Tightness calculation. Estimated determination of the standards of tightness of vessels and apparatuses. Compression force calculation

UDC 517.958: 532.5, 621: 007

SOFTWARE MODULE FOR CALCULATION OF LEAKAGE

BASIS OF AXISYMMETRIC SEALS BASED ON

FINITE ELEMENT MODEL

A mathematical model of the flow of a liquid medium in axially symmetric end seals is presented, taking into account both the waviness and roughness of the working surfaces. A software module for calculating the leakage of the working environment based on finite element modeling is proposed. The results of model experiments are shown, showing the adequacy of the use of this scheme for calculating the tightness of compounds.

Key words: axially symmetric mechanical seals; tightness calculation; software module; finite element model.

One of the most important problems in the design of elements of new technology in mechanical engineering, machine tool building, power machine building, and in the aviation and aerospace industry is the problem of isolating working media and ensuring a given degree of tightness of various devices, vessels, pipe fittings, etc. To solve this problem, they use a large a variety of sealing devices, as a rule, structurally simple, but often playing a decisive role in ensuring the reliability of the product as a whole. One of the characteristic types of sealing devices, combining many of the most common properties and performance characteristics, are metal-metal seals (Fig. 1). Such seals are widely used in many industries.

Fig. 1.   Types of metal-metal seals by contact shape:a   - flat; b - conical; in - linear;


g - conical spherical;R, l, d   - curvature radius, girdle width and seal working diameter

By the specifics of the sealing mechanism, these compounds are contact-type, and their performance is determined by the complex nature of the influence of the geometric and physico-mechanical parameters of the working surfaces on the dynamics of their contact interaction. The complex structure of the joint, on the other hand, creates certain problems for the mathematical description of the movement of working media in compounds.

The aforementioned led to the fact that up to the present, a unified theoretical model and algorithms for calculating the leakage of working media in sealed joints have not been developed, taking into account the real topography of the working surfaces of the joint of the joints and the conditions of their operation.

The lack of design models leads to the need for a long and laborious experimental selection of materials, technological methods of manufacturing and assembly for each new sealable compound, which significantly lengthens and increases the cost of the preparatory stage of production and prevents the development of CAD.

The article proposes a model of the working fluid flow in axisymmetric metal-metal seals using the parameters of the actual topography of the surfaces being sealed. The calculation is based on the finite element method implemented for the Reynolds equation in polar coordinates.

Formulation of the problem. The model of the working fluid flow in the seal, taking into account the effect of roughness, can be described by the equation for the pressure field of a liquid medium in thin layers obtained by Patir and Zhen in the conditions of the Reynolds approximation:

https://pandia.ru/text/79/265/images/image006_1.gif "width \u003d" 211 height \u003d 23 "height \u003d" 23 "\u003e,

where https://pandia.ru/text/79/265/images/image008.gif "width \u003d" 52 "height \u003d" 23 "\u003e, are the undulations of the lower and upper working surfaces of the seal relative to the middle planes, respectively; is the gap between medium wavy planes (constant value); - clearance in the seal, taking into account the topography of the waviness; https://pandia.ru/text/79/265/images/image013.gif "width \u003d" 49 "height \u003d" 21 src \u003d "\u003e - pressure in the channel formed by the gap. To calculate the function EN-US "\u003e

where https://pandia.ru/text/79/265/images/image016_0.gif "alt \u003d" (! LANG: Signature:" align="left" width="241 height=255" height="255">!}

Here is the annular region; - trial function satisfying the following boundary conditions:

where https://pandia.ru/text/79/265/images/image025.gif "width \u003d" 16 "height \u003d" 24 src \u003d "\u003e are the radii of the outer and inner borders of the seal, respectively (Fig. 2).

The region is represented as a finite element model ..gif "width \u003d" 229 height \u003d 25 "height \u003d" 25 "\u003e, font-size: 14.0pt"\u003e - a separate final element; - generalized parameters depending on the element .. gif "width \u003d" 21 "height \u003d" 25 src \u003d "\u003e and font-size: 14.0pt"\u003e,

where https://pandia.ru/text/79/265/images/image039.gif "width \u003d" 21 "height \u003d" 24 "\u003e is an elementary contribution to the functional

.

