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BRITISH STANDARD Industrial thermoprocessing equipment Ð Part 5: Particular safety requirements for salt bath thermoprocessing equipment The European Standard EN 746-5:2000 has the status of a British Standard ICS 25.180.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BS EN 746-5:2000 BS EN 746-5:2000 National foreword This British Standard is the official English language version of EN 746-5:2000 The UK participation in its preparation was entrusted by Technical Committee MCE/3, Safeguarding of machinery, to Subcommittee MCE/3/8, Thermoprocessing equipment - Safety, which has the responsibility to: Ð aid enquirers to understand the text; Ð present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; Ð monitor related international and European developments and promulgate them in the UK A list of organizations represented on this subcommittee can be obtained on request to its secretary Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled ªInternational Standards Correspondence Indexº, or by using the ªFindº facility of the BSI Standards Electronic Catalogue A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages to 24, an inside back cover and a back cover The BSI copyright notice displayed in this document indicates when the document was last issued This British Standard, having been prepared under the direction of the Engineering Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 November 2000 BSI 11-2000 ISBN 580 35979 Amendments issued since publication Amd No Date Comments EUROPEAN STANDARD EN 746-5 NORME EUROPÉENNE EUROPÄISCHE NORM September 2000 ICS 25.180.01 English version Industrial thermoprocessing equipment - Part 5: Particular safety requirements for salt bath thermoprocessing equipment Equipements thermiques industriels - Partie 5: Prescriptions particulières de sécurité pour les équipements thermiques bain de sel Industrielle Thermoprozeßanlagen - Teil 5: Besondere Sicherheitsanforderungen an SalzbadWärmebehandlungseinrichtungen und -anlagen This European Standard was approved by CEN on 22 November 1999 CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Central Secretariat: rue de Stassart, 36 © 2000 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members B-1050 Brussels Ref No EN 746-5:2000 E Page EN 746-5:2000 Contents Page FOREWORD INTRODUCTION SCOPE NORMATIVE REFERENCES 3.1 3.2 DEFINITIONS Salt Bath Thermoprocessing Equipment Components 6 LIST OF HAZARDS 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 SAFETY REQUIREMENTS AND/OR MEASURES General Liquids in the salt bath area Leaking or Overflowing Salt Slipping or falling of persons into the molten salt Outlets from Cooling Systems Salt Splashes Overheating of the Bath Fumes, Dusts and Gases Breakage of fastening points Breakage of protection tube of thermo-couple Solidification and subsequent remelting of the salts in the bath Workpiece supports Ergonomic Requirements 9 10 10 11 11 11 12 12 13 13 13 14 14 6.1 6.2 6.3 VERIFICATION OF SAFETY REQUIREMENTS AND/OR MEASURES General Suggested test for safety device and automatic shut down Suggested test for function of the agitator system 14 14 14 15 7.1 7.2 INFORMATION FOR USE General Specific information to be provided 15 15 16 ANNEX A (INFORMATIVE) Examples of salt bath furnace set-ups 20 ANNEX ZA (INFORMATIVE) Clauses of this European Standard addressing essential requirements or other provisions of EU Directives 24 Page EN 746-5:2000 FOREWORD This European Standard has been prepared by Technical Committee CEN/TC 186 "Industrial thermoprocessing - Safety", the secretariat of which is held by DIN This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by March 2001, and conflicting national standards shall be withdrawn at the latest by March 2001 This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s) For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this standard According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom The working group that drafted this Part of EN 746 comprised experts from the following countries: France, Germany, Italy, Sweden and United Kingdom This standard forms one part of a series safety standards covering Industrial Thermoprocessing Equipment The full list of parts of EN 746 is given below: EN 746 Industrial Thermoprocessing Equipment Part 1: Common Safety Requirements for Industrial Thermoprocessing Equipment Part 2: Safety Requirements for Combustion and Fuel Handling Systems Part 3: Safety Requirements for the Generation and Use of Atmosphere gases Part 4: Particular Safety Requirements for Hot Dip Galvanising Thermoprocessing Equipment Part 5: Particular Safety Requirements for Salt Bath Thermoprocessing Equipment Part 6: Particular Safety Requirements for Material Melting, Remelting and Liquid Phase Maintaining Thermoprocessing Equipment Part 7: Particular Safety Requirements for Vacuum Thermoprocessing Equipment Part 8: Particular Safety Requirements for Quenching Equipment An assessment of the foreseeable risks arising from the use of the equipment was carried out when this standard was prepared Page EN 746-5:2000 The annexes A and ZA are informative INTRODUCTION The EN 746-1 General Safety Requirements contains the common safety provisions and devices for all types of industrial thermoprocessing