ISA 12 04 04-2012 Pressurized Enclosures.pdf

1、 AMERICAN NATIONAL STANDARD ANSI/ISA-12.04.04-2012 Pressurized Enclosures Approved 25 July 2012 ANSI/ISA-12.04.04-2012, Pressurized Enclosures ISBN: 978-1-937560-58-4 Copyright 2012 by the International Society of Automation (ISA). All rights reserved. Printed in the United States of America. No par

2、t 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 of the publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, Nort

3、h Carolina 27709 - 3 - ANSI/ISA-12.04.04-2012 Preface This preface is included for information purposes and is not part of ANSI/ISA-12.04.04-2012. This document 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 docu

4、ment 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

5、 (919) 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. Th

6、e Department 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

7、in all 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) Provide an operating shaft with a bushing that is 0.

8、5 in. (12.7 mm) or longer and the opening between the bushing and the operating shaft is less than 0.005 in. (0.13 mm); or c) Provide a bezel around a through-the-enclosure component to reduce the opening to less than 0.005 in. (0.13 mm). 6.2.2 Vents should be protected to reduce the risk of the rel

9、ease of ignition-capable particles by one of the following methods: a) Provide the vent with a hub (so that it may be used with pipes or ducts that exhaust into a unclassified location); b) Provide suitable baffles to deflect any particles away from the vent; or c) Provide the vent with a substantia

10、lly noncombustible screen or filter. NOTE Materials rated as 94 V-0 or 94 5V (as described in ANSI/UL 94 and CSA C22.2 No. 0.17) are considered as substantially noncombustible. CAUTION PROVIDING A SCREEN OR FILTER MAY REDUCE VENTING CAPACITY AND MAY REQUIRE A DESIGN WITH A LARGER VENT. 7 Non-metalli

11、c enclosures, non-metallic parts of enclosures and components that protrude through the enclosure One or more of the following methods is permitted where there is the possibility that damage to the protected enclosure or to a component that completes the enclosure may result in exposing a potential

12、ignition source, but not result in reducing the pressure, within the enclosure below the minimum value. Use a component that is certified for the hazardous location external to the protected enclosure. Verify that the part of the enclosure that may be damaged is capable of passing the impact test de

13、scribed in 8.2. - 13 - ANSI/ISA-12.04.04-2012 Recess the potential ignition source at least 2.5 mm behind the enclosure wall to insure outward flow of protective gas through any damage in the enclosure will prevent ingress of the explosive atmosphere. Provide an additional cover over the potential i

14、gnition source (such as a keypad), see 7.1. Limit the energy to the component, see 7.2. 7.1 The volume within the additional cover should also be maintained at a positive pressure of at least 25 Pa when the cover is closed. The cover or enclosure adjacent to the cover should be marked not to open if

15、 the equipment within the enclosure is energized when an explosive atmosphere is present. The cover should require a key to open for Type X and Type Y pressurized equipment. 7.2 The component is protected by a type of protection suitable for Division 1 or Zone 1 for a Type X or Type Y pressurized en

16、closure or protected by a type of protection suitable for Division 2 or Zone 2 for a Type Z pressurized enclosure. 8 Protecting hot surfaces and ignition-capable components 8.1 Electrical components mounted internally and electrical components mounted through the enclosure shall be protected so that

17、 likely failure or abuse will not expose a hot surface or an ignition-capable arc to the external flammable atmosphere. (Additional information is located in Annex A.) NOTE 1 Ignition-capable arcs can occur either during normal operation or as a temporary arc occurring as a result of the likely fail

18、ure or abuse. NOTE 2 Ignition by a hot surface is discussed in NFPA 496. EXCEPTION: Equipment that (1) does not normally create ignition-capable particles, (2) is for use in Class I, Division 2 HAZARDOUS LOCATIONS, and (3) has an ALARM to notify the user when PRESSURIZATION fails does not require fu

19、rther protection. 8.2 The enclosure, external components, and nonmetallic parts of the enclosure that protect internal components should not be damaged when exposed to the impact levels in Table 2. Parts that can be removed without the use of a tool are to be removed before tes ting. Table 2 Impact

20、levels for enclosure parts Type of part Impact energy (joules) Drop height factor (meters-kg) Light-transmitting parts with guard (tested without guard) 2 0.204 Light-transmitting parts not guarded 4 0.408 Other parts of enclosure 7 0.714 Compliance is verified by subjecting the electrical apparatus