After substituting the expression for the trial function, the expression for the elementary contribution is transformed to

where https://pandia.ru/text/79/265/images/image043.gif "width \u003d" 69 "height \u003d" 28 "\u003e, are the coefficients expressed in terms of the coordinates of the element nodes.

At the minimum point, the derivatives of the functional with respect to each nodal value vanish:

where w, s, t  - numbers of grid nodes included in the element e. The integral in the expression can be calculated numerically.

The resulting dependencies are summed up and equal to zero. Together, they form a system of linear equations:


where https://pandia.ru/text/79/265/images/image049.gif "width \u003d" 25 "height \u003d" 23 "\u003e. gif" width \u003d "23" height \u003d "23 src \u003d"\u003e) and internal () boundaries are calculated by the following relationships:

https://pandia.ru/text/79/265/images/image055.gif "width \u003d" 200 "height \u003d" 52 "\u003e. gif" width \u003d "25" height \u003d "21 src \u003d"\u003e - grid step by angular coordinate; - the number of partitions in the angular coordinate; - the number of partitions in the radial coordinate; https://pandia.ru/text/79/265/images/image061.gif "width \u003d" 39 "height \u003d" 25 src \u003d "\u003e - pressure value at the nodal point on the last inner circle; EN-US"\u003e MSIU RondWave 2D (software product registration certificate No.). Built in this way, it allows you to analyze the tightness of the connection immediately immediately after the measurement of the waviness of its working surfaces.

The module is called from the “Modeling” item of the main menu of the agro-industrial complex control program (Fig. 4). When starting the simulation process, the parameters window of the model under study initially opens (Fig. 5) .. gif "width \u003d" 21 "height \u003d" 23 "\u003e. Gif" width \u003d "24" height \u003d "23"\u003e - the guaranteed gap between the maximum peak unevenness of one working surface and maximum peak unevenness of the second working surface; - discretely defined function characterizing the effect of roughness.

font-size: 10.0pt "\u003e Figure 4.   Built-in module for numerical simulation

The roughness influence functions (flow coefficients) are calculated by the previously developed software package and exported to this software module. Each function is a text file located in a folder functions. The first line of these files contains the number of points at which the function is set. The following lines contain pairs of values \u200b\u200b- the gap and its corresponding value, separated by a space. In the intervals between the set values \u200b\u200bof the gap, the function is interpolated linearly. At the boundaries it is interpolated by constant functions and, respectively, for the upper and lower boundaries in terms of the gap https://pandia.ru/text/79/265/images/image074.gif "alt \u003d" (! LANG: Signature:" align="left" width="390 height=385" height="385">Информация о топографии волнистости поверхности соединения, а также о его геометрических размерах задается через основную программу комплекса MSIU RondWave 2 D .!}

After entering the parameters of the test compound, finite element modeling is carried out, as a result of which a report on the tightness of the joint is formed (Fig. 6). The report includes a map of the pressure distribution inside the gap between the working surfaces of the connection, the scheme and parameters of the connection, the total leakage of the working medium and a graph of the distribution of local leaks along the angular coordinate.

Fig. 6 . Connection Leakage Report


Checking the accuracy of leak calculations through axisymmetric end connections using a software module. To verify the adequacy of the developed model, a series of model experiments was carried out to study leaks in absolutely smooth axial-symmetric mechanical seals. For such compounds, there are analytical methods for finding volumetric leaks. Comparison of the results obtained by analytical calculations with the results of numerical modeling allows us to determine the adequacy of the software package.

The following analytical model is proposed for calculating leakage through axisymmetric seals:

, (2)

where https://pandia.ru/text/79/265/images/image078.gif "width \u003d" 16 "height \u003d" 15 "\u003e is the angular velocity of rotation of the joint. Given that the joint is stationary, equation (2) takes the form

.

