1、BRITISH STANDARD Industrial thermoprocessing equipment - Part 5: Particular safety requirements for salt bath thermoprocessing equipment The European standard EN 74662000 has the status of a British Standard ICs 26.180.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYBIGEiT LAW BS EN
2、746-5:ZOOO STD-BSI BS EN 74b-5-ENGL 2000 1b24bb9 0879060 210 a BS EN 746-6:2000 National foreword This British Standard is the official Engish ianguage version of EN 74 - heating systems; - cooling systems; - environmental control systems; - electrical and control systems; - systems to cover ergonom
3、ic requirements and - washing and agitating systems. 3.2 Components Workpieces or any other object immersed in the salt bath. 4 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 elabora
4、ted. 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 5 and
5、7 where further detail is given. Table 1 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. 1 Item - 1 1.1 - - 1.2 - 1.3 - 1.4 - 1.5 - 2 2.1 - - 2.2 STDmBSI BS
6、 EN 74b-5-ENGL 2000 Lb24bb9 08790b7 b75 = Hazardous situations Page 7 EN 746-5:2OOO I ferences Re- Preventative measures Table 1: List of Hazards, Hazardous Situations and Preventative Measures 2 Hazard techanical :rushing/ ;hearing/ intangle- nent ;lipfrip 41s hawing-in 3 I 4 I 5 Mechanical handlin
7、g system - lift - continuous metal conveyor belt - continuous feeding equipment for wire/strip - floor surface - walkway - spilled fluids (e.g. watedsalt) - into bath - onto equipment - strip processing equipment - washing and agitating system Breakage of fastening points of pot or tank during trans
8、portation Injury to persons hermal molten salt Molten salt break-through due to the loss of stability of metal or ceramic pot or tank For all cases, fit fixed guard or provide protective fence and interlocking or light beam to prevent unauthorised entry to danger zone. Provide non-slip surfaces ando
9、r checkered plate/wire mesh walkway surfaces. Ensure that information for use contains advice on good housekeeping Fit protective fencing For both cases, fit fixed guard or provide protective fence and/or interlocking or light beam to prevent unauthorised entry to danger zone. Design to give adequat
10、e strength and corrosion resistance Use electric or pneumatic systems wherever possible Avoid use of hydraulic systems near the molten salt Design furnace either to prevent molten salt flowing out of the casing or to convey the molten salt to a no danger zone EN 746-1:1997, 2.U2.3 and 2.4 4.1.2,4.2.
11、2.2 3.22.1 EN 292-2: 199 1, EN 292-11991, EN 746-1:1997, 5.2.1 1 5.4 EN 746- 1 : 1997, 222.3 and 2.4 4.1.2,4.2.2.2 EN 292-1:1991, 3.22.1 5.9 7.2.9 EN 292-2: 199 1, 5.2 5.6 5.3 6 Verifi- cation meam*) 1 1 land3 1 1 land2 (continued: *) see Note to clause 6 for explanation of numbers STD-BSI BS EN 74b
12、-5-ENGL 2000 W Lb24bb9 08790b8 501 .4 .2.11 5.5 Page 8 EN 746-5:2OOO Table 1: (continued) 2 Hazard 3 Hazardous situations Breakage of thermocouple protection tubes Breakage or leakage in cooling systems Foreign liquids entering the molten salt 2omponents with closed hollows x tube-like components im
13、mersed n molten salt oorly designed workpiece iupports can trap sait and cause :xplosions ersons falling into bath :ontact by person with hot cooling luid 4 Preventative measures Design for effective safe shut down Prevent cooling system blockage. Preferably use external cooling. Preferably use air
14、cooling Do not use internal cooling witi liquids above 250 “C bath temperature. In closed cooling systems set safety device to avoid overpressure. Process parts/tools to be dry. Rell with dry salts. Prevent drips of water into bath. Protective equipment to be used. Do not immerse closed hollow or tu
15、be like components in salt bath or design such components to have sufficient strength to prevent bursting. Design of workpiece supports Provision of guards Design of enclosure Use covers ?rotect outlets 5 Re- ferences 5.10 5.2 5.5 5.2 5.6 7.2 l.2.7 i.12 6 Verifi cati01 land3 means land2 1 1 land2 la
16、nd2 1 1 land2 1 I and 2 (continued: *) see Note to clause 6 for explanation of numbers STD*BSI BS EN 74b-S-ENGL 2000 = lb24bb9 0839069 448 Inhalation of fumes, dusts and gases emitted from salt 2 Hazard Design effective exhaust system 5.8 1 and 3 Page 9 EN 746-512000 The equipment shall be designed
17、in such a way that there is no hindrance to technical aids and possiblility for mod working nostures Table 1: (concluded) 5.13 3 Hazardous situations Salt splashing Pressure build-up during remelting after solidification of salt bath surface Overheating of bath 4 Preventative measures Design of agit
18、ator system Handling of componentdtools hotective equipment Design of heating system Insiruction handbook Maintenance of the salt bath Design ofsalt bath equipment 5 Re- ferences 5.6 7.2.2 5.11 7.2.8 5.7 6 Verifi- cation means*) 3 1 1 1 and 2 1 1 land2 4.1 Unhealthy posture or excessive efforts caus
19、ing impaired judgement or poor visibility during charging or discharging 1 5 SAFETY REQUIREMENTS AND/OR MEASURES 5.1 General The manufacturer of the equipment shall be required to meet the conditions detailed in this part to this standard. See EN 746- 1 and EN 746-2 for general safety requirements r
20、elating to Thermoprocessing Equipment. Machinery shall comply with the provisions of this clause. They also shall comply with EN 292: 1991 for hazards which are relevant but not significant and which are not covered by this standard. In addition equipment shall comply as appropriate, with other rele
21、vant parts of this standard listed in clause 2 (e.g. EN 746-8:2000) as well as with EN 292:1991 for hazards which are not covered in these standards. *) see Note to clause 6 for explanation of numbers For requirements relating to signs and warning labels refer to EN 61310-1 for further information.
