Conditions /Temperature / Thermal shock / Pressure / General operating data

Permissible operating conditions

The permissible values for operating temperature and pressure must always be seen in combination. The reason for this is the thermal stresses that result from temperature differences between the inner and outer surfaces of the glass component. These stresses are superimposed on the stresses resulting from the working pressure.
Higher thermal stresses therefore result in a reduction of the permissible working pressure. Thermal insulation reduces the thermal stresses and can, therefore, become a requirement of an installation.

Permissible operating temperature

Borosilicate glass only deforms at temperatures which approach its transformation temperature (approximately 525 ºC) and up to this point it retains its mechanical strength. The permissible operating temperature is, however, considerably lower – normally around 200 °C – for glass components, provided that there is no sudden temperature shock and that the components are not specially marked (see page 1.8). In exceptional cases, which call for special precautions, temperatures up to 300°C are also possible.
At sub-zero temperatures tensile strength tends to increase. Borosilicate glass 3.3 can, therefore, be used safely at temperatures as low as -80 ºC.
These temperature limits should be regarded only as a guideline and must always be modified in accordance with the actual operating conditions of a given application. The individual operating conditions of some components in this catalogue must also be considered. Where such operating limits apply, they are detailed in the individual catalogue sections and component descriptions.

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Thermal shock

Rapid changes in temperature across the walls of glass components should be avoided during operation both indoors and outside. They result in increased thermal stress in the glass which, as described above, has an adverse effect on the permissible operating pressure of the plant components. Although it is not possible to give a definite figure applicable to all the operating conditions likely to be encountered in practice, a maximum permissible thermal shock of 120 K can be taken as a general guide.

Permissible operating pressure

Glass components in all nominal sizes that are basically cylindrical, domed and spherical can be used with full vacuum (-1 bar g), provided they are not specially marked otherwise.
Likewise the maximum permissible operating pressures (ps) shown in the tables apply to these glass components as a function of their principal nominal size DN or diameter D (in the case of spherical vessels) and the internal (product side) and external (ambient) temperature difference (DQ). Further details with regard to the sizing of borosilicate glass 3.3 components can be found in the technical information of the catalogue.

Depending on the shape and the particular working conditions, glass components can be used under certain circumstances at higher internal pressures. In these cases, the glass component is specially marked on in accordance with EN 1595.

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General operating data

Operating temperature TB = 200 °C
Temperature differences DQ £ 180 K
Heat transfer coefficient inside µi = 1200Wm-²K-1, outside µa = 11,6Wm-²K-1
All components are suitable for full vacuum ps = -1 bar g

Tables:

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