Method for preparing X90 steel-grade bent pipes and pipe fittings

Abstract

The invention relates to a method for preparing X90 steel-grade bent pipes and pipe fittings. The steel for making the bent pipes and pipe fittings comprises the following components in percentage by mass: 0.11 to 0.25 percent of C, 1.35 to 2percent of Mn, 0.3 to 0.5 percent of Si, no more than 0.010 percent of P, no more than 0.005 percent of S, 0.01 to 0.05 percent of Al, 0.002 to 0.005 percent of Ca, no more than 0.008 percent of N, and the balance of Fe, wherein elements Nb, Ti, V, Mo, Ni and Cr can also be added. The method comprises the steps that: hot rolled steel plates are obtained by smelting, rolling and air-cooling; hot rolled steel plates are prepared into longitudinal submerged arc welding pipes by forming and longitudinal submerged arc welding; the longitudinal submerged arc welding pipes undergo induction heating and thermal treatment to form bent pipes or under to a plurality of thermo mechanical forming processes to form pipe fittings. The bent pipes and pipe fittings prepared according to the method have high intensity, low-temperature toughness and welding performance.

Description

technical field [0001] The invention relates to a method for preparing bent pipes and pipe fittings with a strength level up to X90 steel grade and excellent toughness. The bent pipes and pipe fittings are suitable for connecting large-diameter high-pressure gas transmission pipeline engineering main lines and station pipelines. Background technique [0002] In the construction of large-diameter high-pressure gas transmission pipelines in my country, a large number of station steel pipes, elbows and pipe fittings are required for compressor stations, gas transmission and distribution stations and valve rooms. The limit temperature of the station reaches -30~-40℃, and the lowest temperature of some stations is lower than -46℃, and the thickness reaches 50-70mm. According to the design requirements of pipeline technology, some station steel pipes, bend pipes and pipe fittings need to be exposed to the cold external environment, which is a severe challenge to the material's abi...

AI Technical Summary

Problems solved by technology

At present, my country is still unable to produce elbows and pipe fittings with an impact toughness of -30°C and below. The average Charpy impact toughness is not less than 50J, and the minimum value is not less than 40J, especially when the wall thickness is large. The safety requirements of pipelines in low-temperature environments below 30°C urgently require steels and manufacturing processes for elbows and fittings that have both high strength and excellent low-temperature toughness