UDC 517.958:532.5, 621:007

SOFTWARE MODULE FOR CALCULATING TIGHTNESS

AXIALLY-SYMMETRICAL MECHANICAL SEALS BASED ON

FINITE ELEMENT MODEL

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

Key words: axisymmetrical mechanical seals; calculation of tightness; software module; finite element model.

One of the most important problems when designing elements of new technology in mechanical engineering, machine tool building, power engineering, in the aviation and aerospace industries is the problem of isolating working environments and ensuring a given degree of tightness of various devices, vessels, connections of pipeline fittings, etc. To solve this problem, a large number of a variety of sealing devices, usually 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 that combine many of the most common properties and performance characteristics are metal-to-metal seals (Fig. 1). Such seals are widely used in many industries.

Rice. 1. Types of metal-to-metal seals based on contact shape: a - flat; b - conical; c - linear;

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

Due to the specific nature of the sealing mechanism, these connections are classified as contact connections, 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 the mathematical description of the movement of working media in the joints.

The above has led to the fact that to date a unified theoretical model and algorithms for calculating leakage of working media in sealed joints have not been developed, taking into account the real topography of the working surfaces of the joints and their operating conditions.

The lack of calculation models leads to the need for a lengthy and labor-intensive experimental selection of materials, technological methods of manufacturing and assembly for each new sealed joint, which significantly lengthens and increases the cost of the preparatory stage of production and hinders the development of CAD.

The article proposes a model of the flow of the working medium in axisymmetric metal-to-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 compaction, taking into account the influence 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">, are the heights of waviness of the lower and upper working surfaces of the seal relative to the middle planes, respectively; is the gap between average 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 function EN-US">

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

Here is a ring area; – test 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 compaction, respectively (Fig. 2).

The area is represented as a finite element model ..gif" width="229 height=25" height="25">,font-size:14.0pt"> – a separate finite element; – generalized parameters that depend 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 substituting the expression for the test 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 coefficients expressed through 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 mesh nodes included in the element e. The integral present 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="25" height="23">.gif" width="23" height="23 src=">) and internal () boundaries are calculated according to the following relations:

https://pandia.ru/text/79/265/images/image055.gif" width="200" height="52">.gif" width="25" height="21 src="> – grid spacing by angular coordinate; – number of partitions along the angular coordinate; – number of partitions 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 (software product registration certificate No.). Built in this way, it allows you to analyze the tightness of the connection immediately after completing the measurement of the waviness of its working surfaces.

The module is called from the “Modeling” item of the main menu of the APK control program (Fig. 4). When starting the modeling process, the parameters window of the model under study initially opens (Fig. 5)..gif" width="21" height="23">.gif" width="24" height="23"> – the value of the guaranteed gap between the maximum the peak of unevenness of one working surface and the maximum peak of unevenness of the second working surface; – discretely specified function characterizing the influence of roughness.

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

The influence functions of roughness (flow coefficients) are calculated by a 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 ​​- gap and its corresponding value, separated by a space. In the intervals between specified gap values, the function is interpolated linearly. At the boundaries it is interpolated by constant functions and, accordingly, for the upper and lower boundaries according to the gap size https://pandia.ru/text/79/265/images/image074.gif" alt=" 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 joint under study, finite element modeling is carried out, as a result of which a report on the tightness of the joint is generated (Fig. 6). The report includes a map of pressure distribution inside the gap between the working surfaces of the connection, a diagram and parameters of the connection, total leaks of the working fluid and a graph of the distribution of local leaks along the angular coordinate.

Rice. 6 . Joint tightness report

Checking the accuracy of leakage calculations through axisymmetric end connections using a software module. To verify the adequacy of the developed model, a series of model experiments were carried out to study leaks in absolutely smooth axisymmetric end seals. For such connections, 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.

To calculate leaks through axisymmetric seals, the following analytical model is proposed:

, (2)

where https://pandia.ru/text/79/265/images/image078.gif" width="16" height="15"> is the angular velocity of rotation of the connection. Taking into account the fact that the connection is stationary, equation (2) takes the form

.

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

Parameter

Designation

measurements

Accepted

values

Pressure outside the seal

1·105

Pressure inside the seal

Radius of the outer boundary of the seal

Radius of the inner seal boundary

2.5 10-2

Gap between sealing surfaces

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)

A 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 leakage on the average gap are presented 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 influence of waviness on the tightness of the connection. A numerical study was carried out to study the effect of waviness on the tightness of joints. A model compound with the characteristics listed in Table 1 was chosen as the object of study. 2. The upper working surface was assumed to be 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 unity.

