RU2117544C1 - Method for securing ends of thin-wall tubes in openings of tube plates - Google Patents

Abstract

FIELD: machine engineering, namely production of different-purpose apparatuses including tubes mounted in openings of tube plates. SUBSTANCE: method comprises steps of placing end portions of thin-wall tubes in openings of tube plates; preliminarily cold expanding that portions; introducing insert-branch pipes into end portion of tubes and realizing their common expanding. EFFECT: enhanced reliability of tube end securing. 6 dwg

Description

 The invention relates to the field of power engineering, chemical engineering, mechanical engineering for the food and refrigeration industry and can be used in the manufacture of apparatuses for various purposes, containing pipes as structural elements, namely shell-and-tube and other heat exchangers.

 A known method of fastening the ends of thin-walled pipes in the holes of the tube sheets, which consists in the fact that the ends of the pipes are placed in the holes of the tube sheets, insert the nozzles into them and jointly expand them (SU, copyright certificate, 625817, B 21 D 39/06, 1978) [1].

 The specified known method [1] does not provide the required strength and tightness when fastening pipe ends with wall thicknesses from 0.2 to 0.4 mm in tube sheets.

 The technical problem to which the claimed invention is directed is to increase the reliability of the connection by increasing the adhesion of the pipe to the grill.

 The problem is solved in that in the known method of fastening the ends of thin-walled pipes in the holes of the tube sheets, which consists in the fact that the ends of the pipes are placed in the holes of the tube sheets, insert the nozzles into them and jointly expand them, before installing the insert nozzles carry out preliminary the flaring of the ends of the pipes in the holes of the gratings, and preliminary and joint flaring is carried out in the cold state.

 In FIG. 1 shows a tube sheet assembly with a thin-walled pipe and a nozzle insert; in FIG. 2 - node A in FIG. one; in FIG. 3 - connection of the tube sheet to the pipe without insertion pipe; in FIG. 4 - connection of the tube sheet to the pipe using the insert pipe; in FIG. 5 - connection of the tube sheet with a thin-walled pipe, in the cavity of which a mild steel cylinder is placed; in FIG. 6 - the same, in the presence of an insert pipe.

 A device that implements the method comprises a heat exchanger housing 1, a tube sheet 2 is connected to it, in the openings of which the ends of the thin-walled pipes 3 are first expanded, and then, together with the pipes, the thin-walled insert-nozzles 4.

 Example. The effectiveness of the proposed method for fastening the ends of thin-walled pipes in the holes of the tube sheets was initially verified by calculating the contact pressure between the outer surface of the flared pipe and the surface of the hole of the tube sheet in two versions: without and without a thin-walled pipe insert.

 It is the magnitude of the contact pressure in the connection of the pipe with the tube sheet that determines the strength of their connection. The magnitude of the contact pressure, in turn, is inversely proportional to the sum of the radial ductility of the tube sheet and the tube expanded in its hole.

Radial compliance was calculated in accordance with the recommendations in connection with the manufacture of tube heat exchangers made of stainless steel 12X18H10T having an outer diameter d = 16 mm and an inner diameter d ₁ = 15.2 mm (tube wall thickness 0.4 mm) with a tube sheet from steel 45.

 The calculated compound is shown in FIG. 3, 4. The connection comprises a tube sheet 1, in the opening of which a thin-walled tube 2 is expanded (Fig. 3), and then the insert-pipe 3 (Fig. 4).

 Option 1. The connection is made without the insert pipe (Fig. 3).

1.1. The coefficient of radial ductility of the tube is calculated by the formula
λ ₁ = d {[1+ (d ₁ / d) ² ] / [1+ (d ₁ / d) ² ] -ν ₁ } / 2E ₁ ,
where d = 16 mm is the landing diameter; d ₁ = 15.2 mm is the inner diameter of the tube; E ₁ = 18800 cr / mm ² is the elastic modulus for steel 12X18H10T; and ν ₁ = 0.3 is the Poisson's ratio for steel 12X18H10T.

Calculation according to the formula (1) gives
λ ₁ = 8.176 • 10 ^-3 mm / kg
1.2. The coefficient of radial compliance of the tube sheet is calculated to the formula
λ ₂ = d {[1+ (d / d ₂ ) ² ] / [1+ (d / d ₂ ) ² ] + ν ₂ } / 2E ₂
Where
d = 16 mm - landing diameter;
d ₂ = 28 mm - the outer diameter of the tube sheet, in the opening of which one thin-walled tube with a diameter of 16 / 15.2 mm was expanded for subsequent tests on the strength of their connection on a tensile testing machine;
E ₂ = 20,000 kg / mm - modulus of elasticity of steel 45;
ν = 0.3 - Poisson's ratio for steel 45.

