RU2500512C2 - Method to retard flaw development and device to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to repair, particularly, to flaw development retardation. Pre-tension spring insert with lugs is fixed at locking frame. Then, said lugs are secured to part outside of said flaw zone to withdraw said locking frame. Note here that pre-tension of said spring insert makes ΔL to be defined by the formula: $$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _1^n{k}_i}}$$

where β is the factor equal to 1…1.5, σ is strain-in flawless zone, S_def is part defect zone area, k_i is factor of stiffness on i^th spring in spring insert, n is quantity of spring in said insert.

EFFECT: higher efficiency, decrease sizes.

9 cl, 15 dwg

Description

The invention relates to the repair of a wide class of structures containing elements and components with defects, for example, on pipelines, buildings of building structures and engineering structures, vehicles, gas holders and other shell and plate structures.

Known methods of inhibiting the growth of through holes fatigue cracks in the product, including drilling holes in the tops of the cracks on both sides of the exit to the front surface of the parts through holes, additional drilling holes on both sides of the plane of the cracks symmetrically with respect to each other and at the same distance from the holes in the vertices cracks, dynamic mutual movement of the banks of fatigue cracks, the gradual cessation of dynamic loads, installation of fasteners in the holes, their pairwise tightened in planes passing simultaneously through the holes at the tops of the cracks, and holes located in the middle of the cracks, followed by tightening the fasteners. Before installing the fastener, the surface of the holes is smoothed at the tops of the cracks, surface plastic deformation is performed in the holes, edges and on the surface of the part on both sides in the crack growth plane and in front of its vertices in the zone of the crack extension, two half-sleeves are installed in the holes at the crack tops , they are oriented by the plane of their section perpendicular to the plane of the crack, a fastener is installed in the holes formed by half-sleeves, with a radial interference in the plane the bones of the crack, and pairwise tightening of the fasteners from the side of the back surface of the part is carried out in two mutually parallel planes passing through the holes at the top of the crack and the nearest hole to the middle part of the crack, as well as in the plane passing through the remaining free holes in the middle part of the crack (a No. 1401892 according to M.C. - C21D 1/04, publ. 05/15/1994) (analog).

The disadvantages of the known methods is the complexity and high complexity of the technology.

There are also known methods for repairing body parts with cracks, in which repairs are carried out using a device made in the form of a U-shaped clamping element formed by a jumper resting on the surface of the part and legs extending from the jumper. One leg is rigidly fixed on the jumper, and the other is formed mounted rotatably mounted in the jumper hole with a cylindrical section coaxial with it. A shank is connected on one side of this section, and on the other side is a section located with an eccentricity “e” relative to the axis of the section. In a part having a crack, pairs of holes are drilled that are located on a straight line, perpendicular to the direction of the crack. The holes of each pair are located on opposite sides of the crack, installing in one pair of holes the leg of the clamping element and the section of the other leg. Then, rotating this leg by the shank, its eccentric section is applied to one edge of the crack until it closes with the other edge and the crack is completely closed. After that, the crack in this zone is boiled and the device is moved to the next pair of holes until the crack is completely eliminated (patent No. 2055715 according to M.C. - B23P 6/04, publ. 03/10/1996) (analog).

A disadvantage of the known methods is the need to use a complex eccentric mechanism, which reduces reliability.

There is also a method of inhibiting the growth of fatigue cracks in structures with predominantly through cracks, which consists in making holes at the vertices of the cracks, installing half-sleeves in them, and then fasteners in the holes formed by half-sleeves, with a radial interference of 5-10% of the nominal diameter of the hole at the apex cracks under the bushings and axial interference, while performing an additional hole with an axis located in the plane of the crack, in front of its top. Next, additional half-sleeves are installed in this hole, they are oriented with an intersection plane perpendicular to the plane of the crack, additional fasteners are installed, and before tightening the fasteners, spring inserts are placed between them on both sides of the structure and they create compressive stresses in the planes parallel to them in the planes parallel to the crack plane in front of its peak (patent No. 1343689 according to M.C. - B23P 6/00, publ. 04/15/1994) (prototype).

The disadvantages of this method are:

a) the need to create both radial and axial interference;

b) stress concentrators arise in the zone of additional openings, contributing to the accidental destruction of the material;

c) the method is not applicable for a wide range of defects, except for cracks.