Guaranteed joint clearance hΔ was specified 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 top surface to the middle plane of the bottom surface. Calculations were carried out for the values hΔ: 1; 2; 3; 5; 8; 10; 15 and 20 microns. They corresponded to equivalent gaps in a smooth connection: 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 compaction

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. At lower values hΔ this error can increase sharply. In turn, with a large increase in the value hΔ it gradually decreases. The results of the study are displayed in Fig..gif" width="31" height="25 src="> - in combination with smooth walls. font-size:12.0pt">The considered model of the flow of the working medium in axisymmetric metal-to-metal seals using the parameters of the real topography of the sealing surfaces can find practical application in the design of these seals, the designation of technological methods for their manufacture using modern CAD systems. Based on this model, it has been developed a software package that allows for quick and effective assessment of the 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, A. A. Application of finite element method (FEM) for calculation of flow factors in seals / A. A. Sheipak, V. V. Porohsyn, D. G. 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: reference book /,. – M.: Mashinostroenie, 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.: Mechanical Engineering, 2006. - No. 12.

V.T. Barchenko, M.L. Vinogradov

St. Petersburg State Electrotechnical University "LETI" (SPbSETU), st. Professora Popova, 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 standard for a vacuum-sealed product and calculating the time dependence of the change in pressure 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. Shown are new products for organizing tightness control at enterprises.

The portable helium leak detector provides reliable recording of helium flow down to 1 . 10 -7 Pa. m 3 / s (7.6 . 10 -4 l. µm Hg. / s).

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

Let's consider a graph of the statistical distribution of leaks detected when working with helium leak detectors. The graph shown in Figure 2 overlays 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

Analysis of this statistical distribution allows us to conclude that the sensitivity range of a portable helium leak detector includes the vast majority of real through leaks that need to be detected when monitoring leaks.

Leak flow 10 -9 mm Hg. . l/s and less are determined primarily by:

o permeability of vacuum seals,

o gas diffusion and conduction through product materials (for example, through polymers),

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

Leaks 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. During further leak tests, leaks with a flow rate of 7.5. 10 -7 mm Hg. Art. . l/s and more can be detected using a portable helium leak detector.

Pressure gauge leak detector for integral leak testing

Manometric leak detector is an automatic leak detector for monitoring the tightness of products, providing measurement of 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 leak detector system is designed in such a way that it is possible to implement manometric, vacuum-metric methods of tightness control, as well as leak detection by measuring gas flow.

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

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

1) Leak detection based on pressure increase or decrease. Manometric and vacuum methods are used to determine the total leakage. The manometric method is suitable for closed structures in which pressure above atmospheric pressure can be created. Vacuum gauge – for closed structures in which a vacuum can be created.

The principle of calculating the leak flow is based on monitoring the rate of pressure change in the test object. The device contains a reference sealed volume, separated from the measured object by a pressure difference-sensitive membrane. The leak detection method by 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 disrupted and the membrane separating the volumes is deformed. By changing the capacitance of the capacitor, one plate of which is the specified membrane, the amount of leakage in the test object is determined.

2) Leak detection by measuring gas flow. The device measures the amount of air that penetrates the object in the event of a leak. Tests are carried out using a gas flow sensor. The device is calibrated using a test leak installed in a special leak detector port 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 leak testing.

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

RD 26.260.011-99

GUIDANCE DOCUMENT

METHODOLOGICAL INSTRUCTIONS

CALCULATION DETERMINATION OF TIGHTNESS STANDARDS
VESSELS AND DEVICES

APPROVAL SHEET

RD 26.260.011-99

METHODOLOGICAL INSTRUCTIONS

CALCULATION DETERMINATION OF TIGHTNESS STANDARDS OF VESSELS AND DEVICES

General Director of JSC "VNIIPTkhimnefteapparatura" ________________________	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
Head of Development, Senior Researcher ___________________________	V.P. Novikov
Process engineer II cat. ______________________________	N.K. Lamina
Standardization Engineer I cat. ______________________	BEHIND. Lukina
AGREED
Deputy General Director for scientific and production activities OJSC "NIIKHIMMASH" ____________________________	V.V. Rakov

Preface

1. DEVELOPED by JSC Volgograd Research and Design Institute of Chemical and Petroleum Equipment Technology (JSC VNIIPTkhimnefteapparatura).