22、NOTE: The following preventative measures have been detailed to show how the hazards and hazardous situations detailed in table 1 can be minimised. An explanation of the hazard is given at the beginning followed by an explanation of the preventative measure. The general references to design in table
23、 1 to this standard are intended to draw attention to the need to consider design in this area. More detailed consideration is given to this matter in the sections which follow this general introduction. 5.2 Liquids in the sait bath area Steam will be generated if liquids fall into a salt bath espec
24、ially when the salt bath temperature exceeds 250 OC. This steam which will be under pressure will spray hot salt into the surrounding work area. Measures which can be used to avoid these situations shall include: a) Use electric or pneumatic systems for movement wherever possible; (1) b) Do not posi
25、tion hydraulic, cooling or washing systems so that the liquids can get into the bath (e.g. not over the bath or below salt bath level); (1) c) Position water quenching and salt tanks in such a way as to avoid water getting into the salt bath (e.g. not over the bath or below salt bath level); (1) d)
26、Preference for air cooling systems. (1) 1) Where water cooling is used it shall be an open system and restricted to a salt bath maximum temperature of 250 OC; (1) 2) Design pipes and piping cooling systems to reduce the possibility of a blockage (e.g. covering with scale). To confm visibly that the
27、liquid flow through the pipes and piping systems is not blocked (e.g. fit flow meter/alarm, provide open break in pipe or fit a tundish); (1 and2) e) Design to prevent furnace parts liable to collect condensation from being located over the bath. (1 and 2) 5.3 Leaking or Overtlowing Sait If molten s
28、alt overflows the furnace or leaks from it, then persons standing close to or operating the furnace could be burned by contact with the molten salt. In addition flammable materials could catch fire. a) Design the furnace so that if the pot breaks then the molten salt shall be prevented from escaping
29、 via the casing: STDeBSI ES EN 74b-5-ENGL 2000 Lb24bb9 0879073 OTb Page 11 EN 746-5:2000 For example by: - ensuring the integrity of the casing (e.g. corrosion resistant coating on inside of - providing means to collect escaping molten salt (such as reservoirs, pits, runaway - if not containable, us
30、e channels to take salt away from operators and bystanders; casing); channels); (1 and 2) b) Tanks and pots to be filled with nitrates, nitrites or mixtures of them shall be made of material resistant to both oxidation and thermal degradation when temperatures will exceed 550 OC, e.g. heat resising
31、steels and alloys (EN 10095). (1 and 2) 5.4 Slipping or falling of persons into the molten salt Because persons working at a salt bath furnace wear personal protective equipment and therefore consequently have restricted movement and vision, the hazard of slipping or falling into molten salt is high
32、. The designer should therefore pay particular regard to the placing and need of guarding and other physical protection means. a) The rim of the bath shall be at a minimum height of 0,9 m in respect to the floor level. If this is not possible then a balustrade of height 1 m above floor with a mid ra
33、il shall be provided in the identified area; (1) b) At the operators working position(s) the rim of the bath or the balustrade rail can be lowered to 0,7 m but only if the distance between the pot and balustrade is 0,2 m or more. (1) 5.5 Outlets from Cooling Systems In order to avoid the build up of
34、 pressure in the cooling system, it is common practice to run the cooling system liquid or air to waste through an open drain. Hazardous situations can arise which could cause burning of persons or bystanders. a) Open outlets from cooling systems shall be located so that if steam or scalding water i
35、s ejected it will not cause injury (e.g. by the provision of guards (e.g. EN 953) and/or installations or by locating outlets where no person is present or by the location of an exhaust system over the outlet). The surface temperature of any guard this fitted shall not exceed the requirements of EN
36、563; (1 and 2) b) Open outlets from cooling systems shall be protected to prevent them from being contacted by persons (e.g. by the provision of guards (e.g. EN 953) and/or installations). (1 and2) c) The outlets shall also be far enough away from the molten salt to avoid the possibility of water en
37、tering the molten salt. (1 and 2) 5.6 Salt Splashes Salt splashes can cause serious injuries. They can occur from either the rotating agitator itself or from the salt garlands on agitator shafts or by the result of dropping workpieces into the bath. STD-BSI BS EN 74b-5-ENGL 2000 M Lb24bb9 0879072 T3
38、2 Page 12 EN 746-5:2O00 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
39、the manufacturers 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 operators presence within the danger zone in the chargingldischarging parts of the fu
40、rnace. NOTE: These devices are particularly useful if the components are tubes or tube like. 5.7 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
41、 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 1 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
42、or aluminium alloys then additional independent controls and cut-off systems shall be provided in accordance with category 4 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
43、; (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 OC; (1 and 2) d) Provide separate monitoring thermocouple with an alarm to cut power. (1 and 3) 5.8 Fumes, Dusts and Gase
44、s 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 persons breathing zone (e.g. fitting hoods, rim extraction, enclosures and/or exhaust syste
45、ms 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
46、equipment in this standard. (1 and 2) STDmBSI BS EN 74b-5-ENGL 2000 Lb24bb9 0877073 979 Page 13 EN 746-512000 NOTE: The design, number and location of exhaust points will depend upon factors such as: temperature, airflow, equipment size, heat input, product etc. 5.9 Breakage of fastening points In t
47、he 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 o
48、f 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:
49、 Information for use (clause 7,7.2.10 gives details of the inspection requirements). 5.10 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 1 of EN 954-1, to ensure that any failure of a thermo
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