WO2008145292A1 - Apparatus, measuring arrangement, and method for measuring slow movements of a test piece - Google Patents

Abstract

The invention relates to an apparatus for detecting slow movements or changes in the length of a test piece (16), particularly by applying a tensile force that affects the test piece (16). Said apparatus comprises a measuring brace (26) that has two spaced-apart legs (28) and is to be attached to the test piece (16) as well as an extension-sensitive sensor (38) which is disposed on the measuring brace (26). The invention further relates to a method for measuring slow movements or changes in the length of a test piece (16), especially by applying a tensile force that affects the test piece (16). In said method, the changes in the length of the test piece (16) are detected by means of a measuring brace (26) that is attached thereto and at least one extension-sensitive sensor (38) which is disposed on the measuring brace (26).

Description

 description

Device, measuring arrangement and method for measuring slow-running movements of a sample piece

The present invention relates to a device and a measuring arrangement for detecting slow-running movements of a sample piece. The invention further relates to a method for measuring slow-running movements of a sample piece.

Normalized tensile tests are often performed to test materials and determine material properties. Here, specimens are subjected to defined tensile loads, at the same time the expansion and / or fracture behavior is detected. With these tensile tests, a variety of insights into the strength and ductility characteristics of the material investigated can be obtained. The results of the experiments carried out under standardized conditions are suitable for the definition of characteristic values and for the characterization of the materials. If the material is additionally subject to certain external influences, this may greatly influence the measurement results. Such influences may be, for example, high pressure, high or low temperatures and / or aggresive media to which the material is exposed.

In order to obtain information on the behavior of materials that are exposed to such influences, superimposed tests are useful, for example a so-called slow tensile test (SSRT test: Slow Strain Rate Tensile Test), in which the material under investigation simultaneously defined at low strain rate Environmental exposure is exposed. Especially with materials that are used in power plant construction, such tests are necessary to estimate the required component dimensions and to predict the typical life and the failure behavior of the components can. This applies in particular to materials that are used in the field of nuclear power plants, since conditions can occur here that can significantly influence the component behavior.

BESTÄT1GUNGSKOPIE The invention is based on the object to provide a measuring method and a measuring arrangement for detecting the expansion behavior of a material sample available, with which a particularly reliable estimation of the material behavior is possible when used in the field of nuclear power plants.

This object is achieved by a device for detecting slow-moving movements or changes in length of a specimen with the features of independent claim 1.

The invention is based on the consideration that the resistance of materials to medium-influenced cracking and subsequent crack propagation by e.g. Media-assisted crack corrosion is an essential prerequisite for the design and implementation of technical applications which have surfaces in contact with the medium.

For example, in the selection of materials for the steam cycle of power plants for power generation in addition to the mechanical properties that maintain the integrity of the system, to ensure sufficient resistance to the corrosive medium. To increase the efficiency in the water vapor circuit, an elevated pressure (eg 170 bar) and a high operating temperature of the cooling medium (eg 350 ⁰ C) is used. The medium is referred to in the specialist literature as high-temperature water (HTW) or dissolved oxygen in the water as oxygen-containing high-temperature water. This water is an aggressive medium in which many materials fail due to the corrosive damage with superposition of mechanical and corrosive load and only a few materials are suitable for the construction of pressure-enclosing components. Especially at low strain rates in typical orders of magnitude between about ⁴ to 10 ^"3 s ^{' 1 there} may be an increased corrosive susceptibility to medium-influenced cracking. The same applies to the measuring technology used under these environmental conditions (eg for strain measurement). The problem can be aggravated if ionic impurities increase the damaging effect of the medium.

