1、 AMERICAN NATIONAL STANDARD ANSI/ISA-71.04-2013 Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants Approved 16 August 2013 Copyright 2013 ISA. All rights reserved. ANSI/ISA-71.04-2013 Environmental Conditions for Process Measurement and Control Systems: Airbo
2、rne Contaminants ISBN: 978-0-876640-41-8 Copyright 2013 by ISA. All rights reserved. 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 o
3、therwise), without the prior written permission of the publisher. ISA 67 Alexander Drive P.O Box 12277 Research Triangle Park, North Carolina 27709 www.isa.org ANSI/ISA-71.04-2013 Copyright 2013 ISA. All rights reserved. 3 Preface This preface, as well as all footnotes, is included for informational
4、 purposes and is not part of ANSI/ISA-71.04-2013. This standard has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static, but should be subject to periodic review. Toward this end, the Society
5、 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 (919) 549-8411, e-mail: standardsisa.org. The ISA Standards and Practices Department is aware of
6、 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 Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to th
7、e 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 all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standa
8、rd for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing and Materials as IEEE/ASTM SI 10, and future revisions, will be the reference guide for definitions, symbols, abbreviations, and conversion factors. It is the policy of ISA t
9、o encourage and welcome the participation of all concerned individuals and interests in the development of ISA standards, recommended practices, and technical reports. Participation in the ISA standards-making process by an individual in no way constitutes endorsement by the employer of that individ
10、ual, of ISA, or of any of the standards, recommended practices and technical reports that ISA develops. CAUTION ISA DOES NOT TAKE ANY POSITION WITH RESPECT TO THE EXISTENCE OR VALIDITY OF ANY PATENT RIGHTS ASSERTED IN CONNECTION WITH THIS DOCUMENT, AND ISA DISCLAIMS LIABILITY FOR THE INFRINGEMENT OF
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15、VIEWING THIS DOCUMENT WHO IS AWARE OF ANY PATENTS THAT MAY IMPACT IMPLEMENTATION OF THE DOCUMENT NOTIFY THE ISA STANDARDS AND PRACTICES DEPARTMENT OF THE PATENT AND ITS OWNER. ANSI/ISA-71.04-2013 4 Copyright 2013 ISA. All rights reserved. ADDITIONALLY, THE USE OF THIS DOCUMENT MAY INVOLVE HAZARDOUS
16、MATERIALS, OPERATIONS, OR EQUIPMENT. THE DOCUMENT CANNOT ANTICIPATE ALL POSSIBLE APPLICATIONS OR ADDRESS ALL POSSIBLE SAFETY ISSUES ASSOCIATED WITH USE IN HAZARDOUS CONDITIONS. THE USER OF THIS DOCUMENT MUST EXERCISE SOUND PROFESSIONAL JUDGMENT CONCERNING ITS USE AND APPLICABILITY UNDER THE USERS PA
17、RTICULAR CIRCUMSTANCES. THE USER MUST ALSO CONSIDER THE APPLICABILITY OF ANY GOVERNMENTAL REGULATORY LIMITATIONS AND ESTABLISHED SAFETY AND HEALTH PRACTICES BEFORE IMPLEMENTING THIS DOCUMENT. THE USER OF THIS DOCUMENT SHOULD BE AWARE THAT THIS DOCUMENT MAY BE IMPACTED BY ELECTRONIC SECURITY ISSUES.