equipment This part of the standard details in addition those extra safety requirements which need special attention against the equipment listed in the scope This European Standard is a type C standard as defined in EN 292:1991 The extent to which hazards are covered is indicated in the scope of this standard SCOPE This part of EN 746 gives the specific hazards and safety requirements for the melting and use of molten salt that shall be provided by the manufacturer for Salt Bath Industrial Thermoprocessing Equipment, whether it is used as an independent unit or an integrated part of a plant The limits of the equipment will include any transportation equipment which is located wholly or partially in the bath This part of EN 746 does not cover the handling, storage, transport, disposal, transfer or regeneration of the salts and processed material outside the limits of the equipment This part of EN 746 applies not only to the normal operation of the equipment but also to the safety of personnel and property when foreseeable faults occur Examples of salt bath furnace set-ups are shown in Fig 1, Fig 2, Fig and Fig NOTE: There are many variations in the design of salt bath equipment Only three examples of the various types are given in this text NORMATIVE REFERENCES This European Standard incorporates by dated or undated references, provisions from other publications These normative references are cited at the appropriate places in the text and the publications are listed hereafter For dated references, subsequent amendments to or revisions of any of these publications apply to this European standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies EN 166 Personal eye-protection - Specifications EN 292-1:1991 Safety of machinery - Basic concepts, general principles for design Part 1: Basic terminology, methodology EN 292-2:1991 Safety of machinery - Basic concepts, general principles for design Part 2: Technical principles and specifications Page EN 746-5:2000 EN 345 Specification for safety footwear for professional use EN 346 Specification for protective footwear for professional use EN 469 Protective clothing for firefighters - Requirements and test methods for protective clothing for firefighting EN 531 Protective clothing for industrial workers exposed to heat (excluding fire fighters' and welders' clothing) EN 563 Safety of machinery - Temperatures of touchable surfaces - Ergonomics data to establish temperature limit values for hot surfaces EN 614-1 Safety of machinery - Ergonomic design principles Part 1: Terminology and general principles EN 746-1:1997 Industrial Thermoprocessing Equipment Part 1: Common Safety Requirements for Industrial Thermoprocessing Equipment EN 746-2:1997 Industrial Thermoprocessing Equipment Part 2: Safety Requirements for Combustion and Fuel Handling Systems EN 746-8:2000 Industrial Thermoprocessing Equipment – Part 8: Particular Safety Requirements for Quenching Equipment EN 953 Safety of machinery - Guards - General requirements for the design and construction of fixed and movable guards EN 954-1 Safety of machinery - Safety related parts of control systems Part 1: General principles for design prEN 1005-2:1998 Safety of machinery - Human physical performance Part 2: Manual handling of machinery and component parts of machinery prEN 1005-3:1998 Safety of machinery - Human physical performance Part 3: Recommended force limits for machinery operation EN 1070 Safety of machinery - Terminology EN 1093-4 Safety of machinery - Evaluation of the emission of airborne hazardous substances Part 4: Capture efficiency of an exhaust system - Tracer method EN 10095 Heat restisting steels and alloys Page EN 746-5:2000 EN 61310-1 Safety of machinery - Indication, marking and actuation Part 1: Requirements for visual, auditory and tactile signals (IEC 61310-1:1995) DEFINITIONS For the purposes of this standard the definitions given in EN 1070 apply Additional definitions specifically needed for this part of this standard are added below: 3.1 Salt Bath Thermoprocessing Equipment Equipment which melts and/or contains various molten salt or salt mixtures into which workpieces are partially or fully immersed for a predetermined time interval in order to modify the structure and/or the physical properties of the workpiece, or in which salt is circulated as a heat transfer system The equipment includes the unit for melting salt plus that handling equipment used immediately in the vicinity to treat either single or multiple components: This equipment may include for example: 3.2 mechanical handling systems; heating systems; cooling systems; environmental control systems; electrical and control systems; systems to cover ergonomic requirements and washing and agitating systems Components Workpieces or any other object immersed in the salt bath LIST OF HAZARDS An assessment of the foreseeable risks arising from the use of the industrial thermoprocessing equipment has been carried out when this standard was elaborated The clause has been condensed into a table (see table 1) It summarises those areas which require consideration by the manufacturer For ease of reference the table indicates the need for safety features or instructions in columns The table shall only be used in conjunction with clauses and where further detail is