RU2096682C1 - Method of removal of tubes from tube sheets - Google Patents

Abstract

FIELD: repair jobs. SUBSTANCE: cavity is made in tube by means of cutting tool forming flat end located below rear circular groove. Then axial force P is applied to end surface of this cavity to cause plastic tension of material of tube at area of location of circular grooves, after which axial force is additionally applied to remaining cross section of tube. EFFECT: reliable protection of holes in tube sheets against deformation and distortion of geometric sizes of their circular grooves. 4 dwg

Description

 The invention relates to the field of dismantling, in particular to mechanical work to remove pipes from the tube sheets of non-rigid heat exchangers, and can be used when performing repair work on heat exchangers.

There is a known method of removing pipes from tube sheets, in which the tube is placed vertically, it is fixed, a drill is installed coaxially with the tube axis with a diameter smaller than the tube outer diameter, a part of the tube volume is drilled within the tube sheet thickness with the formation of a “shirt” and subsequently the “shirt” is removed " [1]
The known method of removing pipes from tube sheets has the following disadvantages:
very unproductive, because provides for a lot of manual labor;
the quality of the work performed mainly depends on the qualifications of the worker;
local drilling of a hole in the tube sheet is possible, due to the misaligned location of the drill and the tube axis.

 There is also known a method of removing pipes from the tube sheet, in which the tube sheet is separated from the beam, fixed in a horizontal position with the free surface of the sheet above, and then the pipe is removed from the sheet by applying axial force to the pipe end [2] (prototype).

 The known method of removing pipes from tube sheets has the main disadvantage that, with respect to tube sheets containing ring grooves in their holes, the application of axial force to the pipe end is accompanied by deformation of the hole in the pipe sheet and distortion of the geometric dimensions of the ring grooves.

 The basis of the present invention is the creation of a method for removing pipes from tube sheets, which would not cause deformation of the holes in the tube sheets and distortion of the geometric dimensions of the annular grooves.

 This problem is solved by the method of removing pipes from the tube sheet, in which the tube sheet is separated from the bundle, fixed in a horizontal position with the free surface of the tube above, and then the tube is removed from the tube by applying axial force to the pipe end, according to the invention, for tube sheets, having a front and rear, relatively free surface, tube sheets, annular grooves, a cavity is made in the pipe by removing part of the volume of material, for example, with a cutting tool to form Gloss end being located below the rear of the annular groove, and then applying an axial force to the end surface of the cavity, causing initial stretching plastic pipes by location of the material of annular grooves, whereupon further axial force is applied to the remaining tube cross section.

 Implementation of the proposed method for removing pipes from tube sheets allows you to eliminate the deformation of the holes of the tube sheets of the geometric dimensions of the annular grooves.

 This is because the removal of pipe material from the annular grooves of the tube sheet at the first stage takes place due to tensile stresses generated within the ring grooves of the tube sheet. If we take into account that the depth of the annular grooves does not exceed 0.5 mm and the filling with pipe material is not absolute, then tensile stresses are easily realized by applying axial force to the cross section of the pipe below the rear annular groove. An additional application of axial force to the remaining cross-section of the pipe stabilizes the process and is aimed at maintaining the geometric dimensions of the annular grooves.

 In FIG. 1 shows a fragment of a tube sheet before removing part of the volume of pipe material; in FIG. 2, the initial position of the fragment of the tube sheet and tool (step punch) before the process of stretching the pipe; in FIG. 3 initial stage of application of additional force to the remaining cross-section of the pipe; in FIG. 4 stage of removal of the pipe from the hole of the tube sheet under full loading of the cross section of the pipe.

 An embodiment of a method for removing pipes from tube sheets is as follows.

 The tube sheet 1, for example, of steel 3 with the pipe 2 rolled in it, for example, of steel 10, is placed on a plate 3 having a through hole with a diameter exceeding the outer diameter D of the pipe 2 (Fig. 1). The grating 1 is fixed on the plate 3. It should be emphasized that the free surface of the tube grating 1 (relative to the beam) is thus placed on top. Two annular grooves are made in the opening of the tube sheet 1: front and rear (relative to the free surface of the tube sheet 1). The annular grooves of the tube sheet 1 are usually filled only partially with the material of the pipe 2.

