CZ35292U1 - Equipment for sample preparation for determining the material properties of metals and their alloys - Google Patents

Description

In the registration procedure, the Industrial Property Office does not determine whether the subject of the utility model meets the conditions for eligibility for protection pursuant to Section 1 of Act no. E. 478/1992 Sb.

CZ 35292 UI

Equipment for sample preparation for determining the material properties of metals and their alloys

Field of technology

The technical solution concerns material engineering, specifically the preparation of samples for determining the material properties of metals and their alloys.

Prior art

At present, samples of degraded material are obtained by sampling from specific technical equipment, or the samples are prepared in the laboratory by the simple action of temperature, or by the action of temperature and uniaxial tensile or compressive stress.

Tests of material properties either in the area of Hooke's law or during creep are largely regulated by standard procedures, which, among other things, determine the size, resp. the ratios between the individual dimensions of the test specimens and their minimum number.

Material creep can be defined as an increase in plastic deformation with time under the action of a load below the yield point, at elevated temperatures, which can lead to fracture of the part after a certain time, which depends on the magnitude of the applied load and temperature.

Creep testing is performed in two ways:

a) Constant stress, where the magnitude of the applied force decreases during the test so that the stress remains constant during the test. In this case, the test is terminated after a certain time, unless there is a breach.

Schematic description of this test: A load of a special shape is suspended on a test specimen - a bar. For example, this weight is immersed in a liquid. The test specimen is subjected to tensile load. During the test, the rod is extended and the weight is immersed in the liquid more and more. The greater part of the immersed weight is subjected to a greater buoyancy force, which reduces the load on the sample so that the stress in the sample has a constant value.

b) Constant load, where the stress increases during the test due to the decreasing cross-section. There is an increase in stress and strain rate until failure. Schematic description of the test: A load is suspended on the test specimen - rod, which loads the specimen with the same force throughout the test. The test specimen is subjected to tensile load.

A variety of test equipment has been developed for both of these test methods. Their common feature is that they exert a uniaxial tensile stress in the tested sample, while the sample is placed in an oven, which ensures its heating to the required temperature.

Since the first works and construction of the creep machine (Andrade 1910 to 1914), a number of testing machines have been developed in which the samples are loaded for a long time with tensile force and kept at temperature. This means that the sample is experimentally subjected to uniaxial tensile stress and the results obtained in this way are used to evaluate real devices operating in the creep region.

The problem, however, is that the decisive part of the devices operating in the creep region is not loaded by uniaxial tensile stress, but by spatial stress. The largest share in this area are piping systems, ie equipment subjected to stress caused by internal overpressure. A classic example is high-pressure steam pipelines in power plants and heating plants.

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A common disadvantage of all these devices is that they are not able to create an inhomogeneous stress field in the sample, while creep damages are not only temperature dependent but also on the magnitude of the stress. Information about the actual creep damage can be obtained only by taking samples from operated, mostly pressure, equipment, which is always technically and financially demanding and in many cases even excluded, because it is not possible to create a quality repair weld on degraded materials.

In order to obtain the material data required, for example, for determining the residual life, it is necessary to produce these test specimens from degraded material. In the event that an operationally degraded sample of material is not available, resp. the costs associated with cutting this sample from the pressure system are disproportionately high, resp. the possibility of irreparable damage to the pressure system is too high, it is necessary to produce the degraded material for testing purposes, while both the operating temperature and the stress in it should be as close as possible to the actual operation. A large part of pressure equipment is stressed not only by temperature but also by internal overpressure. The device is designed for this type of loading.

The essence of the technical solution

The above-mentioned shortcomings are largely eliminated by the sample preparation device for determining the material properties of metals and their alloys, according to this technical solution. Its essence is that it contains a spatial body made of the tested material with a vacuum-tight interior. substances which, after heating the space body to the required degradation temperature, form saturated or superheated steam in the given internal space of the required density and this density corresponding to the internal overpressure. It further comprises a pump for removing air from the interior space, another pump for introducing the calculated amount of chemically pure substance and a vacuum-tight closure of the interior space. The spatial body is located in the expelled space.

The chemically pure substance is preferably in a state selected from the group consisting of liquid, solid and gaseous.

The expelled space is preferably formed by a bath and / or a furnace.

The device is used for the preparation of degraded material, degradation caused by the simultaneous action of temperature and stress caused by internal overpressure induced by the pressure of steam in a defined closed internal volume.

Equipment for the production of creep-exposed samples also brings other advantages over taking exposed samples from actual infections. The first advantage is the ability to expose several different types of metals, respectively. alloys from which it is possible to produce a new casting in advance of the actual production and on the basis of a relative comparison to select the most suitable one. The second advantage is the possibility to evaluate creep damage in several time sections before using several bodies. The advantage is also a significantly lower price for the use of exposed samples. In addition to the costs of the actual sampling of the sample, welding of the pressure system, annealing to remove stress, performing tests prescribed by the state supervision of the reserved equipment, the costs of non-production of decommissioned equipment must be included, which for example represents 200 million units daily.

Laboratory production of exposed samples also has a major advantage in eliminating other influences that can never be ruled out in real cases.

The use of several samples simultaneously exposed also brings the possibility of eliminating random errors, the influence of local imperfections, the influence of unrecorded non-technological states using statistical methods of evaluation of more theoretically identical results.

