L.J. Star Incorporated provides a comparative look at different glass types used in making industrial sight glass. http://www.ljstar.com/products/products.aspx?pl=6

1. Comparison of Glass Types by Use
Benefits of Metaglas Sight Glass
Sight Glass Research
Understanding Glass
Options for Sight Glass

2. 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.

3. 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.

4. 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

5. Glass Specifications
Borosilicate
• 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.

6. Sight Glass Specifications
Soda 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.

7. Corrosion Resistance

8. 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.

9. Coefficients of Expansion
Borosilicate Glass
32
Example:
32x10-7
IN/IN/0
C
Soda Lime
93
Example:
93x10-7
IN/IN/0
C

10. Compression Requirements of
Borosilicate 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.

11. Compression Requirements of
Soda 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.

12. Compression Process

13. 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

14. View Comparison of Sight Glass
Options

15. Customers Prefer a Large View
Soda LimeBorosilicate
Dwg. 180-SLDwg. 180-LV

16. 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.

17. 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

18. 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 Incorporated
P.O. Box 1116
Twinsburg, OH 44087
• Telephone: (330) 405-3040
FAX: (330) 405-3070