Where Sight Glass Strength Comes From

Comparison of Glass Types by Use

Benefits of Metaglas Sight Glass

Sight Glass Research

Understanding Glass Options for Sight Glass

Importance of Sight Glass

• Industrial sight glass provides visual inspection of industrial and pharmaceutical processes.

• Sight Glass is used in conjunction with lights that illuminate tank and pipe interiors.

• However, glass is often the weakest link in any process.

Importance of Sight Glass

• Sight glass cannot be eliminated because the observation of the interior of vessels and pipelines is necessary.

• Sight glasses are highly engineered products.

• Different glass materials have different specs that have tremendous importance for worker safety, sanitary processes, and maintenance costs.

Glass Types (review)

• Borosilicate• High Chemical Resistance• Higher Temperature Capability• Low Thermal Coefficient of Expansion

• Soda Lime• Low Chemical Resistance• Low Temperature Capability• High Thermal Coefficient of Expansion

• Quartz• High Temperature Capability• Very Low Thermal Coefficient of Expansion• Good Resistance to Steam

Glass SpecificationsBorosilicate

• Borosilicate• Borosilicate glasses are used for baking & cooking dishes,

chemical laboratory glassware, boiler gage glasses, sight glasses,

glass pipe, etc. Their compositions are usually similar to the

following.

• Silica - SiO2 …………………………...…...80%• Boric Oxide - B2O3…………...14%• Soda - Na2O ……………………….………....4%

• Alumina -Al2O3 …………...……2%

• Reasonable manufacturing cost coupled with high chemical stability,

low coefficients of thermal expansion, high heat shock resistance and

excellent electrical resistivity make borosilicate glasses the best choice

for most industrial applications.

Sight Glass SpecificationsSoda Lime

• Soda Lime• Soda lime glasses (or lime glasses) are used for lamp envelopes, bottles, and

window glass and are melted from silica that has been fluxed with lime (CaO),

and soda (Na2O) plus small quantities of other oxides. Their compositions are

usually similar to the following:• Silica - SiO2…………………...…..72%• Soda - Na2O…………………...………....15%• Lime - CaO……..………………..…….…..9%• Magnesia - MgO…..…………….....3%• Alumina - Al2O3…………………………...…..1%

• Lime glasses are low in cost, easily hot-worked and are usually specified for

service where high heat resistance and chemical stability are not required.

Corrosion Resistance

Coefficients of Expansion

• The most important point, when analyzing a piece of glass

equipment is the coefficient of expansion.

• Ordinary house windows are called 93 glass.

• Borosilicate Glass is called a 32 glass.

• Vycor® is called 8 glass.

• Borosilicate has a much lower coefficient of expansion,

approximately 1/3 of Soda Lime.

Bottom Line: Borosilicate has greater resistance to thermal shock.

Coefficients of Expansion

Borosilicate Glass32

Example:

32x10-7 IN/IN/0C

Soda Lime93

Example:

93x10-7 IN/IN/0C

Compression Requirements ofBorosilicate 32

• Borosilicate (32)• Because of Borosilicate (32)’s lesser coefficient of

expansion, a metal ring with a larger width is required.

• Therefore there is more radial compression on the glass.

Compression Requirements ofSoda Lime (93)

• Soda Lime (93)• Because of Soda Lime (93)’s greater coefficient of

expansion, a metal ring with a narrow width is required.

• Therefore there is less radial compression on the glass.

Compression Process

Compression Comparison

• Borosilicate has 3 times the compression

than Soda Lime

• Borosilicate has 4-1/2 times the pressure

capability than Soda Lime

• Fused Borosilicate is the stronger choice

View Comparison of Sight Glass Options

Customers Prefer a Large View

Soda LimeBorosilicate

Dwg. 180-SLDwg. 180-LV

Importance of Metaglas Sight Glass

• Metaglas, the ultimate in sight window safety, is made by fusing pure borosilicate glass within stainless steel rings. The result is a sight glass that has been described as having the transparency of glass with the strength of steel.

• Proven in thousands of installations, Metaglas is the #1 selling sight glass.

White Papers on Sight Glass

• Duplex Steel is Preferred Over 316L Steel in Process Equipment By Dr. Hira Ahluwalia

• Glass Selection for Process Industrial Applications By Harvey Travers, Engineering Consultant

• Compression vs. Fusion in Sight Glass Construction By Karl Schuller, Herberts Industrieglas GmbH

• Trade Names Can Confuse Sight Glass Selection By Jeff Watkins, New Brunswick Scientific

• Competitive Claims and Misconceptions About Sight Windows By Andrew Obertanec, L.J. Star

Metaglas Sight Glass• For More Information• Visit L.J. Star Incorporated for more information on

the Metaglas Sight Glass.• Contact us directly:• Mailing Address:

L.J. Star IncorporatedP.O. Box 1116Twinsburg, OH 44087

• Telephone: (330) 405-3040FAX: (330) 405-3070