CS219441B1 - The method of carrying out the underpressure loading test for low pressure double-shell standing tanks - Google Patents

Abstract

In order to verify the safety against loss of stability, the tested tank is closed when the daily temperature maximum is reached. All its openings are blinded except for the pressure difference meter. The decrease in atmospheric temperature is used to perform the negative pressure load test. As the air temperature inside the tank decreases depending on the atmospheric pressure, the difference between the atmospheric pressure and the pressure inside the tank is measured until the prescribed negative pressure is reached. This completes the load test. To equalize the pressures, the interior is gradually connected to the surrounding atmosphere.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method of performing a vacuum load test on low-pressure, double-walled, large-volume, vertical storage tanks operated from a pressure close to atmospheric pressure up to an overpressure of 0.1 MPa. The vacuum load test is carried out especially after completion of the assembly to verify the safety of the tank against loss of stability.

In a known manner, the vacuum test is carried out, for example, by discharging water from the inner tank of the tank. However, this method is unusable when a fiber or rigid or flexible insulation is placed on the inner vessel or in the intermediate shell, which would be deteriorated by the moistening of the inner tank rosettes.

Another known method uses a vacuum pump to vacuum the air from the tank to perform the load test. However, this means that the pumps must be procured and installed, including electrical installation and power supply. energy. The pump is not part of the operating set and must be provided only for the vacuum load test.

The disadvantages of the known methods are overcome by the proposed method of performing a vacuum load test on low pressure double-skinned, vertical tanks to verify safety against loss of stability according to the invention. The essence of the invention is that the test tank, with the exception of the pressure difference meter, closes when the daily temperature maximum is reached; then, as the air temperature inside the tank decreases as a function of atmospheric pressure, the difference between the atmospheric pressure and the pressure inside the tank is measured until the prescribed vacuum is reached when the load test is completed. To equalize the pressures, the inside of the tank is slowly connected to the surrounding atmosphere.

The advantages of the method according to the invention are that it is easy to achieve the required vacuum for the load test and only natural conditions are used. Advantageously, this method can be used for tanks with a fixed part of the insulation in the intermediate shell or on the inner vessel, for example for liquefied gas tanks where water cannot be used to generate a vacuum. It is also not necessary to provide a vacuum pump to extract air from the tank.

Vacuum load test according to vy2. Δ t = -LPlabel P2

P vacuum is the desired vacuum value, P2 is the partial air pressure at which the temperature a changes

T is the mean temperature of the part involved in the tank defrost (1/6).

During atmospheric temperature drop, the measurement of the pressure drop in the tank against atmospheric pressure, for example U-trunalysis, is carried out to verify the safety of the low pressure double-shell tank against loss of stability, for example under the following conditions:

Low-pressure double-wall large-volume standing tanks, which operate from a pressure close to atmospheric pressure up to an overpressure of 0.1 MPa, will be subjected to negative pressure. When performing a vacuum load test, the absolute pressure inside the external tank is lower by the vacuum value than the absolute pressure outside the vessel, ie the momentary atmospheric pressure.

Thus, the negative pressure inside the external vessel is equivalent to the value of the external pressure, that is, the value by which the atmospheric pressure exceeds the absolute value of the pressure inside the tank. For the design of external tanks, a calculation is made for stability on the vacuum load under the influence of wind and snow. The liquefied gas tank with a fixed part of the insulation in the intercoat space or on the inner tank shall be fitted with vacuum relief valves and a vacuum fuse and differential pressure measurement for testing. The vacuum fuse must ensure that the test vacuum is not exceeded. The best fit for this situation is a hydraulic lock type fuse.

The safety of a low-pressure, double-walled, upright tank against loss of stability shall be verified by a vacuum test carried out, for example, as follows:

Example 1

At constant atmospheric pressure, when the daily temperature maximum is reached, the tank shall be closed and all its openings shall be sealed except for the vacuum fuse which ensures that the test vacuum is not exceeded and with the exception of the differential pressure gauge. The atmospheric temperature drop is used to perform the vacuum test; heat is emitted from the tank, thereby lowering the temperature of the air content in the tank, creating a negative pressure in the tank against atmospheric pressure.

Assuming that at least one-sixth of the total air content of the tank is exposed to the changes in air temperature when exposed to the sun, the equation of state of the gases PV = GRT for a vacuum of eg 490 Pa

T = 8.4 K = 8.4 ° C, where water-filled grinders. When the required vacuum is reached, eg 490 Pa, ie 50 mm water column, the load test is carried out. Since further pressure drop in the tank is dangerous, a gradual connection of the inside of the tank to the surrounding atmosphere is made, thereby gradually equalizing the pressure in the tank with the atmospheric pressure. The speed of the vacuum test po219441 according to the invention depends on the rate of drop of atmospheric temperature from the daily maximum temperature or the rate of drop of the tank temperature resulting from the decrease in sunshine of the tank.

Another alternative of Example 1 is different only in terms of the amount of air involved in the temperature change in the tank. If half of the air in the tank is involved in the temperature change, a vacuum test of 2.8 ° G of that half of the air in the tank is sufficient to carry out the load test. The average daily temperature amplitude, e.g.

Deň: 32 ° C. Required tank air temperature change 2Δΐ = 2.8 ° C <8 ° C, which is acceptable provided the tank surface temperature is equal to atmospheric ambient temperature. In natural convection (without sunlight), for example, a temperature difference of 5 ° C is required to produce the necessary heat flux within a reasonable time. 2.8 + 5 <8 ° C, so a daily amplitude of 8 ° C is suitable for performing a vacuum test at constant atmospheric pressure.

Under sunlight, a higher daily temperature maximum of air in the tank is achieved than in convection, and also a drop in air temperature in the tank is higher and therefore more favorable for performing a vacuum load test according to the method of the invention.

Example 2

At atmospheric pressure drop, at

Claims (1)

A method of performing a vacuum load test on low pressure double-walled standing tanks to verify safety against loss of stability, characterized in that the test tank, with the exception of the pressure difference meter, closes when the daily temperature maximum is reached. The only difference is that the atmospheric pressure drop has to be compensated for by a larger drop in the air temperature in the tank. For example, for a pressure drop of 2.5 Torr in 12 hours, a 15 ° C drop in the tank air temperature from a daily maximum is sufficient to perform a vacuum load test. Example 3 As the atmospheric pressure rises, the vacuum test is also carried out in the same manner as in Example 1. The only difference is that the increase in atmospheric pressure contributes to the formation of the necessary vacuum in the tank. To achieve the required vacuum, a smaller drop in the air temperature in the tank is sufficient. E.g. with an atmospheric pressure increase of 2.5 Torr per 12 hours, a 2.7 ° C reduction in tank air temperature is sufficient. The air temperature in the tank is changed according to known laws on heat transfer by convection and sun radiation. Permanent anticyclone weather causes small changes in atmospheric pressure. The daily amplitude in such a situation is 107 to 133 Pa. The load test according to the invention can be carried out in 2 to 12 hours. In accordance with the present invention, the air inside the tank is measured as a function of atmospheric pressure to measure the difference between the atmospheric pressure and the pressure inside the tank until the prescribed negative pressure is reached when the load test is completed.