RU2776894C1 - Method for fixing pipes in the tube grids of heat exchangers and a tool for its implementation - Google Patents

Abstract

FIELD: heat engineering.

SUBSTANCE: invention relates to heat engineering and can be used for fixing pipes in the tube grids of shell-and-tube heat exchangers. In the rounding machine, a cylindrical expansion roller is fixed, having a body, a spindle and rollers, and a preliminary expansion of the pipe section is performed. After reaching the set torque value, the expansion roller is removed from the pipe, the inner diameter of the pipe is measured on the expanded section with this taken into account, a tool is prepared for continuous expanding of the pipe in the form of a tape-screw cone expansion roller. The tool contains a conical body with windows, a spindle with a nut, washer and shank, on which the adjusting washers and rollers are placed. The mentioned tool is installed in a pre-expanded section of the pipe, connected to a rounding machine. The drive of its rotation and the supply of cooling emulsion are turned on and the pipe is expanded to the entire thickness of the pipe grid in one pass of the tool.

EFFECT: as a result, the technological capabilities of the method are expanded, the quality of the obtained compounds is improved and the wear resistance of the tool is increased.

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Description

The invention relates to heat engineering, in particular to the technology of fixing pipes in tube sheets of heat exchangers with a thickness of at least 4 times the diameter of the pipes being fixed, that is, in thick lattices.

Of all the known methods for connecting pipes and tube sheets, the most productive are pulsed, which include methods for attaching pipes by explosion and an electrohydropulse method based on the use of blast wave energy during the explosion of gunpowder in a closed volume or during the instantaneous evaporation of a wire inside a cartridge with liquid. However, there are serious drawbacks that limit their practical application, namely:

- when using the method of fastening pipes by explosion (A.I. Lukovkin, V.A. Semenov. Technology of fastening pipes in heat exchangers and boilers by explosion. L .: LDNTP, 1968 - 28 p.), the energy of the blast wave does not provide a stable connection quality , since the explosion has a negative effect on the internal structure of the pipe and often leads to the appearance of longitudinal cracks on the inner surface of the pipe being fixed; in addition, a specially equipped room is required for blasting;

- when using the method of expanding pipes with hydrostatic pressure, which is mainly used when fixing pipes of small diameters of 20-25 mm, (B.Ya. Mazurovsky, V.S. Kozlovsky, V.V. Buneeva. Shipbuilding technology, Electrohydraulic expansion of pipes in tube sheets heat exchangers, 1973, No. 8, pp. 17-20), a liquid pressure of up to 3500 kg/cm is created inside the fixed end of the pipe. The main disadvantage of this method is its high cost, associated with the need to use calibrated pipes, as well as the need to make accurate holes in the tube sheet, providing minimal initial gaps in the joints.

In addition, the hydrostatic method is preliminary, since the deformation of the pipe is carried out only until the “selection” of the gap between the pipe and the hole, which does not ensure the occurrence in the connection of the contact pressures necessary for tightness and strength. After the pipes are expanded by hydrostatic pressure, the pipes are usually “rolled” by mechanical roller rolling in two “belts”: at the outer surface of the tube sheet and in the area where the pipe exits into the heat exchange cavity.

Currently, the most common method of fastening pipes in thick tube sheets is the method of “step-by-step” flaring of the ends of the pipes, in which the pipes installed in the tube sheet are preliminarily fixed by welding, then - with a length-adjustable tool - by rolling "CP". In this case, the flaring of each pipe is carried out sequentially, in separate "steps" ("belts"), with mutual overlapping of the "belts" of 4-6 mm. The SPbGMTU NITL catalog (https://nitl.ru/catalog/valcovki_razlichnyh_serij/valcovki_serii_sr) illustrates the technology of this method, in which, first, all pipes in the tube sheet are expanded with the first “belt”, then the stop on the threaded section of the rolling body is moved to reconfigure the tool to the next "step" and expand all the pipes with the second "step", and so on, until all the pipes are expanded over the entire thickness of the tube sheet. Depending on the thickness of the grating and the length of the rolling rollers, the “belts” of fastening (“steps”) can be from 2 to 20 or more.

The advantage of the “step-by-step” method of fastening is the fact that the flaring of each “belt” is performed by a drive with torque control, which, in turn, ensures the same (optimal) value of contact pressures in each “belt” and, therefore, high quality of the obtained rolled joints.

The disadvantages of the described method include the duration of the process of fixing pipes in the tube sheet, associated with unproductive time spent on removing the rolling from the pipe, reconfiguring the rolling to a different rolling depth of each "belt", stopping and switching the drive from direct rotation to reverse. Obviously, the thicker tubesheet, the more “steps” to complete, and the more time wasted.

The closest technical solution to the proposed method of fixing pipes in a tube sheet is the method of continuous expansion, which was first used in the mid-1960s in the manufacture of heat exchangers with thick tube sheets. With this method, pipe expansion is carried out in one pass of the tool for the entire thickness of the tube sheet (Yuzik S.I. Shipbuilding technology, Tape-screw method of pipe expansion. 1966, No. 7).

