RU2442969C2 - Test block for tests in conditions of internal pressure cyclic drop - Google Patents

Abstract

FIELD: piping.

SUBSTANCE: test block contains the simulation of rigid fixing of welded self-compensating convoluted tube, tool for measurement of cyclic elastoplastic deformations of the pipe in form of tension sensors with measuring base of two types - long and short, glued to the tube in several zones. In the zone of welds crossing the short-base foil sensors are installed, in the zone of weld crossing the corrugation the short-base foil tension sensors ate installed, and in the zone of transfer from corrugation to the cylindrical part of pipe the long-base tension sensors are installed. In near-weld zone of spiral weld the tension sensors are glued across the corrugation on the different sides of weld so that short-base sensors are on one side of the weld and the long-base sensors are on another side of the weld.

EFFECT: increased validity of results of endurance tests of self-compensating tubes, as well as the possibility to measure cyclic elastoplastic deformations.

3 cl, 2 dwg

Description

The invention relates to testing equipment, in particular, to stands for testing flexible pipe elements (self-compensating pipes, bellows, metal hoses, etc.) for a resource under conditions of cyclic differential pressure with the simultaneous determination of the fields of elastoplastic deformations.

During the operation of main oil pipelines, heating mains of thermal power plants and other types of main and technological pipelines, unsteady cyclic loading by internal pressure takes place, which can contribute to the accumulation of damage during operation of the structural material in the most loaded zones beyond the elastic limit and lead to premature failure of highly loaded pipeline elements according to the criteria low cycle fatigue. To reduce the impact of this effect, various technical means and devices are used. The material below refers to the so-called self-compensating pipes (SKT) and methods for testing them for a resource in conditions close to operational. The main effect produced by SKT is self-compensation of the longitudinal and transverse deformations of the pipeline from cyclic changes in internal pressure, temperature and other influences.

In order to increase the operational reliability of pipelines for various purposes, a number of devices have been developed for testing them under conditions close to operational. In particular, a bench is known for testing steam pipelines in conditions of difficult stress (ed. St. USSR 207450, publ. 01.01.1968), containing a frame with a loading device and a device for creating internal pressure installed on it. In order to load the specimen by tension-compression, it is equipped with a two-arm lever, which is mounted on one end of the specimen, which is rigidly connected by the other end to the bed. In this case, the free ends of the lever are connected through hinges with a loading device.

The disadvantage of this stand is the low reliability of the test results, the inability to use the installation for testing SKT for a resource due to a possible loss of stability of the samples and other reasons (lack of automated systems for providing cyclic loading and systems for measuring strain fields).

The closest analogue of the claimed invention is the installation for testing pipes and other similar elements of building structures (ed. St. USSR 93378, publ. 01/01/1952) using hydraulic or other jacks to carry the applied load, made in the form of a support installed on the foundation frames with a fixed and movable traverse along the frame, equipped with holes for passing and fastening test pipes in them with glasses fixed to their ends with caps for filling pipes with water, stretched or with pressed by jacks installed inside or outside the support frame, depending on the nature of the test.

The disadvantage of this device is the low reliability of the test results, the inability to use the installation for testing SKT on the resource due to the possible loss of stability of the samples and other reasons (lack of automated systems for providing cyclic loading and systems for measuring strain fields).

The technical result of the invention is to increase the reliability of the results of tests of SKT for a resource, as well as the ability to measure cyclic elastoplastic deformations.

The specified technical result is achieved as follows.

A test bench is proposed for testing pipes under conditions of cyclic differential pressure using a pump station, containing four or more couplers mounted on two rigid plates, a support rotary mechanism that supports the test pipe in a horizontal position and allows its rotation, the inner pipe, and two welded elliptical plugs, a transition element from the diameter of the test sample to the inner tube, a fitting for supplying a working medium and a manometer for measuring internal pressure.

The figure 1 shows a longitudinal section of the proposed stand.

