impact strength on the structure and phase composition of the ZNS metal, formed during welding with different cooling rates, and also standard specifications for welded annular joints of steel Kh80 pipes are provided. Parameters are calculated for a manual arc welding regime for an annular joint and the recommended regime parameters are indicated for providing the required ZNS metal cooling rate.A promising direction for the development of power generation units of the country is the use of high-strength steels of the strength category Kh80 or above for gas pipeline construction. This is a steel of a new generation with a ferrite-bainite structure. The high mechanical properties (strength, ductility, brittle failure resistance) are provided as a result of alloying and the optimum thermomechanical rolling regime. In contrast to the extensively use pipe steels with a ferrite-pearlite structure, an increase in the operating properties of these steels is provided with a low (0.05-0.08%) carbon content, a high (up to 1.8-1.9%) manganese content and microalloying with strong carbide-forming elements: molybdenum, niobium, vanadium, titanium. A very fine ferrite-bainite structure is formed as a result of completing deformation during thermomechanical rolling close to the critical point Ar 3 and rapid cooling to about 500°C.The possibility of using steels of this group for pipeline construction is governed to a considerable degree by the use of rational welding technology providing the required set of welded joint mechanical properties.The aim of this work is to calculate arc welding regime parameters for circular pipeline joints made of high-strength steel Kh80.A structural diagram is given in Fig. 1 (F is ferrite, B is bainite, M is martensite) of the most critical area, i.e., the zone near the seam (ZNS) of a steel Kh80 welded joint and the dependence of hardness and impact strength on the structurephase composition (SPC) of ZNS metal formed during welding with different cooling rates w 8-5 in the austenite diffusion transformation temperature range.