A Unified Marking System for Ex Equipment

Transcription

1 CERTEX Appointed Ex Laboratory Reg No: 1999/027771/07 (Pty) Ltd Government Approved Inspection Authority T0104 PO Box 467 Tel: +27 (11) Olifantsfontein Fax: +27 (11) E- mail: Johannes Auret SAFA Symposium November 2009 SUMMARY The International Electrotechnical Commission (IEC) is implementing changes to their explosion protection standards that will introduce a unified marking system for Ex equipment. The details of the system is discussed and also the issues that the South African industry will have to reckon with. CONSULTIING Testing and Certification Certification Mark for Explosion Protected (Ex) Equipment Area Classification / Explosion Risk Assessment Inspection of New or In-service Ex Equipment & Installations Management System for Ex Installations Consultation Presentations & Workshops Training Courses

2 Page 2 of 10 Contents Page 1. INTRODUCTION BENEFITS AND PITFALLS OF A UNIFIED MARKING SYSTEM OVERVIEW OF COMMON MARKING SYSTEMS THE NEW IEC UNIFIED MARKING SYSTEM Examples Other marking requirements STATUS OF STANDARDS DEVELOPMENT CONCLUSION... 6 Annex 1: Summary of Risk Assessment versus Statistical Approach to Equipment Selection 7 Annex 2: Progress with Implementation of New Unified Marking System... 9

3 Page 3 of INTRODUCTION Various developments in Ex standards are currently taking place that is leading to changes in the marking of Ex equipment, notably the following: - Introduction of Risk Assessment as an alternative to the well-known Statistical approach to equipment selection. Refer to Annex 1 for more information. - Grouping similar techniques with different levels of protection together. - Development of dust versions for traditional gas standards. - As a result, a unified marking system is being introduced for the explosion protection rating of Ex equipment. It is imperative that industry role players cooperate to ensure that these changes are phased in smoothly and that the new requirements are implemented and understood. This presentation takes a look at the most critical changes. 2. BENEFITS AND PITFALLS OF A UNIFIED MARKING SYSTEM A unified marking system has the following obvious advantages: 2.1 A unified system is simpler. 2.2 It allows more application information to be given to the user. 2.3 It allows equipment for gases and dust to be marked using the same format. The biggest disadvantages are that 2.3 It will take time for industry to assimilate this information. 2.4 The various generations of equipment with different marking is bound to cause confusion, especially amongst users. 2.5 Because the IEC working groups, committees and subcommittees each have their own scope of work and timetable, the various standards having to reflect the new marking system do not get published at the same time. 3. COMPARISON OF COMMON MARKING SYSTEMS The marking employed for explosion protection rating of Ex equipment differs between standards. The table below shows how an explosion protected pressure sensor rated as intrinsically safe, category ia with equipment group and temperature class of respectively IIC and T4 may be marked. The last entry shows the new unified system.

4 Page 4 of 10 Standard Marking Score out of 3 for showing key aspects Technique Zone (or equivalent) Gas group Temp. class TOTAL North America (Intrinsically safe.) Suitable for use in Class I, Division 1. Groups ABCD IEC/SABS Ex ia IIC T CENELEC EEx ia IIC T (EC) AND IEC Unified Marking System Ex ia IIC T4 Ga OR Ex ia IIC T4 II 1 G OVERVIEW OF THE NEW IEC UNIFIED MARKING SYSTEM 4.1 Further examples of explosion protection rating Requirements for the new unified marking system are contained in IEC Edition 5, published in June 2009 as SANS Edition 4. This means that our national (SABS) standard now complies with the latest IEC standard. NOTE Some information from IEC Edition 6 (draft) is also covered. The following examples illustrate the new marking system further. a) An intrinsically safe instrument for use in mines and on surface: Ex ia I T4 Ma Alternative Ex ia I T4 Ex ia IIC T4 Ga Ex ia IIC T4 b) A flameproof motor for use on surface: Ex d IIC T3 Gb Alternative Ex db IIC T3 c) A pressurized panel for an explosive gas atmosphere on surface and containing an intrinsically safe barrier for connection to a field device, with the same gas group: Ex px [ia] IIC T4 Gb Alternative Ex pxb [ia] IIC T4 and with different gas groups: Ex px [ia IIB Ga] IIC T4 Gb Alternative Ex pxb [ia IIB] IIC T4 d) A pressurized panel for an explosive gas atmosphere on surface and containing an intrinsically safe pressure switch connected to the safe area: Ex ia px IIC T4 Gb Alternative Ex ia pxb IIC T4

5 Page 5 of 10 e) An intrinsically safe isolator for installation in a safe area and connection to an instrument in an explosive gas atmosphere: [Ex ia Ga] IIC Alternative [Ex ia] IIC f) An increased safety light installed in an explosive gas atmosphere on surface: Ex e IIC T3 Gb Alternative Ex eb IIC T3 g) An intrinsically safe flowmeter for an explosive gas atmosphere on surface as well as an explosive dust atmosphere on surface: Ex ib IIC T5 Gb Alternative Ex ib IIC T5 Ex ib IIIC T90 C Db Alternative Ex ib IIIC T90 C 4.2 Other marking requirements A number of related marking requirements have been introduced. These are: - Marking must be visible before and after installation. - When marking is placed on a removable part (e.g. a terminal box lid), it is recommended that the marking must be duplicated in the interior of the equipment. - The serial number must be shown; alternatively the batch number may be used. - The format of the certificate reference is specified, e.g. XPL Specific conditions of used can be indicated either by advisory marking or an X after the certificate number. - Equipment with maximum temperature above 450 C must be marked with the maximum temperature and not T1 (e.g. 600 C). - If the same equipment has different temperature classes, e.g. because of multiple ambient temperatures, then the X must be applied and the temperature class range must be shown, e.g. T6. T3. - The symbols for combined types of protection must be shown in alphabetical order, e.g. Ex d e not e d. - Double protection is shown as for example, Ex d + e. - Battery packs must be marked Use on. plus the type of equipment. Likewise VSD driven motors must be marked with For converter supply, the speed range, the minimum switching frequency, the type of torque and the type of VSD. 5. IMPLEMENTATION OF NEW MARKING As mentioned in the introduction, the various amendments to be made to IEC standards to fully introduce the new marking system take different periods to complete. In essence, for each Ex technique the relevant standard must be updated to call up Edition 5 of IEC In addition, in each country a process is followed to consider and adopt any amended IEC standard. This means that for some Ex techniques, implementation will be quick, while for others the process will take years to complete. Annex 2 illustrates how the Equipment Protection Level (EPL) rather than the Zone is used to select Ex equipment.

