1、Standard Method for theEvaluation of External Leakageof Manual and AutomatedOn-Off ValvesApproved 15 January 2000ANSI/ISA93.00.011999FormerlyANSI/ISAS93.00.011999AMERICAN NATIONAL STANDARDISA The Instrumentation,Systems, andAutomation Society TMCopyright 1999 by the Instrument Society of America. Al
2、l rights reserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission o
3、f the Publisher.ISA67 Alexander DriveP.O. Box 12277Research Triangle Park, North Carolina 27709ANSI/ISA93.00.011999Standard Method for the Evaluation of External Leakage of Manual and Automated On-Off ValvesISBN: 1-55617-712-7 3 ANSI/ISAS93.00.011999PrefaceThis preface, as well as all footnotes and
4、annexes, is included for information purposes and is not part of ANSI/ISA-93.00.01-1999.This document has been prepared as part of the service of ISA, the international society for measurement and control, toward a goal of uniformity in the field of instrumentation. To be of real value, this documen
5、t should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (9
6、19) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org.The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The De
7、partment is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in a
8、ll new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing b) the viscosity of the gas;c) the pressure differential cau
9、sing the flow;d) the absolute pressure in the system;e) the length and cross section of the leak path; and f) the temperature of the gas.For the purposes of this Standard, the last four factors are considered constants between the measured gas and methane. The primary modes of leakage that can resul
10、t from these factors are molecular, transitional, and viscous (both laminar and turbulent).C.2 Molecular leakageMolecular leakage results when the mean free path of both gases being correlated is greater than the cross-sectional dimension of the leak orifice. The mean free path is defined as the dis
11、tance a molecule travels between successive collisions with other molecules in the vapor state. When this type of leakage is encountered, the measured leakage (concentration in ppm) of any gas can be correlated to methane leakage per the following formula:ML= (LT) (MWT)1/2/ (MWM)1/2ML= Methane equiv
12、alent leakage, ppmLT= Measured leakage of test gas, ppmMWT= Molecular weight of the test gas, atomic mass unitsMWM= Molecular weight of methane, atomic mass unitsNOTE Molecular leakage typically occurs when the flow is extremely low such as is encountered in vacuum systems.C.3 Transitional leakageTr
13、ansitional leakage results when the mean free path of both gases being correlated is approximately equal to the cross sectional dimension of the leak orifice. When this type of leakage is encountered, the measured leakage (concentration in ppm) of any gas can be correlated to methane leakage per the
14、 following formula:Methane equivalent leakage, ppm = ( Measured leakage of test gas, ppm ) x ( Molecular weight of test gas, atomic mass units ) x ( Absolute temperature, Kelvin ) 1/2 ( Molecular weight of methane, atomic mass units ) x ( Absolute temperature, Kelvin ) 1/2ANSI/ISAS93.00.011999 24 NO
15、TE Transitional leakage occurs under conditions intermediate between molecular and viscous (laminar) flow. This transition between molecular and laminar leakage is gradual.C.4 Viscous leakageViscous leakage, both laminar and turbulent, results when the mean free path of both gases being correlated i
16、s smaller than the cross sectional dimension of the leak orifice. As the velocity of the gas flow increases, the leakage will go from laminar to turbulent. In laminar flow, particles follow a nearly straight path, while in turbulent flow, the path is more erratic. Provided the flow of both gases bei
17、ng correlated is either laminar or turbulent, the measured leakage (concentration in ppm) of any gas can be correlated to methane leakage per the following formula: Methane equivalent leakage, ppm = (Measured leakage of test gas, ppm) x (Viscosity of test gas)(Viscosity of methane)NOTE Viscous leaka
18、ge occurs in high pressure systems and is the most common mode encountered in probing type leakage tests.C.5 Concluding remarksIt is important to note that the relationships defined by the above equations are most applicable when comparing gases of similar molecular size and viscosity. This is not t
19、o say that they cannot be used to correlate gases of significantly different molecular size and viscosity; however, the range of equation applicability must be established experimentally since it is possible for one of the gases being correlated to be governed by one leakage mode while the other gas
20、 is governed by another leakage mode.ISBN 1-55617-712-7Developing and promulgating technically sound consensus standards, recommended practices, and technical reports is one of ISAs primary goals. To achieve this goal, the Standards and Practices Department relies on the technical expertise and effo
21、rts of volunteer committee members, chairmen, and reviewers.ISA is an American National Standards Institute (ANSI) accredited organization. ISA administers United States Technical Advisory Groups (USTAGs) and provides secretariat support for International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO) committees that develop process measurement and control standards. To obtain additional information on the Societys standards program, please write:ISAAttn: Standards Department67 Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709