The method was called tape-screw, since the ends of the rollers in the tool - pipe expander in the process of rolling the pipe and its simultaneous movement in the axial direction leave a mark in the form of a narrow screw ribbon on the inner surface of the pipe.

The disadvantage of this method is the low wear resistance of the body and the expander rollers associated with the kinematic scheme of rotation transmission, in which the rotation from the drive to the rollers is transmitted not by the spindle, but by the expander body. Such a scheme requires an increased torque (more than 3 times compared to classical cylindrical rolling), which can lead to twisting of the body in the window area, as well as to mutual intense wear of the rollers and side surfaces of the body windows.

St. Petersburg State Marine Technical University has developed a combined method for expanding pipes in thick tubular grids using classical cylindrical and tapered tape-screw expanding. The technical result of using the method is to reduce unproductive time of expanding pipes in thick tube sheets, expanding technological capabilities (the ability to expand thick-walled pipes of small diameters in tube sheets of almost any thickness), improving the quality of expanded joints and increasing the wear resistance of the tool used in the implementation of the proposed method.

To achieve this result, the proposed method of rolling is carried out as follows. First, the pipe is pre-flared with one "belt" of depth L by a standard cylindrical roller expanding using a drive with torque control, which ensures the creation of optimal contact pressures between the pipe and the tube sheet, which are responsible for the tightness and strength of the joint. After flaring, the value of the diameter Dp is measured, to which it is required to flare the pipe over the entire thickness of the tube sheet. To do this, prepare the tool for one-way rolling by adjusting the number of adjusting washers on the spindle so as to ensure that the required diameter Dp is obtained. Further, the pipe is expanded for the entire thickness of the tube sheet.

The proposed method for fixing pipes in thick tube sheets, due to the precise determination of the flaring diameter in each specific case, ensures high strength and tightness of the joints.

In practice, the method is carried out in the following sequence: a standard cylindrical rolling is adjusted to the required depth L of the “belt” of preliminary rolling, the spindle is connected to the rolling machine, then, having moved the rolling body towards the thin part of the spindle, the rolling is inserted all the way into the end of the pipe, the spindle is moved to contact with the rollers, turn on the machine for direct rotation (clockwise), expand the pipe with one “belt” until the drive stops, after reaching the set torque value and after the end of the flaring process, switch the machine to reverse, then remove the flaring from the pipe and measure the value of the diameter Dp , up to which it is required to expand the pipe over the entire thickness of the tube sheet; further, the rolling tool is prepared for this diameter by adjusting the number of shims on the rolling spindle and, since the working section of the spindle is conical, an increase in the number of shims reduces the diameter of the exit of the rollers and, accordingly, reduces the resulting inner diameter after flaring, and a decrease in the number of shims increases the diameter roller output. Then the tool is installed in the pre-flared section, attached to the expanding machine, the supply of cutting oil (coolant) to the expanding zone is turned on and the expanding drive is turned on for direct rotation, expanding the pipe for the entire thickness of the tube sheet, then the coolant is turned off, the drive is switched to reverse and remove the tool from the pipe.

Thus, having a section on each pipe flared with a control of the torque value, it is possible to quickly select a tool for this pipe - a flaring tool for the required flaring diameter, necessary for the subsequent radial expansion of the pipe in one pass.

There is a fairly large selection of tools - standard cylindrical expanders and expanders manufactured by domestic and foreign companies, for example, Krais (Poland) - series 800 rolling, Maus Italia (Italy) - series R, SPbGMTU NITL - series R, which can be used as for "step-by-step", in the case of thick gratings, and for expanding pipes with one "belt".

Also known is a tape-screw pipe expander used to implement the tape-screw method of expanding pipes (Yuzik S.I. Shipbuilding technology, Tape-screw method of expanding pipes. 1966, No. 7), in the body of which a through axial channel is made, in which a pusher is placed , a rod with a vernier and an adapter for fixing the rod in a given position and limiting the movement of the pusher, a replaceable sleeve for adjusting the depth of entry of the tool into the pipe, as well as in the body, which is the drive element, there are windows that transmit rotation to the rollers installed in them by the side walls, in turn resting on a "floating" spindle.

The mutual arrangement of the rollers and the spindle during the operation of the prototype tool was determined by the limiting torque clutch, which was part of the expander device. The coupling at the beginning of the flaring process automatically "adjusts" the tool to the desired amount of expansion of the pipe. This tool was used in the period from 1960 to 1980 at some domestic enterprises for expanding pipes using the tape-screw method in tube sheets up to 200 mm thick. The reason why pipe expanders have ceased to be used is their design complexity, which makes them expensive to manufacture, reduces reliability and wear resistance during operation.

To implement the above method of fixing pipes in thick tube sheets of heat exchangers for expanding pipes, a simpler and more reliable tool was required, and such a tool was developed at the St. rolling, reliability and ease of use, increased wear resistance.

To achieve the technical result, the body of the rolling mill is made of a conical shape with windows for placing rollers that interact with the spindle located inside the body with adjusting washers and an extension connected to the rolling machine.

