RU2296657C2 - Method of making butt welds on pipes - Google Patents

Abstract

FIELD: mechanical engineering; welding.

SUBSTANCE: invention relates to plastic metal working, particularly, to process of forming butt welds in making of pipe studs. According to proposed method, preparatory operations are carried out and pipes are assembled with subsequent argon-arc welding of pipe ends by non-consumable electrode with use of filler material. Two butt welds are made with subsequent hot deformation. Ends of pipes to be connected are expanded from cylinder to cylinder and, during assembling, by means of mandrel, filling material in form of bushing with ring groove on inner surface is installed between ends pipes to provide contact between mated end face surfaces of ends of pipes calibrated by expansion with end face surfaces of bushing. Welds are formed by welding of pipe material with material of intermediate member. Intermediate member is heated and then hot radial upsetting of intermediate member is carried out by concentrating initially its deformation in inner layers according to location of ring groove, welds and near-weld zones on mandrel, and outer diameter is formed of size equal to initial outer diameter of pipes.

EFFECT: improved quality of weld owing to cladding of pipe butt joint, reduced input of hand labor.

7 dwg

Description

The invention relates to the field of metal forming, in particular to the processes of the formation of butt welds when receiving pipe hairpins of U-shaped beams using the effect of localized hot plastic deformation of the weld and adjacent heat-affected zones.

A known method of the formation of butt welds on pipes in the production of pipe hairpins, including the cut length of the pipe lengths for straight sections of the studs, the measured length of the pipe for manufacturing flexible to a given kalach radius, cleaning the outer surface of the mating ends of the connected elements, their subsequent welding with the formation of two welds in the resulting stud (see GOST 14245-79 Shell-and-tube heat exchangers with U-shaped pipes).

The main disadvantages of the known method of formation of butt welds should include the insecurity of the inner surface of the joint from the effects of an aggressive working environment during operation of the tube bundle, as well as the increased cost of their production. Firstly, large waste of pipe billets due to the multiple use of working lengths. And, secondly, the increased cost, which is also determined by the high percentage of defective welds due to defects determined by the presence of atmospheric gas (oxygen and nitrogen) during the welding process. The quality of one-piece joints in this case is entirely determined by professional skills and the ability of the welder to intensively perform the necessary actions during welding. It should be emphasized and such disadvantages as the presence of heat-affected zones with reduced mechanical characteristics and internal burr, which reduces the cross section of the joint relative to the original cross section of the connected pipes.

There is also a known method for the formation of butt welds on pipes when receiving pipe studs, including preparatory operations on pipes for welding, their assembly and subsequent argon-arc welding of the mating ends of pipes with filler material using a non-consumable electrode (see RD 153-34.1-003-01 Welding, heat treatment and control of pipe systems of boilers and pipelines during installation and repair of power equipment, Moscow, PIO OBT 2001 - prototype).

The disadvantage of this method is that the weld and heat-affected zones are formed without cladding the inner surface of the joint in order to increase its anticorrosion properties, and they also do not undergo final plastic deformation, eliminating possible defects in welds and hardening material in heat-affected zones. As a result, defects in welds are possible and similar studs are rejected. During welding, the process of formation of an internal burr is not amenable and each time the resulting joint has its geometrical dimensions in terms of inner diameter, which requires a control operation — rolling the studs with a control ball with a diameter of 0.8 D, where D is the inner diameter of the pipe.

The objective of the invention is to develop such a method for the formation of butt welds when receiving pipe studs of U-shaped beams, which would protect the inner and outer surfaces of the joint from the effects of aggressive media during operation of the tube bundle, and also eliminate defects in the welds by their finish hot stamping.

