Bsi bs en 00746 5 2000

/home/gencode/overflow/cen/w746p5/746 1 9957 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |[.]

Part 5: Particular safety requirements for

salt bath thermoprocessing equipment

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 0 580 35979 4

Amendments issued since publication

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.

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 à bain de sel

Industrielle Thermoprozeßanlagen - Teil 5: Besondere Sicherheitsanforderungen an Salzbad- Wärmebehandlungseinrichtungen 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

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Central Secretariat: rue de Stassart, 36 B-1050 Brussels

© 2000 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members.

Ref No EN 746-5:2000 E

7.2 Specific information to be provided 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

This European Standard has been prepared by Technical Committee CEN/TC 186 "Industrialthermoprocessing - 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 nationalstandards shall be withdrawn at the latest by March 2001

This European Standard has been prepared under a mandate given to CEN by the EuropeanCommission 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 ofthis 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 UnitedKingdom

The working group that drafted this Part of EN 746 comprised experts from the followingcountries: 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

EquipmentPart 2: Safety Requirements for Combustion and Fuel Handling Systems

Part 3: Safety Requirements for the Generation and Use of Atmosphere gasesPart 4: Particular Safety Requirements for Hot Dip Galvanising

Thermoprocessing EquipmentPart 5: Particular Safety Requirements for Salt Bath Thermoprocessing

EquipmentPart 6: Particular Safety Requirements for Material Melting, Remelting and

Liquid Phase Maintaining Thermoprocessing EquipmentPart 7: Particular Safety Requirements for Vacuum Thermoprocessing

EquipmentPart 8: Particular Safety Requirements for Quenching Equipment

An assessment of the foreseeable risks arising from the use of the equipment was carried outwhen this standard was prepared

The annexes A and ZA are informative.

The EN 746-1 General Safety Requirements contains the common safety provisions anddevices for all types of industrial thermoprocessing equipment This part of the standarddetails in addition those extra safety requirements which need special attention against theequipment 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

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 islocated wholly or partially in the bath

This part of EN 746 does not cover the handling, storage, transport, disposal, transfer orregeneration 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 thesafety of personnel and property when foreseeable faults occur

Examples of salt bath furnace set-ups are shown in Fig 1, Fig 2, Fig 3 and Fig 4

NOTE: There are many variations in the design of salt bath equipment Only three

examples of the various types are given in this text

This European Standard incorporates by dated or undated references, provisions from otherpublications These normative references are cited at the appropriate places in the text and thepublications 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 byamendment or revision For undated references the latest edition of the publication referred toapplies

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

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 IndustrialThermoprocessing 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 designprEN 1005-2:1998 Safety of machinery - Human physical performance

Part 2: Manual handling of machinery and component parts of

machineryprEN 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

EN 61310-1 Safety of machinery Indication, marking and actuation

-Part 1: Requirements for visual, auditory and tactile signals(IEC 61310-1:1995)

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 whichworkpieces are partially or fully immersed for a predetermined time interval in order tomodify the structure and/or the physical properties of the workpiece, or in which salt iscirculated 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:

mechanical handling systems;

heating systems;

cooling systems;

environmental control systems;

electrical and control systems;

systems to cover ergonomic requirements and

washing and agitating systems

Table 1 shows the Hazard, Hazardous Situation, Preventative Measures and the VerificationMeans (as pointed out in clause 6) identified for the equipment type described in this part tothis standard

4 Preventative measures

5 Re- ferences

6 Verifi- cation means *)

continuous metal conveyor belt

continuous feeding equipment for wire/strip

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, 4.1.2, 4.2.2.2

EN 292-1:1991, 3.22.1

1 1 1

Provide non-slip surfaces and/or checkered plate/wire mesh walkway surfaces.

EN 746-1:1997, 5.2.11

1 1 1

1.2 Slip/Trip
floor surface

walkway

spilled fluids (e.g water/salt)

Ensure that information for use contains advice on good housekeeping

1

1.3 Falls
into bath

onto equipment

Fit protective fencing 5.4 1

1.4 Drawing-in
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

1 1

1.5 Breakage of fastening points of pot

or tank during transportation Injury to persons

Design to give adequate strength and corrosion resistance

5.9 7.2.9

1 2.1 High pressure liquid injected into

molten salt

Avoid use of hydraulic systems near the molten salt

1

2.2 Molten salt break-through due to

the loss of stability of metal or ceramic pot or tank

Design furnace either to prevent molten salt flowing out of the casing or to convey the molten salt to a no danger zone

4 Preventative measures

5 Re- ferences

6 Verifi- cation means *)

1 and 2

Process parts/tools to be dry 5.2

5.6 7.2

1

Components with closed hollows

or tube-like components immersed

in molten salt

Do not immerse closed hollow

or tube like components in salt bath or design such components

to have sufficient strength to prevent bursting.