Then, using a cutting tool, a drill and a mill, a cavity 2 with a depth H and a diameter D _{1 is formed} in the pipe 2. We emphasize that the end surface of the cavity lies below the level of the rear annular groove in the hole of the tube sheet 1.

A three-stage punch 4 is installed in the cavity. Its smaller step of length l is made in diameter with a minimum clearance with respect to the inner diameter D _{0 of the} pipe 2.

,
где σ_0,2 предел текучести материала трубы при испытании на растяжение;
τ_сдв напряжение на сдвиг материала трубы;
F_кон площадь боковой поверхности усеченного конуса с образующей аб.The absolute value of the length l of the smaller step of the punch 4 is selected from the inequality:

,
where σ _{0.2 the} yield strength of the pipe material during tensile testing;
τ _{shear shear} stress of the pipe material;
F _{con the} area of the lateral surface of the truncated cone with the generatrix ab.

.If we assume that τ _sdv 0.5, then the value of l is determined by the geometric dimensions of the pipe 2 and the cavity made in it:

.

The diameter D _{1 the} cavity is set from the conditions:
D ₁ (0.9 0.92) D
The largest step of the punch 4 is made with a minimum gap with respect to the diameter of the hole in the tube sheet 1 and is spaced from the end of the pipe 2 at a distance of "l ₁ " (Fig. 2).

When exposed to a force P on a stepped punch 4 cause its movement in the axial direction. As a result, at a certain point in the length of the pipe 2, tensile stresses are created at the location of the annular protrusions equal to the yield strength σ _{0.2 of the} material of the pipe 2. There is an elongation of the pipe due to tensile strain of its material at the location of the annular protrusions (Fig. 3 ) The latter leads to the fact that the stepped punch 4 in the axial direction will pass the distance l ₁ and the loading force P will additionally affect the remaining cross-sectional area of the pipe 2 (Fig. 3).

 Therefore, the imposition of preliminary tensile stresses on the material of the pipe 2 at the location of the annular protrusions in combination with the additional axial force applied to the remaining cross section of the pipe end 3, eliminates the radial pressure on the walls of the holes in the tube sheet 1, as well as the possibility of distorting the geometric dimensions of its annular grooves (Fig. 4).

 To refine the technological process of removing pipes from tube sheets, we used 60 mm thick grids of steel 3 with 25 mm diameter pipes and 2.5 mm wall thickness of steel 10. The grids had two annular grooves of 3 mm wide and 0.5 mm deep. The distance between the annular grooves was 9 mm. The front annular groove was located at a distance of 5 mm from the free surface of the grating.

A cutting tool (drill and cutter) in the pipe made a cavity with a diameter of 22.5 mm and a depth of 23 mm. The removal of the pipe from the tube sheet was carried out by a three-stage punch made of U8 A steel with hardness after quenching HRC _e 56-58 units. The executive dimensions of the stepped punch were performed according to the 7th accuracy class.

 The loading force applied to the end of the pipe was created by means of a PSU-250 hydraulic press.

 A preliminary axial force of up to 35 kN caused the pipe to stretch by 2.1 mm, which caused sampling of the initial clearance between the stepped punch (its large step and the pipe end). Subsequent loading of the pipe end was carried out with a force of 55 kN.

 The tensometric assessment of the hole deformation in the tube sheet did not reveal any noticeable values, which confirms the legitimacy of using the above physical model of the process of removing pipes from the tube sheets.

 Visual analysis of the condition of the annular grooves did not reveal their distortion.

 The invention is applicable for repair work on heat exchangers of oil refining, petrochemical and other industries.

Claims (1)

 The method of removing pipes from the tube sheets, in which the tube sheet is separated from the beam, is fixed in a horizontal position, placing the free surface of the sheet by applying axial force to the pipe end, characterized in that for pipe sheets with holes having a front and rear, relatively free surface , the annular grooves in the pipe perform a cavity by removing part of the volume of material, for example, with a cutting tool to form a flat end located below the rear annular groove, then applying axial force to the end surface of the cavity, initially plastic stretching of the pipe material is caused by the location of the annular grooves, after which an axial force is additionally applied to the remaining cross section of the pipe.

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