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Glass Joint

Column Components | Couplings | Glass Joint | Heat Exchangers | Measurement & Control | Pipeline Components | Rotary Film Evaporator | Sight Glasses | Stirrers | Structure & Supports | Typical Units | Valves | Vessels

Tapered glass joints are predominantly used in Industrial Glass Equipment in India. This design has high ratio of axial force to redial force which frequently leads to breakage while making the joint. The higher breakage had deterrent effect on buyers.

It was recognized that a glass cylinder stands better in the application of axial force rather than in application of radial force. To exploit this feature of glass, we have come up with a new design of glass joints. It can be seen in the graph below that with the same axial force the effective radial force is 3 times smaller than is tapered joints.

Joints are practically may times stronger than conventional tapered joints as far as tightening of joints is concern. It is tested that a joint, does not break even at a tarque of 20Nm, as against tapered joints which starts breaking at 6-7 Nm tarque. At times it may happen that because of overtightening, a metal backing flange breaks or the threads of nut-bolts give way but glass joint remains intact.

Most of the old glass installations in India contain equipments with tapered glass joints. Glass joints are fully compatible with these tapered joints i.e. a joints equipment can replace another tapered equipment and vice versa in any existing unit. This interchangeability makes glass joint design more adaptable in Indian conditions and change over cost is negligible.

Glass joints which was mainly discovered as an "Answer to breakage" has found to have many other advantages like follows.

a. Usually all the glass joints possess a little or more ovality. Tapered joints are highly sensitive to ovality. However in glass Joint ovality hardly effects and gives no breakages.

b. Due to force and temperature inserts of backing flanges in tapered joints sticks to the glass as well as metal flange. The makes dismantling of unit more difficult and breakage prone. In glass joint design insert does not sticks and makes the dismantling safe.

c. In tapered joints long threaded bolts are because while tightening the soft inserts keep on compressing and slipping Over the tapered surface. The result in requirement of more Labour and time for tightening. The design of glass joints has reduced the length of tightening of bolts to less than a half and saves time and labour.

d. In Indian conditions of manufacturing glass joints are easy and fast to produces. This is because it require to process less length Of a raw glass tube.

With so many benefits and particularly low breakage risk, we have adopted design for all equipment manufactured by Shiva and its group companies. The glass joints is widely accepted and adopted by users as well as manufactures of Glass Equipments in India


DN D D1 D2 H1 H2 A B
25 41 27 34 13 8 65 9
40 56 40 49 14 9 65 9
50 69 52 62 16 11 65 9
80 98 79 91 18 12 65 9
100 132 108 123 20 17 65 9
150 184 159 166 22 19 65 9
225 258 229 233 24 26 65 9
300 340 308 315 24 26 65 9
400 463 405 425 25 35 65 9
450 535 455 499 25 50 65 9
600 684 600 640 25 60 65 9


Borosilicate glass represents unmatched standardized glass for construction of plant and piping in the chemical, dyestuff, food pharmaceutical petrochemical industries. Its steadily growing use is due to many advantages over conventional materials.

  • Outstanding corrosion resistence
  • Smooth pore free surface
  • Transparency
  • Catalytic intertness.
  • No effect on taste and odour
  • Physiological intertness.

Borosilicate glass is chosen for its unique chemical and physical properties. Borosilicate glass can be considered as being composed of oxides. Silica (SIO) Magnesia (MgO) and lead oxide (PbO) are the principle modifiers/fluxes.

The chemical and physical properties of any glass depends on a varying degree on chemical composition of glass.



SiO2-80.6% B2 O2 -12.5%

Na2 O-4.2% Al2 O3 -2.2%


Borosilicate glass is inert to almost all materials except hydrofluoric acid (HF) Phosphoric acid (H3PO4) and hot strong caustic solutions. Of these. Hydroflouric acid has the most serious effect, even when it is present in PPM parts per million) in solutions. Where as phosphoric acid and caustic solutions cause no problems when cold but at elevated temperature corrosion occurs. In case of caustic solution upto 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 or decrease the rate of attack. So it is possible to give exact figures for corrosion by caustic solutions.


Linear coefficient of thermal expansion

The coefficient of thermal expansion of borocilicate glass over the temperature 0-300ēC is 33 x 10-7/ēC. This is very low when compared with other glasses and metals. That is why, borosilicate glass is often called low expansion borocilicate glass.

Specific heat

Specific heat between 25ēC and 300ēC is average to be 0.233Kcal/Kg, ēC

Thermal Conductivity

Thermal conductivity is 1.0 Kcal/hr,mēC 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 relive internal stresses. Careful cooling under controlled conditions is essential to ensure that no stresses are reintroduced by chilling/cooling.


In the given below are shown characteristic temperature at a determined viscosity essential for glass reshape.


The lack of ductility of glass prevents the equalization of stresses at local irregularities or 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 & sulpho chlorination can be performed in it.


Working Pressure For Glass Pipelines & Vessels

The permissible internal operation pressure on the nominal diameter of the glass components and on working temperature.

In case of unit various combination like vessels, filters heat exchange, the over all permissible internal gauge pressure is always governed by the 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 .

Working Temperature

Borosilicate glass retains its mechanical strength and will deform only at temperature which approach 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 thermalshok it can be operated safety at temperatures upto 250ēC

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 200ēC. Operating temperature may be 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 stresses due to operating conditions stresses imposed in supporting the equipment the wall thickness of the glass. It is therefore undesirable accommodated.

As sub zero temperature the tensile strength of borosilicate glass tends to increase and equipment can be used with safety at temperatures as low as -50ēC for components.


The last two decades have seen the new or further developments of particularly 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 safe and economic construction.

Borosilicate glass/PTFE

Borosilicate glass with PTFE is of particularly decisive importance for construction f 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 temperature of PTFE is considered as - 50ēC to + 200ēC


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 200ēC

The dielectric coefficient varies with current frequency.


Density of glass at 20ēC (J) = 2.23g/cc

Modulus of elasticity (E) = 6.3 KN/mm2

Poissions ratio = 0.2