RU2545373C1 - Method to prepare fuel storage tank for leakage checking - Google Patents

Abstract

FIELD: machine building.SUBSTANCE: proposed method to prepare a fuel storage tank for leakage checking involves the following: tanks 11 are put into a sealed chamber 1, atmospheric air is removed from the chamber and the tank 1 by vacuum pump 4, 5. Then the tank 11 surfaces are treated by solvent supplied through nozzle units 6, 7 provided that flow rates of the supplied and removed solvent are equal. At the first stage of the preparation process the tank 11 surfaces are treated by solvent jets heated up to the permissible temperature with the total flow rate providing for the removal of surface contaminations and heating of the tank 11 up to the temperature of the supplied solvent during the specified process time. The next stage involves alternating operations of affecting the surfaces by atomized solvent with its total flow rate providing for keeping of laminar-flowing down solvent film on the tank surfaces, and vacuum drying operations. The total duration of periodic treatment operations ?, regardless of the total time required for the removal of residual liquid and steam solvent phases from the tank before every vacuum drying operation, ?=?+?+?, where ?- required total duration of time to remove soluble clogging contaminations from the channel of through microleaks by extraction with the solvent; ?- required total duration of time to remove capillary moisture from the channel of through microleaks at vacuum drying; ?- required total duration of time to remove solvent from the channel of through microleaks at vacuum drying. Duration of every period of solvent action and vacuum dryingwhere n - total number of affection periods determined by the condition:where ?- duration of time required for the removal of residual liquid and steam solvent phases from the tank before every vacuum drying operation; the duration of treatment by solvent ?and of vacuum drying ?in each period are determined asEFFECT: increased efficiency and reliability of preparing fuel storage tanks for leakage checking, reduction of labour and financial expenditures on the performance of such works.1 dwg, 1 tbl

Description

The invention relates to mechanical engineering, in particular to the cleaning of product surfaces from contaminants, as well as to the preparation of products for leak testing - the operation consisting in releasing the channels of through micro-leaks arising during the manufacture of products from various kinds of clogging substances (mineral oils, cutting lubricants liquids, various technological environments with which contact is possible between the surfaces of products during the manufacturing process, as well as capillary moisture - the result of contact between surfaces aquatic environments and atmospheric moisture). The preparation operation is required to be performed before the highly sensitive tightness control, providing high reliability of detection and identification of through micro-leaks of ultra-small sizes.

For cleaning and degreasing the surfaces of the shells of fuel tanks, they are treated with solvents. At the same time, methods are used to fill the container volumes with a solvent, circulating, jet and steam condensate cleaning (see B. I. Ivanov. Cleaning metal surfaces with fireproof compounds. M: Engineering, 1978). Solvents are also used to remove soluble contaminants from the channels of through micro-densities, and the main method of removing them from the depth of channels of through micro-leaks is dissolution and extraction with solvents (see OST 92-4281-74 “Methods, means and modes of preparation of product surfaces before leak tests” ) The removal of water and volatile liquids from the depth of the channels of through micro-densities is carried out by drying methods (see OST 92-0019-78 "Methods and modes of drying products before leak testing"). By sequentially performing surface cleaning operations and freeing through micro-leaks from soluble contaminants by extraction, evaporating moisture and other volatile liquids, they allow penetration through micro-capillaries of through leaks of control gas molecules (helium, argon, SF6, etc.) with highly sensitive tightness control.

Closest to the proposed invention include solutions regulated by industry regulations OST 92-4281-74 and OST 92-0019-78.

In the known methods regulated by OST 92-4281-74, an article placed in a sealed washing chamber is treated with a solvent for a time sufficient to dissolve and remove surface contaminants, as well as to dissolve and extract non-volatile contaminants (mineral oils, fats, various liquid technological media) concentrated in the depth of the through micro-density.

In the known methods regulated by OST 92-0019-78, the product placed in the drying chamber is maintained after heating under the condition of intensive removal of the released vapor of liquids, while the evaporation of liquids (capillary moisture, solvents) from the channels of through micro-densities occurs.

The described methods are applied using individual specialized technological means, and in succession: initially, surface cleaning and extraction cleaning of micro-leaks from clogging soluble contaminants are performed, and then drying operations are performed to remove clogging volatile liquids (moisture, solvents).

The lack of effectiveness and reliability of such a technology for preparing products for leak testing is caused by the following factors.

