RU2586176C2 - Method of joining pipes with tube plates and device therefor - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: group of inventions relates to method and device for welding stack of pipes with tube plates. Pipe made from copper-containing material is installed in holes of tube plate made of stainless steel. Method comprises expansion of each tube to make lap joint with tube plate. Obtained lap joint is rigidly fixed along perimeter in device for welding. Method comprises argon-arc welding by non-consumable electrode with filler wire from copper-containing material in pulsed mode with frequency equal to 45 Hz, wherein during welding heat is removed from tube plate. Device for welding is equipped with base, made with possibility of rotation around its axis mounted on housing with annular flange on its upper part, wherein housing is made in form of closed shell and to feed inert gas on back side of joint made, and pressure cover rigidly fixing tube plate along perimeter relative to flange. Base is equipped with brake for fixation of housing in position for welding.

EFFECT: use of group of inventions provides minimum deformation of tube plate, guaranteed density and high corrosion resistance of weld joints.

4 cl, 2 dwg

Description

The group of inventions relates to the field of engineering, in particular, for the manufacture of small-sized heat exchangers in which tube boards of small thickness are used, with a large number of tube holes and a high density of their arrangement, operating under conditions of elevated temperatures and high vibrational loads.

One of the main factors determining the reliable operation of shell and tube heat exchangers is to ensure the density and strength of the connection of the tubes with the tube plates.

Currently, there are various types of pipe joints with tube boards: rolling, gluing, soldering, welding, combined (rolling with subsequent welding or welding with subsequent rolling) [A. Fras, M. Otsisk. Calculation and design of heat exchangers. Per. from English M., Atomizdat, 1971: Heat exchangers of power plants. Ed. Yu.M. Brodova. Yekaterinburg, Socrates, 2003. RF patent №2347657, publ. 02/27/2009].

However, there are a number of requirements for the manufacture and repair of heat exchangers. According to OST 26-02-1015-85, it is recommended to use two types of pipe connection with pipe boards:

- milling joints,

- combined joints obtained by welding pipes with tube sheets with subsequent expansion.

Known methods of connecting tubes using rolling (German patent No. 3425382 (publ. 02/28/1985), US patent No. 2152260 (publ. March 28, 1939)), which provide a fairly high degree of tightness in most cases of operation at moderate temperatures and slight vibration loads. However, at high temperatures, the creep of the metal lowers the initial stress due to flaring, and leads to relaxation of the pipe walls and, accordingly, to a violation of the tightness of the connection. Violation of the integrity of such compounds can also cause vibration loads (RF patent No. 2488470, publ. 07.27.2013). It should be borne in mind that this method is quite time-consuming and can cause deformation of tube sheets having a small thickness (of the order of 4-10 mm), which is not always permissible (RF patent No. 2347657, published on February 27, 2009).

To ensure a higher degree of tightness and reliability of the connection of pipes with the tube sheet, soldering or various welding methods are used.

Soldering can be implemented in several ways. The best result is achieved when brazing in salt baths or furnaces with an inert or reducing atmosphere, since there are no significant stresses and deformations in the connection of pipes with the tube sheet (due to the uniform heating of the product) [A. Fras, M. Ocisic. Calculation and design of heat exchangers. Per. from English M., Atomizdat., 1971] However, the implementation of these methods requires expensive equipment and large production programs that allow you to fully load the equipment. It should also be noted that there are stringent restrictions on the dimensions of soldered products when implementing brazing in a furnace.

Gas-flame soldering solves these problems, however, due to uneven heating of the tube sheet, deformations can occur, and also in the case of minimum distances between the axes of adjacent tubes and a small thickness of the tube sheet (of the order of 4-10 mm), depressurization of already sealed joints located near from the place of soldering.

There are various methods of welding pipes with tube sheets, as well as various designs of their connection.

A known method of friction welding (RF patent No. 2488470 dated 12/19/2008), the disadvantage of which is the deformation of tube plates.

There is also a known method of assembling a heat exchanger, which consists in preparing the landing surfaces in the tube sheets for heat exchanger tubes, installing the tubes and connecting them to the tube sheets by welding with various options for cutting the edges of the parts to be welded (US patent No. 5101892 dated 05/02/1991). The disadvantage is that the application of the method is possible only with a sufficiently large diameter of the tubes and their small number.

The closest in technical solution is the method of welding a heat exchanger, which consists in installing copper-nickel tubes in a stainless steel tube sheet and welding them using a machine for automatic argon-arc welding and copper-nickel alloy wire (Bfe10-1-1) with a diameter of 0 , 8 mm as an additive with a current of 60-120 A (Patent of the People's Republic of China No. 1016073441 of 04.16.2009). However, the application of this method is possible only with a sufficiently large thickness of the tube sheet and free access to welded joints for the possibility of using the installation for automatic welding. The specified method is taken as a prototype.