2. APPROVED AND PUT INTO EFFECT by Technical Committee No. 260 “Chemical and oil and gas processing equipment” with an Approval Sheet dated June 24, 1999.

3. INSTEAD “Methods for calculating the tightness standards of vessels and apparatuses.”

4. REISSUE 2000 July with CHANGE No. 1, approved by the Approval Sheet dated June 27, 2000.

GUIDANCE DOCUMENT

METHODOLOGICAL INSTRUCTIONS CALCULATION DETERMINATION OF TIGHTNESS STANDARDS OF VESSELS AND DEVICES

Date of introduction 1999-07-01

1 AREA OF USE

This guidance document is intended to establish standards for the design and leak testing of vessels and apparatus manufactured in accordance with 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

References to the following standards, codes and other sources are 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 area, 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 must be less than or equal to the maximum permissible concentration of these substances according to GOST 12.1.005.

When installing process equipment in an open area, which is typical for most oil and gas processing enterprises, 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 standard of a vessel or apparatus in accordance with GOST 26790 is defined as the highest total consumption of a substance through leaks that ensures the operable condition of the vessel or apparatus and is established by the normative and technical documentation for this vessel or apparatus.

The tightness standard is measured in gas flow units:

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

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

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

Vp h - 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 at least 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 formula (), formula () takes the following form:

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

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 according to GOST 12.1.007

In milligrams per cubic meter

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 standard of a vessel or apparatus is allowed to take the value 0.01 mg/m 3

Appendix B

Table B.1 - Air exchange rates for industrial premises

Name of the originalproducts used in production or premises	Air exchange rate, h -1							Coefficient increases for hot products
	in the absence of sulfur compounds			in the presence of sulfur compounds			Warehouses
	compressor	pumping	production	compressor	pumping	production
Ammonia
Production of acetaldehyde withmercury catalyst
Butane, hydrogen, methane, propane, butylene,pentane, paraldehyde,propylene, ethane, ethylbenzene, ethylene,cracked gas, crude oil and other substances with MPC 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 3 inclusive
Bromine and other substances with MPC 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 a maximum permissible concentration of 10 mg/m 3 or 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 1. This table should be used if there is no data on the amount of harmful substances released from equipment, fittings, communications, etc. 2. Maximum permissible concentrations 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 sanitary standards and in GOST 12.1.005. 3. The specified air exchange rates take into account the possibility of containing harmful substances in the supply air of no more than 0.3 MPC. 4. Petroleum products and gases with a sulfur content of 1% or more by weight are considered sulfurous. 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 fully corresponds to the data in the table from the Instructions for the design of heating and ventilation of oil refining and petrochemical enterprises VSN 21-77.

Appendix B

Table B.1 - Leakage classes of seals and corresponding specific leakages *

Class	Specific leakage			Criterion for qualitative (visual) assessment	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 sweating	Rubber membranes, 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 drip formation	Heavy-duty UN, elastomeric UPS and UV
	" 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 stuffed, slot-compensated
4 - 2	" 50 - 5 10 2			Frequent drops
	" 5 10 2			Continuous leaks	UPS, UV contactless
	" 10 3
	" 10 3
Note - For gas media instead Q the criterion is specific leakage B -14. Vss = 0.1V = 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 intended for a mixture of natural hydrocarbons with a hydrogen sulfide content of up to 25% (Мр = 16.4) at a pressure Рр = 2.5 MPa and a temperature of 100 °C (373 K) and has a volume of 10 m 3; MPCrz - 3 mg/m3, Kg = 1. When installed in an open area, the vessel tightness standard is according to the formula (): This corresponds to the fifth class of tightness according to OST 26-11-14. Standard of tightness of welded joints of a vessel: Vss = 0.1V = 2.0 10 -6, m 3 Pa/s, which also corresponds to the fifth class of tightness according to OST 26-11 -14.

RD 26.260.011-99

METHODOLOGICAL INSTRUCTIONS

CALCULATION DETERMINATION OF TIGHTNESS STANDARDS OF VESSELS AND DEVICES

General Director of JSC "VNIIPTkhimnefteapparatura" ________________________	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
Head of Development, Senior Researcher ___________________________	V.P. Novikov
Technological engineer II category. ______________________________	N.K. Lamina
Standardization engineer Cat. I ______________________	BEHIND. Lukina
AGREED
Deputy General Director for scientific and production activities OJSC "NIIKHIMMASH" ____________________________	V.V. Rakov

