Borosilicate glass 3.3 differs from other materials of construction used for process plant not only because of its virtually universal resistance to corrosion (see above) but also because of its very low thermal expansion coefficient. There is, therefore, no need for expensive measures to compensate for thermal expansion resulting from changes in temperature. This becomes of particular significance in the layout of long runs of glass pipeline.
The most important physical properties for the construction of plant are listed below (see also ISO 3585 and EN 1595).

Mean linear thermal expansion coefficient	a 20/300	=	(3,3 ± 0,1) x 10-6 K-1
Mean thermal conductivity between 20 and 200°C	l 20/200	=	1,2 W m-1 K-1
Mean specific heat capacity between 20 and 100°C	Cp 20/100	=	0,8 kJ kg-1 K-1
Mean specific heat capacity between 20 and 200°C	Cp 20/200	=	0,9 kJ kg-1 K-1
Density at 20°C	r	=	2,23 kg dm-³

 

Mechanical properties

The permissible tensile strength of borosilicate glass 3.3 (see table 4) includes a safety factor which takes into account practical experience on the behaviour of glass and, in particular, the fact that it is a non-ductile material. Unlike other materials of construction used for similar purposes, it is not able to equalise stresses occurring at local irregularities or flaws, as happens in the case of ductile materials such as metals. The safety factor also takes into account additional processing which components may have undergone (ground sealing surfaces), handling of the glass (minute surface damage) and permissible pressures and temperatures to which it may be subjected in use.

The design figures indicated in the table below and specified in EN 1595 therefore apply to the permissible tensile, bending and compressive stress to which glass components may be subjected taking into account the likely surface condition of the glass in service.

 

Strength parameters	Tensile and bending strength	K/S = 7 N mm-²
	Compressive strength	K/S = 100 N mm-²
Modulus of elasticity		E = 64 kN mm-²
Poisson‘s ratio (transverse contraction figure)		n = 0,2