21、 to the effect of a test mass falling vertically from a drop height (h). The drop height (h), in meters, is determined by dividing the value shown in the drop height factor column by the mass of the test mass in kilograms. The impact head of the test mass should be a 25 mm (1 in.) diameter hardened

22、steel hemisphere. Components fail the test if hot surfaces or arcing contacts are exposed or if an ignition -capable arc occurs. Enclosures fail if hot surfaces or arcing contacts are exposed. 9 Protecting against enclosure rupture 9.1 Failure of the PROTECTIVE GAS SUPPLY pressure regulator could re

23、sult in flying fragments from the enclosure. Personnel should be protected from injury by either of the following methods: ANSI/ISA-12.04.04-2012 - 14 - a) The inlet should be restricted by either the supply connector size or by an additional orifice such that the leakage openings in the enclosure a

24、nd any pressure relief devices will be able to prevent the internal pressure from exceeding the rated MAXIMUM OPERATING PRESSURE, verified by the test in 11.1 and 11.2; or EXCEPTION: The test in 11.1 may be replaced by a calculation of the relief valve size for the enclosure based upon the MAXIMUM O

25、PERATING PRESSURE, the inlet size, the pressure relief outlet size and pressure relief operating point. b) Instructions should require the user to limit the pressure as specified in 9.3. 9.2 High internal pressures can cause doors or covers to open violently. Personnel should be protected from injur

26、y by methods such as the following: a) Use of multiple fasteners so that the enclosure will safely vent before all fasteners are released; b) Use of a two-position fastener to allow safe venting of the pressure when opening the enclosure; or c) Limiting the maximum internal pressure to not greater t

27、han 10 in. H 2O (2.5 kPa). 9.3 When instructions require the user to limit the pressure, the MAXIMUM OPERATING PRESSURE should be marked on the enclosure, and the instructions should contain either of the following: a) Requirements for the user to install a PROTECTIVE GAS SUPPLY that will not exceed

28、 the MAXIMUM OPERATING PRESSURE of the enclosure under single-fault conditions. The fault should be self-revealing. Protection can be either with a redundant regulator or with an external pressure relief valve that is capable of handling the maximum flow rate; or b) Requirements for the user to use

29、only a blower system and not compressed air for the PROTECTIVE GAS SUPPLY. Compliance is checked by inspection of the instructions and markings. 10 PURGING requirements Airflow through the enclosure during PURGING should be designed to avoid air pockets. Air pockets can be avoided by properly locati

30、ng the PROTECTIVE GAS SUPPLY inlet and outlet and by minimizing the effect of partitions as follows: 10.1 For gases or vapors that are heavier-than-air (i.e., with a specific density greater than 1.0), the inlet for the PROTECTIVE GAS should be near the top of the enclosure, and the outlet near the

31、bottom of the enclosure. 10.2 For gases or vapors that are lighter-than-air (i.e., with a specific density less than 1.0), the inlet for the PROTECTIVE GAS should be near the bottom of the enclosure, and the outlet near the top of the enclosure. NOTE 1 The specific densities of many gases and vapors

32、 are specified in NFPA “Fire Protection Guide to Hazardous Materials”. NOTE 2 Locating inlets and outlets at opposite sides of the enclosure promotes cross ventilation. 10.3 Internal partitions (e.g., circuit boards) should not obstruct the flow of PROTECTIVE GAS. Where the flow is significantly obs

33、tructed, either a) the PROTECTIVE GAS should be directed by baffles or a manifold, or b) the enclosure should pass the PURGING test described in 11.3. - 15 - ANSI/ISA-12.04.04-2012 11 Tests 11.1 Verifying ability of enclosure to limit internal pressure This test is applicable where required by 9.1 (

34、i.e., where an enclosure is designed for use with compressed air or other compressed gas) and where leakage, vents, or pressure relief devices are relied upon to limit the maximum internal pressure. WARNING THE FOLLOWING TESTS CAN BE INHERENTLY DANGEROUS UNLESS ADEQUATE SAFEGUARDS FOR PERSONNEL AND

35、PROPERTY ARE EMPLOYED. 11.1.1 The enclosure is tested with 100 psi (690 kPa) applied to the PROTECTIVE GAS SUPPLY inlet. The 100 psi pressure shall be maintained at the inlet until the maximum internal pr essure is measured. NOTE The inlet includes any restricted tubing or orifices that are part of