The technical result is achieved by the fact that in the method of forming butt welds on pipes in the production of pipe rods, including preparatory operations on pipes for welding, their assembly and subsequent argon-arc welding of the mating ends of pipes with filler material using a non-consumable electrode, two butt welds with their subsequent hot deformation, for which the pre-mating ends of the pipes are distributed from cylinder to cylinder, when assembling by means of a mandrel between their ends, pour the intermediate element from the filler material in the form of a sleeve with an annular groove on the inner surface, reaching contact between the mating end surfaces of the ends calibrated by the distribution of pipes with the end surfaces of the sleeve, welds are formed by fusing the pipe material with the material of the intermediate element, the intermediate element is heated, then the intermediate element is heated, then hot radial crimping of the intermediate element, initially concentrating its deformation in the inner layers at the location annular grooves, welds and heat-affected zones on the mandrel, giving their outer diameter a size equal to the original outer diameter of the pipes.

Implementation of the proposed method for the formation of butt welds on pipes upon receipt of U-shaped tube bundle hairpins allows cladding the external and internal surfaces of the joint, providing improved anti-corrosion characteristics, as well as eliminating defects in welds by their final hot plastic deformation, changing the structure and mechanical properties in near-weld zones, form the inner surface of the joint without burrs.

This is explained by:

- filler material is selected with the condition of increased anticorrosion properties, as well as mechanical properties not lower than the corresponding properties of the pipe material;

- carry out activation by plastic deformation (distribution) of the volumes of the mating ends of the pipes, welded subsequently;

- using an intermediate element in the form of a sleeve with an annular groove on the inner surface of cladding material (for example, stainless steel), an effective plastic flow of the filler material is achieved;

- cladding of the joint surfaces is carried out with reduced deforming forces, but high quality formation of the inner layers of the pipe joint;

- plastic deformation of the weld and heat-affected zones eliminates possible defects in the welds and strengthens the material in the heat-affected zones (the rate of hardening of the material in the heat-affected zones exceeds the rate of softening from hot deformation).

The invention is illustrated by drawings, where figure 1 shows the mating end of the pipe assembly, which has undergone preparatory operations for welding, and a rigid punch before performing the operation of distributing the pipe from cylinder to cylinder; figure 2 - the end of the stage of distribution of the end of the pipe with a rigid punch; figure 3 - the mating ends of the pipes, the sleeve with an annular groove of filler material on the mandrel after the formation of welds by fusion; figure 4 - heated pipe joint, placed in a detachable (3-segment) matrix of a horizontal hydraulic press; figure 5 - stage hot stamping of the intermediate element with a concentration of deformation in its inner layers; weld and heat-affected zones on the mandrel; figure 6 - the end of the hot stamping of the intermediate element, welds and heat-affected zones with the formation of the inner and outer surfaces of the pipe junction; Fig.7 - high-quality welded joint.

An embodiment of the invention is as follows.

On rectilinear heat exchange tubes 1 (Fig. 1), operations are performed to prepare the outer surface of each end for welding: straightening the tubes in a straight-line straightening machine, cutting their measured lengths and cleaning the outer surfaces to a metallic sheen.

Next, the mating ends of the pipes are calibrated by the operation of distributing them from cylinder to cylinder by means of a rigid punch 2.

The bend of the forming pipes forms, within the limits of the thickness of their wall, plastic hinges, selected in the form of areas of a triangular type by dots (Fig. 2).

The assembly of the pipes on the mandrel 3 before welding is carried out using a sleeve 4 of filler material, for example, stainless steel grade X18H10T. An annular groove is made on the inner surface of the sleeve with a depth not falling on the wall thickness of the calibrated pipe ends. In other words, the diameter of the annular groove is less than the inner diameter of the calibrated pipe ends (less than the maximum diameter of the rigid punch).

Between the mating ends of the pipes and the sleeve of filler material achieve the necessary contact.

The formation of welds on both sides of the ring is carried out by fusion (figure 3) according to the modes regulated by technical documentation.

The relatively large dimensions of the sleeve along its length require additional heating of the pipe joint to optimal temperatures of hot deformation. Temperature control is carried out with a portable thermocouple.

A hot pipe joint is placed in a detachable (3-segment) matrix 5 of a horizontal hydraulic press (Fig. 4).

The message to the segments of the matrix of the radial movement in the direction of the axis initially causes the action of the combs of the working surface of the matrix on the side surface of the sleeve of filler material. The reactive force from the side of the mandrel on the mentioned effect leads to localization of the deformation of the intermediate element in its inner layers. There is an extension of the annular groove in the axial direction with simultaneous bending of the generatrices of the calibrated pipe sections and shear deformation of the welds and heat-affected zones (Fig. 5).