A device is known for the manufacture of long products, the construction of which implements the possibility of supplying a protective gas to the root of the seam of the welded edges (RF patent No. 98109065 from 05/14/1998). However, the design of the device does not provide for the free circulation of the protective gas from the reverse side of the seam to reduce its exit through the joint of the welded parts, which can lead to a decrease in the quality of the finished welded joint.

It is also known a device for welding a thin-walled conical shell, which is a rigid crimping frame that prevents deformation of the welded assembly. This technical solution is the closest solution to the claimed (RF patent No. 128143, publ. 05/20/2013) and is selected as a prototype. However, the design of the device does not allow welds to be welded in a position convenient for welding or requires a tilting operation after each weld has been completed; heat removal from the product has not been implemented to reduce its ultimate deformations and welding time.

The task to which the group of inventions is directed is to manufacture and restore heat exchangers in which tube sheets of small thickness are used, with a large number of tube holes for installing tubes and a high density of their arrangement, operating at elevated temperatures and high vibrational loads.

As a result of using the proposed group of inventions, the following technical result is achieved - minimal deformation of the tube sheet, guaranteed density and high corrosion resistance of welded joints, ensuring the operation of the heat exchanger under conditions of elevated temperatures and high vibration loads.

The specified single technical result in the implementation of the group of inventions on the object - the method is achieved by the fact that the method of connecting the tube package with tube sheets of small size and small thickness includes the installation of tubes made of corrosion-resistant and heat-resistant steel, followed by welding the ends of the tubes to the tube sheet with a non-consumable argon-arc welding electrode using filler wire made of copper-containing material.

Distinctive features of the proposed method are the expansion of the protruding ends of the tubes without the formation of a permanent connection with the tube sheet, its rigid fixation in the device for welding, filling its internal volume with inert gas and manual welding by beat-up in a pulsed mode, followed by cooling of the unit in the clamped state. This will provide the guaranteed density and corrosion resistance of welded joints, ensuring the operation of the heat exchanger under conditions of elevated temperatures and high vibrational loads.

The specified single technical result in the implementation of the group of inventions on the object - the device is achieved by the fact that the device for welding a package of pipes with tube sheets of small size and small thickness, consisting of a housing with an annular flange in its upper part and fixing elements, in contrast to the known, has a base providing rotation around its axis of the housing mounted on it, made in the form of a closed glass with the possibility of supplying inert gas from the back of the seam by filling its inner volume, and a pressure cap that rigidly fixes the tube sheet relative to the flange. And also the device has a brake, which ensures its fixation in a position convenient for welding with the exception of its arbitrary movement. The pressure cap has channels for circulating coolant around the perimeter and central rib. Along the perimeter of the flange there are also channels for the circulation of coolant. The presence of a ring in the device eliminates the deformation of the pressure cap when tightening the bolted joints. In addition, the pressure cap has a central rib fixing the tube sheet in its central part.

The proposed design of the device allows for rigid fixation of the tube sheet and eliminates its deformation, heat removal from it, protection of the reverse side of the welds from the atmosphere of the air by filling its internal volume with inert gas, rotation of the assembly relative to the axis. The result is a significant reduction in the time taken to produce the assembly and minimal deformation of the tube sheet is ensured, thereby improving the quality, density of welded joints and achieving their high strength, which ensures the operation of the heat exchanger under conditions of elevated temperatures and high vibrational loads.

The claimed group of inventions meets the requirements of the unity of invention, since the group of diverse inventions forms a single inventive concept, and one of the claimed objects of the group — a device for welding a pipe package with small size and small thickness tubes — is designed to implement another claimed object of the group — a method of connecting a pipe package with tube sheets of small size and small thickness.

In this case, both objects of the group of inventions are aimed at solving the same problem with obtaining a single technical result.

The analysis of the prior art by the applicant, including a search by patents and scientific and technical sources of information and identification of sources containing information about analogues of the claimed group of inventions for both the method object and the device object, allowed to establish that the applicant did not find analogues for both method, and for the device of the claimed group, characterized by features identical to all the essential features of both the method and the device of the claimed group of inventions. The determination from the list of identified prototype analogues for both the method and the device as the closest in the set of features of analogues made it possible to identify the set of essential features in relation to the technical result perceived by the applicant for the distinctive features for each of the claimed objects of the group set forth in the claims.

Therefore, each of the objects of the group of inventions meets the condition of "novelty."

To verify the compliance of each object of the claimed group of inventions with the condition "inventive step", the applicant conducted an additional search for known solutions in order to identify signs that match the distinctive features of the selected prototypes for each object of the claimed group of inventions. The search results showed that each object of the claimed group of inventions does not follow explicitly from the prior art for the specialist, since the influence of the transformations provided for by the essential features of each of the objects of the claimed group of inventions on the achievement of the technical result is not revealed from the prior art.

