SU698314A1 - Method for making steel structures - Google Patents

Description

The invention relates to the field of engineering, in particular to the manufacture of welded pressure vessels for the gas and petrochemical industries.

A known method of manufacturing welded structures, including the normalization of sheet steel at a metallurgical plant, its rolling into shells, welding of longitudinal joints of shells, hot calibration, welding of ring joints, normalization of ring welds and tempering of a finished welded structure in order to relieve welding stresses [1]. The disadvantage of this method is that it does not allow to realize the possibilities of a specific steel composition to increase the strength characteristics of steel and its toughness due to hardening heat treatment (hardening with subsequent tempering). So, for example, for steel type 09G2S widely used in petroleum engineering, an increase in the mechanical properties after thermal hardening as compared to normalization will be about 60% in yield strength, 25% in tensile strength, and impact strength at a temperature of 40 ° C increases by 4 times .

The aim of the invention is to increase the strength properties and toughness of welded pressure vessels.

This goal is achieved by the fact that in the known method of manufacturing welded 5 structures, including rolling of the shells, welding of longitudinal joints, hot calibration, welding of the ring joints and tempering, after hot calibration of the shells they are heated to a temperature of 10 hardening, hardening is performed, and welding of the ring joints produce with controlled cooling.

The technological process of manufacturing a welded pressure vessel from low 15 alloyed structural steels is as follows.

Shells are milled from hot-rolled sheet metal, and a longitudinal joint is welded. Due to the fact that in 20 subsequent shells will be thermally processed, it is possible to use high-performance welding methods (for example, electroslag, automatic at high linear energies), without fear, 25 that this will cause an adverse change in the properties of the welded joint. For the next calibration operation of the process, the shell is heated, and the heating temperature 30 depends on the specific steel grade and its thickness. After calibration, the metal has a sufficiently high temperature, which saves energy during the next quenching operation. Hardening can be carried out either in methodological furnaces, or using a generator of high-current or industrial frequencies, or using sources of gas coolants followed by cooling with water. Welding of the ring joint to exclude the effect of welding heat on the structure of the hardened metal is carried out with regulation of the thermal cycle. Moreover, the regulation of the parameters of the thermal cycle 1 welding, regardless of thermal power

The name of the operation of the technological process of the arc, for which it is intended, for example, concomitant water-air cooling, allows for high performance. The last operation of the technological process is tempering of the finished structure, which reduces welding stresses to regulated values and provides the necessary level of properties of welded equipment in terms of strength, ductility and brittle fracture resistance. In the table, for example, steel 10G2FR type (40 mm thick) used for gas and petrochemical mechanical engineering shows 5 modes of basic operations performed in the manufacture of welded equipment.

Operation mode

Rolling

Longitudinal joint welding

Quenching

Calibration

Ring joint welding

Vacation

The heating temperature is 950 ° C.

Electroslag welding q, v = 130 kcal / cm.

The number of passes 1.

The heating temperature is 950 C.

The temperature of the end of calibration is 700 ° C.

Heating temperature .950 ° С, exposure

1.5-2 min / mm.

Water cooling.

Electroslag with regulation of the thermal cycle qlv = l'3O kcal / cm.

Number of passes 3.

Heating temperature 680—700 “C, exposure

3-4 min / mm.

The proposed method for manufacturing welded structures was tested in the manufacture of a dust collector sample from 09G2S steel with a size of 1600X50 mm and designed for a pressure of P = 55 atm. The chemical composition and mechanical properties of 09G2S steel in the initial state after normalization were as follows: C = 0.08%; MP = 1.48%; Si = 0.69%; S = 0.023%; P = 0.028%; Cr = 0.07%; Ni = 0.06%; Cu = 0.1%; σ _Β = 49 kg / mm ² ; στ = 32.5 kg / mm ² ; os = 33%; _and 4 ° e 12.5 kgm / cm ² .

Steel in its initial state does not meet the requirements of the industry standard for the technological process in terms of impact strength. The shells immediately after calibration were placed in a furnace for heating under quenching. The heating temperature corresponded to 930–950 ° С and the heating rate was about 200 ° С / h. Oven shell exposure

1.5-2 hours. The shells were cooled in a tank with running water after the operation of welding ring joints according to the regimes using the regulation of thermal cycles. Welding was carried out in 5 passes at 7 = 1150 A; 77 _d = 48 V; Usb = 12 m / h and water flow = 15 l / h and air pressure = 2 atm. The finished apparatus was tempered at a temperature of 650 ° С to relieve welding stresses and obtain the required properties.

The heat treatment of 09G2S steel made it possible to favorably affect the entire complex of mechanical properties. The tensile strength and yield strength reach 55 and 42 kg / mm ² , respectively, the relative elongation is 29%, and the impact strength at a temperature of 40 ° C was

18.5 kgm / mm ² .

Claims (1)

Formula of the invention ³⁰ A method for manufacturing welded structures, mainly pressure vessels, including milling of shells, welding of longitudinal joints, hot calibration, welding of ring joints and tempering, ³⁵ characterized in that, in order to increase the strength properties and impact strength, after hot calibration of their shells heated to a hardening temperature, hardened, and the welding of the ring joints ^{40 is} carried out with controlled cooling.