Known union nuts made of plastic, having two halves and made using a connection using hooks and a connection using spring clips. In this case, the first half of the nut has an end made in the form of a hook for fastening in the corresponding through hole in the plate molded at the end of the second half of the nut. On the other end of the first half of the nut, a protrusion is molded to fix in the corresponding hole of the lining molded on the other end of the second half of the nut (M.C. patent No. F16B 37/08, F16B 37/10, publ. 05.27.2007) (analogue).

Known screw clamps for tightening joints, containing two pivotally connected and connected by a spring tensile two-arm levers. In the threaded hole of the first lever, a sleeve is self-unscrewing under the action of axial force. In the threaded hole of the sleeve there is a screw self-braking under the action of axial load in contact with the second lever. The torsion spring mounted on the sleeve is mounted on the first lever, and its geometrical axis coincides with the axis of the screw. A rotation limiter is mounted on the sleeve, interacting with a spring-loaded latch mounted on the first lever (M.C. patent No. F66B 21/06, publ. 30.01.1994) (analogue).

The closest technical solution to the device for implementing the inventive method is a fastener containing two side walls and a base, while the side walls are made of material with the property "shape memory effect", and they are located at an angle to each other and in the Central part the areas of junction with each other have an elongated cutout, and the bases are made in the form of paws attached to the side walls and directed outward (RF patent No. 2380585 according to M. Cl. - F16B 5/06, published on 01/27/2010) (prototype )

The disadvantages of such a fastener are:

a) expensive material with the property of “shape memory effect” is used;

b) the mounting element has a large height, which leads to large dimensions of the device;

c) for the device to operate, it is necessary to supply heat of a given temperature from a special energy source.

The objectives (goal) of the invention are to simplify the technology, increase the efficiency of the delay in the development of defects, reduce energy consumption, reduce the size and cost of the device.

These tasks are achieved by the fact that in the method of delaying the development of defects in structural elements, including fixing a pre-stretched spring insert with tabs in the fixing frame, attaching the tabs of the spring insert to the structural element outside the defect zone and removing the locking frame, pre-stretching the spring insert is carried out by ΔL which is determined by the formula:

, $$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,

where β is a coefficient equal to 1 ... 1,5;

σ is the stress in the defect-free region of the structural element;

S _def is the area of the defective area of the structural element;

k _i is the stiffness coefficient of the i-th spring in the spring insert;

n is the number of springs in the spring insert.

In the device for implementing the method for delaying the development of defects in structural elements containing a spring insert made in the form of paws with eyes, on which the ends of the springs are fixed, and a fixing frame on which the spring insert is fixed in a pre-stretched charged state, the spring insert is pre-stretched by an amount ΔL:

, $$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,

where β is a coefficient equal to 1 ... 1,5;

σ is the stress in the defect-free region of the structural element;

S _def is the area of the defective area of the structural element;

k _i is the stiffness coefficient of the i-th spring in the spring insert;

n is the number of springs in the spring insert.

In particular, in the spring insert, a set of either helical coil springs or snake springs is used. The locking frame is generally made in the form of a profile of a U-shaped cross section and has stops for fixing the spring insert. The locking frame consists of two pivotally connected parts, on each of which a sector with holes is fixed to fix the relative position of the parts at a given angle between them. In the absence of a sector, these parts are connected by a hinge and a fixing pin. The locking frame has locking pins to temporarily hold the springs of the spring insert in a stretched state. The locking frame represents a single part, for example, an all-metal casing.

Figure 1 presents a General view of the spring insert with springs of the type "snake"; figure 2 - spring insert, side view; figure 3 is the same, a top view; figure 4 - spring insert with coil springs; figure 5 - fixing frame (in its simplest version); figure 6, 7, 8 shows a section of the spring insert of figure 4; figure 9 shows a section of a device for delaying the development of defects in structures, for example, in cylindrical bodies (in particular, in pipelines) with one flip fixing pin; figure 10 is the same with several locking pins; figure 11 shows a device for delaying the development of defects in structures, consisting of two flat articulated parts, assembled; on Fig - shows a device for delaying the development of defects in structures, consisting of two flat articulated parts, in working condition; on Fig shows a device for delaying the development of defects in structural elements, consisting of two flat articulated parts with locking sectors; on Fig - the same, top view, on Fig shows a photograph of one of the embodiments of the device.

A method of delaying the development of defects in structural elements is as follows.