All model studies were conducted for diesel fuel grade A, which has the characteristics presented in table. 1. The gap in the compound ranged from 1 to 2 microns. The calculation was performed without taking into account the effect of roughness (a single function 624 "style \u003d" width: 467.8pt; margin-left: 5.4pt; border-collapse: collapse; border: none "\u003e

Parameter

Designation

measuring

Accepted

the values

Pressure outside seal

1 · 105

Pressure inside seal

The radius of the outer border of the seal

The radius of the inner boundary of the seal

2.5 · 10-2

Clearance between seal faces

1 · 10-6; 1.2 · 10-6;

1.4 · 10-6; 1.6 · 10-6;

1.8 · 10-6; 2 · 10-6

The coefficient of dynamic viscosity of the working environment

kg / (m·from)

Comparison of the results of numerical modeling (https://pandia.ru/text/79/265/images/image052.gif "width \u003d" 23 "height \u003d" 23 src \u003d "\u003e) with analytical leaks showed that the difference between them is not more than 0.5%. The results of the study in the form of the dependence of leaks on the average gap are shown in Fig. 7. Thus, it was shown that this software package satisfies the analytical model for the simplest cases of compounds.

Numerical modeling of the effect of undulation on the tightness of a joint.To study the effect of undulation on the tightness of compounds, a numerical study was performed. As the object of study, a model compound was selected that has the characteristics indicated in the table. 2. The upper working surface was taken perfectly flat. Since the purpose of the experiment was to determine the degree of influence of surface undulations on leaks, the roughness influence coefficient was assumed to be constant and equal to unity.

Guaranteed joint clearance hΔ was defined as the distance between the maximum peak of the lower working surface and the plane of the upper working surface. The equivalent gap in a smooth joint was calculated as the distance from the plane of the upper surface to the middle plane of the lower surface. Calculations were performed for values hΔ: 1; 2; 3; 5; 8; 10; 15 and 20 microns. Equivalent gaps in the smooth compound corresponded to them: 9.68; 10.68; 11.68; 13.68; 16.68; 18.68; 23.68 and 28.68 microns.

table 2

Characteristics of the experimental model seal

Parameter

Designation

measuring

Value

Pressure outside seal

1 · 10 5

Pressure inside seal

5 · 10 5W a, the calculation method without taking into account the waviness leads to a 20% error. At lower values hΔ this error can increase sharply. In turn, with a large increase in value hΔ it gradually decreases.

The results of the study are shown in Fig. .Gif "width \u003d" 31 "height \u003d" 25 src \u003d "\u003e - in conjunction with smooth walls.

font-size: 12.0pt "\u003e The considered model of the flow of the working medium in axisymmetric metal-metal seals using the parameters of the real topography of the sealed surfaces can find practical application in the design of these seals, the appointment of technological methods for their manufacture using modern CAD systems. Based on this model, developed software package that allows you to quickly and efficiently assess the tightness of mechanical seals.

List of references

1. Patir, N. An Average Flow Model for Determining Effects of Three-Dimensional Roughness on Partial Hydrodynamic Lubrication / N. Patir, H. S. Cheng // ASME Journal of Lubrication Technology. - 1978. - Vol. 100. - No. 1. - P. 12-17.

2. Sheipak, AA Application of finite element method (FEM) for calculation of flow factors in seals / AA Sheipak, VV Porohsyn, DG Bogomolov // Abstracts of papers from 2nd world tribology congress (Vienna, Austria, September 3 - 7, 2001) . - P. 173-174.

3. Norrie, D. Introduction to the finite element method / D. Norry, J. de Vries. - M .: Mir, 1981. - 304c.

4. Kondakov, and sealing equipment: reference book,. - M.: Mechanical Engineering, 1986.- 464 p.

5. Poroshin, a software package for three-dimensional analysis of the waviness of the surface of parts in mechanical assembly production /, // Assembly in mechanical engineering, instrument making. - M.: Engineering, 2006. - No. 12.

V.T. Barchenko, M.L. Vinogradov

St. Petersburg State Electrotechnical University "LETI" (SPbGETU), ul. Professors Popov, 5, St. Petersburg, 197376, Russia,, This email address is being protected from spambots. You must have javascript enabled to view it.

This article provides a method for determining the tightness rate for a vacuum product and calculating the time dependence of the pressure change in the device in the presence of a leak. The ratio of helium leakage flows and tightness for various types of penetrating substances is presented. Shows the latest parting for the organization of control tightness in enterprises.

