SCHOTT solutions no. 1/2015 > Sight glasses

BOROFLOAT® 33 sight glass
For Dr. Dirk Rost from Roth & Rau AG, sight glasses must offer the highest ­mechanical strength. The German company develops technologies for surface coatings with plasma and ion beam devices and uses BOROFLOAT® 33 sight ­glasses. Photo: SCHOTT

Safe viewing of critical processes

Sight glasses are used throughout many industries like oil and gas production or food and chemical processing as they allow to directly peer into pipes and boilers even under extreme conditions. BOROFLOAT® 33 borosilicate glass performs exceptionally well in these areas.

Alexander Lopez

Oil prices have fallen worldwide, primarily due to a significant rise in oil and natural gas production in the United States – which at times increased by more than 50 percent between 2010 and 2014. This growing output makes it all the more important to sustain the greatest possible efficiency and safety in industrial engineering. Electronic sensors are increasingly being used to monitor and guide processes, however quick discovery and assessment of deviations still need the direct supervision of a well-trained expert looking at the flow of materials in conveyance systems, pipes, and reservoirs.
Kathleen Burke Schweizer, Vice President of SWIFT Glass
Kathleen Burke Schweizer, Vice President of SWIFT Glass Company, examines sight glass. The US company has been working with SCHOTT since 1994. Photo: SCHOTT
Specialized sight glasses make this possible. They can withstand the extreme conditions that often occur in such closed systems, for instance high temperatures, extreme pressure, chemical processes and the use of aggressive media. Conventional soda-lime glass cannot stand up to that kind of stress, but specialized glass such as SCHOTT’s BOROFLOAT® 33 can. Its roots go back to 1887 when Otto ­Schott invented the first borosilicate glass. It was extremely durable at high temperatures and during rapid temperature changes and became the material of choice for the light bulb bracket cylinders used in Europe’s first street lights. The unique qualities of BOROFLOAT® 33 borosilicate glass are valued in many applications to this day – from cookware to coated insulator panels on space shuttles. BOROFLOAT® glass was introduced in 1993 when SCHOTT began using the float glass manufacturing process which allows for highly consistent, flat surfaces as the molten glass floats over a bed of molten tin and is then homogeneously cooled.

Boron the key element

When used as sight glass, BOROFLOAT® 33 scores points with its extremely high transparency and unique thermal and chemical characteristics. ”The element boron, which gives borosilicate glass its name, is very crucial in the glass manufacturing process, as it determines the glass’s thermal expansion and the strength of the bonds in the glass network,” explains Christiane Gallo, Manager Applications & Logistic Services at SCHOTT in Louisville, Kentucky.

Higher amounts of silica, fewer alkali oxides, added boron trioxide in combination with alumina create a much more compact network compared to regular soda-lime glasses, and this is the reason why BOROFLOAT® 33 glass offers such excellent chemical and thermal resistance and exhibits such extraordinarily low thermal expansion behavior allowing it to handle sudden temperature changes extremely well.

With 3.25 x 10-6 1/K, it reaches only a third of the thermal expansion coefficient of soda-lime glass. Sight glasses made of BOROFLOAT® 33 can therefore be exposed for short periods (up to ten hours) to temperatures up to 500 °C and for longer periods up to 450 °C. However, if temperature gradients or pressure differences occur, these must be taken into consideration to ensure material stability. Borosilicate glass can also withstand the high compressive load that often occurs in these applications – partly by selecting the right glass thickness relative to the surface area of the glass and partly through thermal pre-stressing. This increases its compressive strength and makes the material even more resistant to impact and more stable during temperature changes.
SCHOTT partners perform the final processing of BOROFLOAT® 33 into actual sight glass. Photo: SCHOTT

”Wide acceptance in the market”

BOROFLOAT® sight glasses have become very popular in a wide range of applications and are used in oil and gas production, chemical, pharmaceutical, and electronics industries, the food and beverage business, agriculture, nuclear power, and mining. SCHOTT engineers help customers identify the glass specifications needed for each respective application. And our partners perform the final processing of the actual sight glass as they have recognized ­BOROFLOAT® 33’s potential very quickly. Kathleen Burke Schweizer, Vice President of the SWIFT Glass Company, says, ”We have been working with SCHOTT since 1994.” This family business from ­Elmira, New York, has been around for almost 100 years and is now one of the world’s leading high-quality glass processors, supplying sight glass for an extremely wide range of applications. ”In principle, there is a wide range of usable materials. But ­BOROFLOAT® 33 borosilicate glass has excellent characteristics and is versatile. It has very high acceptance in the market and our partnership with SCHOTT is outstanding,” says Burke Schweizer. <