RU2523056C1 - Method of checking leak-tightness - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: container is filled with a working or control medium (liquid or gas). Pressure of the medium is raised to a test value and held to allow the medium that has penetrated micro-leaks of the inner casing to accumulate in the interlayer space. Concentration of the accumulated medium is then measured through check holes lying uniformly on the surface of the outer casing. An estimate of the overall leakiness of the inner casing is calculated. The area of location of an end-to-end micro-defect is predefined as a region bounded by check points where the measured concentration of the control or working medium assumes a maximum value.

EFFECT: high efficiency and reliability of checking.

2 cl, 1 dwg

Description

The invention relates to the field of mechanical engineering, namely to testing equipment. In recent years, the construction of the fuel tanks of aircraft (rockets, aircraft, spacecraft) uses two-layer shells fastened with honeycomb spacers. In addition to the weighty perfection of such structures, such positive qualities as increased strength, rigidity, resistance to axial compressive loads, increased bearing capacity, etc. are achieved.

For containers made of two-layer shells, the inner shell is always crucial in achieving the required degree of tightness. Therefore, an effective technology for checking its tightness in the general manufacturing process is so important.

A number of known methods for checking the tightness of products, for example, GOST 24054-80, GOST P 51780-2001.

Also known is a method of monitoring the tightness of the inter-wall space of double-walled tanks by continuously monitoring the inert gas pressure drop in the inter-wall space using appropriate sensors according to TU 4575-001-81017117-2007. Such methods of tightness control do not have high sensitivity.

Known methods for monitoring the tightness of fuel tanks, namely, that the product is placed in a test chamber, its volume is filled with a control medium (gas, liquid or its vapor), the pressure rises to the pressure of the working medium, an exposure is made to accumulate molecules penetrating through the leakage of the container shell medium, and the concentration of the control medium accumulated during the exposure time in the volume of the test chamber, assess the degree of leakage (see OST 92-1527-89 "Products of the industry. Test methods leak test using mass spectrometric leak detectors ”).

Such methods cannot be implemented when testing the tightness of containers made of two-layer shells, since the penetrating control medium will accumulate primarily in the interlayer space. Moreover, due to the fact that the distribution of control medium molecules between the layers will be carried out by the diffusion mechanism, with prolonged accumulation, the concentration of control medium molecules in the interlayer space will be extremely uneven: maximum in the outflow region, minimum or zero at a sufficient distance from the outflow site.

The invention should allow the assessment of the flow of penetrating through end-to-end micro-densities of the control medium based on discrete information on the field of its concentration in the interlayer space.

The objective of the invention is to develop a method for monitoring tightness, which allows to evaluate the degree of general leakage of a two-layer shell of fuel tanks according to the test results, as well as to localize the place of a defect.

The problem is solved due to the fact that in the proposed method of leak testing of fuel tanks made of two-layer shells fastened with honeycomb spacers, the tank volume is filled with a working or control medium (liquid or gas), the pressure of the filling medium rises to a test value , an exposure is made to accumulate in the interlayer space penetrating through the micro-tightness of the inner shell of the medium, and then through the control holes uniformly located on surface of the outer shell, the concentration measurements performed accumulated medium C _i, g / dm ^3, wherein the duration of accumulation medium penetrating into the interlayer space τ _n is determined by the ratio

, с, $${\tau }_n\ge \frac{V_m\cdot C_{\min }}{{\text{Q}}_{\text{additional}}}$$

, from,

where Q _add - the permissible value of the general leakage of the inner shell, g / s;

V _m - the volume of the interlayer space of the shell, dm ³ ;

C _min - the sensitivity of the recording equipment to the concentration of the penetrating medium in the gas filling the intershell cavity, g / dm ³ ;

and an estimate of the degree of general leakage of the inner shell Q _{0 is} calculated by the ratio:

, г/с, $$Q_0=\frac{V_m}{{\tau }_n}\cdot \frac{\mathrm{one}}{n}{\displaystyle \sum _{i=\mathrm{one}}^n{C}_i}$$

g / s

where n is the total number of control points for the concentration of the penetrating medium in the interlayer space, units;

is selected based on the size of the tank, the conditions for ensuring the necessary measurement accuracy Q ₀ , the necessary accuracy of the preliminary determination of the location zone of the microdefect leakage;

in addition, preliminarily, the zone of location of the through microdefect is set as the region bounded by the control points at which the measured concentrations of the control or working medium have maximum values.

To accurately determine the location of the microdefect, the pressure of the control gas is applied to the volume of the interlayer space of the shell, and leak detection is performed by known methods on the inner surface of the shell.