18、THE COMMITTEE HAS NOT YET ADDRESSED THE POTENTIAL ISSUES IN THIS VERSION. The following people served as voting members of ISA71 in developing this standard: NAME AFFILIATION C. Muller, Chair Purafil, Inc. J. Gilsinn, Managing Director Kenexis Consulting D. Brown Bechtel Corporation D. Childers Engi
19、neered Air Systems Inc. R. Cowles International Paper Co. J. Huza Full Circle Protection A. Kazi Dell Inc. P. Singh IBM B. Stanley AAF International G. White Hewlett Packard This standard was approved for revision by the ISA Standards and Practices Board on 3 July 2013. NAME AFFILIATION E. Cosman, V
20、ice President The Dow Chemical Company D. Bartusiak ExxonMobil Chemical Co. P. Brett Honeywell Inc. J. Campbell Consultant M. Coppler Det Norske Veritas Certification Inc. B. Dumortier Schneider Electric D. Dunn Aramco Services Co. J. Federlein Federlein for example, the movement of force coils or g
21、alvanometer movements can be severely restricted or entirely demobilized by magnetic substances accumulating in air gaps of the permanent magnets. Likewise, electrical motors can be seriously damaged by magnetic materials accumulating between rotor and stator. 6.2.2 Thermal conductivity The thermal
22、insulating properties of some solid particles can cause overheating of cooling systems, which become insulated by surface deposits of these substances. For example, the cooling fins of power electronics can be seriously insulated by textile fibers. 6.2.3 Electrical conductivity Solid substances are
23、divided into two groups, electrically conductive and highly insulative substances. Electrical conductors, such as metals, carbon blacks, and coal dusts, can cause short circuits when settling between terminals. Insulating substances can accumulate static charges that upset the functioning of compute
24、rs and integrated circuits. Some insulators absorb moisture under conditions of high relative humidity. This causes an increase in conductivity and can result in equipment failures due to electrical leakage. 6.2.4 Adhesiveness This characteristic causes a contaminant to adhere to and accumulate on s
25、urfaces. This intensifies undesirable effects, such as thermal insulation, high voltage discharge, and bearing failures. Adhesive qualities may be inherent to the contaminant, such as tobacco smoke, which contains sticky tars. 6.2.5 Corrosivity Airborne particulate matter varies from hard crystallin
26、e structures, such as metallic ores, to soft porous structures, such as atmospheric dust, fly ash, and smoke. Dust particles may absorb gaseous contaminants and moisture and thus become corrosive. Dust that may be benign when dry can become corrosive in environments with relative humidity levels abo
27、ve the deliquescent relative humidity of the dust. Annex A describes a technique that can be used to measure the deliquescent relative humidity of dust. 6.2.6 Abrasiveness Abrasiveness is a significant factor in mechanical erosion by high velocity solid contaminants. It also contributes to the accel
28、erated wear of moving parts. 6.3 Explanation of Table 2 Solid particulates are classified by size. The environment should be described in terms of concentration severity level for each class: Classes SA through SD. Table 2 Classification of airborne particulates Severity level (concentration measure
29、d in g/m3) Particle size Class 1 2 3 X 1 mm SA 60% RH. To determine the deliquescent relative humidity, particulates (dust, etc.) should be lifted off easily accessible surfaces of electronic components, collected in clean plastic bags, and with at least one sample from individual cabinets or rooms
30、shipped to a laboratory for analysis (speciation, chemical composition). Replicate samples of the dust should be sprinkled on the interdigitated areas of a surface insulation resistance (SIR) test circuit board (Figure A1, part number IPC-B-24 may be obtained from vendors listed in the IPC website h
31、ttp:/www.ipc.org/ContentPage.aspx?pageid=Test-Board-Vendors). The spacing between the interdigitated combs is 0.5 mm, and the sprinkled dust should bridge these gaps. The circuit board should then be placed in a humidity chamber with a starting relative humidity of 20% at room temperature and 10V bi
32、as applied across the combs. The relative humidity should be raised at a constant rate from 20% to 90% over the period of a week and the leakage current between the combs plotted as a function of time. The relative humidity at which the leakage current rises sharply is the deliquescent relative humi
33、dity of the particulate contamination. Figure A1. IPC-B-24 test board Copyright 2013 ISA. All rights reserved. This page intentionally left blank. ANSI/ISA-71.04-2013 Copyright 2013 ISA. All rights reserved. 21 Annex B Corrosive contaminants B.1 The following paragraphs describe how various contamin
