Tightness calculation. Calculated determination of the standards of tightness of vessels and apparatus. Compression force calculation

UDC 517.958: 532.5, 621: 007

TIGHTNESS CALCULATION SOFTWARE MODULE

END 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 waviness and roughness of the working surfaces. A software module for calculating leaks of a working medium based on finite element modeling is proposed. The results of model experiments showing the adequacy of the application of this scheme for calculating the tightness of joints are presented.

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

One of the most important problems in the design of elements new technology in mechanical engineering, machine tool building, power engineering, in aviation and aerospace the problem of isolating working media and ensuring a given degree of tightness of various devices, vessels, pipe fittings connections, etc. ... One of characteristic species sealing devices, combining many of the most common properties and performance characteristics, are metal-to-metal seals (Figure 1). These seals are widely used in many industries.

Rice. 1. Types of metal-to-metal seals by contact form: a - flat; b - conical; в - linear;


g - cone-spherical; R, l, d - radius of curvature, width of the shoulder and working diameter of the seal

According to the specifics of the sealing mechanism, these connections are related to contact, and their performance is determined by the complex nature of the influence of the geometric and physical-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 mathematical description movement of working media in connections.

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

The lack of computational models leads to the need for a long and laborious experimental selection of materials, technological methods manufacturing and assembly for each new sealed joint, 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 medium flow in axisymmetric metal-metal seals using the parameters of the real topography of the sealed surfaces. 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 flow of the working medium in the seal, taking into account the effect of roughness, can be described by the equation for the pressure field of the liquid medium in thin layers obtained by Patir and Zheng under the conditions of the Reynolds approximation:

https://pandia.ru/text/79/265/images/image006_1.gif "width =" 211 height = 23 "height =" 23 ">,

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

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

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

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

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

where https://pandia.ru/text/79/265/images/image039.gif "width =" 21 "height =" 24 "> is an elementary contribution to the functionality

.

After substitution of the expression for the trial function, the expression for the elementary contribution is transformed to the form

where https://pandia.ru/text/79/265/images/image043.gif "width =" 69 "height =" 28 ">, are the coefficients expressed in terms of the coordinates of the element's 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 present in the expression can be calculated numerically.

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


where https://pandia.ru/text/79/265/images/image049.gif "width =" 25 "height =" 23 ">. gif" width = "23" height = "23 src =">) and internal () boundaries are calculated according to the following relationships:

https://pandia.ru/text/79/265/images/image055.gif "width =" 200 "height =" 52 ">. gif" width = "25" height = "21 src ="> - grid step by angular coordinate; - number of partitions by angular coordinate; - number of splits along the radial coordinate; https://pandia.ru/text/79/265/images/image061.gif "width =" 39 "height =" 25 src = "> - pressure value at the nodal point on the last inner circle; EN-US"> MSIU RondWave 2D (registration certificate software product No.). Built in this way, it allows you to analyze the tightness of a joint 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 control program of the APK (Fig. 4). At the start of the modeling process, the window of parameters of the model under study is initially opened (Fig. 5) .. gif "width =" 21 "height =" 23 ">. Gif" width = "24" height = "23"> - the value of the guaranteed gap between the maximum the peak of the unevenness of one working surface and the maximum peak of the unevenness of the second working surface; - discretely given function characterizing the effect of roughness.

font-size: 10.0pt "> Figure 4. Built-in numerical simulation module

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 the folder functions. The first line of these files contains the number of points at which the function is specified. Subsequent lines contain pairs of values ​​- a gap and its corresponding value, separated by a space. The function is linearly interpolated between the specified clearance values. At the boundaries, it is interpolated by constant functions and, accordingly, for the upper and lower boundaries in terms of the gap size https://pandia.ru/text/79/265/images/image074.gif "alt =" (! 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 connection, finite element modeling is carried out, as a result of which a report on the tightness of the connection is generated (Fig. 6). The report includes a map of the pressure distribution inside the gap between the working surfaces of the connection, the diagram and parameters of the connection, the total leaks of the working medium and the graph of the distribution of local leaks along the angular coordinate.