Preface

1 area of ​​use. 2 3. General provisions. 3 4. Determination of the tightness standard for a vessel or apparatus installed indoors. 4 5. Determination of the tightness standard for a vessel or apparatus installed in an open area. 5 6. Determination of the standard of tightness of welded and detachable connections of a vessel or apparatus. 5 Appendix A. 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 according to GOST 12.1.007. 6 Appendix B. Air exchange rates for industrial premises. 6 Appendix B. Seal leakage classes and corresponding specific leakages. 7 Appendix D. Leak tolerance distribution. 8 Appendix E. Examples of calculating the tightness norm of a vessel or apparatus. 8

GUIDANCE DOCUMENT

2. REGULATORY REFERENCES

References to the following standards, codes and other sources are used in this guidance document:

GOST 12.1.005-88 SSBT. General sanitary and hygienic requirements for the air in the working area

GOST 12.1.007-76 SSBT. Harmful substances. Classification and general safety requirements

GOST 26790-85 Leak detection technology. Terms and Definitions

OST 26-291-94 Welded steel vessels and apparatus. General technical conditions

PB 10-115-96 Rules for the design and safe operation of pressure vessels

PNAE G-7-010-89 Equipment and pipelines of nuclear power plants. Welded joints and surfacing. Control rules

VSN 21-77 Instructions for the design of heating and ventilation of oil refineries and petrochemical enterprises

Protective means in mechanical engineering. Calculation and design. Directory. - 1989

Seals and sealing technology. Directory. - 1986

3. GENERAL PROVISIONS

3.1. Substances circulating and released into the air of the working area of ​​enterprises in the chemical, petrochemical, oil and gas processing industries in the event of a violation of the tightness of vessels, apparatus and pipelines are divided into 4 hazard classes in accordance with GOST 12.1.007.

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 area, 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 must be less than or equal to the maximum permissible concentration of these substances according to GOST 12.1.005.

When installing process equipment in an open area, which is typical for most oil and gas processing enterprises, 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 standard of a vessel or apparatus in accordance with GOST 26790 is defined as the highest total consumption of a substance through leaks that ensures the operable condition of the vessel or apparatus and is established by the normative and technical documentation for this vessel or apparatus.

The tightness standard is measured in gas flow units:

B = (DV/t) P = (DP/t) V, (1)

where B is the gas flow through the through microchannel, m 3 Pa/s;

DV/t - volumetric gas flow, m 3 /s;

P - pressure in the vessel, Pa;

DP/t - change in pressure in the vessel, Pa/s;

V - volume of the vessel, m 3

In nuclear engineering (PNAE G-7-010) and in chemical and petroleum engineering (OST 26-11-14), tightness classes of vessels, apparatus and their connections have been established, which differ in the maximum values ​​of the total characteristics of detected through defects (see Table 1 OST 26-11-14).

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

M = (1/t) ], (2)

where M is the leakage coefficient, h -1

(can also be measured by pressure drop per hour as a percentage of test pressure:

M% = (100/t) ];

t is the holding time of the vessel, apparatus, pipeline under pressure, h;

Рн and Рк - absolute pressure (the sum of manometric and barometric pressure), respectively, at the beginning and end of the test, MPa;

Tn and Tk are the absolute temperature of the gas used for testing at the beginning and end of the test, respectively, K.

At a constant temperature of the gas used for testing, taking into account that Рн = Рр, formula (2) takes the form:

M = DP/(t PP), (3)

where Рр is the working pressure in the apparatus, MPa.

3.5. As can be seen from formulas (1) and (3), the tightness standard and the leakage coefficient are related by the relation:

B = (DP/t) V = M Pp V (10 6 /3600) = M Pp V [(1 10 4)/36] (4)

3.6. The amount of a harmful substance in kilograms per hour released from a normally operating vessel or apparatus, based on test results, can be determined by the formula:

where Kg is the safety factor (for a newly manufactured vessel, apparatus, Kg = 1.0; for a vessel, used apparatus, Kg = 1.5 - 2.0, depending on the number of flange connections);

Mi and Mp are the molecular masses of the test gas and working substance;

Ti and Tr are the absolute temperature of the test gas and working substance, K.

3.7. The release of a harmful substance into the air of the working area should not lead to exceeding the maximum permissible concentration of this substance in the air of the working area, therefore the condition obtained from formulas (4) and (5) must be met.