6 Page 6 of CONCLUSION The focus of this paper is mainly on the possible dilemma of industry users of Ex equipment in the face of fast changing standards. Institutions like training providers and SAFA have to play a key role in transferring not just data but knowledge. The Equipment Protection Level (EPL) is brought into consideration as part of the area classification process, by determining the appropriate EPL for the various hazardous areas (zones). It is recommended that this information must be included on all future classification documents.

7 Page 7 of 10 Annex 1: Summary of Risk Assessment versus Statistical Approach to Equipment Selection 1.1 Statistical approach and Zones In the past, a strictly statistical approach to equipment selection was followed, which means that the probability of a fire or explosion is pegged at a certain allowed maximum. The probability of a fire or explosion occurring can be expressed as: Where - p e is the probability of a fire or explosion occurring; - p g is the probability that an explosive atmosphere will be present in a particular place at a particular time (given by the zone); and - p i is the probability that the above explosive atmosphere can be ignited. p e and consequently the product p g x p i must be acceptably low. (A probability of 10-5 is considered acceptable, refer to Hickes and Brown). This means that if the probability of an explosive atmosphere being present increases, the probability that it can be ignited must decrease and vice versa. Equipment protection is selected in accordance with the zone in this approach. 1.2 Risk-based approach The equipment selection standard now also allows for a risk-based approach. In a risk-based approach, the consequence of an explosion is also taken into account, together with the probability of an explosion. This means quite simply that under certain circumstances, the occurrence of an explosion is more tolerable (or less tolerable) than normal. Example: A typical example is of two neighbouring plants of similar design, but due to differences in the materials being handled, the one is Zone 1 and the other Zone 2. Some engineers will decree that Zone 1 equipment is used even in the Zone 2 plant, because the danger exists that the wrong replacement equipment will be selected from stores during a breakdown. 1.3 Discussion To facilitate the risk-based approach, the concept of Equipment Protection Level (EPL) was introduced. The EPL for each explosion protection technique has been determined and ranges from Very High to High to Normal. 1.4 Selection p e = p g x p i If risk is normal, which is mostly the case, the probability of an explosion is the only controlling factor and a direct relationship between EPL and Zone exists that is used to select equipment:

8 Page 8 of 10 Table 1.1 Equipment protection level (EPLs) where only zones are assigned Zone Minimum Equipment Protection Level (EPL) 0 Ga 1 Gb 2 Gc 20 Da 21 Db 22 Dc Where in exceptional circumstances, the risk is not normal, a higher or lower EPL than that defined in the table may be required. It is recommended that the requirement protection level (EPLs) requirements are recorded on the area classification drawing, even if the risk-based approach has not been followed.

9 Page 9 of 10 Annex 2: Progress with Implementation of New Unified Marking System Protection EPL Type of protection Code According to Conditions of afforded Group I Group II Group III standard operation Very High Ma Same as Ga Equipment remains functioning when explosive atmosphere present Very High Ga Intrinsically safe ia SANS Equipment remains Encapsulation ma SANS Two independent type of protection each meeting EPL Gb Protection of equipment and transmission systems using optical radiation SANS SANS functioning in Zones 0, 1 and 2 Very High Da Intrinsically safe id SANS Equipment remains Encapsulation md SANS functioning in Zones 20, 21 and 22 Protection by enclosure td SANS High Mb Same as Gb Equipment deenergised when explosive atmosphere present High Gb Flameproof enclosures d SANS Equipment remains Increased safety e SANS Intrinsically safe ib SANS Encapsulation m mb SANS Oil immersion o SANS Pressurized enclosures p, px SANS or py Powder filling q SANS Fieldbus intrinsically safe concept (FISCO) SANS functioning in Zones 1 and 2 Protection of SANS equipment and transmission systems using optical radiation High Db Intrinsically safe id SANS Equipment remains Encapsulation md SANS functioning in Zones Protection by td SANS and 22 enclosure Pressurized enclosures pd SANS Normal Gc Intrinsically safe ic SANS Equipment remains Encapsulation mc SANS functioning in Zone Non-sparking n or SANS na Restricted breathing nr SANS Energy limitation nl SANS Sparking equipment nc SANS Pressurized enclosures pz SANS Fieldbus non-incendive SANS concept (FNICO) Protection of SANS equipment and transmission system using optical radiation Normal Dc Intrinsically safe id SANS Equipment remains

10 Page 10 of 10 Protection afforded EPL Type of protection Code According to Group Group Group standard I II III Conditions of operation Protection by td SANS functioning in Zone enclosures 22 Pressurized enclosures pd SANS