given Table shows the Hazard, Hazardous Situation, Preventative Measures and the Verification Means (as pointed out in clause 6) identified for the equipment type described in this part to this standard Page EN 746-5:2000 Table 1: List of Hazards, Hazardous Situations and Preventative Measures Item Hazard Mechanical 1.1 Crushing/ Shearing/ Entanglement 1.2 Slip/Trip Hazardous situations Mechanical handling system lift continuous metal conveyor belt continuous feeding equipment for wire/strip floor surface walkway spilled fluids (e.g water/salt) Preventative measures References For all cases, fit fixed guard or provide protective fence and interlocking or light beam to prevent unauthorised entry to danger zone EN 746-1:1997, 2.2/2.3 and 2.4 EN 292-2:1991, 1 4.1.2, 4.2.2.2 EN 292-1:1991, 3.22.1 Provide non-slip surfaces and/or checkered plate/wire mesh walkway surfaces EN 746-1:1997, 5.2.11 1 Ensure that information for use contains advice on good housekeeping 1.3 Falls 1.4 Drawing-in into bath onto equipment Fit protective fencing 5.4 strip processing equipment washing and agitating system For both cases, fit fixed guard or provide protective fence and/or interlocking or light beam to prevent unauthorised entry to danger zone EN 746-1:1997, 2.2/2.3 and 2.4 EN 292-2:1991, 4.1.2, 4.2.2.2 EN 292-1:1991, 3.22.1 5.9 and 7.2.9 Breakage of fastening points of pot Design to give adequate strength and corrosion or tank during transportation resistance Injury to persons 1.5 Verification means*) Thermal 2.1 2.2 High pressure liquid injected into molten salt Molten salt break-through due to the loss of stability of metal or ceramic pot or tank Use electric or pneumatic systems wherever possible 5.2 5.6 Avoid use of hydraulic systems near the molten salt Design furnace either to prevent 5.3 molten salt flowing out of the casing or to convey the molten salt to a no danger zone and (continued) *) see Note to clause for explanation of numbers Page EN 746-5:2000 Table 1: (continued) Item Hazard Hazardous situations Preventative measures References 2.3 Breakage of thermocouple protection tubes Design for effective safe shut down 5.10 2.4 Breakage or leakage in cooling systems Prevent cooling system blockage 5.2 5.5 2.5 2.6 2.7 2.8 Verification means*) and and Preferably use external cooling Preferably use air cooling Do not use internal cooling with liquids above 250 C bath temperature and In closed cooling systems set safety device to avoid overpressure and Foreign liquids entering the molten Process parts/tools to be dry salt 5.2 5.6 7.2 Refill with dry salts Prevent drips of water into bath and Protective equipment to be used Components with closed hollows or tube-like components immersed in molten salt Do not immerse closed hollow 7.2.7 or tube like components in salt bath or design such components to have sufficient strength to prevent bursting Poorly designed workpiece supports can trap salt and cause explosions Design of workpiece supports 5.12 and Persons falling into bath Provision of guards 5.4 7.2.11 Design of enclosure Use covers Contact by person with hot cooling Protect outlets fluid 5.5 (continued) *) see Note to clause for explanation of numbers Page 12 EN 746-5:2000 a) Access to the agitator shaft(s) shall be prevented by the provision of fixed guards (e.g EN 953); (1 and 2) b) A sign at the equipment shall ensure that the agitator paddle (see 7.2.8 f)) only operates when it is under the surface of the molten salts and that it is set at the manufacturer's recommended depth to prevent splashing when operating normally; (1 and 2) c) Give consideration to the inclusion of automatic, mechanical or special handling devices for workpieces to minimise the operator's presence within the danger zone in the charging/discharging parts of the furnace NOTE: 5.7 These devices are particularly useful if the components are tubes or tube like Overheating of the Bath When the bath is being used overheating can occur and this can cause bath-eruptions, overflowing or explosions a) Provide sensor to check for overheating which gives an alarm; (1 and 2) b) Provide additional independent controls and cut-off systems (such as a thermostat which switches off the heating input) in accordance with category of EN 954-1; (1 and 2) c) When nitrite, nitrate or mixtures of them form the constituents of the bath particularly when treating aluminium or aluminium alloys then additional independent controls and cut-off systems shall be provided in accordance with category of EN 954-1; (1 and 2) 1) The temperature limit for treating aluminium and aluminium alloys shall be 550 °C and it is normal to use pots made from plain carbon or mild steels; (1 and 2) 2) For temperatures exceeding 550 °C pots made from heat resistant steels shall be used; (1 and 2) 3) The temperature limit for treating steel components shall be 650 °C; (1 and 2) d) Provide separate monitoring thermocouple with an alarm to cut power (1 and 3) 5.8 Fumes, Dusts and Gases Fumes, dusts and gases from the process can be harmful to health if contacted on the skin, ingested or inhaled Provide means to ensure that all harmful fumes dusts and gases are prevented from entering any person's breathing zone (e.g fitting hoods, rim extraction, enclosures and/or exhaust systems to remove pollutants) (1 and 2) The manufacturer