Calculation according to the formula (2) gives; λ ₂ = 9.078 • 10 ^-4 mm / kg
1.3. The contact pressure in the connection of the tube with the tube sheet is determined by the formula
q = δ / 2 (λ ₁ + λ ₂ )
where δ = O, 1 mm is the amount of interference in the joint, so that we have
q = 0.1 / 2 (8.176 • 10 ^-3 + 9.078 • 10 ^-4 ) = 5.5043 kg / mm ²
Option 2. Connection with insertion pipe
We believe that the insert pipe is made of the same 12X1810T steel and has the same wall thickness of 0.4 mm as the thin-walled tube into which it is inserted.

Then, at the place of flaring in the tube sheet of the thin-walled tube and the nozzle inserted into it, the diameter of the seat (d = 16 mm) is preserved, and the inner diameter of the tube with the nozzle becomes equal
d $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ = d _{int. inserts} = 16 -4 • 0.4 = 14.4 mm.

2.2. Коэффициент радиальной податливости трубной решетки сохраняет свою величину

= 9,078•10^-4 мм/кг
2.3. Контактное давление в соединении трубки со вставкой с трубной решеткой при натяге δ = 0,1 мм равно

= 0,1/2. (3,926•10^-3 + 9,078•10^-4) = 10,3438 кг/мм².2.1. The coefficient of radial compliance of the tube with the insert-pipe is determined by the formula (1) as follows

2.2. Coefficient of radial compliance of the tube sheet retains its value

= 9.078 • 10 ^-4 mm / kg
2.3. The contact pressure in the connection of the tube with the insert with the tube sheet with an interference fit δ = 0.1 mm is

= 0.1 / 2. (3.926 • 10 ^-3 + 9.078 • 10 ^-4 ) = 10.3438 kg / mm ² .

The ratio of contact pressures in the connection of the tube sheet and thin-walled tube in options 1 and 2 is equal to k = q ₂ / q ₁ = 1,879
Thus, the calculations show that the application of the cold expansion of thin-walled pipes using a thin-walled insert-pipe increases the contact pressure, and, therefore, the strength of their connection with the tube sheet is almost doubled.

 Numerical calculations were supplemented by bench tests of the strength of the connection of the tube sheet and the thin-walled tubes made of stainless steel 12X18H10T described above without and without a pipe insert.

The outer and inner diameters of the tubes, insert inserts, and tube sheet during the tests for the strength of the joints were the same as those indicated in the above calculations: the outer diameter of the tube d = 16 mm, the inner diameter of the tube d ₁ = 15.2 mm, and the inner diameter pipe inserts, d $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ = 14.4 mm, the outer diameter of the tube sheet d ₂ = 28 mm.

Tubes with a length of L = 250 mm each were flared at one end (with and without insertion pipe) in the hole located in the center of a tube sheet made of steel 45 and having an outer diameter (d ₂ = 28 mm with a thickness of 20 mm).

 Using a torque device, certain torque values were set at the end of the flaring process. At the opposite end of the thin-walled tube, a solid mild steel cylinder was inserted with a minimum clearance (Fig. 5, 6).

 The tube sheet with a flared thin-walled tube without an insertion pipe or with it and the opposite end of the thin-walled tube with a mild steel cylinder installed in it were fixed to the grips of a P-5 tensile testing machine.

 For the representativeness of the test results, we studied the joint strength of the six above-mentioned “assemblies” when flaring thin-walled tubes in the hole of a tube sheet without pipe inserts and the same number of “assemblies” when sequentially flaring in a tube sheet of a thin-walled tube and then a pipe insert in it .

 When testing in all six “assemblies” without an insert, the thin-walled tube was pulled out without destruction from the hole of the tube sheet, and out of all six “assemblies” with the insert-nozzle, the thin-walled tube was not pulled out of the hole of the tube sheet and, with a certain force, was deformed and then collapsed .

 Thus, the invention provides high strength of the connection of a thin-walled pipe with a tube sheet, and, therefore, the reliability of devices created with its use, which are leakproof under thermal stresses arising from temperature differences between media moving inside the tubes and in the annulus. It is used by the authors in the manufacture of highly efficient heat exchangers for hot water and heating systems.

Claims (1)

 The method of fastening the ends of thin-walled pipes in the holes of the tube sheets, which consists in the fact that the ends of the pipes are placed in the holes of the tube sheets, insert the nozzles into them and jointly expand them, characterized in that prior to installing the insert nozzles, the pipe ends are pre-expanded into the holes of the gratings, and preliminary and joint expansion is carried out in the cold state.

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