Portable helium leak detector provides reliable registration of helium flow up to 1. 10 -7 Pa. m 3 / s (7.6. 10 -4 l. μm mercury column / s).

Like large-sized stationary leak detectors, the portable leak detector has a function of zeroing the background, which serves to bind the concentration of helium in the room to zero, and allows leak testing independently of a constant helium level near the object.

Consider a graph of the statistical distribution of leaks detected when working with helium leak detectors. The graph shown in Figure 2 is superimposed on the sensitivity ranges of a portable leak detector in professional and standard versions.


Figure 2. Statistical distribution of the number of detected leaks of various streams

An analysis of this statistical distribution allows us to conclude that the absolute majority of real through leakages that need to be detected during leak testing are in the sensitivity range of a portable helium leak detector.

Leak flow 10 -9 mm Hg . l / s and less due primarily to:

o the permeability of vacuum seals,

o gas diffusion and conductivity through the materials of products (for example, through polymers),

o desorption and evaporation from the inner walls of the product.

Leakage due to the listed reasons should be prevented at the stage of design development and selection of product materials, as well as by preparing the product for testing according to the methods described in. For further leak tests, leak with a flow of 7.5. 10 -7 mmHg Art. . l / s and more can be detected using a portable helium leak detector.

Manometric leak detector for integrated leak testing

Manometric leak detector - an automatic leak detector for monitoring the tightness of products, providing a measurement of total leakage up to 10 -4 Pa. m 3 / s and higher.

The leak detector is equipped with two types of sensors: pressure and gas flow. The vacuum system of the leak detector is constructed in such a way that it is possible to implement manometric, vacuum and pressure tightness control methods, as well as leak detection for measuring gas flow.

Figure 3. Leak detectors: a - portable helium, b - manometric

Leak detection principles implemented in this device are divided into two types.

1) Leak detection by rising or falling pressure. Gauge and vacuum methods are used to determine the total leakage. The manometric method is suitable for enclosed structures in which pressure above atmospheric pressure can be created. Vacuum - for enclosed structures in which a vacuum can be created.

The principle of calculating the leakage flow is based on controlling the rate of change of pressure in the monitoring object. A sealed reference volume is installed in the device, separated from the measured object by a membrane that is sensitive to differential pressure. The leak detection method for measuring differential pressure is that both the object and the reference volume are pumped out or filled with gas to the same pressure.

If there is a leak in the test object, the pressure balance is violated and the membrane separating the volumes is deformed. By changing the capacitance of the capacitor, one membrane of which is the specified membrane, is made about the magnitude of the leak in the test object.

2) Leak detection for measuring gas flow. The device measures the amount of air that enters the object in the event of a leak. Tests are carried out using a gas flow sensor. The device is calibrated using a control leak, installed a special port of the leak detector, and an external gas flow meter.

Literature

1. Loktev I.I. / Control of large and small leaks in fuel elements // Vacuum equipment and technology, volume 10, No. 3, 2000

2. The US Particle Accelerator School Vacuum Fundamentals, Lou Bertolini, Lawrence Livermore National Laboratory, January 19, 2004

3. OST 5.0170-81. Non-destructive testing. Metal constructions. Gas and liquid tightness control methods.

4. PNAE G-7-019-89. Unified control method for basic materials (semi-finished products), welded joints and surfacing of equipment, and NPP pipelines. Tightness control. Gas and liquid methods.

When analyzing the performance of various products in the chemical or oil and gas industries, problems arise of studying the tightness of sealing elements. This article describes an approach to numerically modeling the tightness of a sealing ring using the finite element method.

O-rings are often used to ensure the tightness of structures, for example, they are installed at the joints of piping components. Sealing elements are often made of hyperelastic materials, for example, rubber. Such materials exhibit elastic behavior during large deformations, that is, their stress-strain state depends only on the actual state of the body, and both stress and strain are expressed through the potential energy of elastic deformation. The form of the potential energy function is specified when choosing a particular material model in the calculation. There are various models: polynomial, Muni-Rivlina, neo-Gukovskaya and others, all of these models are presented in the ANSYS finite element package, which is used for calculation. The deformation diagram of such materials is essentially nonlinear, Figure 1 shows an example of the dependence of stress on deformation for a hyperelastic material.