Distinctive features of the proposed method of tightness control are the following:

- regulated by a specific ratio, the duration of the penetration of the penetrating medium in the interlayer space τ _n ;

- the methodology for calculating the degree of general leakage of the inner shell Q ₀ ;

- the ability to determine the location of the microdefect is established.

Analysis of the known technical solutions in the art shows that the proposed method has features that are not found in the known technical solutions, and using them in the claimed combination makes it possible to obtain a new technical effect: the justification of a well-controlled, reliable and highly sensitive technology for testing products on tightness minimized by the cost of necessary funds and labor.

The practical implementation diagram of the proposed method of tightness control is shown in the drawing.

Capacity 1 is made by welding from two-layer shells containing an internal airtight 2 and external power 3 shells, which are fastened together by spacers 4. On the outer shell there are control holes 5 that provide the possibility of local sampling of gas filling the inter-shell cavity 6. Moreover, if necessary it is possible to seal control holes with technological or standard plugs.

The tightness control of the inner shell, which is crucial in achieving the desired degree of tightness of the tank as a whole, is performed as follows. Test holes on the outer shell are pre-sealed with process plugs. The internal volume of the tank is filled with a control or working medium, the pressure of the medium rises to the operating value, and exposure is made to accumulate penetrating into the intershell cavity through the through leaks of the inner shell of the control or working medium. Excerpted over time:

, с, $${\tau }_n\ge \frac{V_m\cdot C_{\min }}{{\text{Q}}_{\text{additional}}}$$

, from,

where Q _add - the permissible value of the general leakage of the inner shell, g / s;

V _m - the volume of the interlayer space of the shell, dm ³ ;

C _min is the sensitivity of the recording equipment to the concentration of the penetrating medium in the gas filling the intershell cavity, g / dm ³ .

Then sequentially removing technological plugs, gas samples are taken from each control hole, and the content of the control or working medium in each of the samples is evaluated.

Assess the degree of general leakage of the inner shell Q ₀ , which is calculated by the ratio:

, с, $$Q_0=\frac{V_m}{{\tau }_n}\cdot \frac{\mathrm{one}}{n}{\displaystyle \sum _{i=\mathrm{one}}^n{C}_i}$$

, from,

where n is the total number of control points for the concentration of the penetrating medium in the interlayer space, units

The number of control points is set based on the dimensions of the tank, as well as the conditions for ensuring the necessary measurement accuracy Q ₀ , the necessary accuracy of the preliminary determination of the location of the microdefect leakage.

If the measured value of Q ₀ exceeds the permissible degree of general leakage of the inner shell, pre-set the zone of location of the through microdefect as the area bounded by the control points at which the measured concentrations of the control or working medium have maximum values.

The pressure of the control or working medium in the tank volume is reduced to atmospheric value, the medium is removed and the volume is ventilated to remove residual liquid and vapor phases. To accurately determine the location of the defect, the control holes are again sealed with technological plugs, the intershell cavity is filled with the control gas, its pressure rises, after which the leak detection is carried out by the inspection of the inner surface of the shell in the pre-installed defect location zone, and the exact location of the defect is determined.

Practical application of the proposed method will provide high efficiency testing the tightness of products made from two-layer shells, for example, fuel tanks of rocket and space technology, aircraft. The use of the claimed device provides a high level of tightness and reliability of such products.

Claims (2)

1. The method of monitoring the tightness of containers made of two-layer shells fastened with honeycomb spacers, which consists in the fact that the volume of the tank is filled with a working or control medium (liquid or gas), the pressure of the filling medium rises to a test value, exposure is made to accumulate penetrating in the interlayer space through micro-leaks of the inner shell of the medium, and then through the control holes uniformly located on the surface of the outer shell, concentration measurements are performed the accumulated medium C _i , g / dm ³ , and the duration of the penetration of the penetrating medium in the interlayer space is τ _n

, c,
where Q _add - the permissible value of the general leakage of the inner shell, g / s;
V _m - the volume of the interlayer space of the shell, dm ³ ;
C _min is the sensitivity of the recording equipment to the concentration of the penetrating medium in air, g / dm ³ ;
and the assessment of the degree of general leakage of the inner shell Q _{0 is} calculated by the ratio

g / s
where n is the total number of monitoring points of the concentration of the penetrating medium in the interlayer space, units, is selected based on the size of the tank, the conditions for ensuring the necessary measurement accuracy Q ₀ , the necessary accuracy of preliminary determination of the location zone of the microdefect leakage;
in addition, preliminarily, the zone of location of the through microdefect is set as the region bounded by the control points at which the measured concentrations of the control or working medium have maximum values. 2. The method according to claim 1, characterized in that for the accurate determination of the location of the microdefect in the volume of the interlayer space of the shell pressure of the control gas is supplied and leak detection is performed on the inner surface of the shell.