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Examples of technical solution

An exemplary sample preparation device for determining the material properties of metals and their alloys comprises a spatial body of test material with a vacuum-tight interior change. space for calculating the amount of a substance which, after heating the space body to the desired degradation temperature, produces saturated or superheated steam of the desired density in this interior space and of this density corresponding to the internal overpressure. It further comprises a pump for removing air from the interior space, another pump for introducing the calculated amount of chemically pure substance and a vacuum-tight closure of the interior space. The spatial body is located in the expelled space. The chemically pure substance is in a state selected from the group of liquid, solid and gaseous. The heated space consists of a bath and / or a furnace.

First, a three-dimensional body with an internal vacuum-tight volume of variable size is formed. Subsequently, the magnitude of the change in internal volume with the temperature given by the thermal expansion of the walls of the spatial body is determined. The amount of substance which, after heating the space body to the desired degradation temperature, produces saturated or superheated steam of the required density and corresponding to the internal overpressure in a given internal volume is determined. Then the interior is cleaned of possible impurities and air is removed from the interior. This is followed by the incorporation of the calculated amount of chemically pure substance, most often in the liquid state, although it is also possible to incorporate this substance in the solid or gaseous state. Finally, a vacuum-tight closure of the interior is performed.

After heating the entire charge, ie the space body, to the selected temperature, eg in a bath or furnace, a saturated overpressure is created inside, resp. superheated steam, corresponding to the equation of state. The magnitude of the required internal overpressure is directly determined for a given temperature by the density of superheated steam in the internal enclosure. The casing is thus stressed by temperature and spatial stress from internal overpressure. The advantage of the charge is the minimal requirements for the measuring charge, because the temperature due to the physical validity of the equation of state corresponds to the internal overpressure given by the density of superheated steam inside. The only sensor monitoring the process is a temperature transducer, which can be, for example, a thermocouple connected to a recording device, such as a datalogger.

An example is a geometrically simple shape - a cylinder corresponding to a steam pipe. The tested operating temperature is 625 ° C. The internal volume of the charge was dm ³ . The internal overpressure is 24 MPa and the substance inside is water vapor.

The description of the possible procedure is as follows.

State behavior. For a given quantity of a substance enclosed in a volume V, the temperature T, the pressure p are not independent quantities. There is a general relationship between them:

f (p, V, T) = 0 called the equation of state. For an ideal gas is:

nRT RT where Vm is the molar volume, which can be calculated from the density V _m = M _r / p, where M _r is the molar mass, and R = 8.314 J / K / mol is the molar gas constant. For real substances, this is a simple equation

-3 CZ 35292 UI usually inaccurate. The equations that significantly better capture the actual behavior of the substance, while remaining quite simple, are the cubic equations of state. The most used are Van der Waals and Redlich-Kwong.

Van der Waals equation:

The RT and úu - & Kn constants a and b are determined from the critical temperature T _c and the pressure p _c :

phi ² TZ, l /? Tr = ---- = b - p -64, ₈

Redlich-Kwong equation:

RT a, 2 ^1/3 -lRL.

^ = 5 (57577) - ^ = - 77

Water has T _c = 647.14 K, p _c = 22.064 MPa and M _r = 18.02 g mol ¹ . The constants of the Van der Waals equation are: a = 0.5535 Pa m ⁶ mol ^-2 , b = 3.048E-5 m ³ mol ¹ . The constants of the Redlich-Kwong equation are based on: a = 14.27 Pa m ⁶ mol ^-2 K ⁰⁵ , b = 2.113E-5 m ³ mol ¹ .

This issue is addressed, for example, by the publications Van der Waals, J. Die Continuitát des gasfórmigen und flůssigen Zustandes. Barth, Leipzig, 1899 and Redlich, O., and Kwong, J. N. S. The thermodynamics of solutions. V. An equation of state. Fugacities of gaseous solutions. Chemical Reviews 44 (1949), 233-44.

The exact state behavior of water can be found in the tables "Thermodynamic Properties of Water: Tabulation from the IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use".

Example

A pressure pipe with an internal volume of 1 dm ³ , at a temperature of 625 ° C and a pressure of 24 MPa is considered. How much water is in the pipe?

From the tables of water status behavior (IAPWS) we can find by interpolation the density of water at 625 ° C and 24 MPa, which is 64.56 kg / m ^3, ie 64.56 g / dm ³ . Thus, 64.56 g of water is in the pressure tube. We verify the result according to the above equations of state by calculating the pressure from the known density and temperature by substituting it directly into the equation. The results are shown in Table 1.

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Table 1: Estimated water pressure at a temperature of 625 ° C and a density of 64.56 kg m ^-3 . The actual pressure is 24 MPa.

Method p (MPa) A (MPa) Ideal gas 26.8 -2.8 Van der Waals 22.9 1.1 Redlich-Kwong 23.3 0.7 Peng-Robinson 23.8 0.2

For complete control, it is sufficient to measure a constant temperature using thermocouples.

Industrial applicability

The device according to this technical solution will find application mainly in testing laboratories, that is

Claims (3)

CLAIMS FOR PROTECTION 1. A sample preparation device for determining the material properties of metals and their alloys, characterized in that it comprises a spatial body of test material with a vacuum-tight inner space of measurable size, in which there is a temperature sensor and to which a device for calculating the change in internal volume is connected. with a temperature given by the thermal expansion of the walls of the space body, another device for calculating the amount of heated substance, a pump for removing air from the interior space, another pump for introducing the calculated amount of chemically pure substance. Device according to Claim 1, characterized in that the chemically pure substance is in a state selected from the group consisting of liquid, solid and gaseous. Device according to Claim 1 or 2, characterized in that the heated space is formed by a bath and / or a furnace.