In addition to the tolerable stress, the elongation of the round tensile specimens used when reaching the tensile strength or breaking the specimen in oxygen-containing high-temperature water is an important parameter for statements on the resistance to medium-influenced cracking. So far, no length measuring systems are available, which under the specific environmental conditions of the primary circulation of boiling water reactor plants or of pressurized water reactor plants under the high pressures prevailing there, ie 1 to 170 bar, the high medium temperature, ie 25 to 350 ⁰ C ₁ and an oxygen content of 0 ... 8 ppm dissolved oxygen a permanent measurement of changes in length under the aggressive described above Ambient conditions (oxygen-containing high-temperature water) with possibly chemical transients due to ionic impurities (eg chloride, sulphate, etc.) at a corresponding resolution of the length measurement lead to satisfactory measured values.

The device according to the invention has a measuring bracket with two legs spaced apart from one another for fixing to the sample piece and a strain-sensitive sensor arranged on or assigned to the measuring bracket. The device is particularly suitable for measuring the length or strain of the specimen to which a defined tensile force is applied.

So far, when testing materials under ambient conditions, both for single-sample and multi-sample tests, the strain was not measured directly on the material sample (in the autoclave) - based on the initial length of the gauge length of the round tensile specimen used - but the strain due to the applied path of the Machine traverse determined with appropriate conversion. Due to a non-ideal and usually different machine rigidity, this leads to falsified measured values, which has an effect in the calculation, for example, of the modulus of elasticity. The invention, however, makes it possible to provide a measurement technique for recording the change in length available, in which the length changes directly on used sample body or on the respective Rundzugprobe under different media influences with high resolution at the corresponding measuring length of the sample body used can be measured.

The device according to the invention is particularly suitable as a so-called extensometer, which can deliver reliable measured values even under unfavorable environmental conditions. The device is therefore also suitable, for example, for use in so-called high-temperature water (HTW), so that the measurement technique for recording changes in length directly on the respective round tensile specimen in oxygen-containing high-temperature water with high resolution at the corresponding gauge length of the round tensile specimens used. All disturbances related to the measurement of the change in length by external inductive displacement measurement, e.g. the frictional forces due to the seals of the drawbar with respect to the autoclave, the interior or by the rigidity of the abutment are avoided by the measuring arrangement according to the invention or the extensometer, as is measured directly on the sample.

A preferred variant of the invention provides that the strain-sensitive sensor is arranged adhering flat on the measuring bracket. As a result, a robust measuring arrangement is made available in which measured value distortions due to relative movements between the sensor and measuring bracket are almost impossible.

The measuring bracket may optionally have a U-shaped, an arcuate, an annular or a C-shaped connecting portion between the legs. In addition, further designs and forms of the measuring bracket are possible. An essential aspect of the invention is that the measuring bracket has an extended measuring section which deforms substantially uniformly over the path change of the sample and whose deformation behavior can be measured substantially more precisely by means of the sensor than when the sensor is applied directly to the lateral surface of the sample piece , The measuring bracket thus provides a path translation, which transmits the very small changes in length of the specimen in precisely measurable changes in shape or changes in radius on the measuring bracket. A sectionally regularly shaped or curved contour ensures the desired linearity of the measured data. For example, a C-shaped connection Section with a circular arc-shaped contour, in which the circular arc has a constant radius, particularly good for detecting their deformation behavior, since the arc uniformly opens at a change in length of the specimen between the fixed thereto connecting legs, wherein the connecting portion uniformly deformed.

The legs may, for example, have clamping connections for fixing on the sample piece. In addition, other connection options are conceivable, for example. Screw or adhesive connections o. The like. It is important that the points of contact between the measuring bracket and the sample does not slip, which would make the measurement results unusable. At the same time, the connection is preferably designed in such a way that no notch effect on the surface of the specimen arises through the attachment of the clamp connections during the experiment.

The strain-sensitive sensor may in particular be formed by at least one strain gauge. Alternatively, several strain gauges may be arranged on the measuring bracket, either in parallel or in a bridge circuit. As a result, if necessary, temperature and / or other environmental influences can be taken into account and computationally compensated. The strain gauges can supply measured values of different types, for example capacitive measured values or changes in an ohmic resistance.

