Borosilicate Glass Properties
PROCESS PLANT IN BOROSILICATE GLASS 3.3
GP Scientific Glass Works glass plants, pipelines, & components are fabricated as per the following international standards.
> BS EN 12585:1999 – Glass plant, pipeline & fittings compatibility & interchangeability
> BS EN 1595:1997: General rules for design, manufacture, & testing.
The full range of standard components & associated equipment available is described in the following sections of the catalog.
CHEMICAL COMPOSITION OF BOROSILICATE GLASS 3.3
The Borosil Glass 3.3 used in the fabrication generally has the following chemical composition:
PROPERTIES OF BOROSILICATE GLASS 3.3
The very wide use of this material throughout the world in the chemical and pharmaceutical industries as well as many other allied areas, is mainly due to its chemical and thermal properties (see also ISO 3585) together with a great number of other benefits that distinguish borosil glass 3.3 from other materials of construction. These include special properties e.g
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Smooth non-porous surface
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Transparency
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Outstanding corrosion resistance
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No adverse physiological properties
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Neutral smell and taste
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Non-flammability
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Catalytic inertness.
CHEMICAL RESISTANCE
Borosilicate glass 3.3 is resistant to corrosion by almost all chemicals. This makes its resistance more comprehensive than that of other well-known materials. It is highly resistant to water, saline solutions, organic substances, halogens & many acids. There are only a few chemicals which cause noticeable corrosion of glass namely, hydrofluoric acid, concentrated phosphoric acid & strong caustic solutions at elevated temperature.
The curves in fig .1 show a maximum corrosion for different acids in the concentration range between 4 and 7 N (HCI for example at the azeotrope with 20.2 wt%). Above that reaction, speed decreases markedly so that the eroded layer amounts to only a few thousandths of millimeter after some years. There is, therefore, the justification for referring to borosilicate glass 3.3 as an acid-resistant material.
Fig. 1
Acid attack on borosilicate glass 3.3 as a function of concentration
It can be seen from the corrosion curves in fig .2 that the attack on the glass surface initially increase as the concentration of the caustic solution increases but after exceeding a maximum it assumes a virtually constant value. Rising temperatures increase the corrosion, While at low temperatures the reaction speed is so low that reduction of the wall thickness is hardly detectable over a number of years.
Fig. 2
Alkali attack on borosilicate glass 3.3 as a function of temperature & Concentration
OPTICAL PROPERTIES
Borosilicate glass 3.3 shows no appreciable light absorption in the visible range of the spectrum, thus it is clear & colorless. Transmission of UV light is significant in the middle spectrum compared to normal glass. Borosilicate glass 3.3 is ideally suited for photochemical reactions such as chlorination & sulphochlorination.
THERMAL SHOCK
Quick 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°C can be taken as a general guide.
PERMISSIBLE OPERATING TEMPERATURE
PERMISSIBLE OPERATING PRESSURE
The permissible internal operating working pressure depends on the nominal diameter size of glass components and external temperature. The maximum working pressure for a complete glass plant is determined by the lowest rated components in the system. All glass components are suitable at full vacuum over the entire temperature range. Bar g is a measure of absolute pressure.
COMPOSITE MATERIALS
The last two decades have seen further developments of, particular corrosion resistant plant construction materials. Typical examples of these are PTFE, tantalum, titanium, graphite and of course, borosilicate 3.3 glass.
The combination of different corrosion resistant materials with the utilization of the specific advantages of each permits both safe and economic construction.
Borosilicate glass/PTFE
Borosilicate Glass with PTFE is of particular importance for the construction of glass installation. For example, In Seals, Bellows, Stirrers, Heat Exchangers, Column Inserts etc.
PTFE is used with Glass 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 has cryogenic stability with the non-wetting property. Service temperature of PTFE is considered as – 50°C to + 200°C
ANNEALING
Annealing of glass is the process where the glass is heated and kept for a defined period of time to relieve internal stresses.
Borosilicate glass retains its mechanical strength and will deform only at a temperature which approaches its strain point. The practical upper limit for operating temperature is much lower and is controlled by the 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 subject to rapid change in temperature, creating undue thermal shock, it can be operated safely at temperature up to 250°C
It must be realized that in complete plants, composed not only of borosilicate glass, but also include other materials such as PTFE. The recommended max. Operating temperature is 200°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.
At sub-zero temperature, the tensile strength of borosilicate glass tends to increase and equipment can be used safely at a temperature as low as – 50°C for Sigma Flat Buttress end components.