Figure 1 - An example of a deformation diagram for a hyperelastic material

To determine the parameters of the models, field tests are carried out. The following experiments are commonly used: uniaxial tension / compression, biaxial tension / compression, plane tension / compression, volumetric tension / compression. The obtained experimental data in the form of a dependence of engineering stresses on engineering deformations can be processed by ANSYS internal tools, for example, Curve Fitting Tool. This tool allows the least squares method to calculate the parameters necessary for approximating the strain diagram to determine the function of the potential energy of elastic deformation.

After selecting and calibrating the material model for the seal, the tightness calculation is performed. During operation of the product, the tightness of which must be ensured, the seal is in a compressed state. This condition is often achieved by preloading the sealing element. It should be noted that since the properties of the sealant material are substantially non-linear during compression, this is why it is necessary to use non-linear models.

As an example, the task of studying the tightness of a sealing ring installed in a special groove in a steel part is considered. In the initial state, the height of the seal is greater than the height of the groove for the subsequent creation of a preload in it. The problem is considered in a two-dimensional axisymmetric formulation. Figure 2 shows the cross section of the seal, on the left is the inside of the seal, on the right is the outer.

Figure 2 - Cross section of the seal

The tightness calculation is carried out in a static setting with two loading steps. At the first step, the seal is shrunk between the metal surfaces of the groove, that is, the contact problem is solved. In the second step, the influence of the medium (for example, liquid) on the sealant is set. To do this, use the Fluid Pressure tool.

A Fluid Pressure type load simulates the action of a fluid or gas that surrounds the body being examined and can penetrate between contacting bodies. This load can be set both between deformable bodies and between solid and deformable. The problem statement can be two-dimensional and three-dimensional.

The area of \u200b\u200bapplication of the load is determined in the calculation process at each iteration. At the beginning of the iteration, the algorithm determines the starting points to which the load is applied. For the first iteration, the start points are set by the user. Then, the points at which the penetration criterion is met are determined, and the liquid pressure is applied to them, and their nodes closest to these points become the starting points for the next iteration, this process is repeated until the calculation is completed. In this case, a connected area is always constructed containing a starting point, therefore, for example, if there is a surface with an open contact status on the body under study, but there are no starting points on this surface, then the load will not be applied to it.

Penetration criteria are used to determine the area of \u200b\u200bapplication of the load. Two types of criteria are possible:

Contact status - in the case of an open contact status, liquid penetrates;

Contact pressure - if the contact pressure between the test bodies is lower than specified by the user, then liquid penetrates; permissible pressure can be determined in the form of a tabulated function depending on the loading step.

In the considered problem, a liquid under a pressure of 5 MPa enters the internal cavity of the sealant, therefore, the node on the left side of the sealant is selected as the starting point. Figure 3 shows the distribution of fluid pressure on the seal obtained using Fluid Pressure.

Figure 3 - Distribution of fluid pressure, MPa

The pressure distribution shows that the fluid is applied only from the inside of the seal, that is, no leakage occurs, and tightness is ensured.

When analyzing the health of the product, you can add additional design steps to take into account the loads acting on the structure, and you can modify the penetration criterion to take into account the gradually changing pressure of the medium.

When designing sealed products, two tasks arise: the calculation of the compression force, which ensures the tightness of the connection, for example, the case and cover (with a gasket between them), and the calculation of gas leakage through the connection.

Compression force calculation

The absence of sound mathematical models for the depressurization of bulk compounds does not allow us to accurately determine the compression pressure, taking into account the properties of the medium, the material of the gaskets and the characteristics of the microgeometry of their surface. Therefore, empirical formulas for determining the compression pressure have become widespread. They are valid only in the range of variation of the parameters in which the experiments were performed.

Knowing the necessary compression force you can determine the tightening force of the connection, for example, screws tightening the gasket between the cover and the housing.