Since the legs of the measuring yoke are not suitable for measured value detection, the strain-sensitive sensor or strain gauges is expediently adhesively bonded to the connecting section of the measuring yoke. The strain-sensitive sensor or the strain gauges may in particular be adhesively bonded to an outer side of the connecting section or the measuring yoke, since at this point the greatest change in the path of the measuring yoke takes place when the sample is stretched. Thus, the fixation on the outside of the arc of the connecting portion is best suited for detecting highest possible measured values.

According to the preferred applications of the device according to the invention, the strain-sensitive sensor or strain gauges against pressure, Temperature and / or media influence to be encapsulated. As a result, the device which is resistant to corrosive phenomena is suitable for use in oxygen-containing high-temperature water, wherein the pressure values which occur can be, for example, between about 1 to 170 bar or more. The temperature range may, for example, between about 25 ⁰ C to about 350 ⁰ C or more. The oxygen content of the water or of the liquid or gaseous medium can be, for example, between 0 and 8 ppm of dissolved oxygen.

It is expedient to use an encapsulated electrical connection line in applications in such environments, so that the strain-sensitive sensor or the strain gauge along with its connection lines is encapsulated against pressure, temperature and / or media influence. The electrical connection line of the strain-sensitive sensor or of the strain gauge can, for example, have a largely rigid enclosure and at least one electrical supply embedded therein in ceramic material.

An embodiment of the invention provides that at least the connecting portion of the measuring bracket is formed of a resilient material. The measuring bracket or its connecting portion may in particular be formed from a high-temperature, pressure and / or media-resistant material. As a material is, for example, a suitable nickel-based material or a stainless steel that is not attacked or damaged even by the aggressive high-temperature water, for example. By stress corrosion cracking.

For example, a suitable stainless steel such as Inconel ^600® (registered trademark of the Special Metals Group of Companies) may be used as the material for the measuring bracket and the connecting section, a nickel-chromium alloy with good resistance to oxidation and corrosion at high temperatures. The fields of application of such a material include components of furnaces, the chemical industry, the food processing industry and the nuclear industry. The measuring bracket thus has sufficient resistance when used in oxygen-containing high-temperature water. In addition, it is not damaged by media-based Risskorrosionsseffekte at small strains in the elastic range. The invention further comprises a measuring arrangement for detecting slow-moving movements or changes in length of a sample piece exposed to a defined tensile force or change in length. The measuring arrangement comprises a sample piece or a sample body and a measuring device fixed thereto in accordance with one of the previously described embodiments. The measuring arrangement can in particular be coupled to a data acquisition and / or data evaluation system. This data acquisition and / or data evaluation system can in turn be coupled to a storage, display and / or printing device, so that visualization and / or recording with further analysis of the acquired measured values is possible.

Before using the device or the measuring arrangement according to the invention, it is expedient to carry out a calibration with regard to the temperature- and path-dependent changes of the measuring signal according to suitable calibration data or regulations.

Finally, the invention comprises a method for measuring slow-moving movements or changes in length of a sample piece, in particular by applying a tensile force acting on the sample piece, in which the changes in length of the sample piece are detected by means of a measuring bracket fixed thereto and with at least one strain-sensitive sensor arranged on the measuring bracket be set, which are in terms of pressure, temperature and chemical composition of the surrounding medium conditions substantially similar to those in the coolant circuit of an operating boiling water reactor plant or a pressurized water reactor plant.

That is, the material trials take place under simulated environmental conditions of a boiling water reactor or pressurized water reactor in an autoclave of a corresponding simulation environment or according to the in-situ principle even locally in a boiling or pressurized water reactor itself. The inventive method can be carried out in particular with a device and / or with a measuring arrangement according to one of the previously described embodiments. The method makes it possible to perform changes in length of specimens in aggressive media such as. In high-temperature water with high resolution. Disturbance variables, which falsify the measured value recording, can be largely filtered out or excluded.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1 is a schematic representation of the measuring principle of a measuring arrangement according to the invention and

Fig. 2 is a schematic representation to illustrate the principle of operation of the measuring arrangement.