Considering that pneumatic testing is carried out with air (Mi = 29) at a temperature of 20 °C (Ti = 293 K), formula (6) is simplified:

4. DETERMINATION OF TIGHTNESS STANDARDS FOR A VESSEL, DEVICE INSTALLED IN THE PREMISES

4.1. Air exchange in production premises in cubic meters per hour, ensuring a reduction in the content of harmful substances in the air of the working area to the maximum permissible concentration during normal operation of the equipment is determined by the formula:

L = (W 10 6)/(MPKrz - MPCpr), (8)

where MPCrz is the maximum permissible concentration of a harmful substance in the air of the working area, mg/m 3 (determined according to GOST 12.1.005 or accepted as the minimum for the hazard class of the substance according to GOST 12.1.007);

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

4.2. By introducing the values ​​from formula (8) into formula (7), we obtain a formula for calculating the tightness standard of a vessel or apparatus installed in a room:

4.3. To design determine the standard of tightness of a vessel or apparatus installed in a room, it is recommended to determine the air exchange in this room, taking into account the standard air exchange rate for this room using the formula:

L = Kv · Vрз, (10)

where Kv is the standard air exchange rate in the room, h -1 (see Appendix B);

Vpз is 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 at least 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 formula (10), formula (9) takes on the following form:

5. DETERMINATION OF TIGHTNESS STANDARDS FOR A VESSEL, DEVICE INSTALLED IN AN OPEN AREA

5.1. For the design calculation of the tightness standard of a vessel or apparatus installed in an open area (taking into account the location of most enterprises of the chemical, petrochemical, oil and gas processing industries in climatic zones where the total number of windless days exceeds a third of the year, and the continuous duration of windless weather exceeds a third of the month) , it can be assumed that during normal operation of the equipment for 10 days or 240 hours, the concentration of a harmful substance in the air of the working area should not exceed the MPC value according to GOST 12.1.005:

PDKrz? [(W · tp)/Vрз] · 10 6 ; W? MPCrz · (Vрз · 10 6) · tr (12)

where tp is the time of continuous operation of the vessel or apparatus in calm weather, hours (in the absence of the climatic characteristics of the enterprise, it is assumed that tр = 240 hours, and Kg = 1.0).

5.2. By introducing the values ​​from formula (12) into formula (7), we obtain a formula for calculating the tightness standard of a vessel or apparatus installed in an open area:

at Vpз = 9 m 3

for other values ​​of Vрз (13)

6. DETERMINATION OF TIGHTNESS STANDARDS OF WELDED AND DETACHABLE JOINTS OF A VESSEL, APPARATUS

6.1. The standard of tightness of welded and detachable joints of a vessel or apparatus for selecting the optimal sensitivity of a particular method of tightness control is determined according to Appendix B of this guidance document and Table 1 of OST 26-11-14.

In the absence of data on the tightness class of detachable connections, it is recommended to use the data in Appendix D of this guidance document.

APPENDIX A

(informative)

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 according to GOST 12.1.007

In milligrams per cubic meter

Appendix B

(informative)

Table B.1 - Air exchange rates for industrial premises

Name of the starting products used in the production or premises	Air exchange rate, h -1							Increase factor for hot products
	in the absence of sulfur compounds			in the presence of sulfur compounds
	compressor	pumping	production	compressor	pumping	production
Production of acetaldehyde with mercury catalyst
Butane, hydrogen, methane, propane, butylene, pentane, paraldehyde, propylene, ethane, ethylbenzene, ethylene, cracked gas, crude oil and other substances with MPC more than 50 mg/m 3
Selective solvents, ether, leaded gasoline, divinyl acetate, dichlorostyrene, vinyl chloride, methylene chloride and other substances with a maximum permissible concentration of 5 - 50 mg/m 3 inclusive
Bromine and other substances with MPC 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 a maximum permissible concentration of 10 mg/m 3 or less
Natural petroleum gas
Naphtha, motor fuel, fuel oil, cracking residue, bitumen (commercial)
Ethylene liquid								influx of jobs stifling
Lubricating oils, paraffin (in the absence of solvents)
Alkaline solutions
Notes 1. This table should be used if there is no data on the amount of harmful substances released from equipment, fittings, communications, etc. 2. Maximum permissible concentrations 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 sanitary standards and in GOST 12.1.005. 3. The specified air exchange rates take into account the possibility of containing harmful substances in the supply air of no more than 0.3 MPC. 4. Petroleum products and gases with a sulfur content of 1% or more by weight are considered sulfurous. 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 fully corresponds to the data in the table from the Instructions for the design of heating and ventilation of oil refining and petrochemical enterprises VSN 21-77.

