PSI - Issue 28

G.N. Gusev et al. / Procedia Structural Integrity 28 (2020) 2328–2334 Gusev G.N., Shardakov I.N/ Structural Integrity Procedia 00 (2019) 000–000

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within the model assumptions concerning the initial stress-strain state of the tank to be verified experimentally. Logically, the next step to the problem solution is the performance of a full-scale experiment accompanied by further verification of the developed models. 3. Experiment During the third stage, a full-scale hydro-test experiment was organized and performed. For this purpose, a test program was elaborated, the locations of the measurement points and deformation limits were determined, and a number of preparatory works were carried out to ensure the accuracy of measurements and the uninterrupted automatic gathering of data on the stress-strain state of the structure. Control over the stress-strain state of the tank wall was carried out for three zones. The first zone is a calm zone or section, where no buckling is present. In this section, according to the calculated models, the stress level does not exceed the value corresponding to the normal operation of the structure at 315 MPa. Two other zones (zones with buckling) are located opposite each other, in the zones of vertical welded seams. The choice of points and measurement zones is caused by the results of tacheometric surveys (Khoroshilova and Khoroshilov, 2012). The calculation models have shown that in the free zone the maximum stresses are present in the lower rings of the tank, and they decrease with increasing height. Based on these results, sensor locations were determined. Strain gauge type sensors, separately designed on the basis of foilconstantan strain gages assembled in a full bridge, were located at 32 control points. Two strain gages were used to measure the longitudinal deformation, and the other two for thermocompensation. Potentiometer is needed to balance the bridge. For ease of installation, the sensors were assembled on a textolite board. Compensating strain gauges were glued to the steel plate (steel 09G2S), which was connected to the board as well. The plate had a hole to contact with the tank wall through the thermal interface KPT 8 (Fig.3). All the sensors were tested on a calibration beam and in a climatic chamber in order to check temperature compensation using the plate made of steel 09G2S. The sensor accuracy error was ±20∙10 -6 .

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b

Fig. 3. a) Basic diagram of a strain gage b) Strain gage glued to the steel plate(steel 09G2S).

The sensors were glued to the previously prepared surface of the tank wall using a cyanoacrylate adhesive. Surface preparation involves grinding of the part of the tank wall to a smooth surface, which should be free from corrosion products and ensure the best adhesion (Fig.4). The sensors operated under high humidity conditions and under the influence of temperature differences throughout the experiment. It periodically rained on the site with wet snow. Daily temperature fluctuations reached 60 degrees in amplitude. Despite this, all sensors worked normally. The strain gages were connected via the six-wire circuit to the input signal units of the firm “OVEN” МV110 224.4TD. The measurement error of this device is 0.05%. The modules were combined via two common RS-485 buses