Rice. 6 ... Leak tightness report


Verify the accuracy of axisymmetric end connection leakage calculations using the software module. To check the adequacy of the developed model, a series of model experiments was carried out to study leaks in absolutely smooth axially symmetric end 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 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 =" 16 "height =" 15 "> is the angular speed of rotation of the connection. Taking into account that the connection is motionless, equation (2) takes the form

.

All model studies were carried out for diesel fuel grade A, with the characteristics presented in table. 1. The gap in the joint was varied in the range from 1 to 2 µm. The calculation was carried out without taking into account the effect of roughness (single function 624 "style =" width: 467.8pt; margin-left: 5.4pt; border-collapse: collapse; border: none ">

Parameter

Designation

measurements

Accepted

meaning

Pressure outside the seal

1 · 105

Pressure inside the seal

Radius of the outer edge of the seal

Radius of the inner border of the seal

2.5 10-2

Gap 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

Dynamic viscosity coefficient of the working medium

kg / (m·with)

Comparison of the results of numerical modeling (https://pandia.ru/text/79/265/images/image052.gif "width =" 23 "height =" 23 src = ">) 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 connections.

Numerical modeling of the effect of waviness on the tightness of the joint. To study the effect of waviness on the tightness of joints, a numerical study was carried out. As the object of the study, a model compound was selected with the characteristics indicated in 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 waviness on leaks, the coefficient of influence of roughness was taken constant and equal to one.

Guaranteed joint clearance hΔ was set as the distance between the maximum peak of the lower working surface and the plane of the upper working surface. Equivalent clearance in a smooth joint was calculated as the distance from the plane of the upper surface to the median plane of the lower surface. The calculations were carried out for the values hΔ: 1; 2; 3; 5; eight; ten; 15 and 20 microns. They corresponded to the equivalent clearances in a smooth joint: 9.68; 10.68; 11.68; 13.68; 16.68; 18.68; 23.68 and 28.68 microns.

table 2

Experimental Model Seal Characteristics

Parameter

Designation

measurements

Meaning

Pressure outside the seal

1 · 10 5

Pressure inside the seal

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

The research results are shown in fig..gif "width =" 31 "height =" 25 src = "> - in conjunction with smooth walls.

font-size: 12.0pt "> The considered model of the working fluid flow in axisymmetric metal-metal seals using the parameters of the real topography of the sealed surfaces can find practical use when designing these seals, prescribing technological methods for their manufacture using modern CAD systems. Based on this model, a software package has been developed that allows fast and effective assessment tightness of mechanical seals.

Bibliography

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, 3 - 7 September 2001) ... - P. 173-174.

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

4. Kondakov, and sealing technology: a reference book /,. - M .: Mashinostroenie, 1986 .-- 464 p.

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

V.T. Barchenko, M.L. Vinogradov

St. Petersburg State Electrotechnical University "LETI" (SPbGETU), st. Professor Popova, 5, St. Petersburg, 197376, Russia, This address Email protected from spambots. You need JavaScript enabled to view it.

This article provides a methodology for determining the tightness rate for a vacuumized product and calculating the time dependence of the pressure change in the device in the presence of a leak. The ratio of helium leakage and leakage fluxes for various types of penetrating substances is presented. Shown are the novelties of partings for the organization of tightness control at enterprises.

The portable helium leak detector provides reliable helium flow registration up to 1. 10 -7 Pa. m 3 / s (7.6. 10 -4 liters. μm Hg / s).

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

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


Figure 2. Statistical distribution of the number of detected leaks for different flows

The analysis of this statistical distribution allows us to conclude that the absolute majority of real through leaks, which must be detected during tightness control, fall within the sensitivity range of a portable helium leak detector.

Leaks with a flow of 10 -9 mm Hg. ... l / s and less are primarily due to:

o permeability of vacuum seals,

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

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

Leakages 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. With further tests for tightness, leaks with a flow of 7.5. 10 -7 mm Hg. Art. ... l / s and more can be detected with a portable helium leak detector.

Gauge Leak Detector for Integral Tightness Testing

A manometric leak detector is an automatic leak detector for monitoring the tightness of products, which measures the total leakage up to 10 -4 Pa. m 3 / s and above.