Leak calculation

When calculating leakage (leakage rate) through a seal, two models are used. One of them is a leak through round capillaries, the other is a laminar flow through a flat gap (Poiseuille formula). The calculations made on these models diverge from practice, as the latter do not take into account factors such as contact pressure, characteristics of the surface microgeometry, as well as the physicomechanical properties of materials of components to be sealed, etc. Meanwhile, not all factors affect the leakage to the same extent; therefore, for each case, many authors processed the experimental results and obtained empirical formulas, the calculations of which give good convergence with practical data.

Statistical average slot height and contact pressure R to  providing normal seal gaskets are related by

where R- a parameter characterizing the ability of a material to compact surface microroughnesses. Leak through an elastomer seal is equal.

Conductivity (leakage per unit differential pressure and perimeter of the sealing surface B)

Here FROM 0 - conductivity in the absence of the introduction of the gasket in the microroughness of the sealing surface.

Formulas 1-3 are valid for gases that do not create obliteration, which reduces leakage due to overgrowing of the gap.

Gas leakage through the gap between the gasket and flanges for the best elastomers ranges from 8 · 10 -6 ... 4 · 10 -11 Pa · cm 3 / s (8 · 10 _6 ... 4 · 10 -11 atm cm 3 / s) per 1 cm of the gasket length and depends on its material and temperature,

Mass gas flow through leakages in the joint of a sealed connection (4)


where R and - . gas pressure in the product,

R 0 - environmental pressure;

R- gas constant

h 0 - average slot height in the absence of contact pressure at the junction;

TO 0 - the Kozen constant, depending on the shape of the cross section of the gap (for a round gap To=2);

t is the tortuosity coefficient ();

- viscosity of the condensed medium (gas);

T-absolute temperature;

Accordingly, the outer and inner radii of the sealing surfaces;

(t \u003d 1,2) - the highest height of the roughness profile of the sealing surfaces;

Sm  - average step of profile irregularities (GOST 2789-73);

Ra- arithmetic mean deviation of the profile;

Coefficient of proportionality;

The coefficient characterizing the physico-mechanical properties of the material of the sealing surfaces;

M i - Poisson's ratio of the material,

E i - modulus of elasticity of the material;

r- the average radius of curvature of the vertices of microroughness $

in 1   - the total parameters of the reference curves of the contacting surfaces;

Reference curve parameter

- gamma function.

The requirement for a high degree of tightness of microassemblies, for example, housings of semiconductor devices and IPinextricably linked to ensuring their reliability and durability.

As a result of leaks, moisture, corrosive substances, as well as foreign particles, which will cause damage to individual elements of the microassembly or short circuit, can get inside the case.

The tightness of the cases of microassemblies is very high and the mass flow rate can reach 10 -8 ... 10 -9 cm 3 / s. For comparison, we indicate that through a hole with a diameter of 10 μm, the gas flow rate is 5 · 10 -9 cm 3 / s. When reducing the diameter of the hole to 0.1 μm, the gas flow rate decreases by four orders of magnitude and is 5 · 10 -13 cm 3 / s. The ego causes great difficulties in choosing methods and means for checking the tightness of microassemblies, especially in mass production. Of the existing control methods, the gas distribution (with the help of a helium leak detector) was obtained.

As practice has shown, the leakage of the microassembly bodies depends not only on the pressure of the indicator gas that is being tested, the time it takes to continue this pressure, the time interval after the pressure has been removed, but also on the size of the internal (free) volume of the test case for tightness of the case.

For accurate estimation of helium leakage from measurement results

where R -measured leak, atm · cm 3 / s;

L  - equivalent standard leak, atm · cm 3 / s;

- molecular weight of air and tracer gas, respectively;

t 1 - time under pressure

t 2 - exposure time before measurement after depressurization;

U -body volume, cm 3.

