Borosilicate glass represents unmatched standardized glass for construction of Pilot plants and piping in the chemical, dyestuff, food pharmaceutical, petrochemical industries, its steadily growing use is due to many advantages over conventional materials such as,
Borosilicate glass is chosen for its unique chemical and physical properties. Borosilicate glass can be considered as being composed of oxides. Silica (SIO2) Magnesia (MgO) and lead oxide (pbo) are its principle modifiers.
The chemical and physical properties of any glass depends on a varying degree on chemical composition of glass.
The composition of borosilicate glass used for chemical plants has following approximate composition.
Sio2-80.6% B2 O2-12.5%
RESISTANCE TO CHEMICAL
Borosilicate glass is insert to almost all materials except hydrofluoric acid (HF) phosphoric acid (H3PO4) and hot strong caustic solution up to 30% concentration can be handled safely at ambient temperature.
Under actual operating conditions, the effect of turbulence, and traces of other chemicals in the solution may increase of decrease the rate of attack. So it is not possible to give exact figures for corrosion by caustic solutions.
Linear coefficient of thermal expansion
The coefficient of thermal expansion of borosilicate glass over the temperature 0-300◦C is 3.3x 10-6/0c.This is why borosilicate glass is often called low expansion borosilicate glass.
Specific heat between 25◦C and 300◦C is average to be 0.233Kcal/Kg,◦C.
Thermal conductivity is 1.0Kcal/hr,m◦C. Over the permissible operating temperature range.
Annealing of glass is the process where the glass is heated and kept for a defined period of time to relive internal stresses. Careful cooling under controlled conditions is essential to ensure that no stresses are reintroduced by chilling/cooling.
the lack of ductility of glass prevents the equalization of stresses at local irregularities of flaws and the breakage strength varies considerably about a mean value. This latter is found to occur at a tensile strength of about 700kg/cm2.
In order to allow for the spread of breaking stress, a large factor of safety is applied when determining the wall thickness requirement to allow operation up to values given in the table of working pressure.
Borosilicate glass show no appreciable absorption in the visible region of spectrum and therefore appears clear and colour less.
In photo chemical processes the transparency of ultra violet is of particular importance.it follows from the transmittance of material in UV region that photo chemical reactions such as chlorination & sulpha chlorination can be performed in it.
PERMISSIBLE OPERATING CONDITIONS
WORKING PRESSURE FOR Glass pipelines & vessels
The permissible internal operation pressure depends on the nominal diameter of glass components and on working temperature.
In case of unit with various combination like vessels, filters, heat exchangers, the overall permissible internal gauge pressure is always governed by the components with the lowest permissible operating gauge pressure all components are suitable
for full vacuum.
Bar is a measure of absolute pressure. The figure given for maximum recommended working pressure represents pressure above atmospheric.
Borosilicate glass retains its mechanical strength and will deform only at temperature which approach its strain point. The practical upper limit for operating temperature differentials in the glass which depends on the relative temperature of the contents of the equipment and the external surroundings. Provided borosilicate glass is not subjects to rapid change in temperature, creating under thermal shock, it can be operated safely at temperatures up to 250◦c.
It must be realised that in complete plants, composed not only of borosilicate glass, but also including other materials such as PTFE the recommended max. Operating temperature is 20◦c. Operating temperatures may have to be modified so as to compensate for the effects of other factors such as pressure, thermal cycling, rapid heating & cooling etc.
The degree of thermal shock (usually defined as sudden chilling or heating) which it can withstand depends on many factors such as stress due to operating conditions, stresses imposed in supporting the equipment, the wall thickness of the glass. It is therefore undesirable to give sudden temperature changes. But up to 120◦C can be accommodated.
As sub Zero temperature, the tensile strength of borosilicate glass tends to increase and equipment can be used with safely at temperatures as low as 50*c for XTRONG and components.
The last two decades have seen the new of further developments of particulars corrosion resistant plant construction materials typical examples of these are PTFE, tantalum, titanium, graphite and of course glass.
The combination of different corrosion resistant materials with the utilization of the specific advantages of each permits both sale and economic construction.
Borosilicate glass with PTFE is of particularly decisive importance for construction of glass installation for example.in seals, bellows, stirrers, pumps, heat exchangers, column inserts etc.
PTFE is used in above because of its excellent mechanical & thermal properties. They have near universal fluid compatibility. Wear life when compared with others is very low. Particularly PTFE is maintenance free and have cryogenic stability with non-wetting property.
Service temperatures of PTFE is considered as -50◦C to + 200◦C.
Glass being a poor electrical conductor, surface, conductivity is insignificant and varies with the quantity of water absorbed on glass surface. The specific conductivity is 10◦ohm/cm at temperature of 200◦c.
The dielectric coefficient varies with current frequency.
Density of glass at 20◦C (j) = 2.23g/cc
Modulus of elasticity (E) = 6.3kn/mm2.