Properties of Borocilicate


Properties Of Borosilicate Glass

The advantage of using glass process plant and pipeline components as a basis for the construction of complete process systems have long been recognized throughout the world’s chemical, pharmaceutical, food and drink and allied industries. 

All the glass components detailed in this catalogue are manufactured exclusively from borosilicate glass type 3.3. Its principal features are its almost universal resistance to corrosion and its low coefficient of thermal expansion which allows great thermal strength and resistance to thermal shock.

Borosilicate glass plant and pipeline is used in both internal pressure and vacuum applications.

All the glass components in this catalogue comply with ate above specifications. In addition, components with butteress ends DN 25 to DN 450 comply with the dimensional and wall thickness requirements of ISO 3585.

For information on the testing, handling and use of glass plant, pipeline and fitting, please refer to ISO 3586.




Chemical Composition

The borosilicate glass used in the manufacture of our range of process plant and pipe line components  has the following approximate composition.  

Component% by weight
Al²O³ 2.2  
Others 0.5  




Chemical Resistance

Borosilicate glass is resistant to almost all substances except hydrofluoric acid, phosphoric acid and hot strong caustic solutions. Of these, hydrofluoric acid has the most serious effect and, even when a solution contains a few parts per million, corrosion will occur. 

Phosphoric acid and caustic solution cause no problem when cold but at elevated temperatures corrosion occurs. Caustic solution up to 30% concentration can be handled safely at ambient temperature. Under actual service conditions, the effect of turbulence and traces of other chemical is the solution may increase or decrease the rate of attack. Therefore, it is not possible to give precise figure for corrosion by caustic solutions, but Figure 1 shows typical rates.




Physical Properties

Coefficient of mean linear thermal expansion

(20°C to 300°C)                     a = (3.3 ± 0.1) x 10-6 k –1

Mean thermal conductivity

(20°C to 200°C)                     l = 1.3 W/mK

Mean specific heat capacity

(20°C to 200°C)                     Cr = 910 j/kgk

Density  at 20°C                   u = 2.23 g/cm³






Optical Properties

With borosilicate glass, the transmission of ultra-violet light – which is the great importance for photo-chemical reaction- is somewhat greater in the middle spectrum that with normal window glass.

If photosensitive substances are being processed, the glass can be amber stained to special order. This permanent coating reduces the ultra violet light transmission to a minimum. Figure 2 shows a comparison of the light transmission for plain and amber glass.  




Mechanical Properties

The mechanical properties of the glass differ from those of metals. The lack of ductility of the glass prevent the equalization of stresses at local  irregularities or flaws and the breaking strength varies considerably.

Whilst the average breaking tensile stress of borosilicate  glass with flawless fire polished surface is approximately 70N/mm² the allowable design stress is considerably lower. AD-N4 specifies the allowable design stress in tension, bending and compression taking into account the likely glass surface condition in service

In addition the thermal stresses resulting from differential expansion of the inner and outer glass surface must be considered.  



Permissible Operating Conditions

Thermal Shock  

The permissible values for working temperature and    pressure must always be considered together as thermal stresses  resulting from high temperature differences between the inner and outer glass surfaces reduce the permissible working pressure (see Figures 3 to 8).

If  the  internal temperature is less than the external - For example: in low temperature applications or for vessels with external heating – the thermal stresses require detailed consideration and we recommend that our Technical Department is consulted.  



Permissible Operating Temperature

Borosilicate glass retains its mechanical strength and will deform only at temperature which approach its strain point, approximately 510°C. The permissible operating temperature is, however, considerably lower – normally at about 200°C – for glass components, provided that there is no temperature shock.

In exceptional circumstances, higher temperatures can be achieved possibly up to 300°C  (see AD-N4). However, additional precautions are required and we recommend that our technical department is again consulted.

At sub-zero temperatures, the tensile strength of borosilicate glass tends to increase and equipment can be used at temperatures as low as -50°C.

These temperature limits should be regarded only as a guideline and must always be modified in accordance with the actual operating conditions in any given application. The individual operating condition of some of the components detailed in this catalogue must also be considered. Where such operating limits apply, they are detailed in the individual catalogue section and component description

Under normal operating conditions, rapid changes in temperature should be avoided as this will result in increased stress in the glass. Experience has shown however that under exceptional conditions, a degree of thermal shock can be tolerated.

It is undesirable to give an overall figure but, as a general guide, sudden temperature change of up to around 120°C can be accommodated.  



Permissible Operating Pressure

The maximum permissible operating pressure and the reduction in permissible pressure with increasing temperature difference between the process and ambient (Du) are shown in figure 3 to 8. Figure 3 and 4 are valid for all glass components with the exception of valves and filters (see figure 5 and 6), spherical vessels (see figure 7 and 8) and heat exchanger internal (see section 5 - Heat Exchangers).

Depending on the shape and working conditions, glass components can be used, under certain circumstance, at higher internal pressure. In these cases, the component will be marked in accordance with AD-N4.

Unless otherwise stated all standard glass components are suitable for operating at full vacuum subject to the temperature limits shown in Figure 3 to 8

In cases where glass in operated under a gas pressure or vacuum we are recommend that our technical department is consulted for further information on suitable external protection.