7.2.7 1 2.6

Poorly designed workpiece supports can trap salt and cause explosions

Design of workpiece supports 5.12 1 and 2

Provision of guards 5.4

7.2.11

1 Design of enclosure 1 2.7 Persons falling into bath

4 Preventative measures

5 Re- ferences

6 Verifi- cation means *)

Design of agitator system 5.6

7.2.2

3 Handling of components/tools 1 2.9 Salt splashing

Protective equipment 1 Design of heating system 5.11

7.2.8

1 and 2 Instruction handbook 1

2.10 Pressure build-up during remelting

after solidification of salt bath surface

Maintenance of the salt bath 1 2.11 Overheating of bath Design of salt bath equipment 5.7 1 and 2

3 Materials and Substances

3.1 Inhalation of fumes, dusts and

gases emitted from salt

Design effective exhaust system 5.8 1 and 3

4 Neglecting ergonomic principles

4.1 Unhealthy posture or excessive

efforts causing impaired judgement

or poor visibility during charging

or discharging

The equipment shall be designed in such a way that there is no hindrance to technical aids and possiblility for good working postures

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 bythis standard

In addition equipment shall comply as appropriate, with other relevant parts of this standardlisted in clause 2 (e.g EN 746-8:2000) as well as with EN 292:1991 for hazards which are notcovered 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

NOTE: The following preventative measures have been detailed to show how the

hazards and hazardous situations detailed in table 1 can be minimised Anexplanation of the hazard is given at the beginning followed by an explanation

of the preventative measure

The general references to design in table 1 to this standard are intended to drawattention to the need to consider design in this area More detailed

consideration is given to this matter in the sections which follow this generalintroduction

5.2 Liquids in the salt bath area

Steam will be generated if liquids fall into a salt bath especially when the salt bath

temperature exceeds 250 °C This steam which will be under pressure will spray hot salt intothe 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 position hydraulic, cooling or washing systems so that the liquids can get intothe 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 thesalt bath (e.g not over the bath or below salt bath level); (1)

d) Preference for air cooling systems (1)

1) Where water cooling is used it shall be an open system and restricted to a salt bathmaximum temperature of 250 °C; (1)

2) Design pipes and piping cooling systems to reduce the possibility of a blockage(e.g covering with scale) To confirm visibly that the liquid flow through thepipes and piping systems is not blocked (e.g fit flow meter/alarm, provide openbreak in pipe or fit a tundish);

(1 and 2)

e) Design to prevent furnace parts liable to collect condensation from being located overthe bath (1 and 2)

5.3 Leaking or Overflowing Salt

If molten salt 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 flammablematerials could catch fire

a) Design the furnace so that if the pot breaks then the molten salt shall be prevented fromescaping via the casing:

For example by:

ensuring the integrity of the casing (e.g corrosion resistant coating on inside ofcasing);

providing means to collect escaping molten salt (such as reservoirs, pits, runawaychannels); (1 and 2)

if not containable, use channels to take salt away from operators and bystanders;b) Tanks and pots to be filled with nitrates, nitrites or mixtures of them shall be made ofmaterial resistant to both oxidation and thermal degradation when temperatures willexceed 550 °C, e.g heat resising 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 fallinginto molten salt is high The designer should therefore pay particular regard to the placing andneed 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 Ifthis is not possible then a balustrade of height 1 m above floor with a mid rail shall beprovided in the identified area; (1)

b) At the operator's working position(s) the rim of the bath or the balustrade rail can belowered to 0,7 m but only if the distance between the pot and balustrade is 0,2 m ormore (1)

5.5 Outlets from Cooling Systems

In order to avoid the build up of pressure in the cooling system, it is common practice to runthe cooling system liquid or air to waste through an open drain Hazardous situations can arisewhich could cause burning of persons or bystanders

a) Open outlets from cooling systems shall be located so that if steam or scalding water isejected it will not cause injury (e.g by the provision of guards (e.g EN 953) and/orinstallations or by locating outlets where no person is present or by the location of anexhaust system over the outlet) The surface temperature of any guard this fitted shallnot exceed the requirements of EN 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 and 2)

c) The outlets shall also be far enough away from the molten salt to avoid the possibility ofwater entering 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 thebath

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 operateswhen it is under the surface of the molten salts and that it is set at the manufacturer'srecommended depth to prevent splashing when operating normally; (1 and 2)

c) Give consideration to the inclusion of automatic, mechanical or special handling devicesfor workpieces to minimise the operator's presence within the danger zone in the

charging/discharging parts of the furnace

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 and 2)

b) Provide additional independent controls and cut-off systems (such as a thermostat whichswitches 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 particularlywhen treating aluminium or aluminium alloys then additional independent controls andcut-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; (1 and 2)2) For temperatures exceeding 550 °C pots made from heat resistant steels shall beused; (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 enteringany person's breathing zone (e.g fitting hoods, rim extraction, enclosures and/or exhaustsystems 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 isnot possible to give details of the exhaust equipment in this standard (1 and 2)