Technical Information


All Glass items shown in this catalogue are manufactured from borosilicate glass 3.3 are widely used as the basis for the construction of complete process systems all over the chemical, dyestuff, food pharmaceutical, and petrochemical industries. The abbreviation for the coefficient of linear expansion which is (3.3 ± 0.1) x 10-6 K-1. This is lower than any other industrial glass. Since this glass expands less, the tensile stresses in the glass wall during heating are less, which means that it is able to withstand a greater thermal shock and the maximum working pressure for a given operating temperature is greater.

One reason for this widespread used is the special properties of borosilicate glass 3.3 (see below), complemented by the use of other highly corrosion resistant materials such as PTFE and ceramics.

Chemical Composition of Borosilicate Glass 3.3

The Borosilicate glass 3.3 used in the fabrication by SIGMA complies generally with the following chemical composition.

Component % by weight
SiO2 80.6
B2O3 12.5
Na2O 4.2
Al2O3 2.2
Others 0.5


Borosilicate glass 3.3 is highly resistant to water, neutral and acid solutions, concentrated acids and acid mixtures, and to chlorine, bromine, iodine and organic substances. The chemical resistance of this glass is superior to that of most metals and other materials, even when exposed to long processing periods and temperatures above 100°C. At higher temperatures and in more concentrated forms the glass surface is subject to increased attack by hydrofluoric acid, hot phosphoric acid and alkaline solutions.


The very large 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 make a distinction borosilicate glass 3.3 from other materials of construction. These include special properties e.g.

Smooth non-porous surface


Outstanding corrosion resistance

No adverse physiological properties

Neutral smell and taste


Catalytic inertness

Physical Properties

Borosilicate glass 3.3 differs from other materials of construction used for process plant not only because of its virtually universal resistance to corrosion 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).

Mechanical Properties

The required of ductility of glass prevent the equalization of stresses at local irregularity or flaw 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, the safety factor is applied when determining the wall thickness requirement to allow operation up to values given in the table of working pressure.

Density 2.23 x 103 Kg/m3
Modulus of elasticity E 6500/ mm2
Permissible Tensile and bending stress K/S 6 N /mm2
Permissible Compressive stress K/S 100 N mm-2
Poisson's ratio (transverse contraction figure) $ 0.2


Borosilicate glass 3.3 shows no considerable light absorption in the visible area of the spectrum, and consequently it is clear and colorless.

Borosilicate glass 3.3 in photochemical processes the transparency of ultra violet is of particular importance. It follows from the transmittance of material in ultra violet region that photochemical reactions e.g. chlorination & sulpho chlorination can be performed in it.


All Glass components and complete plant can be operated safely at temperature 200° C provided that there is no sudden temperature shock.

This practical working temperature limit is set by the physical properties of the sideline equipments like gaskets, PTFE bellows, couplings and structure & supports, but not the glass components.


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 operatpressure 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 K can be taken as a general guide.


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.




The glass process plant and pipeline components detailed in this catalogue have standard Flat buttress end as per our standard, which are inter-changeable with any international standard .We can also supply Ball & socket (Spherical end forms), and tapered type buttress end as per international standard on request.

The major dimensions of the safety flat buttress ends can be found in the table below, in conjunction with the illustrations alongside.

Nominal bore DN mm Buttress end diameter D mm Tolerances
25 42.5 (+)0.0, (-) 1.5
40 57.5 (+)0.0, (-) 1.5
50 70 (+)0.0, (-) 1.5
80 99.5 (+)0.0, (-) 1.5
100 133 (+)0.0, (-) 2.0
150 185 (+)0.0, (-) 2.0
200 232 (+)0.0, (-) 2.0
225 259 (+)0.0, (-) 2.0
300 340 (+)1.0, (-) 3.0
400 464 (+)1.0, (-) 4.0
450 525 (+)1.0, (-) 4.0

FLANGE DIMENSIONS BALL SOCKET (as per International Standard)


DN d2(mm) dm° (mm) R6(mm)
15 30 23 18
25 44 34 25
40 62 51 40
50 76 63 50
80 110 96 80
100 130 116 100
150 184 169 150
200 233 220 200
300 338 321 300
400 465 435 -
450 526 492 -
600 684 646 -
800 916 871 -
1000 1088 1050 -


Though any damaged glass equipment can be repaired, mostly it is not economical to do so. Generally the repair, which involves less than a third of its original work, is worth to carry out repairing. Repair work is costly because:

It generally requires greater skill than making a new one

Since it involves high risk of total breakage, the risk of total loss of time spent on its repairing goes along with.

The work involved in receiving a damaged equipment, identifying it throughout the handling, cleaning it, estimating its repairing charges, re-estimating the repairing charges in case damage extends etc are relatively expensive.

Each job requires individual attention throughout the execution.

However, while sending equipment for repairing, following care must be taken:

Inform the nature of breakage and get an estimate of repairing charges in advance to avoid the loss of transportation expenses in case it is uneconomical to go for repairing.

Since repairing takes longer time to fit into production schedules and completion of repairing is highly uncertain, it is generally suggested to arrange for a substitute equipment to continue the work.

Equipment to be repaired should be clean. Since it can be cleaned better and at less cost at owner's premises. It should be cleaned before sending it for transportation. This also makes it safer to transport.

Pack with extra care, since cracks in glass have a tendency to extend with every jerk.

If Possible, send broken pieces along with it.

Generally repairing work is accepted only for the equipment manufactured by us, and is repaired at owner's risk only.


The tolerances on length L together with dimensions L1, L2 and L3 of Components, unless otherwise specified for given components in this catalogue.

Nominal Bore DN Length (L, L1, L2, L3)
DN 15 to 40 ±3 mm
DN 50 to DN 225 ±3.5 mm
DN 300 to DN 450 ±4.0 mm
DN 600 ±5.0mm


DIN ISO 3585, DIN ISO 3586, DIN ISO 3587, DIN ISO 4704, BSEN 1595,


Key to successful growth oriented business relations between Glass Users & Suppliers. Adopt following Instructions and feel free of stations regarding Glass Plants/Units.

Leakage of Glass Plants / Units

During installation / erection of glass plants / units at your site, provide your one person for required training of tightening assembled glass components in case of any minor leakage in future. Keep replacing PTFE "O" Rings and Couplings as & when required.

In case of heavy leakage please call us immediately.

End of suppliers Responsibility

On installation of glass plants/units & after successful water & vacuum testing the plant/unit, handed over to the buyer. The suppliers cut-off time starts & all responsibilities ends here.

Technical Services

The following technical staff is available on per day charge basis:

(1) Engineer (2) Skilled Fitter (3) Semi Skilled Fitter (4) Helper


Order Confirmation

Place your Order in written form only & ask for written confirmation.

Delivery Schedule

Glass Components are custom made fabricated Items, to attain quality, reasonable specific time is required for making & anneal. Hence plan your requirements well in advance & place order accordingly.


Glass is fragile, breaking risk persists during transit & in-case of any damage, disputes /dissatisfaction starts because offered rates were ex-works. To avoid, pick-up any one facility details as under:-

(1) Transit (cost to be charged by the buyer for transportation of glass components on behalf of buyer & freight on To-pay basis. In case of damage, the buyer is liable to pay Invoiced amount as per terms & conditions.

(2) Personal delivery facility against lum-sum charges (called as delivery charges) inclusive of freight charges, risk charges & as well delivery boy expenses.

Packing & Forwarding

Proper & safe packing is essential for safety & P&F Charges extra.

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