DGUV Regel 109-605e - Metals heat treatment sector

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Abschnitt 4.2 - 4.2 Annex: Structural requirements set out in DGUV Regel 109-007 (concerning guidelines for the heat treatment of steel and other heavy metals in salt baths; formerly BGR 153)

Knowledge of the requirements to which plants were subject at the time of their placing on the market may be useful for their assessment when in operation. The requirements of BGR 153 (formerly ZH 1/412), April 1990 edition, were binding for a long time for plants employing salt baths for the heat treatment of metals.

Excerpt from BGR 153, containing guidelines for the heat treatment of steel and other heavy metals in salt baths, April 1990 edition, concerning structural requirements:

2. Definitions

2.1 Examples of equipment in this context are equipment for ventilation, temperature control and limitation, charging, extraction, washing and cleaning, ancillary equipment and quenching baths.

2.2 Salt baths in the sense of this rule are furnaces heated electrically or by combustible fuel for the heat treatment of workpieces in molten salt. During normal operation the furnaces are filled with molten salt.

...

2.4 Temperature control devices in the sense of this rule are devices which control the heating power as a function of the measured temperature of the molten salt.

2.5 Temperature limiting devices in the sense of this rule are safety devices which prevent permissible temperatures of the molten salt from being exceeded.

4.5 Temperature control and temperature limiting devices

4.5.1 Salt baths must be equipped with temperature control devices.

4.5.2 Nitrate salt baths must be equipped with temperature limiting devices acting separately from the temperature control devices in such cases where the installed heat output allows the temperature of the molten salt to:

  • Exceed 560 °C in furnaces employing steel crucibles Or

  • Exceed 650 °C in furnaces employing crucibles of heat-resistant and scale-resistant steel.

    The temperature limiting devices must switch off the salt bath furnaces automatically when the maximum permissible temperature of the molten salt is exceeded, and must also prevent the furnaces from being switched on again automatically.

    Temperature control and temperature limiting devices acting separately must each possess dedicated temperature sensors and switching devices (valves, contactors).

    Fuses are examples of temperature limiting devices.

4.5.3 Sensors for temperature control and temperature limiting devices must be situated such that they are not damaged when the salt bath is charged.

4.5.4 The sensors of the temperature limiting devices must be situated at the points in the molten salt at which the highest temperatures are anticipated.

4.5.5 Equipment for measuring, controlling, limiting and indicating the temperature of the molten salt must be situated or covered such that it is protected against direct thermal radiation and salt spatter.

4.6 Disconnection from the power supply

4.6.1 Facility must be provided for salt baths and upstream and downstream equipment for treatment to be disconnected from the power supply.

This is achieved for example by means of fuses, plugs or plug-in couplings or main control devices in accordance with Section 4.6.2.

Isolation from the power supply is necessary for example for the performance of maintenance or repair work.

4.6.2 Salt bath installations must be equipped with a separate main control device for each form of energy.

The following constitute salt bath installations:

  • Salt baths.

  • Facilities for treatment upstream and downstream of the salt bath.

    Or

  • Salt baths with facilities for treatment upstream and downstream of the salt bath which are connected to a common power supply.

Examples of main control devices are main switches and main valves.

With regard to main switches, see DIN VDE 0721-911, Industrial electroheat installations; general safety regulations

4.6.3 Facility must be provided for main control devices to be operated from outside the danger zone.

The danger zone is the area in which persons may be at risk of injury or harm, for example by thermal radiation, spatter of hot molten substance or liquids, open flames, hot workpieces, substances presenting a health risk, and crushing and shearing points.

4.6.4 Main switches shall be able to be secured against inadvertent or unautorized activation in the off-position.

4.6.5 Actuators of main control devices must be easily accessible and be designed, situated and identified such that their assignment, direction of operation and operating state are clearly identifiable.

...

4.11 Water supply to the plant

Water for the water quenching baths must be supplied through pipes with unobstructed inlets.

Where supply pipes are immersed in the quenching water, reverse suction and thus discharge of quenching water is possible.