RU2177851C2 - Method for securing tubes in tube plates - Google Patents

Abstract

FIELD: plastic metal working, possibly formation of combined rolled joints of tubes with tube plates of heat exchanging apparatuses. SUBSTANCE: method comprises steps of calibrating tube end according to its outer diameter along portion whose length exceeds thickness of tube plate; reducing part of calibrated portion of tube end for forming annular rigidity portion in the form of truncated cone; placing one end of tube in opening of tube plate in such a way that to arrange annular rigidity portion in plane of inner plate; placing tube end over front surface of tube plate; fixing tube against its possible motion; then performing first stage of tube rolling out by means of rollers for mechanical rolling out; providing out-of-contact deformation in radial direction of annular rigidity portion and forming annular tightness portion between inner edge of tube opening of tube plate and annular rigidity portion; welding tube to tube plate and realizing second stage of rolling out. EFFECT: enhanced corrosion resistance and other operational characteristics of combined joints. 9 dwg

Description

 The invention relates to the field of metal forming and, in particular, to processes for securing pipes in tube openings of heat exchangers using the effect of localized directional plastic deformed pipe material.

 A known method of securing pipes in tube sheets, including making corrugations at the end of the pipe, installing the pipe end in the hole of the tube sheet, followed by fixing the pipe in the tube sheet by mechanical action on the inner surface of the pipe end protruding above the front surface of the tube sheet (see a. 1185046, IPC F 28 F 9/16, Bull. 38, dated 10.15.85).

 The main disadvantage of the known method of fixing pipes in tube sheets should be attributed to limited applicability due to the difficulties associated with the installation of such pipes in the holes of the tube sheets.

 There is also known a method of securing pipes in tube sheets with the formation of a combined rolling connection, including installing the pipe at one end in the hole of the tube sheet with the end of the pipe above the front surface of the tube sheet, fixing the pipe from possible movement, welding it with the tube sheet and forming a rolling joint by rolling pipes with mechanical rolling rollers (see OST 26-02-1015-85. Fastening pipes in tube sheets, Moscow, Ministry of Chemical and Petroleum Engineering, 1985 g. - prototype).

 With regard to thin-walled tube sheets (wall thickness 20-30 mm), a disadvantage of the known method of fixing pipes in the tube sheets is warpage of the tube sheet from mechanical impact on the walls of the tube hole and thermal stresses during the welding operation of the pipe with the front surface of the tube sheet. The result of warping of the tube sheet is a violation of the contact between the connected elements from the side of the inner surface of the tube sheet. The latter, taking into account the presence of a weld and the thinness of the tube sheet, leads to intense crevice corrosion.

 The objective of the invention is to develop such a method of securing pipes in tube sheets that, as applied to thin-walled tube sheets, eliminates the possibility of crevice corrosion between the connected elements, guarantees improved service characteristics of the combined joints, including their corrosion resistance.

 The technical result is achieved by the fact that in the method of fixing the pipes in the tube sheets with the formation of a combined rolling connection, including installing the pipe at one end in the hole of the tube sheet with the pipe end above the front surface of the tube sheet, fixing the pipe from possible movement, welding it with the tube sheet and the formation of a rolling joint by expanding the pipe with rollers of mechanical rolling, according to the invention, the pipe end is pre-calibrated by the outer diameter on a section of a length exceeding the thickness of the tube sheet, after which a portion of the calibrated pipe section is crimped to obtain a section of ring stiffness in the form of a truncated cone, the pipe is installed in the pipe hole with the section of ring stiffness located in the plane of the inner surface of the tube sheet, and the pipe is expanded in two stages the first of which is carried out before welding the pipe with the tube sheet with non-contact deformation in the radial direction of the section of ring stiffness and forming a section of the annular density between the inner edge of the hole of the tube sheet and said section of the annular stiffness of the pipe.

 Implementation of the proposed method of securing pipes in tube sheets allows to obtain combined rolling connections with the possibility of eliminating the formation of crevice corrosion between the connected elements and to guarantee improved performance characteristics of the combined rolling joints, including corrosion resistance.

 This is because the new technological process based on the present invention is strictly linked to the diameter of the pipe hole. So, according to the known diameter of the pipe hole, the end of the pipe is pre-calibrated with a rigid punch, providing a one-sided gap between the pipe and the walls of the pipe hole of not more than 0.025 mm. The length of the calibrated section of the pipe exceeds the thickness of the tube sheet.

 The guarantee of improved service characteristics with an extended turnaround time is achieved at the first stage of pipe expansion by forming annular density between the connected elements on the inner edge of the pipe hole, and also by forming a field of compressive residual stresses in the pipe on the length segment between the weld and the inner ring edge of the pipe hole.

 The operation of welding a pipe with the front surface of the pipe lattice generates thermal stresses that cause compression of the pipe along the length between the weld and the inner edge of the pipe hole, which determines the creation of additional compressive stresses on the contact surface of the connected elements.

 As a result of the second stage of pipe expansion, carried out in strict deformation frames for the connected elements, the achieved state of the latter is recorded.

 The invention is illustrated by drawings, where in FIG. 1 shows a heat exchange tube and a stepped punch before performing a calibration operation on the outside diameter of the tube; in FIG. 2 - stage of calibration of the outer diameter of the pipe; in FIG. 3 - heat transfer tube and tool matrix before performing the crimp operation of the calibrated section; in FIG. 4 - stage end of the operation of crimping the end of the pipe; in FIG. 5 - tube sheet and heat transfer pipe before performing the first stage of pipe expansion; in FIG. 6 - the end of the first stage of pipe expansion with ensuring contact of its external surface with the walls of the pipe hole; in FIG. 7 - pipe and pipe hole after the welding operation; in FIG. 8 - the end of the second stage of pipe expansion; in FIG. 9 - combined milling connection.