RD 26.260.011-99

GUIDING DOCUMENT

GUIDELINES

CALCULATED DETERMINATION OF LEAKAGE STANDARDS
  VESSELS AND APPARATUSES

APPROVAL SHEET

RD 26.260.011-99

GUIDELINES

CALCULATED DETERMINATION OF VALVES AND VALVES OF VESSELS AND VEHICLES

General Director
   VNIIIPTkhimnefteapparatury ________________________

V.A. Panov

Department Head
   Standardization ______________________________________

V.N. Zarutsky

Head of Department No. 29 _____________________________

S.Ya. Luchin

Head of Laboratory No. 56 ________________________

L.V. Ovcharenko

Development Manager
   Senior Researcher ___________________________

V.P. Novikov

Process engineerII   cat. ______________________________

N.K. Lamina

Standardization EngineerI   cat. ______________________

BEHIND. Lukina

AGREED

Deputy CEO
   on research and production activities
NIIKHIMMASH OJSC ____________________________

V.V. Crayfish
Foreword

1. DEVELOPED by OJSC “Volgograd Scientific Research and Design Institute of Technology of Chemical and Oil Apparatus Engineering” (OJSC “VNIIPTkhimnefteapparatury”).

2. APPROVED AND INTRODUCED BY TECHNICAL COMMITTEE No. 260 “Chemical and Oil and Gas Processing Equipment” with the Approval Sheet dated June 24, 1999

3. SUBSTITUTE “Methods of calculation determination of norms of tightness of vessels and apparatuses”.

4. RELEASED 2000 July with AMENDMENT No. 1, approved Approval Sheet of June 27, 2000

GUIDING DOCUMENT

GUIDELINES

CALCULATED DETERMINATION OF VALVES AND VALVES OF VESSELS AND VEHICLES

Date of introduction 1999-07-01

1 AREA OF USE

This guidance document is intended to establish standards in the design and leak testing of vessels and apparatuses manufactured in accordance with OST 26-291 and can be used for any other equipment controlled by the State Technical Supervision Service of Russia, subject to the requirements of PB 03-108, PB 09-170, PB 10-115, SNiP 3.05.05.

2. REGULATORY LINKS

References to the following standards, rules, and other sources have been used in this guidance document:

One of the main indicators that determine the hazard class of a substance according to GOST 12.1.007 is its maximum permissible concentration in the air of the working zone, determined according to GOST 12.1.005.

3.2. During normal operation of equipment and ventilation, the content of harmful substances in the air of the working area should be less than or equal to the maximum permissible concentration of these substances in accordance with GOST 12.1.005.

When installing technological equipment in an open area, which is typical for most oil and gas refineries, ventilation of the working area depends on the atmospheric conditions on the territory of the enterprise and the physical properties of the hazardous substance released.

3.3. The tightness rate of a vessel, apparatus in accordance with GOST 26790 is defined as the largest total consumption of a substance through leaks, ensuring the operational state of the vessel, apparatus and established by the normative and technical documentation for this vessel, apparatus.

The tightness rate is measured in units of gas flow:

3.4. During pneumatic testing of vessels, apparatuses and pipelines, the leakage coefficient is determined by the method of pressure drop:

Maximum concentration limit - maximum permissible concentration of a harmful substance in the supply air, mg / m 3 (should not exceed 0.3 maximum concentration limit).

4.2. When entering values \u200b\u200bfrom the formula () into the formula (), we obtain the formula for calculating the tightness rate of the vessel, apparatus installed in the room:

Vp h - the volume of the working area, m 3 (in accordance with GOST 12.1.005, height 2 m, area according to SN 245 not less than 4.5 m 2, therefore the volume is not less than 9 m 3, in the absence of more accurate data).

4.4. Given the formula (), the formula () takes the following form:

In the absence of data on the tightness class of plug-in connections, it is recommended to use the data from the appendix of this guidance document.

Table A.1 - The values \u200b\u200bof the maximum permissible concentration of harmful substances in the air of the working area, depending on the hazard class of this substance according to GOST 12.1.007

In milligrams per meter cubic

Hazard class of harmful substance according to GOST 12.1.007

Maximum permissible concentration of harmful substances (MPC) in the air of the working area

less than 0.1

0,1 - 1,0

1,1 - 10,0

more than 10

Note -   The lower limit of hazard class 1 for calculating the tightness rate of a vessel, apparatus is allowed to take a value of 0.01 mg / m 3

Appendix B

Table B.1 - Values \u200b\u200bof the rate of air exchange for industrial premises