1 shows a schematic representation of the measuring principle of a measuring arrangement 10 according to the invention, which essentially comprises a measuring device 12 in the form of a so-called extensometer 14 (see FIG. 2) as well as a sample piece or a sample body 16 on the / the extensometer 14 is fixed. By means of a downstream evaluation unit 18, the measured values of the extensometer 14 can be detected, processed and, if appropriate, delivered to a downstream visualization and / or storage unit designated generally by the reference numeral 20. The reference numeral 20 may also indicate a printed or screen-displayed stress-strain diagram or other suitable graphical representation of the measured values.

In addition to the measured values supplied by the extensometer 14 or the measuring device 12, the evaluation unit 18 can furthermore detect and process the mechanical load 22 applied to the sample body 16 and / or the environmental parameters 24, which respectively influence the measurement. The mechanical load 22 is typically a tensile load acting on the elongated specimen 16 from both end faces. The environment parameters 24 include the definition of the medium (eg high temperature water - HTW), its oxygen content (eg O ₂ = 0 ... 8 ppm), the medium temperature (eg T = 25 ... 350 ⁰ C) and the pressure prevailing in the medium (eg p = 1. .. 170 bar).

Such environmental conditions are provided within a pressure vessel 25, also referred to as an autoclave, in which the extensometer 14 together with the material sample is arranged. The evaluation unit 18 as well as the visualization and / or storage unit 20 connected downstream on the data side are expediently arranged outside the pressure vessel 25. For electrically connecting the extensometer 14 or the sensors arranged thereon to the evaluation unit 18, a connection line 42, which is encapsulated at least in the interior of the pressure vessel 25, is guided in the wall of the pressure vessel 25 by a pressure-resistant cable feedthrough.

The schematic representation of FIG. 2 illustrates the functional principle of the measuring arrangement 10 according to the invention, which in turn comprises a measuring device 12 in the form of the extensometer 14 and the elongate, rod-shaped sample body 16 to which the extensometer 14 is fixed. The extensometer 14 and the measuring device 12 form a so-called measuring bracket 26. This measuring bracket 26 comprises two spaced-apart legs 28, which are fastened in each case by means of fastening elements 30, for example. In the form of clamping connections 32 on the sample body 16. In the Fig. 2, only the upper clamp connection 32 is shown, while the lower clamp connection has been omitted for the sake of simplicity. However, the lower clamp connection of the lower fastener 30 is i.d.R. The legs 28 are fixed to the sample body 16 so that no negative notch effects are formed, which could reduce the strength of the sample body 16 in the tensile test or its resistance to crack initiation.

The symmetrically arranged, each L-shaped legs 28 open into short parallel portions 34, to which a closed, annular, elastic connecting portion 36 connects, on the outside of a strain sensor 38 in the form of a high temperature water resistant, encapsulated strain gauge 40 (so-called . DMS) is fixed with its entire surface resting. The strain gauge 40 may, for example, be glued or welded onto the connecting section 36 in order to transmit the spring movements to the strain gauges 40.

The strain gauge 40 may additionally be embedded in a densified oxide ceramic powder, thereby improving the transmission of the signal from the connection portion 36 to the strip 40. As a result, losses are reduced by relative movements of the Dehnmessstreifens 40 to a minimum.

Also visible is an electrical connection line 42 of the strain-sensitive sensor 38 or the strain gauge 40, which is encapsulated against pressure, temperature and / or media influence. The electrical connection line 42 establishes a connection to the evaluation unit 18 (see FIG.

As a material for the measuring bracket 26 and the connecting portion 36 is, for example, a suitable stainless steel in question, whereby the measuring bracket 26 is given a sufficient resistance in its intended use in oxygen-containing high-temperature water. As a stainless steel for the measuring bracket is, for example, a nickel-chromium alloy with good resistance to oxidation and corrosion at high temperatures. The fields of application of such a material include components for the nuclear industry. The measuring bracket can thus have sufficient resistance in its intended use in oxygen-containing high-temperature water. In addition, it is not damaged by stress corrosion effects at small strains in the elastic range.

