RU2296658C2 - Method of making butt welds on pipes - Google Patents

Abstract

FIELD: mechanical engineering; welding.

SUBSTANCE: invention relates to plastic metal working and it can be used in making of pipe studs. Methods includes preparatory operations on pipes, assembling of pipes with subsequent argon-arc welding of pipe end by non-consumable electrode with use of filler material. Preliminarily, ends of pipes to be welded are calibrated by expanding in cylinder, and pipes are assembled on mandrel with use of intermediate member in form of ring made of cladding material which is placed between end faces of pipes to provide contact, welds are formed by welding pipe material with cladding material of ring at both sides. The pipe butt joint is heated and is subjected to hot upsetting on mandrel with cladding of surfaces of pipe butt joint at plastic flow of cladding material of ring relative to weld and near-weld zones according to scheme of tri-axial nonuniform compression and outer diameter of pipe butt weld is made equal to initial outer diameter.

EFFECT: improved quality of pipe studs owing to cladding of inner and outer surfaces of welds and elimination of defects in welds.

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 rods, including the cut length of pipe lengths for straight sections of the studs, the measured length of the pipe for manufacturing flexible to a given radius of the thread, cleaning the outer surface of the mating ends of the elements to be joined, their subsequent welding with the formation of two welds in the obtained hairpin (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, determined by a large percentage of rejected 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 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 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 geometric dimensions in terms of internal diameter, which requires a control operation — rolling the stud around 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 pipe joint from aggressive media during operation of the tube bundle, as well as eliminate defects in welds by their finish hot crimping on mandrel.

The technical result is achieved by the fact that in the 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 filler material using a non-consumable electrode, according to the invention, are pre-mated the ends of the pipes are calibrated by distribution into a cylinder, the pipes are assembled on a mandrel using an intermediate element in the form of a ring of cladding material, which they are placed between the ends of the pipes to ensure their contact, the welds are sequentially formed by fusion of the pipe material with the cladding material of the ring on its both sides, after which the pipe joint is heated and hot crimped on the mandrel with the plating of the pipe joint surfaces by plastic flow of the cladding material of the ring with respect to the weld and heat-affected zones according to the scheme of triaxial uneven compression, and giving the outer diameter of the pipe junction their original outer diameter.

Implementation of the proposed method for the formation of butt welds on pipes upon receipt of U-shaped tube bundle hairpins makes it possible to clad the external and internal surfaces of the joint, providing improved anti-corrosion characteristics, as well as eliminating defects in the welded joints with their hot crimp crimping on the mandrel, changing the structure and mechanical properties in the heat-affected zones, form the inner surface of the joint without 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 ring of cladding material (for example, stainless steel), effective cladding of the pipe junction surfaces is achieved, which increases the overhaul time of the difficult beam during its operation;

- 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 from cylinder to cylinder; figure 3 - the mating ends of the pipes, a ring of filler material on the mandrel before the formation of welds by fusion; figure 4 - connected elements after the formation of welds on both sides of the ring; figure 5 - a heated pipe joint, placed in a detachable (3-segment) matrix of a horizontal hydraulic press; Fig.6 - the end of the stage of hot crimping the weld on the mandrel; 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 pipes before welding is carried out using a ring 3 of filler material, for example, stainless steel grade X18H10T, located on the mandrel 4 of hardened steel. Between the mating ends of the pipes and the ring of filler material achieve the necessary contact.

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

The relatively large dimensions of the 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 segments of the matrix of the radial movement in the direction of the axis initially causes the introduction of the scallops of the working surface of the matrix on the surface of the ring of filler material. There is a partial filling of the free volumes between the annular combs and the formation of the outer zone of difficult deformation (Fig.6). At the final stage of this introduction, there is also the formation of an internal zone of difficult deformation (due to friction forces on the surface of the mandrel).

Further 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 (due to the approach of the surfaces of difficult deformation 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 manifest themselves at the stage of pipe deformation in transition 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 ring 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 technological effectiveness, which also determines increased productivity. The absence of an internal burr eliminates the need for a test ball rolling around the studs.

Pilot - industrial verification of the developed method for the formation of butt welds took place 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 to the extent and cleaning of the surfaces of the mating pipes was carried out on the appropriate equipment with the achievement of the required parameters.

Rings with dimensions of 26.2 × 18.3 × 10 mm were made of stainless steel grade X18H10T by deformation of pipe blanks to the appropriate diameter and the necessary cutting operations.

Distribution-calibration of the mating pipe ends was carried out on a double-action horizontal 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 of not more than 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 of formation of butt welds using an intermediate element in the form of a stainless steel ring effectively clad pipe joint surfaces, strengthens the pipe material in the heat-affected zones, allows more efficient cutting of pipe blanks, and reduces the number of workers due to the reduction in manual works, 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 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, characterized in that the pre-mated ends of the pipes are calibrated by distributing into a cylinder, assembly pipes are carried out on a mandrel using an intermediate element in the form of a ring of cladding material, which is located between the ends of the pipes to ensure their contact, sequentially form the welds by fusion of the pipe material with the cladding material of the ring on both sides, after which the joint of the pipes is heated and hot crimped on the mandrel with the cladding of the pipe joint surfaces by plastic flow of the cladding material of the ring relative to the weld and heat-affected zones according to the triaxial uneven compression scheme giving the outer diameter of the pipe junction their original outer diameter.

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