The design of the tape-screw cone rolling is shown in the drawings:

fig. 1 - general view of the LVK;

fig. 2 - LVK in the context;

fig. 3 - LVC in the process of work: a) beginning; b) graduation.

The design of the tape-screw cone rolling, as shown in Fig. 1 and FIG. 2, consists of a body 1 installed in its through axial channel of the spindle 2, nuts 3, washers 4, rollers 5 are installed in the windows of the body 1, kept from falling out by the rolled edges of the windows, adjusting washers 7 are placed on the shank 6 of the spindle 2 and it is connected by an extension cable 8 , at the end of which there is a stop 9 for adjusting the depth of flaring, with a flaring machine (not shown in Fig.).

The angle of rotation of the rollers A is 2°30'-6° and is determined in the process of designing the LVK rolling tool, depending on its size and purpose: pipe expansion in the tube sheet, lining - this is expansion of a thin-walled liner in a thick-walled pipe, with a pipe of the same size, etc.

The operation of the tool - LVC (Fig. 3) is as follows: the front ends of the rollers are inserted into the pipe (Fig. 3a), the LVC is rotated clockwise and, due to the turn of the rollers at a certain angle relative to the body axis, the rolling begins to "tighten" into the pipe in the axial direction, sequentially expanding it over the entire thickness of the tube sheet in one pass (Fig. 3b).

The diameter of the radial expansion of the pipes when working with the LVK rolling is regulated by changing the number of shims 7 (Fig. 1) on the spindle 2. In practice, the number of shims depends on the size of the gap "S", which is measured with the LVK spindle pressed to the stop, in the pre-flared " belt", between the adjusting washers and the rolling body.

If the value of the gap "S" falls within the range from 0.5t to 1.5t, where t is the thickness of the adjusting washer, then the expanding tool is considered prepared for expanding the pipe to the full thickness of the grate. Otherwise, you should select a rolling with a different number of shims.

Thus, comparing with each other all the tools discussed above - rolling "LVK", tape-screw pipe expanders and "step-by-step" rolling "SR" - it can be argued that rolling "LVK" have significant advantages, namely:

- in comparison with pipe expanders, LVK expansion joints are much simpler in design, and therefore more reliable in operation;

- the technological capabilities of these expanders are wider than those of pipe expanders, due to the fact that the drive element in them is a spindle, which allows you to transfer more torque to the rollers and, therefore, expand pipes with large wall thicknesses and to a greater depth.

Under production conditions, LVK rolling joints were tested in 2013 at Uralkhimmash LLC for fixing U-shaped steel pipes with a diameter of 19 mm. with a wall thickness of 3.5 mm. in a tube sheet 500 mm thick. Tests have shown that it takes about 4 minutes to fix one end of the pipe in the tube sheet by rolling "LVK-12" using a pneumatic drive with a rotation speed of 200 rpm.

To expand the same pipe with the same drive, but with the “step-by-step” standard rolling “CP-12”, it would take 20 “steps”, and each “step” takes about 1 minute of time.

In addition, tape-screw cone rolls can be used in production for lining, i.e. for expanding thin-walled stainless pipes inside thick-walled carbon steel pipes in order to protect the latter from corrosion or to restore the functional parameters of pipes after the appearance of corrosion defects.

Claims (2)

1. A method for fixing pipes in tube sheets of heat exchangers, including placing pipes in a tube sheet and expanding each pipe, characterized in that a section of each pipe is preliminary expanded, for which purpose a cylindrical expansion having a body, spindle and rollers, after reaching the set torque value, the cylindrical expansion is removed from the pipe, the inner diameter of the pipe is measured in the pre-flared section, taking into account which a tool is prepared for continuous expansion of the pipe, while as the mentioned tool, a tape-screw conical expansion is used, containing a conical a body with windows, a spindle installed in the body with a nut and washer in the front part and with a shank on which shims are placed, and rollers located in the windows of the body at an angle to its longitudinal axis to ensure interaction with the shaft ten, the preparation of the tool for continuous expansion of the pipe is carried out by adjusting the number of shims, after which the said tool for continuous expansion of the pipe is installed in the previously expanded pipe section, connected to the expanding machine, its rotation drive is turned on and the supply of the cooling emulsion is performed, and the pipe is expanded for the entire the thickness of the tube sheet in one pass of the tool, then the supply of the cooling emulsion is turned off, the rotation drive of the rolling machine is reversed, the tool is removed from the pipe and, by repeating the operations, all the pipes in the tube sheet are expanded in sequence. 2. A tool for fixing pipes in tube sheets of heat exchangers by the method according to claim 1, characterized in that it is made in the form of a tape-screw conical rolling, containing a conical body with windows, a spindle installed in the body with a nut and washer in the front part and with a shank on which shims are placed, and rollers located in the housing windows at an angle to its longitudinal axis to ensure interaction with the spindle, while the shank of the spindle is configured to be connected to the rolling machine by means of an extension with a stop mounted on it to control the flaring depth.

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