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

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

The principles of leak detection implemented in this device are divided into two types.

1) Leak detection by pressure rise or fall. Gauge and vacuum methods are used to determine the total leakage. The gauge method is suitable for closed structures in which a pressure higher than atmospheric pressure can be created. Vacuum - for closed structures in which a vacuum can be created.

The principle of calculating the leakage flow is based on the control of the rate of pressure change in the control object. The device has a sealed reference volume, separated from the measured object by a pressure-sensitive membrane. The leak detection method for measuring the 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 disturbed and the membrane separating the volumes is deformed. According to the change in the capacitance of the capacitor, one plate of which is the indicated membrane, the amount of leakage in the test object is calculated.

2) Leak detection by measuring the gas flow rate. The device measures the amount of air that enters the object in the event of a leak. The tests are carried out using a gas flow sensor. The device is calibrated using a test leak installed in 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 methods of tightness control.

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

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

To ensure the tightness of structures, O-rings are often used, for example, they are installed at the joints of pipeline parts. Sealing elements are often made of hyperelastic materials such as rubber. At large deformations, such materials demonstrate elastic behavior, that is, their stress-strain state depends only on the actual state of the body, while both stresses and deformations are expressed through the potential energy of elastic deformation. The type of the potential energy function is set when choosing a particular model of the material in the calculation. There are various models: polynomial, Mooney-Rivlin, neo-Gukovskaya and others, all of these models are presented in the ANSYS finite element package, which is used for the calculation. The deformation diagram of such materials is significantly nonlinear; Figure 1 shows an example of stress versus deformation dependence for a hyperelastic material.

Figure 1 - Example of a deformation diagram for a hyperelastic material

To determine the parameters of the models, full-scale 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 the dependence of engineering stresses on engineering deformations can be processed by internal ANSYS tools, for example, the Curve Fitting Tool. This tool allows the least squares method to calculate the parameters necessary to approximate the deformation diagram to determine the potential energy function of elastic deformation.

After selecting and calibrating the material model for the sealant, 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 pre-pressing 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 problem 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 compression in it. The problem is considered in a two-dimensional axisymmetric setting. Figure 2 shows the cross-section of the seal, with the inside of the seal on the left and the outside on the right.

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 sealant shrinks between the metal surfaces of the groove, that is, the contact problem is solved. In the second step, the effect of the medium (for example, liquid) on the seal is set. For this, the Fluid Pressure tool is used.

A fluid pressure load simulates the action of a liquid or gas that surrounds the investigated body and can penetrate between the 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 ​​application of the load is determined during 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 starting points are set by the user. Then the points at which the penetration criterion is fulfilled are determined, and the fluid pressure is applied to them, and their nearest nodes to these points become starting points for the next iteration, this process is repeated until the end of the calculation. In this case, a connected area containing a starting point is always built, therefore, for example, if there is a surface with an open contact status on the investigated body, but there are no starting points on this surface, then no load will be applied to it.

The penetration criterion is used to determine the area of ​​application of the load. There are two types of criteria:

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

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

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

Figure 3 - Distribution of fluid pressure, MPa

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

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

When designing sealed products, two problems arise: calculating the compression force that ensures the tightness of the joint, for example, the body and the cover (with a gasket between them), and calculating the gas leakage through the joint.

Compression force calculation

Lack of reasonable mathematical models depressurization of bulk joints does not allow to accurately determine the compression pressure taking into account the properties of the medium, the material of the gaskets and the characteristics of their microgeometric surface. Therefore, empirical formulas for determining the reduction pressure have become widespread. They are valid only in the range of parameter variation in which the experiments were performed.

Knowing the necessary strengthening of the compression you can determine the tightening torque of the connection, for example by screws tightening the gasket between the cover and the body.

Leakage calculation

Two models are used to calculate leakage (leakage rate) through a seal. One of them is leakage through round capillaries, the other is laminar flow through a flat slit (Poiseuille's formula). Calculations made by these models are at odds with practice, since the latter do not take into account such factors as contact pressure, characteristics of the surface microgeometry, as well as the physical and mechanical properties of the materials of the parts to be sealed, etc. Meanwhile, not all factors affect the leakage to the same extent; therefore, many authors for each case processed the experimental results and obtained empirical formulas, the calculations of which give good agreement with practical data.