The essence of the proposed technical solution for the object device is illustrated by drawings, which depict:

Fig. 1 - device for welding a package of pipes with tube sheets;

Fig. 2 - connection of a package of tubes with a tube sheet.

The proposed device for welding a pipe package with tube sheets consists of a base (1), which, due to a set of balls (2), provides rotation around its axis of the device body (3), which has an annular flange (4) in the upper part and is made in the form of a closed glass that allows you to implement protection of the reverse side of the welds from the atmosphere of the air by filling its internal volume with inert gas through the fitting (5). The presence of the nozzle (6) ensures the exit of the protective gas from the housing of the device (3), which eliminates the possibility of a significant increase in pressure inside the housing and, as a consequence, excessive gas escape through the interface of the welded parts. After installing the heat exchanger (7) in the device, the pressure cap (8) rigidly fixes the tube sheet around the perimeter relative to the flange by tightening 6 bolt connections (9), while the presence of the ring (10) (equal in thickness to the tube sheet) eliminates its deformation . Additional heat removal from the tube sheet during the welding process is ensured by the constant circulation of coolant through special channels (I) located along the perimeter of the flange, as well as around the perimeter and in the central ridge (12) of the pressure cap (8). Coolant is supplied / discharged through fittings (13). In addition, the central rib (12) of the pressure cap (8) fixes the tube sheet in its central part, eliminating bending during the welding process. Fixing the device case (3) in a position convenient for welding and the exclusion of its arbitrary rotation is provided by the brake (14), which is equipped with the base of the device (1).

The proposed method is carried out in the following sequence. Perform cleaning and etching of the tubes and tube sheet. Then install the tube into the holes of the tube sheet. Before welding, flaring of the protruding ends of the tubes is carried out. Rolling is not intended for permanent connection and does not directly provide tightness of the connection. In the process of rolling, an lap joint of the tube with the tube sheet is formed, which greatly simplifies the welding process. To reduce the deformation of the tube sheet, protect the reverse side of the welds from the air atmosphere, remove heat from the tube sheet and ease of welding, a special welding device is used. In the process of rolling, a deflection of the tube sheet by 0.5-2 mm occurs, during the welding process, back deflection occurs, which is limited by the pressure cap of the device, resulting in minimal deformation of the tube sheet. Next, the assembled assembly (with flared tubes) is rigidly fixed in the device for welding and its internal volume is filled with inert gas, followed by welding of the tube bundle to the tube grid in the sequence ensuring its uniform heating, by manual argon-arc welding with a nonconsumable electrode in a pulsed mode using a filler wire of oxygen-free copper with a diameter of 1 mm. In the practical implementation of the method, the following welding modes were used:

- Pulse current (II) = 120 A;

- Pause current (I2) = 32 A;

- Pulse frequency = 45 Hz;

- The duration of the pulse current I1 = 37%.

After welding, the assembly in the fixture is cooled in the clamped state for 1-2 hours and the tightness of the welded joints (kerosene, compressed air) is checked, the detected defects are eliminated by welding the defective sections.

The absence of obstacles of a technical, technological or other order for the industrial implementation of the invention and the fact of its implementation at the enterprise in the process of manufacturing heat exchangers make the claimed technical solution consistent with the criteria of the invention “industrial applicability”.

Currently, the company uses the claimed method and device for its implementation for the manufacture of heat exchangers.

Claims (4)

1. A method of welding pipes with tube sheets, including the installation of pipes of copper-containing material in the holes of the tube sheets of corrosion-resistant and heat-resistant steel and argon-arc welding of the ends of the pipes with the tube sheet with a non-consumable electrode with a filler wire of copper-containing material, characterized in that the welding is carried out before welding each pipe with the formation of an lap joint with a tube sheet, then the obtained lap joint is rigidly fixed around the entire perimeter in the device for welding and suschestvlyayut welding in the pulsed mode with a pulse frequency of 45 Hz, while the welding process is carried out by heat tubesheet. 2. A device for welding pipes with tube sheets, comprising a body made with the possibility of filling its internal volume with inert gas, and a fixing element of the tube sheet, characterized in that it is provided with a base made with the possibility of rotation around its axis of the housing mounted on it, made with an annular flange on its upper part, while the body is made in the form of a closed glass and with the possibility of supplying inert gas from the back of the seam, and a clamping cover, firmly fix which holds the tube sheet around the perimeter relative to the annular flange, while the clamping cover is made with a central rib for fixing the tube sheet in its central part and with coolant circulation channels located along its perimeter and in the central rib, and the base is equipped with a brake for fixing the case in position for welding with the exception of its arbitrary movement. 3. The device according to p. 2, characterized in that the flange is made with channels for the circulation of coolant located along its perimeter. 4. The device according to p. 2, characterized in that it is equipped with a ring made with the possibility of eliminating the deformation of the pressure cover when tightening the bolted joints.

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