Each of the above operations is currently carried out using special technological equipment: closed surfaces are used to clean the surfaces with solvents, solvent treatment units for the internal surfaces of fuel tanks, long-term solvent exposure units are used to remove soluble contaminants from through microleakness channels to dissolve and extraction of contaminants from the depth of through micro-densities, for evaporation Riva volatile liquids and moisture apply vacuum drying chamber containers requiring heating device and maintaining the elevated product temperature during dehydration.

Moving fuel tanks of large sizes and masses from one technological installation to another requires a lot of labor and time. In addition, during periods of such movements, repeated blockage of micro-densities is not excluded, for example, during capillary condensation of atmospheric moisture. As a result, the reliability of the subsequent tightness control is reduced.

The disadvantage of this technology is also the fact that with the consistent application of the methods of extraction cleaning and drying of the product for a full period of exposure, it is not always possible to achieve guaranteed release of through micro-densities from clogging substances. In order to effectively apply the preparation methods, it is necessary to clearly understand the nature of the contamination of the channels of through micro-leaks. For example, if there is capillary moisture in the depths of the microleakness and fatty contaminants along the edges, it is necessary to apply the solvent dissolution and extraction method first, and then the vacuum drying technique. Conversely, if moisture is contained at the edges, and mineral oils are in the depths, it is necessary to first apply drying and only then extraction cleaning. The real picture of pollution is not clear from the beginning; in reality, the nature of pollution can be little predictable. The task of cleaning microleakness channels becomes even more complicated when clogging substances (soluble and vaporized) repeatedly alternate along the length of microleakness channels: in this case, guaranteed removal of contaminants by successive extraction cleaning and drying operations for a full exposure period is not possible at all.

The effectiveness of the preparation can be higher if the methods of exposure change periodically: while any of the alternating methods can achieve a positive result, and although the cleaning process becomes discrete, it is more effective in terms of the result achieved.

The task of the invention is to increase the efficiency and reliability of the preparation of fuel tanks for tightness control, reducing labor and financial costs for these works.

The problem is solved by the method of preparing the fuel tank for tightness control, in which the tank is placed in a sealed chamber, atmospheric air is removed from the chamber and tank volumes by a vacuum pump, and then surfaces of the tank (external and internal, either separately or internal or external) are fed through nozzle devices with a solvent, provided that the costs of the solvent supplied and removed from the volumes are equal, according to the invention in the first stage of the preparation process they treat the surfaces of the container with jets of a solvent heated to an acceptable temperature with a total flow rate that ensures removal of surface contaminants and heats the tank to the temperature of the supplied solvent in a technologically established time, and at the next stage, operations on the surface of a finely droplet-sprayed solvent are periodically alternated with a total flow rate ensuring maintenance on the surfaces of the capacity of the laminar-flowing film of the solvent, with operations of vacuum drying, and about Single periodic duration τ _of processing operations excluding the total time spent on the removal of residues from the tank the liquid and vapor phases of the solvent before each operation of the vacuum drying,

τ _about = τ _e + τ _vl + τ _p ,

Where

τ _e is the required total duration of removal from the channel of the through micro-density of soluble clogging impurities by solvent extraction;

τ _is - removing the necessary total length of the channel through mikroneplotnosti capillary moisture by vacuum drying;

τ _p - the required total duration of removal from the channel of the through micro-tightness of the solvent during vacuum drying;

with the duration of each period of exposure to solvent and vacuum drying

, $${\tau }_i=\frac{{\tau }_{\mathrm{about}}}{n}$$

,

Where

n is the total number of exposure periods assigned from the condition:

, где $$n\le \frac{{\tau }_{\mathrm{about}}-{\tau }_{\mathrm{uh}}}{{\tau }_{\mathrm{at}d}}$$

where

τ _beats - the duration of removal from the volumes of residual liquid and vapor phases of the solvent before each operation of vacuum drying;

the duration of the solvent treatment τ _ie and vacuum drying τ _io in each period are determined

The values of τ _e depending on the possible depth of micro-density l, the solvent force of the solvent used, are determined by the recommendations of OST 92-4281-74:

- при одностороннем контакте с растворителем, с; $${\tau }_{\mathrm{uh}}=2\frac{l^2}{D}$$

- in case of unilateral contact with the solvent, s;

- при двустороннем контакте с растворителем, с; $${\tau }_{\mathrm{uh}}=0,5\frac{l^2}{D}$$

- with bilateral contact with the solvent, s;

l is the effective length of the through micro-density, cm;

D is the coefficient of mutual diffusion of the solvent molecules and the solute, cm ² / s

Thus, if only one-sided exposure of the solvent to the surface of the container is possible (for example, when processing only the inner surfaces of the container), the total duration of the preparation operation should be increased in comparison with the duration of two-sided processing by at least 4 times.