Further movement of the matrix segments in the radial direction is associated with the hot deformation of the filler material and, through its plastic flow, the deformation of welds and heat-affected zones (Fig.6). We emphasize that the hot deformation of the weld material is carried out according to a 3-axis scheme of uneven compression stresses, which prevents the destruction of the weld. In this case, axial compressive stresses appear at the stage of pipe deformation in transitional annular zones marked by ellipses.

The formation of the inner surface of the joint is achieved by plastic flow of the filler material relative to the weld, providing cladding of the latter.

The one-piece connection (Fig. 7) is characterized by high mechanical properties (the sleeve material, which perceives the action of the working medium) plays an important role, formed by residual compressive axial stresses, sufficient accuracy for such products, and high manufacturability, which also determines increased productivity. The absence of an internal burr eliminates the need for a test ball rolling around the studs.

A pilot test of the developed method for the formation of butt welds was carried out in the manufacture of single-seam studs from pipes obtained from steel 10.

The initial geometric dimensions of the pipes were: outer diameter - 25 mm, wall thickness - 2.6 mm and lengths of 9 and 3.6 m.

Pipe straightening, cutting in moderation and cleaning of the surfaces of the mating pipes were carried out on the appropriate equipment with the achievement of the required parameters.

A sleeve with dimensions of 26.2 × 18.3 × 12 mm was made of stainless steel grade X18H10T by deformation of the pipe blanks to the appropriate diameter and the necessary cutting operations. An annular groove of a triangular cross section with a width of 7 mm and a diameter of 20.2 mm was made on the side of the inner surface of each sleeve.

Distribution-calibration of the mating ends of the pipes was carried out on a horizontal double-acting hydraulic press of the Yukos Repair and Mechanical Plant design with forces within 30 kN.

The length of the calibrated pipe section was 25 mm with the largest external diameter equal to 25.5 mm. The maximum diameter of the steel mandrel was 18.25 mm.

The formation of welds was performed by argon-arc welding with a non-consumable electrode according to known modes. Hot crimping of the pipe joint was carried out in the temperature range characteristic of steel 10, namely (1200 ÷ 850) ° С, also on a horizontal double-acting hydraulic press with forces not exceeding 300 kN.

The mandrel removal from the long pipe was carried out using the production complex, when the long pipe was placed with a hot joint in a mechanical clamp, fixed from axial movements, and applying a pulling force to the mandrel caused its axial movement. In this case, the stroke of the mandrel with axial force did not exceed 20 mm.

Subsequently, pipes were bent to a given radius.

It has been established that the technological process for the formation of butt welds using an intermediate element in the form of a sleeve with an inner ring groove made of stainless steel effectively clad pipe joint surfaces, strengthens the pipe material in the heat-affected zones, allows for more rational cutting of pipe blanks, and reduces the number of workers from - due to the reduction in the volume of manual work, it is not accompanied by the appearance of defects such as pores, inclusions, etc.

The invention is applicable in the manufacture of tube bundles of heat exchangers for oil refining, petrochemical, gas and other industries.

Claims (1)

A method of forming butt welds on pipes in the manufacture of pipe rods, including preparatory operations on the pipes for welding, their assembly and subsequent argon-arc welding of the mating ends of the pipes with filler material using a non-consumable electrode, characterized in that two butt welds are formed with their subsequent hot deformation, why pre-mating pipe ends are distributed from cylinder to cylinder, when assembling by means of a mandrel, an intermediate element is installed between their ends material in the form of a sleeve with an annular groove on the inner surface to achieve contact between the mating end surfaces of the ends calibrated by the distribution of pipes with the end surfaces of the sleeve, the welds are formed by fusing the pipe material with the material of the intermediate element, the intermediate element is heated, then the radial crimp of the intermediate element is heated initially concentrate its deformation in the inner layers at the location of the annular grooves, welds and okolos ov zones on the mandrel, give their outer diameter a size equal to the original outer diameter of the pipes.

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