Name of sourceproducts used in production or premises

The rate of air exchange, h -1

Coefficient increases for hot foods

in the absence of sulfur compounds

in the presence of sulfur compounds

Warehouses

compressor

pumping

production

compressor

pumping

production

Ammonia

Acetaldehyde production withmercury catalyst

Butane, hydrogen, methane, propane, butylene,pentane, paraldehyde,propylene, ethane, ethylbenzene, ethylene,cracking gas, crude oil and other substances with a maximum permissible concentration of more than 50 mg / m 3

Selective solvents, ether, leaded gasoline,divinyl acetate dichlorostyrene, vinyl chloride, methylene chloride and other substances with MPC 5 - 50 mg / m 3inclusive

Bromine and other substances with a maximum permissible concentration of 0.5–5.0 mg / m 3

Chlorine, acetylene and other substances with a maximum permissible concentration of 0.5 mg / m 3 or less

Nitric, phosphoric and other acids with maximum permissible concentration of 10 mg / m 3 and less

Natural petroleum gas

Petrol

Ligroin, motor fuel, fuel oil, cracking residue, bitumen (commodity)

Ethylene fluid

at current choking workersplaces

you are heavy

Lubricating oils, paraffin (in the absence of solvents)

Alkaline solutions

Notes 1. This table should be used in the absence of data on the amount of harmful substances released from equipment, fittings, communications, etc.

2. The maximum permissible concentrations of harmful substances in the air of the working area (MPC) must be taken according to the list approved by the Ministry of Health and given in the sanitary standards and in GOST 12.1.005.

3. The indicated air exchange rates take into account the possibility of the content of harmful substances in the supply air of not more than 0.3 maximum permissible concentration.

4. Sulfur is considered to be oil products and gases with a sulfur content of 1% or more by weight.

5. At temperatures of oil, oil products and gases above 60 ° C, the air exchange rates indicated in the table should be increased by the factors given in the last column.

6. The data in this table are fully consistent with the data in the table from the Instructions for the design of heating and ventilation of oil refineries and petrochemical enterprises VSN 21-77.

Appendix B

Table B.1 - Leakage classes of seals and their associated specific leaks *

Class

Specific leakage

Quality (visual) assessment criterion

Typical seal types

Q, mm 3 / (m · s)

V, cm 2 / m 2

Qs, mm 3 / (m · s)

0 - 0

Up to 10 -5

Up to 10 -5

Absolute tightness

Metal bellows, polymer membranes

St. 10 -5

St. 10 -5

0 - 1

Up to 10 -4

Up to 10 -3

1 - 1

" 10 -4

" 10 -3

Faint odor, visually invisible fogging

Rubber membranes, sleeves UN elastomeric

"5 · 10 -4

"5 · 10 -3

1 - 2

"5 · 10 -4

Up to 10 -3

"5 · 10 -3

"5 · 10 -3

"5 · 10 -2

2 - 1

"5 · 10 -3

St. 10 -3

"5 · 10 -2

Leakage without drop formation

HC in heavy duty, elastomeric UPS and HC

"5 · 10 -2

up to 10 -2

"5 · 10 -1

2 - 2

"5 · 10 -2

" 10 -2

"5 · 10 -1 -

Drip leaks

HC end, UPS and HC printed, slotted compensated

4 - 2

"50 - 5 · 10 2

Frequent drops

"5 · 10 2

Continuous leakage

UPS, UV contactless

" 10 3

" 10 3

Note   - For gaseous media insteadQ specific leakage criteriaB -14.

Bss \u003d 0.1V \u003d 1.36 · 10 -5, m 3 · Pa / s,

which also corresponds to the fifth class of tightness according to OST 26-11 -14.

2. The source data

The vessel is designed for a mixture of natural hydrocarbons with a hydrogen sulfide content of up to 25% (MP \u003d 16.4) at a pressure of PP \u003d 2.5 MPa and a temperature of 100 ° C (373 K) and has a volume of 10 m 3; MPCrz - 3 mg / m 3, Kg \u003d 1.

When installed in an open area, the tightness rate of the vessel according to the formula ():

This corresponds to the fifth class of tightness according to OST 26-11 -14.

The tightness rate of the welded joints of the vessel:

Bss \u003d 0.1V \u003d 2.0 · 10 -6, m 3 · Pa / s,

which also corresponds to the fifth class of tightness according to OST 26-11 -14.

 

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