A surface is prepared near the defective area (corrosion grooves, cracks, scratches, etc.) for fixing fasteners to structural parts, in particular, if necessary, the surface coating, corrosion products and contaminants are removed. The necessary parameters of the spring insert of the device for delaying the development of defects in the structures are determined, in particular, the value ΔL of the preliminary tension of the spring insert (from the condition of compensating for the force lost in the defective section) is calculated by the formula:

, $$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,

where β is a coefficient equal to 1 ... 1,5;

σ is the stress in the defect-free region of the structural element;

S _def is the area of the defective area of the structural element;

k _i is the stiffness coefficient of the i-th spring in the spring insert;

n is the number of springs in the spring insert.

The compensation coefficient of the loss of bearing capacity β is assigned for local smooth defects (indentations) in the range from 1 to 1.2, and for cracks from 1.2 to 1.5.

Stretch the spring insert of the device, taking into account the calculated value ΔL, and fix the insert in the position of the pre-stretched state. The supporting ends of the device are fixed on the defect-free areas of the part opposite from the defect, for example, by welding, soldering, gluing or using fasteners. The locking elements are removed and thereby create compressive stresses in the defective area by means of spring inserts. Next, protective measures are carried out, in particular, sealing coatings are applied.

A device for implementing a method for delaying the development of defects in structural elements is a spring insert, consisting of a base in the form of legs 1 with eyes 2 with holes in which the ends of the tension spring 3 are fixed. It is desirable that the working surfaces of the legs that will contact the surface of the structure, repeated the configuration of the surface of the structure. If the structure has a flat surface, then the working surface of the legs should be flat. If the structure has a curved surface (for example, a cylindrical surface of the pipeline), then the working surface of the legs should be as close as possible to the configuration of the surface of the structure. The ends of the springs can be pressed directly into the foot 1 or secured by other means. The springs 3 can be either helical cylindrical or “snake” type springs. Thus, the spring insert is a set of either helical cylindrical or coil springs, the ends of which are fixed to the tabs 1.

The spring insert is fixed in a fixing frame that temporarily holds the device in a pre-stretched state by ΔL:

, $$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,

where β is a coefficient equal to 1 ... 1,5;

σ is the stress in the defect-free region of the structural element;

S _def is the area of the defective area of the structural element;

k _i is the stiffness coefficient of the i-th spring in the spring insert;

n is the number of springs in the spring insert.

The spring insert is attached to the fixing frame, for example, by means of threaded connections. The locking frame is made in the form of a profile of a U-shaped cross section and has stops for fixing the spring insert in the extended state.

The locking frame consists of two pivotally connected parts 4 and 5, on each of which on the common axis 6 sectors 7 and 8 are fixed with holes for fixing the relative position of the parts at a given angle and between them. Sectors 7 and 8 are fixed relative to each other using a finger 9. In the absence of a sector, these parts are connected by a hinge and a fixing finger. To avoid distortion of the locking frame, it is recommended to install double pairs of sectors.

In the absence of a hinge, the locking frame has locking pins 10 for temporarily holding the springs of the spring insert in its original position. In this case, the locking frame has a configuration that matches the configuration of the surface of the structure. These pins may be several, depending on the curvature and length of the defective portion of the surface of the structure.

In the simplest case, the fixing frame represents a single part, for example, an all-metal flat or curved casing 11. In the figures of the dashed line, a fragment of structure 12 with defect 13 is conventionally shown.

The device operates as follows.

After assembling the spring insert, it is stretched to the required size on a special machine. A locking frame is attached to the spring insert, which is attached to the tabs 1. Thus, the device is brought into running order and ready for use.

The device is applied to the surface of the structural element near the defective area (on the outskirts of the defective area), while the paws are located outside the defect area, then the paws are firmly attached to the structure, for example, by welding, soldering, gluing, etc.

Next, the pins 10 are removed and the locking frame is removed. In this case, the springs of the spring insert are included in the work and create efforts to pull the legs together. The efforts through the legs are transferred to the shores of the defective area, thereby, in the defective area, the stress concentration is reduced and the destruction of structural elements is prevented. Further, if necessary, the repair area is sealed.

Example. A section of a steel pipeline with a diameter of D = 1020 mm and a wall thickness of t = 10 mm, operating under an internal working pressure of p = 5.5 MPa (55 kg / cm ² ), was examined. The inner diameter of the pipeline is d = 1000 mm. The presence of a longitudinal crack with a length of l = 10 mm and with a maximum depth of h = 2 mm was revealed. The lost area is: S _def = I · h = 1.0 · 0.2 = 0.2 cm ² .

