RU2285595C1 - Method for forming butt welded seams on tubes - Google Patents

Abstract

FIELD: plastic working of metals, namely processes for forming butt welded seams on tubes at making tube studs of U-shaped tube bundles using effect of localized hot plastic deforming of welded seam and near-seam zones.

SUBSTANCE: method comprises steps of preliminarily working tube ends by expanding them from cylinder to cylinder; assembling tubes with use of mandrel and placing intermediate member of additive material between joined end surfaces of end portions of tubes sized by expansion and end surfaces of step ring. Welded seams are formed by argon-arc welding due to melting material of intermediate member at its both sides adjacent to tube ends. The intermediate member is heated up and it is subjected to hot radial squeezing while concentrating its initial deformation in surface layers according to position of ring steps, welded seams and near-seam zones on mandrel for providing size of their outer diameter equal to initial outer diameter of tubes.

EFFECT: improved quality of welded seams.

8 dwg

Description

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

A known 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 the pipes with filler material with a non-consumable electrode using filler material, cutting pipe lengths for straight sections of the studs, measured the length of the pipe for manufacturing flexible to a given radius of kalach, 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 multiplicity of used working lengths. And secondly, the increased cost, which is also determined by the large 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 the pipes for welding, their assembly and subsequent argon-arc welding of the mating ends of the pipes with a non-consumable electrode using filler material (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 also do not undergo final plastic deformation, eliminating possible defects in the welds and hardening material in the 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 localize the volume of melting of the pipe material, 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 welds 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 the pipes for welding, their assembly and subsequent argon arc welding of the mating ends of the pipes with a non-consumable electrode using filler material, according to the invention, the filler material used an intermediate element in the form of a stepped ring, which is installed between the mating ends of the pipes during assembly, while before assembly, we mate the ends of the pipes are distributed from cylinder to cylinder, pipes with an intermediate element on the mandrel are assembled, an axial force is applied to the mating end surfaces of the pipes calibrated by the distribution, providing contact between them and the end surfaces of the stepped ring, welding is performed by melting the steps of the stepped ring on both sides of them the formation of two butt welds, carry out additional heating of the pipe joint with subsequent hot radial crimping, reaching an external diameter of the joint equal to the initial externally the diameter of the pipes to be welded and concentrating deformations in the surface layers at the location of the annular steps, welds and heat-affected zones.

Implementation of the proposed method for the formation of butt welds on pipes upon receipt of studs of U-shaped tube bundles allows to localize the volume of the molten material of the pipes, which means that it eliminates the possibility of carbon burn-out and creates the effect of soldering, cladding the external and internal surfaces of the joint, providing increased anti-corrosion characteristics thereof, as well as eliminate defects in welds by their finish hot plastic deformation, change the structure and mechanical properties in the heat-affected zones, for th e internal interface burr.

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 stepped ring of cladding material (for example, stainless steel), effective melting of the filler material with reactive melting of the pipe material in limited volumes is achieved;

- clad the joint surface with reduced deforming forces, which increases the service life of technological equipment;

- plastic deformation of the weld and heat-affected zones eliminates possible defects in the welds and strengthens the material in heat-affected zones (the rate of hardening of the material in 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, a stepped ring of filler material on the mandrel after the application of axial compression forces; figure 4 - calibrated pipe ends and an intermediate element after the formation of welds by predominantly melting the filler material; figure 5 - heated pipe joint, located in a detachable (3-segment) matrix of a horizontal hydraulic press; figure 6 - stage hot stamping of the intermediate element in its outer layers; Fig.7 - 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; on Fig - 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 on 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 thickness of their walls plastic hinges, selected in the form of conical regions by dots (figure 2).

The assembly of pipes on the mandrel 3 before welding is performed using a stepped ring 4 of filler material, for example, stainless steel grade X18H10T. Two steps are made on the outer surface of the ring, the outer diameter of which exceeds the outer diameter of the calibrated sections of the pipe ends.

By applying an axial compressive force to the mating ends of the pipes, the required contact is achieved between their end surfaces and the end surfaces of the intermediate member of the filler material (FIG. 3).

The formation of welds on both sides of the ring is carried out by fusion (figure 4) according to the modes regulated by technical documentation. At the same time, the volumes of filler material are predominantly melted, forming an electric arc with a non-consumable electrode over the areas of the steps. The melting of the pipe material is carried out reactively (taking into account the axial compressive force applied to the pipes) by the action of the molten filler material on the end surface of the calibrated pipe sections. In other words, there is a localization of the volumes of melting in the pipe material, which does not cause a negative effect of heating on the alloying elements of the pipe material.

The relatively large sizes of the stepped ring along its length require additional heating of the pipe joint to optimal hot deformation temperatures. 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. 5).

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 lateral surface of the stepped ring of filler material. Reduced overall dimensions of the ring determine the localization of the deformation of the filler element initially in its external volumes with the formation of the zone of difficult deformation (Fig.6).

The reactive force from the side of the mandrel on the mentioned impact leads to localization of the deformation of the intermediate element in its inner layers (Fig.7). There is a deformation of the intermediate element with simultaneous cladding of the inner surface of the pipe joint.

Thus, the movement of the matrix segments in the radial direction is associated with hot deformation of the filler material and, through its plastic flow, the deformation of welds and heat-affected zones. 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 minimized volumes of welds, subject to comprehensive uneven compression, are intensively worked out, which does not cause a loss in mechanical properties. In addition, the formation of axial compressive residual stresses of the first kind is observed at the junction of the pipes.

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. 8) is characterized by high mechanical properties (the material of the stepped ring that perceives the action of the working medium plays an important role), formed by residual compressive axial stresses, sufficient accuracy for such products, high adaptability, 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.

Step rings with dimensions of 26.2 × 18.3 × 12 mm were made of stainless steel grade X18H10T, steel 10 by deformation of the pipe blanks to the appropriate diameter and the necessary cutting operations. On the outer surfaces of the rings steps were made with a width of 3 mm (from the ends) and a diameter of 25.8 mm.

Distribution-calibration of the mating ends of the pipes was carried out on a horizontal double-acting hydraulic press of the design of the Repair and Mechanical Plant of NK YUKOS with efforts in the range of 35-40.0 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 displacements, and applying a pulling force to the mandrel caused its axial displacement. 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 stepped ring of stainless steel or steel 10 effectively clad the pipe joint surface, strengthens the pipe material in the heat-affected zones, allows for more rational cutting of pipe blanks, and reduces the number of workers for reducing the amount of manual work, is not accompanied by the occurrence 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 pipes for welding, their assembly and subsequent argon-arc welding of the mating ends of the pipes with a non-consumable electrode using a filler material, characterized in that an intermediate element in the form of a stepped material is used rings, which are installed between the mating ends of the pipes during assembly, while before assembly the mating ends of the pipes are distributed from cylinder to cylinder, with take pipes with an intermediate element on the mandrel, apply axial force to the mating end surfaces calibrated by the distribution of pipes, providing contact between them and the end surfaces of the stepped ring, carry out welding by melting the steps of the stepped ring on both sides with the formation of two butt welds, perform additional heating pipe joint followed by hot radial crimping, reaching the external diameter of the joint equal to the original external diameter of the pipes being welded and concentrating Reformation in the surface layers of the location of the ring steps, welds and heat-affected zones.

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