34、ants contribute to equipment performance degradation. B.1.1 Inorganic chlorine compounds (expressed as Cl2 in Table B1) This group includes chlorine, chlorine dioxide, hydrogen chloride, etc., and reactivity will depend upon the specific gas composition. In the presence of moisture, these gases gene
35、rate chloride ions, which react readily with the copper, tin, silver, and iron alloys. These reactions are significant even when the gases are present at low parts-per-billion levels. For example, the corrosivity of air containing 1 part per billion of chlorine would probably place that environment
36、in the “moderate“ Class G2 category described in 7.3.2. A concentration of 10 parts per billion would probably increase the severity level to Class G3 or GX. These reactions are attenuated in dry atmospheres. At higher concentrations, many elastomers and some plastics are oxidized by exposure to chl
37、orinated gases. Particular care must be given to equipment exposed to atmospheres that contain chlorinated contaminants. Sources of chloride ions, such as cleaning compounds and cooling tower vapors, etc., should be considered when classifying industrial environments. They are seldom absent in major
38、 installations. B.1.2 Active sulfur compounds (expressed as H2S in Table B1) This group includes hydrogen sulfide, elemental sulfur, and organic sulfur compounds, such as the mercaptans. When present at low parts-per-billion levels, they rapidly attack copper, silver, aluminum, and iron alloys. The
39、presence of moisture and small amounts of inorganic chlorine compounds greatly accelerates sulfide corrosion. Note, however, that attack still occurs in low relative-humidity environments. Active sulfurs rank with inorganic chlorides as the predominant cause of atmospheric corrosion in the process i
40、ndustries. B.1.3 Sulfur oxides (expressed as SO2 and SO3 in Table B1) Oxidized forms of sulfur (SO2, SO3) are generated as combustion products of sulfur-bearing fossil fuels. Low parts-per-billion levels of sulfur oxides can passivate reactive metals and thus retard corrosion. At higher levels they
41、attack certain types of masonry, metals, elastomers, and plastics. The reaction with masonry and metals normally occurs when these gases dissolve in water to form sulfurous and sulfuric acid. B.1.4 Nitrogen oxides (expressed as NOx in Table B1) NOx compounds (NO, NO2, N2O4) are formed as combustion
42、products of fossil fuels and have a critical role in the formation of ozone in the atmosphere. They are also believed to have a catalytic effect on corrosion of base metals by chlorides and sulfides. In the presence of moisture, some of these gases form nitric acid which, in turn, attacks most commo
43、n materials. B.1.5 Hydrogen fluoride (expressed as HF in Table B1) This compound is a member of the halogen family and reacts like inorganic chloride compounds. B.1.6 Ammonia and derivatives (expressed as NH3 in Table B1) Reduced forms of nitrogen (ammonia, amines, ammonium ions) occur mainly in fer
44、tilizer plants, agricultural applications, and chemical plants. Copper and copper alloys are particularly susceptible to corrosion in ammonia environments. B.1.7 Photochemical species (expressed as O3 in Table B1) The atmosphere contains a wide variety of unstable, reactive species, which are formed
45、 by the reaction of sunlight with moisture and other atmospheric constituents. Some have lifetimes measured in fractions of a second as they participate in rapid chain reactions. In addition to ozone, a list of examples would include the hydroxyl radical as well as radicals of hydrocarbons, oxygenat
46、ed hydrocarbons, nitrogen oxides, sulfur oxides, and water. Because of the transient nature of most of these species, their primary ANSI/ISA-71.04-2013 22 Copyright 2013 ISA. All rights reserved. effect is on outdoor installations and enclosures. In general, plastics and elastomers are more suscepti
47、ble than metals to photochemical effects. B.1.8 Strong oxidants This includes ozone plus certain chlorinated gases (chlorine, chlorine dioxide). Ozone (O3) is an unstable form of oxygen, which is formed from diatomic oxygen by electrical discharge or by solar radiation in the atmosphere. These gases
48、 are powerful bleaching and oxidizing agents. They attack the surface of many elastomers and plastics. Photochemical oxidation the combined effect of oxidants and ultraviolet light (sunlight) is particularly potent. Ozone may also function as a catalyst in sulfide and chloride corrosion of metals, b
49、ut its precise role is unclear. B.2 Gas concentrations The synergistic effects of various combinations of corrosive gases make the determination of severity levels complex when only examining gas concentration data. In addition to the contaminant gases themselves, temperature and humidity also have a major impact on the corrosion rates. Gaseous contamination limits for the reliable operation of electronic equipment cannot be specified in terms of the concentrations of gaseous contaminants in the air; metal corrosion is too complex a process to allow its rate to be determined
