SU1632988A1 - Process for producing welded pipes - Google Patents

Abstract

The invention relates to metallurgy, in particular to the manufacture of pipes by high-frequency welding. The goal is to improve the quality of the welded joint by increasing the toughness and leveling of the mechanical properties of the welded joint and the base metal of the pipe. After molding and welding of the billet, the welded joint is heated to Asz + (20-100) C, pressed to Ag3- (30-100) ° C, deformed to complete removal of internal burr and cooled in air. 1 z.p, f-ly, 3 tab.

Description

The invention relates to metallurgy, in particular to the manufacture of pipes by high-frequency welding.

The purpose of the invention is to improve the quality of the welded joint by increasing the toughness and comparing the mechanical properties of the welded joint and the base metal of the pipe.

The production method of welded pipes of 530x7.0 mm is carried out as follows.

Low-alloy steel 17G1S triplets are sent to the area-forming tubular billet of the pipe electric welding unit. After molding, the pipe is welded to TESA 203-530 with a welding speed of 0.58 m / s. The remaining modes: power 1200 kW; current 1.15 kA; voltage 0.78 kV; a frequency of 10 kHz, a deposit in the welding caliber of 0.004 m. Then the outer burr is removed.

Local heating of welded joint zones to temperatures above Ac at 20-100 ° C, for example, up to 950 ° C, is produced by a 400 kW high-frequency inductor (Ac, welded connections to low-alloy steels 930 ° C). Chuck the welded joint to a temperature below Arg by 30-100 ° C, for example, up to 830 ° C (AG 5 welded joints of low-alloyed steels 920 ° C). The deformation of the welded joint is made by two barrel-shaped rollers when the tube moves relative to the rollers at a speed of 4.4 m / min. The degree of deformation, which ensures burr expansion without reducing the wall thickness of the pipe, is selected by adjusting the pressure in the hydraulic system of the pressure roller. Cooling at a rate that ensures the recrystallization of hot deformed austekite is carried out in air.

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An experimental batch of pipes of 530x7.0 mm in size from 17PS steel is examined by practicing heat treatment and hot deformation modes at temperatures of 150x500 mm cut from the welded joint of the pipes. The treatment conditions and the toughness of the welded joints of the experienced templates of pipes made of steel G / PS on samples with a round notch at a test temperature of -40 ° C are given in Table. one.

Used modes are used in the manufacture of an experimental batch of pipes of 530x7.0 mm in size from steel 17G1S. The treatment and impact toughness of welded joints of pipes on samples with a circular notch at a test temperature of -40 ° C is given in Table. 2. In this case, the toughness value is 3.5-6 times higher than the impact strength of welded joints of pipes in the initial state and 6-7 times the requirements of GOST for welded joints of pipes made by electric arc welding (0.196 MJ / m2-) . Such an increase in toughness significantly improves the stability of the quality of the welded joint.

The use of the proposed cnocosob allows to eliminate the mechanical non-uniformity of the welded joint, i.e. get welded joint, equal strength base metal. The hardness of the welded joint and the Vickers base metal varies between 160-180HV.

The application of the proposed method in the production of welded pipes allows reducing costs in the construction of gas and oil pipelines through the use of cheaper pipes welded by VPN, increasing the productivity (throughput) of pipelines due to an increase in the operating pressure.

The results of the implementation of the known and proposed methods for pipes 530x7.0 mm in size made of steel 17Г1С, and

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also the magnitude of the impact strength of welded joints of pipes on specimens with a circular notch at a test temperature of -40 ° C is given in Table. 3

From tab. 3 that the proposed method provides an increase in the toughness of welded joints by more than 2 times. In addition, the proposed method is more productive and economical, since the bulk heat treatment operation is eliminated.

Cooling in air after hot deformation for welded joints of steel 17G1C at certain temperatures and degrees of deformation provides recrystallization of deformed austenite, leads to grinding of the products of diffusion transformation of supercooled austenite and increase the toughness of the welded joint. When cooled in water, the recrystallization of hot deformed austenite for this steel is almost completely suppressed.

Claims (2)

1. A method for producing welded pipes with predominantly high-frequency welding, which includes molding, welding billets, heating the welded joint to a predetermined temperature and its hot deformation until complete internal flash is removed, and cooling, in order to improve the quality of the welded joint by increasing the impact viscosity and alignment of the mechanical properties of the welded joint and the base metal of the pipe, the deformation of the welded joint is carried out after its installation; shvani up to (SO-SO) S, and cooling is carried out at a rate that ensures recrystallization of hot deformed austenite. 2. Method according to claim, characterized in that the heating is carried out to Ac3 + (20-100) ° C. Table 1 Note. In the numerator, the minimum n maximum values of 7–10 for incisors made from the metal of three domes are given, in the denominator, the average values. Impact viscosity, mJ / m: 0.14-0.89 0.36 1.13-1.53 1.32 Processing modes Local heating to 930 ° C, deformation of the welded joint by rolling burrs without reducing the wall thickness of the pipe (25-35%), cooling in water from 930 ° C, tempering at 600 ° C (a known method) Local heating of the welded joint to 950 ° C, booster up to 820 ° C, deformation of the welded joint by rolling burr without reducing the wall thickness of the pipe, air cooling Local heating of the welded joint to 950 ° C, boiling up to 820 ° C, warping of the welded joint by rolling burr without reducing pipe wall thickness, cooling in water Table 2 0.60-0.87 0.75 1.27-1.69 1.37 Table 3 Impact viscosity, mJ / m2 0.46-0.72 0.63