36、the PROTECTIVE GAS SUPPLY. The regulators in the PROTECTIVE GAS SUPPLY should be disabled, but bypassing is not necessary. 11.1.2 If there is an internal release, the flow rate into the enclosure should be increased by an amount equal to the maximum rated flow of the internal release. 11.1.3 The tes

37、ted sample should have a leakage rate that is representative of the tightest sealing expected for the enclosure. This can be accomplished by the addition of sealing material to make the unit representative of the likely manufacturing tolerances. 11.1.4 All openings that can be closed during normal o

38、peration of the equipment should be closed. 11.1.5 The measured internal pressure should not exceed the specified MAXIMUM OPERATING PRESSURE. 11.2 MAXIMUM OPERATING PRESSURE test This test is applicable when required by 9.1. 11.2.1 A sample enclosure should be TYPE TESTED or all enclosures should be

39、 ROUTINE TESTED to verify they will not catastrophically fail when subjected to the MAXIMUM OPERATING PRESSURE. 11.2.2 The enclosure should be tested using either of the following: a) TYPE TESTED at 3 times the rated MAXIMUM OPERATING PRESSURE for a minimum of 60 seconds; or b) ROUTINE TESTED at 1.5

40、 times the rated MAXIMUM OPERATING PRESSURE or 0.8 in H2O (0.2 kPa), whichever is greater, for a minimum of 10 seconds. 11.2.3 The enclosure should not fail in a manner that creates flying fragments. 11.2.4 Deformation of the enclosure during the TYPE TEST, whether permanent or not, is permitted; ho

41、wever, the deformation should be repeatable and not just a deformation unique to the one sample tested; e.g., a manufacturing defect in that sample. If in doubt about whether the deformation is unique to that sample, a second sample should be tested. 11.3 PURGING test The following procedure should

42、be used when required by 10.3. 11.3.1 The enclosure should be fitted with a number of small bore tubes, the open ends of which should be located inside the enclosure at sampling points where it is considered that the test gas is most likely to persist during the tests. ANSI/ISA-12.04.04-2012 - 16 -

43、11.3.2 If necessary, operational openings in the pressurized enclosure may be closed to enable the enclosure to be filled with the specified test gas, provided that they are reopened when the PROTECTIVE GAS SUPPLY is turned on. 11.3.3 The enclosure should be filled with the test gas to a concentrati

44、on of not less than 70 percent by volume at any point. When the PROTECTIVE GAS is air and when all permissible flammable gases are to be covered by the test, two tests should be performed one with helium to represent lighter than-air gases and a second with either argon or carbon dioxide to represen

45、t heavier-than-air gases. NOTE It is preferable to use test gas mixtures that are both non-flammable and nontoxic. 11.3.4 As soon as the enclosure is filled, the test gas supply should be turned off, and the PROTECTIVE GAS SUPPLY should be turned on at the minimum purge rate and for the minimum purg

46、e time specified by the manufacturer. At the end of the purge time, the mixture(s) collected from the small bore tubes should not exceed the following applicable limits: a) 1 percent by volume for the helium test and 0.25 percent by volume for the argon or carbon dioxide test; b) A concentration equ

47、ivalent to 25 percent of the most onerous LEL where two tests are performed to cover a specific range of flammable gases; or c) A concentration equivalent to 25 percent of the LEL where one specific flamm able gas is covered. 10.3.5 When a PROTECTIVE GAS other than air is used, the concentration of

48、oxygen after PURGING should not exceed 2 percent by volume. 12 Marking 12.1 In addition to the marking requirements of ANSI/NFPA 496, the following should be included: a) the normal operating pressure range of the enclosure, and b) the type of PROTECTIVE GAS (if not air). 13 Enclosure access for mai

49、ntenance Any enclosure interlock bypass switch used to facilitate maintenance should be self -resetting and require a tool to actuate or a tool should be required to gain access to the switch. EXCEPTION: The switch does not need to be self-resetting if an ALARM is used to indicate that the enclosure interlock switch has been bypassed. For TYPE X PRESSURIZING, a time delay of 30 seconds or less may be used to facilitate opening the door and actuating the enclosure interlock bypass switch. Upon loss of pressure, an ALARM should be energized immediately, but the de-energi