Appendix B

(informative)

Table B.1 - Leakage classes of seals and corresponding specific leakages *

	Specific leakage			Criterion for qualitative (visual) assessment	Typical seal types
	Q, mm 3 /(m s)		Qs, mm 3 /(m s)
				Absolute tightness	Metal bellows, polymer membranes
				Low odor, visually invisible sweating	Rubber membranes, UN elastomeric sleeves
				Leakage without drip formation	Heavy-duty UN, elastomeric UPS and UV
				Leakage with drop formation	UPS in heavy modes, UV cuff, end, stuffed
				Drip leaks	HC end, UPS and HC stuffed, slot-compensated
	" 50 - 5 10 2			Frequent drops
				Continuous leaks	UPS, UV contactless
Note - For gas media, instead of Q, the criterion is the specific leakage Qm, mg/(m.s), and instead of Qs - Qms mg/(m 2 s).

* Table from the books: Protective means in mechanical engineering. Calculation and design: Handbook / S.V. Belov, A.F. Kozyanov, O.F. Partolin et al. - M.: Mashinostroenie, 1989. - 229 p.; Seals and sealing technology: Directory / L.A. Kondakov, A.I. Golubev, V.B. Ovander et al. - M.: Mechanical Engineering, 1986. - 464 p.

Appendix D

(informative)

Table D.1 - Leak tolerance distribution

Appendix D

(informative)

Examples of calculating the tightness standard of a vessel or apparatus

1. Initial data

The vessel is intended for storing phosgene (Mp - 98.92) at a pressure of 1.6 MPa and a temperature of 100 °C (373 K), has a volume of 10 m 3, (MPCrz - 0.5 mg/m 3), Kg = 1.

1.1. When installed in a vinyl chloride production facility

Air exchange rate (see Appendix B) Kv = 10 · 1.2 = 12, h -1.

The vessel tightness standard according to formula (11):

Vss = 0.1V = 2.74 10 -4, m3 Pa/s,

1.2. When installed in an open area, the vessel tightness standard is determined by formula (13):

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

Standard of tightness of welded joints of a vessel:

Всс = 0.1В = 1.36 · 10 -5, m3 · Pa/s,

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

2. Initial data

The vessel is intended for a mixture of natural hydrocarbons with a hydrogen sulfide content of up to 25% (Мр = 16.4) at a pressure Рр = 2.5 MPa and a temperature of 100 °C (373 K) and has a volume of 10 m 3; MPCrz - 3 mg/m3, Kg = 1.

When installed in an open area, the vessel tightness standard is according to formula (13).

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

Calculation of crimping force

The lack of substantiated mathematical models of depressurization of volumetric joints 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 compression pressure have become widespread. They are valid only in the range of parameter changes in which the experiments were carried out.

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

Leakage calculation

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

Average statistical gap height and contact pressure R To, which ensures a more normal seal of the gasket, are related by the relation

Where R- a parameter characterizing the ability of a material to compact surface micro-irregularities. Leakage through the elastomer seal is equal.

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

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

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

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

Mass flow of gas through leaks at the joint of a hermetic connection(4)

Where R And - .gas pressure in the product,

R 0 - ambient pressure;

R- gas constant,

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

TO 0 - Kozeny constant, depending on the cross-sectional shape of the slit (for a circular slit Co.=2);

t - tortuosity coefficient ();

- 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 pitch of profile irregularities (GOST 2789-73);

Ra- arithmetic mean deviation of the profile;

Proportionality factor;

Coefficient characterizing the physical and mechanical properties of the material of the sealing surfaces;

M i - Poisson's ratio of the material,

E i - elastic modulus of the material;

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

V 1 - total parameters of the support curves of the contacting surfaces;

Reference curves parameter,

- gamma function.

The requirement for a high degree of sealing of microassemblies, for example, semiconductor device packages and IP is inextricably linked to ensuring their reliability and durability.

As a result of leakage, moisture, corrosive substances, as well as foreign particles can enter the housing, which can cause damage to individual elements of the microassembly or a short circuit.

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

As practice has shown, leakage of micro-assembly housings depends not only on the pressure of the tracer gas used to test, the duration of this pressure, the time interval after the pressure is removed, but also on the size of the internal (free) volume of the housing being tested for leaks.

For accurate assessment of helium leakage from measurement results

Where R- measured leakage, atm cm 3 /s;

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

- molecular weight of air and tracer gas, respectively;

t 1 - time spent under pressure;

t 2 - holding time before measurement after removing pressure;

U- body volume, cm 3.