The stand is equipped with four ties - 1, which are rigid channels or solid square or circular beams, two rigid plates - 2, a fastening zone - 3 (welding, bolt connection, special connection), a supporting rotary mechanism - 4, which supports the pipe under test horizontal position and allows its rotation to be more efficiently filled and emptied by the working medium, by an internal pipe - 5 to increase rigidity and stability (preferably seamless), two welded elliptical 6 bottoms (plugs) - 6 to ensure the tightness of the inner pipe, petal (conical or other) transition element - 8 from the diameter of the test sample - 7 to the inner pipe, two fittings - 9 for supplying a working medium and two pressure gauges for measuring static excess and cyclic test internal pressure. Pump station - 10 creates excessive static internal pressure in the inner pipe. Automated pumping station - 11 creates a test cyclic internal pressure in the space between the SKT and the inner pipe according to a predetermined experimental program. This station contains a device for automatically terminating the experiment in the event of a pressure drop in the system due to the resulting through defect (the moment of loss of life). Cyclic elastoplastic deformations are determined by tensometry (or by another method: optically sensitive, brittle coatings, laser, etc.) in the following potentially hazardous areas of SKT: 12 - the zone of intersection of the spiral pipe seam and the ring mounting seam, 13 - the zone of intersection of the mounting seam with irregularities in the place of collapse of the corrugation, 14 - zone of transition from the corrugation to the cylindrical part of the end of the pipe in the place of partial collapse of the corrugation, 15 - zone of equidistant corrugations G1 - 16 and G2 - 17, separated by a spiral SKT technological seam.

Thus, the technical effect is ensured by increased rigidity of the stand design (screeds, inner tube, rigid side plates), the presence of an inner tube under static pressure, which prevents the loss of stability of the test SKT sample, using an automated pump station with an emergency shutdown device and a system for determining cyclic elastoplastic deformations.

In the tests, simulated rigid pinching of the pipe was carried out using both longitudinal ties 2 and welding of the inner pipe 3. The SKT was loaded by cyclic pressure increase in the annulus using an automated pump station 11. To prevent loss of stability of the SKT sample, the inner pipe was loaded with an initial pressure with such calculation so that when loading the SKT, the pressure in the annulus does not exceed the pressure in a smooth pipe. This avoided the crushing of the inner pipe and affected the increase in the stiffness of pinching of the ends of the SKT, since the decrease in the pressure difference inside and outside the smooth pipe caused compressive forces in it. The relative elongation of SKT in the first case was 0.08%, in the second - 0.01%.

SCT deformations were measured by the strain gauge method using wire gauges B with a base of 10 mm (30 pcs.), Chains of small-base foil strain gauges B with a base of 2 mm (100 pcs.) And foil sensors A with a base of 1 mm (10 pcs.), Figure 2. In zone 12, sensors A are installed in the immediate vicinity of the welds and at the reinforcement of the seam at the intersection of the seams. Measurements of deformations in zone 13 are carried out by chains of foil strain gauges B. In zone 14, strain gauges B and a chain of 2-mm gauges B. are installed. In zone 15, where the gauges are glued across both corrugations G1 and G2, and in the heat-affected zone of the spiral seam to compare the resolution of the strain gauges with a different measurement base when determining deformations in the SKT corrugation, the corrugation was glued on one side by sensors B, and on the other by sensors B.

The use of strain gauges with a different measurement base makes it possible to determine the general deformed state of the structure and obtain relevant information in concentration zones. According to the measurement results, the components of the strain tensor were determined.

Brief Description of the Drawings

Figure 1 - A longitudinal section of the stand.

Figure 2 - Layout of load cells.

Claims (3)

1. Test bench under conditions of cyclic differential pressure, containing a simulator of rigid jamming of a welded self-compensating corrugated pipe, a means for measuring cyclic elastoplastic pipe deformations in the form of strain gauges with a measuring base of two types - short and long, mounted on the pipe using adhesive joints in several zones so that in the zone of intersection of the welds installed foil sensors with a short base, in the zone of intersection of the weld with corrugation - foil strain gauges with short base, in the transition zone from the corrugation to the cylindrical part of the pipe - load cells with a long base, and in the heat-affected area of the spiral seam, the load cells are glued across the corrugations located on opposite sides of the seam, so that sensors with a short base are installed on one side of the seam, and with the opposite - with a long base. 2. The stand according to claim 1, characterized in that the simulator of rigid jamming is made in the form of longitudinal pipe ties. 3. The stand according to claim 1, characterized in that the simulator of rigid jamming is made in the form of a pipe mounted inside a corrugated pipe and rigidly connected to it by flap conical transitions.

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