In this case, the circumferential stresses acting in the pipeline were determined by the formula:

. $$\sigma =\frac{p\cdot \mathrm{<figure-callout\; id="2"\; label="d"\; filenames="00000011.png,00000012.png"\; state="\{\{state\}\}">d</figure-callout>}}{2\cdot t}$$

.

Substituting the initial data into this formula (with the translation of the dimension in cm), we obtain

. $$\sigma =\frac{55\cdot 100.0}{2\cdot \mathrm{1,0}}=2750\mathrm{to}G/\mathrm{from}{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="00000011.png,00000012.png"\; state="\{\{state\}\}">m</figure-callout>}}^2=275\text{MPa}$$

.

The force required to eliminate the defect was determined by the formula for the example in question:

. $$F={\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}=\sigma S_{def}}$$

.

Substituting the source data, we got:

F = 2750 · 0.2 = 550 kg = 5500 H.

Assigned a spring insert, consisting of 5 coil cylindrical springs of equal stiffness. The force arriving at 1 spring is equal to

. $$F_{\mathrm{one}}=\frac{\mathrm{<figure-callout\; id="5"\; label="F"\; filenames="00000014.png,00000020.png"\; state="\{\{state\}\}">F</figure-callout>}}{5}=110\text{kg}=\text{1100 N}$$

.

We chose springs with an outer diameter of 22 mm from a wire with a diameter of 4.5 mm. For a given spring, the stiffness of one coil is c ₁ = 750.6 N / mm. We took the number of working turns m = 7. Then the rigidity of one spring

. $$k_{{}_{\mathrm{one}}}=\frac{c_{\mathrm{one}}}{m}=\frac{750.6}{7}=107.23\text{mm}$$

.

At β = 1.5, the calculated value of the preliminary extension of the spring insert was obtained to compensate for the defective area:

$$\Delta L=\mathrm{1,5}\frac{5500}{5\cdot 107.23}=10.26\text{mm}$$

Thus, the method and device allows you to create compression forces in the defective area of various structures and reduce the level of stress concentration. This increases the efficiency of the delay in the development of defects, which ultimately helps to prevent structural damage. At the same time, the technology of repairing the structure is simplified, the cost of repair materials and energy costs are reduced, the dimensions and cost of the device are reduced. This development is especially important for maintaining in working condition the existing pipelines of different diameters and section shapes.

Claims (9)

1. A method for delaying the development of defects in details, characterized in that the pre-stretched spring insert with tabs in the fixing frame is secured, the tabs of the spring insert are attached to the part outside the defect zone and the fixing frame is removed, while the spring insert is pre-stretched by ΔL, which is determined by the formula
$$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,
where β is a coefficient equal to 1 ... 1,5;
σ is the stress in the defect-free region of the part;
S _def is the area of the defective area of the part;
k _i is the stiffness coefficient of the i-th spring in the spring insert;
n is the number of springs in the spring insert. 2. A device for delaying the development of defects in details, characterized in that it is equipped with a spring insert made in the form of paws with eyes, on which the ends of the springs are fixed, and a fixing frame on which the spring insert is fixed in a pre-stretched state, while the spring insert pre-stretched by ΔL
$$\Delta L=\beta \frac{{\displaystyle \underset{S_{def}}{\int }\sigma d{S}_{def}}}{{\displaystyle \sum _{\mathrm{one}}^n{k}_i}}$$

,
where β is a coefficient equal to 1 ... 1,5;
σ is the stress in the defect-free region of the part;
S _def is the area of the defective area of the part;
k _i is the stiffness coefficient of the i-th spring in the spring insert;
n is the number of springs in the spring insert. 3. The device according to claim 2, characterized in that the springs of the spring insert are made in the form of coil springs. 4. The device according to claim 2, characterized in that the springs of the spring insert are made in the form of snake springs. 5. The device according to claim 2, characterized in that the locking frame is made in the form of a profile of a U-shaped cross section and has stops for fixing the spring insert. 6. The device according to claim 2, characterized in that the locking frame consists of two pivotally connected parts, on each of which a sector with holes is fixed for fixing the relative position of these parts at a given angle between them. 7. The device according to claim 2, characterized in that the locking frame consists of two pivotally connected parts that are connected by a hinge and a fixing pin. 8. The device according to claim 2, characterized in that the locking frame has locking pins to hold the springs of the spring insert in a stretched state. 9. The device according to claim 2, characterized in that the locking frame is an all-metal casing.

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