shall indicate the hazards incurred and the nature of the emanations Reference shall be made to EN 1093-4 (1) Because the requirements of exhaust equipment vary with the nature of the equipment, it is not possible to give details of the exhaust equipment in this standard (1 and 2) Page 13 EN 746-5:2000 NOTE: 5.9 The design, number and location of exhaust points will depend upon factors such as: temperature, airflow, equipment size, heat input, product etc Breakage of fastening points In the conditions in which salt bath furnaces are required to operate there is a high and severe incidence of corrosion It is essential therefore that, in particular fastening points for transportation purposes are able to withstand these conditions (e.g strap welded or eye-end threaded to the sides of the pot and subject to non-destructive testing (e.g X-ray)) after manufacture and to regular visual and non-destructive testing by the user at intervals recommended by the manufacturer Take account of the possibility of galvanic reaction between the parent metal and the fastening (1 and 2) NOTE: 5.10 Information for use (clause 7, 7.2.10 gives details of the inspection requirements) Breakage of protection tube of thermo-couple The breakage of the protection tube of a thermocouple especially caused by the corrosive influences of salt, air and temperature can cause failure in the control system This can result in overheating in the bath leading to hazards such as burning and explosion Consider the inclusion of safety devices or the provision of automatic shutdown means hazards in accordance with at least category of EN 954-1, to ensure that any failure of a thermocouple does not lead to a hazard (1 and 3) 5.11 Solidification and subsequent remelting of the salts in the bath When the furnace is shut down and the salts remaining in the furnace are allowed to cool and solidify then there are hidden dangers that could occur when the salts are re-liquified This is because the salts nearest the heat source melt first and a solid crust remains Pressure build up in the liquid salt can cause the crust to burst a) A cover shall be provided This cover shall be secured in position (see Fig 1) e.g by catches and constructed to contain any eruption of salt from the salt bath; (1 and 2) b) The general design and, in particular, that of the heating system shall be such as to ensure the safe melting and remelting of salts so as to reduce the probability of pressure build-up in the molten part of the salt bath This can be met by, for example: a heating system which simultaneously melts the salt on and under the surface (1 and 2) NOTE: There are no European Standards for the design and construction of covers for salt bath furnaces The manufacturer is advised to use his experience and state of the art in any particular specific situation requiring such preventative measure Page 14 EN 746-5:2000 5.12 Workpiece supports Workpiece supports shall be designed to eliminate hollows or acure angles during immersion (This will prevent the build-up of pressure which could cause salt ejection under explosive conditions.) (1) Workpiece supports shall be constructed of resisting steel (EN 10095) (1) 5.13 Ergonomic Requirements Operators panels shall be in a good working position in accordance with EN 614-1 and CEN/TC 122/WG (1 and 2) Lifting equipment for charging or discharging shall be available for use (reference shall be made to prEN 1005-2:1998) Reference shall also be made to prEN 1005-3:1998 (1) VERIFICATION OF SAFETY REQUIREMENTS AND/OR MEASURES 6.1 General Verification of the safety requirements and/or the preventative measures given in table and clause can be carried out by visual inspection, functional check or a test to check a specific function NOTE 1: The verification means have been annotated against the preventative measure in Table and also in italics against the preventative measure described in clause In most cases, verification by a test, when given, will be to a specific standard This is quoted, in italics against the specific preventative measure in clause to which it refers The code used to describe the verification means is as follows: = Visual = Functional check = Test to check a specific feature NOTE 2: 6.2 The following tests are only one method of verification, other test methods are permitted Suggested test for safety device and automatic shut down Test method Check calibration of temperature control device Page 15 EN 746-5:2000 With the furnace cold, disconnect the thermocouple and simulate the signal to the controller indicating: a) thermocouple broken; b) thermocouple giving correct signal Check the function of controller: a) Reconnect the thermocouple; b) Re-index the temperature controller, set value higher than the safety device release temperature but lower than the furnace maximum operating temperature Override or disable control/thermocouple Fire furnace and allow to run up to maximum operating temperature Check function of safety device or automatic shut-down device Test criteria Safety or automatic shut-down device shall function to switch-off or place furnace in a safe mode before maximum operating temperature is reached 6.3 Suggested test for function of the agitator system Test Method Check that the protected splash guards are in place before starting