Average statistical gap height and contact pressure R To, providing a normal seal of the gasket, are related by the ratio

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

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

Here WITH 0 - conductivity in the absence of the introduction of the gasket in the microroughness of the sealed surface.

Formulas 1-3 are valid for gases that do not create obliteration, which reduces leakage by clogging the gap.

Gas leakage through the gap between the sealing gasket and the 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 length of the strip and depends on its material and temperature,

Mass flow of gas through leaks at the sealed joint (4)


where R and - .gas pressure in the product,

R 0 - ambient pressure;

R- gas constant,

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

TO 0 - form-dependent Kozeny constant cross section slit (for round slit NS=2);

t is the coefficient of tortuosity ();

- the viscosity of the sealed medium (gas);

T- absolute temperature;

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

(t = 1.2) - the greatest height of the profile irregularities of the sealing surfaces;

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

Ra- arithmetic mean deviation of the profile;

Aspect ratio;

Coefficient characterizing the physical and 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- average radius of curvature of microroughness tops $

v 1 - the total parameters of the supporting curves of the contacting surfaces;

Support curves parameter,

- gamma function.

The requirement for a high degree of tightness of micro-assemblies, for example, semiconductor housings and IP is inextricably linked to ensuring their reliability and durability.

As a result of leaks, moisture, corrosive substances, and foreign particles can enter the inside of the housing, which will cause damage to individual elements of the microassembly or a short circuit.

The tightness of the cases of micro-assemblies is very high and the mass flow rate can reach 10 -8 ... 10 -9 cm 3 / s. Let us point out for comparison that through a hole with a diameter of 10 µm the gas flow rate is 5 · 10 -9 cm 3 / s. When the hole diameter decreases to 0.1 µm, the gas flow rate decreases by four orders of magnitude and amounts to 5 · 10 -13 cm 3 / s. Ego causes great difficulties in the choice of methods and means for testing the tightness of microassemblies, especially in mass production. Of the existing control methods, gas (with the help of a helium leak detector) has become widespread.

As practice has shown, the leakage of the microassembly bodies depends not only on the pressure of the tracer gas used for testing, the time of continuation of this pressure, the time interval after the pressure is removed, but also on the value of the internal (free) volume of the tested body for tightness.

For accurate estimation of helium leakage from measurements

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

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

- molecular weight, respectively, of air and tracer gas;

t 1 - residence time under pressure;

t 2 - holding time before measurement after pressure release;

U - body volume, cm 3.

RD 26.260.011-99

GUIDANCE DOCUMENT

INSTRUCTIONS

CALCULATED DETERMINATION OF THE STANDARDS OF TIGHTNESS
VESSELS AND APPARATUS

APPROVAL SHEET

RD 26.260.011-99

INSTRUCTIONS

CALCULATED DETERMINATION OF THE STANDARDS OF TIGHTNESS OF VESSELS AND APPARATUS

General Director of JSC
"VNIIPTkhimnefteapparatury" ________________________

V.A. Panov

Head of department
Standardization ______________________________________

V.N. Zarutsky

Head of Department No. 29 _____________________________

S.Ya. Luchin

Head of Laboratory No. 56 ________________________

L.V. Ovcharenko

Development Manager,
older Researcher ___________________________

V.P. Novikov

Process Engineer II cat. ______________________________

N.K. Lamina

Standardization Engineer I cat. ______________________

PER. Lukina

AGREED

Deputy General Director
on research and production activities
OJSC NIIKHIMMASH ____________________________

V.V. Rakov
Foreword

1. DEVELOPED by JSC "Volgograd Research and Design Institute of Chemical and Petroleum Engineering Technology" (JSC "VNIIPTkhimnefteapparatury").

2. APPROVED AND PUT INTO ACTION by the Technical Committee No. 260 "Chemical and oil and gas processing equipment" by the Approval Sheet dated June 24, 1999.