Values of τ _vl and τ _p depending on the possible depth of micro-tightness l, method (vacuum or convective), drying temperature, micro-tightness permeability for the control gas (helium, helium-air mixture) are determined from the tables and nomograms OST 92-0019-78.

The operations of cleaning surfaces and cleaning channels of end-to-end micro-tightness from clogging substances are combined on one technological equipment, and multiple periodically repeated alternating operations of solvent exposure on the surface of the product and vacuum drying of the product are used, which increases the reliability of releasing micro-tightness channels from clogging substances.

A distinctive feature of the invention is the first stage of the preparation process for blasting the surfaces of the fuel tank with a solvent heated to an acceptable temperature for a period of time sufficient to remove surface contaminants and heating the tank to a temperature of the solvent, and at the next stage, periodically alternating operations on the surface of the product heated fine droplet-sprayed solvent with a total flow rate ensuring maintenance on the surface x the capacity of the laminar-flowing film of the solvent, and vacuum drying after removal of the liquid and vapor phases of the solvent from the chamber volumes and the containers, and the following are regulated: the total duration of the periodic processing operations, the duration of each individual period of exposure to the solvent and vacuum drying, as well as the processing time of the solvent and vacuum dehydration in each period.

Periodic and repeated repetition of the operations of solvent exposure and vacuum drying during preparation ensures the removal of clogging contaminants for any combination of their localization along the length of the channels of through micro-densities.

The use of a heated solvent, in addition to achieving the effect of increasing the solvent action of the solvent, makes it possible to abandon the use of special means of heating the product inside the vacuum chamber, which is necessary for effective drying. Combining the operations of cleaning surfaces and cleaning channels of end-to-end micro-tightness from clogging substances eliminates labor costs and time for moving the product from one processing unit to others, and also eliminates the possibility of re-clogging through micropores in operations of moving the product.

The analysis of known technical solutions in this technical field shows that the proposed method has features that are absent in the known technical solutions, and using them in the claimed combination makes it possible to obtain a new technical effect: improving the efficiency and reliability of preparing fuel tanks for highly sensitive tightness control, reducing labor and financial costs for the implementation of these works.

The invention is illustrated in the drawing, which shows a diagram of a device for performing operations of preparing fuel tanks for highly sensitive control of tightness.

The device includes a sealed chamber, consisting of a housing 1 and a cover 2, separated and hermetically connected by a flange connector, a storage and pre-heating tank for solvent 3, vacuum pumps 4 and 5, designed to remove atmospheric air from their chamber volumes and products, choking devices and nozzle circuits 6 and 7, designed for jet cleaning of the external and internal surfaces of the product, as well as for supplying a droplet-sprayed solvent to the external and internal surfaces of the product, hyd personal pumps 8 for supplying solvent to the choking devices and nozzle circuits and 9 for pumping solvent from the product volume into the tank 3. Vacuum and hydraulic lines are provided with switching valves K1, K2, K3, K4, K5, K6 and K7. The tank with solvent 3 is provided with a device for heating it 10. The thermometer 12 is designed to control the temperature of the product body (fuel tank) 11. The thermometer 13 is designed to control the temperature of the solvent in the tank 3.

Before starting work, the values of the indicators τ _e , τ _vl , τ _{p are} determined. The value of τ _{e is} determined depending on the possible depth of micro-density l, the solvent power of the solvent used according to the recommendations of OST 92-4281-74. Values of τ _vl , τ _{p are} determined depending on the possible depth of micro-tightness l, drying temperature, moisture vapor pressure and solvent used according to the recommendations of OST 92-0019-78. The value of τ _{o is} defined as τ _o = τ _e + τ _vl + τ _p .