agitator system Switch on the agitator system Test criteria The agitator system shall not cause molten salt to splash outside the perimeter of the furnace at the operator's working position(s) INFORMATION FOR USE 7.1 General The manufacturer shall provide the user instructions which are full and comprehensive for installation, use, maintenance and dismantling of the equipment in accordance with the requirements of EN 746-1 and this standard The manufacturer shall remind the user that training of operators should include tuition in the safe handling of the furnace and its operation The manufacturer shall remind the user that the equipment has been designed for use by trained operators or supervisors in accordance with the following points: Page 16 EN 746-5:2000 7.2 Specific information to be provided 7.2.1 Warning plates and signs A statement that: a) At every entrance to the equipment warning signs, designed in accordance with EN 61310-1 covering the following warnings, shall be displayed where they are readable by all persons 1) Prohibiting the extinguishing of fires with water; 2) Prohibiting the admittance of non-authorised persons; NOTE: A non-authorised person is anyone other than the trained operator, persons under training, the supervisors or their superiors and trained maintenance/ service personnel or any other person identified by the user b) Place inside the equipment warning signs designed in accordance with EN 61310-1, covering the following warnings: Prohibiting eating, drinking and smoking; c) Such signs shall be legible and permanent 7.2.2 Personal protective equipment (PPE) A statement that the following equipment shall be worn when working with salt bath thermoprocessing equipment: a) Face Protection b) Protective suits e.g constructed of self-extinguishing material such as polycarbonate mounted on a suitable helmet in such a form that the face and skin are protected in accordance with EN 166; e.g constructed of cotton with flame resistant chemical impregnation in accordance with EN 531; c) Shirts e.g constructed of cotton, they shall have long sleeves fastened by buttons or velcro in accordance with EN 531; d) Protective gauntlets e.g constructed of heat resistant material They shall be easily removable from the hands in accordance with EN 531; e) Protective shoes e.g constructed of leather with a friction/slip resistant sole in accordance with EN 345 and EN 346 A statement that personal protective equipment shall be regularly cleaned Page 17 EN 746-5:2000 7.2.3 Emergency items A statement that the following items shall be available in or near the salt bath location: a) Fire fighting equipment, e.g protective clothing for firefighters in accordance with EN 469; b) Shower(s); c) Eye wash(es); d) Salt antidotes 7.2.4 Compatibility and use of salts A statement that: a) If different salts are mixed then their compatibility shall be checked and taken into account; b) The user shall take into account any special instructions from the supplier of the salt as to its use 7.2.5 Treatment of Components A statement that: Components shall be clean and dry except for surface cleaning or special treatments with water admixture It is usual to preheat parts up to 300 °C to ensure that they are dry 7.2.6 Material used for processing A statement that: If salt bath temperatures are higher than 250 °C, then all materials used in the process as salts, gases etc shall be kept dry and stored in a dry place 7.2.7 Closed hollows or tube like components A statement that: a) Before components with closed ends or in-built hollows are processed, their strength shall be checked to prevent their unintentional bursting; b) The hollows shall be dry, clean and free from organic substances; c) When tubes or tubelike components are being processed then to prevent ejection of hot salt, operators shall be protected from salt splashes by some means such as hoods Page 18 EN 746-5:2000 7.2.8 Starting and stopping procedures A statement that, in particular the following points shall be included: a) During melting/solidifying the bath shall be covered with a secure cover; b) Desludging requirements and frequency; c) Salt bath level at particular stages of usage; d) Use and condition of the exhaust system; e) Heating/cooling procedures; f) Agitator paddles to operate only when they are under the surface of the salt and that a depth of salt and the depth of dip recommended by the manufacturer be maintained in the bath 7.2.9 Maintenance of the Salt Bath A statement that: The information for use shall define the frequency of desludging and bath analyses and also the necessity to carry out regular bath analyses 7.2.10 Transportation of pots or tanks A statement that: a) Pots or tanks shall only be transported empty or if the salt is completely solidified; b) The need to examine the fastening points of the pot regularly or at least before any transport to check their condition 7.2.11 Maintenance of the equipment A statement that: a) The bath shall be covered during work (repair, maintenance) in the area of the salt bath above the normal operating position; b) The user is advised to carry out the checks like those given as examples in table at the frequencies indicated and that records shall be made of these checks and that records have to be stored for more than years