3. REPLACE "Methods for the calculation of the norms of the tightness of vessels and apparatus."

4. REVISED 2000 July with AMENDMENT No. 1, the approved Approval Sheet dated June 27, 2000.

GUIDANCE DOCUMENT

INSTRUCTIONS

CALCULATED DETERMINATION OF THE STANDARDS OF TIGHTNESS OF VESSELS AND APPARATUS

Date of introduction 1999-07-01

1 AREA OF USE

This guideline document is intended to establish standards for the design and leak testing of vessels and apparatus manufactured according to OST 26-291 and can be used for any other equipment controlled by the Gosgortekhnadzor of Russia, subject to the requirements of PB 03-108, PB 09-170, PB 10-115, SNiP 3.05.05.

2. REGULATORY REFERENCES

Throughout this guidance document, references are made to the following standards, regulations, and other sources:

One of the main indicators that determine the hazard class of a substance in accordance with GOST 12.1.007 is its maximum permissible concentration in the air of the working area, determined in accordance with 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, the ventilation of the working area depends on the atmospheric conditions on the territory of the enterprise and the physical properties of the released harmful substance.

3.3. The tightness rate of a vessel, apparatus in accordance with GOST 26790 is defined as the highest total consumption of a substance through leaks, which ensures the operable state of the vessel, apparatus and established by the regulatory and technical documentation for this vessel, apparatus.

Leakage rate is measured in units of gas flow:

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

MPCpr - maximum permissible concentration of harmful substances in the supply air, mg / m 3 (should not exceed 0.3 MPCrz).

4.2. By entering the values ​​from the formula () into the formula (), we obtain the formula for calculating the tightness rate of the vessel, the apparatus installed in the room:

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

4.4. Taking into account the formula (), the formula () takes the following form:

In the absence of data on the tightness class of detachable joints, it is recommended to use the data in the appendix of this guideline.

Table A.1 - Values ​​of the maximum permissible concentration of a harmful substance in the air of the working area, depending on the hazard class of this substance in accordance with GOST 12.1.007

In milligrams per cubic meter

Hazard class of harmful substances 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 ​​of the air exchange rate for industrial premises

Name of the originalproducts used in production or premises

Air exchange rate, h -1

Coefficient enhancements 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 frommercury catalyst

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

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

Bromine and other substances with MPCrz 0.5 - 5.0 mg / m 3

Chlorine, acetylene and other substances with MPCrz 0.5 mg / m 3 or less

Nitric, phosphoric and other acids with MPCrz 10 mg / m 3 and less

Natural petroleum gas

Petrol

Naphtha, motor fuel, fuel oil, cracking residue, bitumen (commercial)

Ethylene liquid

at current stifling workers places

you are heavy

Lubricating oils, paraffin (in the absence of solvents)

Alkaline solutions

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

2. The maximum permissible concentration of harmful substances in the air of the working area (MPCrz) 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 no more than 0.3 MPCrz.

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

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 coefficients given in the last column.

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

Appendix B

Table B.1 - Seal Leakage Classes and Corresponding Specific Leaks *

Class

Specific leakage

Qualitative (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

Low odor, visually invisible sweat

Rubber diaphragms, UN elastomeric sleeves

"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 droplet formation

UN in heavy duty, elastomeric HIPS and HC

"5 10 -2

up to 10 -2

"5 10 -1

2 - 2

"5 10 -2

" 10 -2

"5 10 -1 -

Drip leaks

End HC, UPS and HC rammed, slotted compensated

4 - 2

"50 - 5 10 2

Frequent drops

"5 · 10 2

Continuous leaks

UPS, UV contactless

" 10 3

" 10 3

Note - For gases instead of Q the criterion is the specific leakage B -14.

Bcc = 0.1B = 1.36 · 10 -5, m 3 · Pa / s,

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

2. Initial data

The vessel is designed for a mixture of natural hydrocarbons with a hydrogen sulfide content of up to 25% (Mp = 16.4) at a pressure of Pp = 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 = 1.

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

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

Leakage rate of vessel welded joints:

Bcc = 0.1B = 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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