. Значение τ_э назначается в зависимости от возможной глубины микронеплотности l, растворяющей силы применяемого растворителя по рекомендациям ОСТ 92-4281-74. Значение n устанавливается из условия:To perform the preparation operation, the chamber lid is opened, and the product (fuel tank) 11 with a pre-mounted scrubbing device and nozzle circuit 7 is placed in the chamber body 1. After connecting the product volume to the atmospheric air pumping line and connecting the scrubbing device and nozzle circuit 7 mounted inside the volume to the solvent supply line, the chamber lid is hermetically closed. The vacuum pumps 4 and 5 are turned on, the valves K1 and K2 open, and atmospheric air is pumped out from the chamber and the product (fuel tank) 11 to a residual pressure of 1.0 ... 10 ^-1 mm Hg. After heating the solvent by heating device 10 in the tank 3 to the allowed value (control by thermometer 13), the hydraulic pump 8 is turned on, valves K4 and K5 are opened, and the solvent is supplied to the choking devices 6 and 7. Pump 9 is turned on, valves K6, K7 are opened, and the supplied solvent is pumped out from the chamber and the product volumes into the tank 3. After heating the product body 11 to the temperature of the solvent supplied on the surface (controlled by thermometer 12), the solvent supply to the nozzle circuits is switched providing supply on the surface of a finely droplet-sprayed solvent. The flow rate of the fine droplet-sprayed solvent supplied on the surface must ensure that the solvent on the surfaces of the laminar-flowing film is maintained over time $${\tau }_{i\mathrm{uh}}=\frac{{\tau }_{\mathrm{uh}}}{n}$$

. The value of τ _e is assigned depending on the possible depth of micro-density l, the solvent power of the solvent used according to the recommendations of OST 92-4281-74. The value of n is established from the condition:

, $$n\le \frac{{\tau }_{\mathrm{about}}-{\tau }_{\mathrm{uh}}}{{\tau }_{\mathrm{at}d}}$$

,

Where

τ _beats - the duration of removal from the volumes of residual liquid and vapor phases of the solvent before each operation of vacuum drying;

the duration of the solvent treatment τ _ie and vacuum drying τ _io in each period are determined

.After the time τ _iе , the residual liquid phase of the solvent is removed from the chamber and article volumes by pump 9, as well as the vapor phase by vacuum pumps 4 and 5 to a residual vapor pressure of 1.0 mm Hg, and with continuous evacuation of the article and chamber volumes vacuum drying operation over time $${\tau }_{io}=\frac{{\tau }_R+{\tau }_{\mathrm{at}l}}{n}$$

.

The described operations are repeated n times.

If only one-sided exposure to the solvent is possible on the surface of the container (for example, when processing only the inner surfaces of the container), the total operation time τ _o should be increased in comparison with the duration of the two-sided treatment by at least 4 times.

For experimental testing, a fuel tank model was used, representing a cylindrical tank with two elliptical bottoms, structural material - AMg-6 alloy, the wall thickness of the tank was 4 mm. The diameter of the container is 1000 mm, the length is 2000 mm. The bottoms of the tank are connected to the cylindrical part by two circular welds, the thickness of the product in the weld zone is ~ 5.0 mm. The total weight of the layout is ~ 80 kg.

Before experimental testing, the layout of the fuel tank and after careful preparation were subjected to a leak test in a vacuum chamber with an excess helium pressure of 5.0 kgf / cm ² in its volume. Subsequent monitoring of the tightness with a helium leak detector using the “probe” method made it possible to detect two tightness defects (through micro-leaks) with helium permeability of ~ 1.5 · 10 ^-4 l μm Hg (~ 2 · 10 ^-8 m ³ Pa / s) and ~ 5 · 10 ^-5 l μm Hg / s (~ 6.65 · 10 ^-9 m ³ Pa / s). The channels of detected through micro-leaks are clogged by alternating pressure of combined fat contamination (mixtures of oils and fats most in contact with the surfaces of products during their manufacture: ATM-65 transformer oil, VM-1 and VM-4 vacuum oils, I-20 industrial oil, turbine oil T-22 oil) and moisture. Clogging of micro-leaks is confirmed by subsequent routine leak tests.

Experimental testing was carried out in two stages:

- at the first stage, the traditional technology for preparing the layout was used — the sequential use of extraction cleaning of micro-leaks with a solvent for 32 hours and subsequent vacuum drying at a temperature of 50 ° C for 8 hours;

- at the second stage, the proposed new methodology for preparing the layout was applied, according to which the preparation process is divided into 8 successively performed sub-stages, each with a total duration of 5 hours; each sub-step includes extraction cleaning to remove fat contaminants from the micro-densities of 240 minutes and vacuum drying to remove moisture and solvent from the micro-densities of a total of 60 minutes.