 An embodiment of the invention is as follows.

 The heat exchange pipe 1 (Fig. 1), for example, of steel 10, which underwent preparatory operations at the ends (dressing, cutting to the best, cleaning the external surfaces to a metallic luster), is subjected to an external diameter calibration operation in accordance with the diameter of the pipe hole. Why the pipe is fixed from possible movement and, introducing a small step of the punch 2 into its hole (Fig. 2), calibrate the external diameter of the pipe over a length greater than the thickness of the tube sheet. Thus, the outer diameter of the pipe becomes less than the diameter of the pipe hole by 0.05 mm.

 Next, the pipe is crimped in the tool matrix 3 (Fig. 3). The latter has two cylindrical cavities connected by a conical section 2 mm wide. Moreover, a cavity with a large hole is designed to accommodate a pipe with an initial diameter. The coaxial movement of the matrix relative to the stationary calibrated pipe section causes plastic deformation of the pipe material and its acquisition of an external diameter determined by the diameter of the matrix cavity with a minimum cross section. The transition from the calibrated section of the pipe to the compressed section is carried out by means of a section having a cross section in the form of a truncated cone. The low height of the cone (2 mm) and the increased mechanical properties of the pipe material allow us to talk about the formed ring stiffness (Fig. 4).

Then the pipe with a profiled end is installed (Fig. 5) in the grooveless hole of the tube sheet 4. On the side of the front surface of the grid around the perimeter of the tube hole, an annular recess is made at an angle of 45 ^° with a leg length equal to the pipe wall thickness. The pipe is installed in the hole of the tube sheet in such a way that the ring stiffness is placed in the plane of the inner surface of the tube sheet. Checking the correct installation of the pipe is carried out by measuring the protrusion of its end above the front surface of the tube sheet.

 A mechanical rolling mill containing working rollers is introduced into the pipe opening, and the first stage of rolling of the pipe is carried out (the applied force from the rolling rollers to the inner surface of the pipe is conventionally shown by arrows). The radial deformation of the pressed end of the pipe during its expansion is accompanied by the fact that the same strain of ring stiffness is observed and, as a consequence, the deformation of the calibrated section of the pipe. So at the completion of the first stage of pipe expansion, an annular density of the connected elements is formed on the inner edge of the pipe hole (Fig. 6).

 After that, the pipe is welded (Fig. 7) with the front surface of the pipe hole (a consumable electrode in a protective medium, for example, argon). The heating of the pipe section during its welding with the tube sheet and subsequent cooling under conditions of the tube being fixed along the inner edge of the tube hole determine the appearance of compressive stresses along the tube length equal to the tube sheet thickness.

 The further strictly regulated second stage of pipe expansion (Fig. 8) does not cause warping of the tube sheet and destruction of the weld, since it is performed without shifting the weld relative to the edge of the hole of the tube sheet.

 The resulting combined connection (Fig. 9) is characterized by high service characteristics and its implementation is not accompanied by warpage of the tube sheet.

 The resulting combined rolling joint is characterized by the presence of predicted (by location) annular densities with controlled deformations of the joint elements while eliminating the causes of weld failure (Fig. 6).

 A pilot test of the developed method was carried out when fixing steel (X18H10T steel) pipes in tube sheets of the same steel with a thickness of 20 mm.

 On the front surface of the tube sheet along the perimeter of the holes, annular recesses of a triangular cross section were made, having the following geometric dimensions: 1.5 x 1.5 mm.

 The initial geometric dimensions of the pipe were: outer diameter - 16 mm, wall thickness - 1, 5 mm and length 1200 mm.

 The technological equipment for calibrating and crimping the ends of the pipe was made of X12M steel, which had hardness after quenching HRC = 56-58 units. , according to the 7th accuracy class.

 The ends of the pipes were calibrated (to a diameter of 16.3 mm) and crimped by a double-acting hydraulic unit with forces of 0.15-0.17 MN, which reduced the external diameter of the pipe to 15.4 mm.

 Trenchless holes in the tube sheet were made with a diameter of 16.35 mm according to standard technology for this case.

 The operation of welding the pipe with the front surface of the tube sheet was carried out by a consumable electrode (stainless steel wire) in a protective argon atmosphere at the recommended standard conditions.

 Flaring of pipes was carried out in two stages by domestic rolling at the stand of Indresco (USA).

 Studies of the strength and density characteristics of the resulting combined rolling compounds revealed their increased (including corrosion resistance) values with respect to similar rolling compounds obtained by traditional technology.

 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 securing pipes in tube sheets with the formation of a combined rolling connection, including installing the pipe at one end into the hole of the tube sheet with the end of the pipe above the front surface of the tube sheet, fixing the pipe from possible movement, welding it with the tube sheet and forming a pipe joint by rolling the pipe with rollers mechanical rolling, characterized in that the pipe end is pre-calibrated according to the outer diameter in a section of a length exceeding the thickness of the pipe p brushes, after which they compress a portion of the calibrated pipe section to obtain a section of ring stiffness in the form of a truncated cone, install the pipe in the pipe hole with the location of the section of ring stiffness in the plane of the inner surface of the pipe lattice, and expand the pipe in two stages, the first of which is carried out before by welding a pipe with a tube sheet with non-contact deformation in the radial direction of the ring stiffness section and the formation of the ring density section between the inside the lower edge of the hole of the tube sheet and the mentioned section of the ring stiffness of the pipe.

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