LIST OF REFERENCE NUMBERS

measuring arrangement

measuring device

extensometer

specimen

evaluation

Display unit mechanical load

environmental parameters

pressure vessel

measuring bracket

leg

fastener

Clamp connection parallel sections

connecting portion

strain sensor

Strain gauge connecting cable

Claims

claims 1. A device for detecting slow-moving movements or changes in length of a specimen (16), in particular under application of a supply to the sample body (16) tensile force, comprising a measuring bracket (26) with two spaced legs (28) for fixing on the specimen (16) and a strain-sensitive sensor (38), which is arranged on the measuring yoke (26), wherein the strain-sensitive sensor (38) is so encapsulated against o pressure, temperature and media influence that a permanent use in oxygen-containing high-temperature water ( HTW) at pressures of 1 to 170 bar, at a medium temperature of 25 to 350 ⁰ C and at an oxygen content of 0 to 8 ppm dissolved oxygen is possible. 2. Device according to claim 1, wherein an electrical connection line (42) of the strain-sensitive sensor is encapsulated against pressure, temperature and media influence. 3. Apparatus according to claim 2, wherein the electrical connection line (42) of the strain-sensitive sensor (38) has a substantially rigid enclosure and at least one embedded therein in ceramic material electrical supply line. 4. Device according to one of claims 1 to 3, wherein the measuring bracket (26) is formed of a high temperature, pressure and media-resistant material, namely of a corrosion-resistant stainless steel or a nickel-based alloy. 5. Device according to one of claims 1 to 4, wherein the strain-sensitive sensor (38) is arranged adhering flat on the measuring bracket (26). 6. Device according to one of claims 1 to 5, wherein the measuring bracket (26) has a U-shaped, an arcuate, an annular or a C-shaped connecting portion (36) between the legs (28). 7. Apparatus according to claim 6, wherein the strain-sensitive sensor (38) is adhesively bonded to an outer side of the connecting portion (36) and the measuring bracket (26). 8. Device according to one of claims 1 to 7, wherein the legs (28) clamping terminals (32) for fixing to the sample body (16). 9. Device according to one of claims 1 to 8, wherein the strain-sensitive sensor (38) by at least one strain gauge (40) is formed. 10. Device according to one of claims 1 to 9, wherein the strain-sensitive sensor (38) or the strain gauge (40) is adhesively bonded flat to a connecting portion (36) of the measuring bracket (26). 11. Device according to one of claims 1 to 10, wherein at least one connecting portion (36) of the measuring bracket (26) is formed of a resilient material. 12. Measuring arrangement for detecting slow-running movements or length changes of a defined tensile force or length change exposed sample body (16), comprising the sample body (16) and a measuring device fixed thereto (12) according to one of claims 1 to 11. 13. Measuring arrangement according to claim 12, which is coupled to a data acquisition and / or data evaluation system (18). 14. Measuring arrangement according to claim 13, wherein the data acquisition and / or data evaluation system (18) is coupled to a storage, display and / or printing device (20). 15. A method for measuring slow-moving movements or changes in length of a sample body (16), in particular by applying a force acting on the sample body (16) tensile force, in which the changes in length of the sample body (16) by means of a fixed thereon Meßbügels (26) with at least one strain-sensitive sensor (38) arranged on the measuring yoke (26), with respect to Pressure, temperature and chemical composition of the surrounding medium conditions are set, which correspond substantially to those in the coolant circuit of an operating boiling water reactor system or a pressurized water reactor system. 16. The method of claim 16, wherein the measurements are made in an autoclave in which oxygen-containing high-temperature water is at pressures of 1 to 170 bar, at a medium temperature of 25 to 350 ⁰ C and at an oxygen content of 0 to 8 ppm of dissolved oxygen , 17. The method of claim 17, wherein the high-temperature water ionic impurities are added.