For experimental testing, the product was placed in a special chamber equipped with a vacuum pumping system to a residual pressure of 5 · 10 ^-2 mm Hg, as well as solvent spray nozzles. A solvent blasting device for the internal surfaces of the welds is also mounted inside the model. The layout volume is connected by a sealed line through a valve to a vacuum pump. After a tight connection of the chamber lid, atmospheric air was removed from the chamber and prototype volumes to a residual pressure of ~ 1 · 10 ^-1 ... 5 · 10 ^-2 mm Hg.

To heat the prototype to a temperature of ~ 50 ° C on its surface, solvent Freon 141b heated to a temperature of 60 ° C with a total flow rate of ~ 0.5 kg / min was supplied through nozzles of the showering devices. Simultaneously with the supply of solvent to the surface, it was returned from the volumes of the breadboard and chamber to the heating tank. At the same time, the temperature of the layout increased to 50 ° C during 30 ... 35 minutes. Simultaneously with the heating of the product, the solvent supplied to the surface of the product performs the function of removing surface contaminants.

At the first stage of the test (option No. 1) after cleaning and heating the product in the first 30 ... 35 minutes for the next 32 hours, an extraction cleaning operation was performed when a finely sprayed solvent was heated on the surface of the product, heated to a temperature of 50 ° C with a total flow rate of 0, 05 kg / min; then, after stopping the supply of solvent and complete removal of its liquid phase from the chamber and prototype volumes, the vapor phase was evacuated with a vacuum pump to a residual pressure of 1.0 ... 0.5 mm Hg, after which the model was vacuum dried at a temperature of 50 ... 45 ° C for 8 hours under the condition of continuous pumping of chamber volumes and layout. At the end of the preparatory work, the achieved result was checked by measuring the permeability of through microdefects for helium at a pressure drop of 4 kgf / cm ² .

At the second stage (option No. 2) after cleaning and heating the product in the first 30 ... 35 minutes, the extraction cleaning for 4 hours and the subsequent vacuum drying at a temperature of ~ 50 ° C for 8 hours were repeated sequentially 8 times. At the end of the preparatory work, the achieved result was also verified by measuring the permeability of through microdefects for helium at a pressure drop of 4 kgf / cm ² .

The results are shown in the table.

As you can see, the efficiency and reliability of the operation of preparing the products for tightness control when performing work according to the second option (in accordance with the proposed new method of preparation) is much higher in comparison with the preparation using traditional technology.

Practical application of the proposed method in the manufacture of fuel tanks of liquid rockets, spacecraft will provide a high level of their tightness when operated in a charged state for many decades.

Claims (1)

A method of preparing a fuel tank for tightness control, in which the tank is placed in a sealed chamber, atmospheric air is removed from the chamber and tank volumes by a vacuum pump and then the surfaces of the tank are treated with solvent supplied through nozzle devices, provided that the flow rates of the solvent supplied and removed from the volumes are equal, characterized in that at the first stage of the preparation process, the surfaces of the container are treated with jets of solvent heated to an acceptable temperature with flow rate, ensuring removal of surface contaminants and heating the tank to the temperature of the supplied solvent in a technologically established time, and at the next stage, operations of exposure to the surface of a finely droplet-sprayed solvent are periodically alternated with a total flow rate ensuring the maintenance of the laminar-flowing film of the solvent on the tank surfaces, with operations vacuum drying, and the total duration of the operations of periodic processing τ _about , without taking into account the total time spent on removal e from the tank of residual liquid and vapor phases of the solvent before each operation of vacuum drying,
τ _about = τ _e + τ _vl + τ _p ,
Where
τ _e is the required total duration of removal from the channel of the through micro-density of soluble clogging impurities by solvent extraction;
τ _is - removing the necessary total length of the channel through mikroneplotnosti capillary moisture by vacuum drying;
τ _p - the required total duration of removal from the channel of the through micro-tightness of the solvent during vacuum drying;
with the duration of each period of exposure to solvent and vacuum drying
$${\tau }_i=\frac{{\tau }_o}{n},$$

Where
n is the total number of exposure periods assigned from the condition:
$$n\le \frac{{\tau }_o-{\tau }_{\mathrm{uh}}}{{\tau }_{\mathrm{at}d}},$$

Where
τ _beats - the duration of removal from the volumes of residual liquid and vapor phases of the solvent before each operation of vacuum drying;
the duration of the solvent treatment τ _ie and vacuum drying τ _io in each period are determined
$${\tau }_{i\mathrm{uh}}=\frac{\tau {}_{\mathrm{uh}}}{n}$$

;
$${\tau }_{io}=\frac{{\tau }_{\mathrm{at}l}+{\tau }_R}{n}.$$