Sight Glasses

For industries in which piping, vessels, chemical reactors, and other industrial equipment is necessary for operations, sight glasses can serve as very useful tools. These visual observation windows allow operators to easily inspect, monitor, and verify the conditions within piping systems, boilers, and other equipment. Sight glasses are constructed by bolting, clamping, or fusing together two metal frames — usually carbon or stainless steel — that hold a glass disc.

Sight glass windows are ubiquitous in a wide range of industries. Chemical and petrochemical, pharmaceutical and biotech, food and beverage, oil and gas, utilities, biogas and biofuels, and wastewater treatment are just a few of the countless sectors utilizing sight glass. 

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Sight glasses, by virtue of the goal they’re used to achieve, are often subjected to harsh conditions, including elevated temperatures, aggressive chemicals, and high pressures. Therefore, to ensure optimal safety, it’s critical to work with the proper substrate for the application at hand.

There are numerous factors to consider when selecting materials for a sight glass. For instance, stainless steel, rather than carbon steel, offers superior corrosion resistance. The glass itself can also be strengthened by way of heat temperance for additional durability, or coated for enhanced visibility and corrosion resistance.

Material Options

Commonly used substrates include glass disc soda lime, fused soda lime, glass disc borosilicate, fused borosilicate, and quartz disc. Soda lime glass should be used for less critical applications, as it can only handle a maximum temperature of 300 °F, which is on the lower end of the spectrum. The most extreme applications will require quartz disc or even sapphire.

Temperature application, thermal shock resistance, corrosion resistance, abrasion resistance, pressure capability, and impact resistance should all be considered during the material selection process. Glass disc soda lime exhibits average properties overall, but offers superior pressure capability. Fused soda lime’s strengths lie in thermal shock resistance, pressure capability, and impact resistance.

Glass disc borosilicate shows excellent characteristics in all categories, from thermal shock, corrosion abrasion, and impact resistance to temperature application and pressure capability. This material is bested by fused borosilicate only in the categories of pressure capability and impact resistance. And finally, quartz disc remains the industry favorite, offering superior thermal shock, corrosion resistance, and abrasion resistance properties. Its impact resistance is also superior to the alternatives.

Plastic Sight Glass

Plastic sight glasses are also a possibility. These can be used for applications in which the sight glass component is not critical to the equipment at hand, as with the food and beverage industry. Plastic sight glasses are also commonly found in household applications, such as the fuel tanks of gas lawn mowers and leaf blowers.

Sight Glass Applications

Sight glasses may be implemented as sight glass windows or as sight port windows. Sight glass windows are created when glass is fused to a metal frame, with the window acting as a single-piece component. This design allows the glass to strengthen as it’s compressed, rather than being under tension, which can cause failure. The metal frame absorbs the stress of the mounting, and the glass remains unaffected by residue, uneven bolts, and general wear and tear. This option is widely considered to be the most cost-effective, reusable solution.

Sight port windows, on the other hand, involve mounting sight glass onto a tank with a lighting component. This allows operators to see inside the container through the sight port window.

Working With Papailias

Papailias Inc. is proud to offer some of the most sophisticated sight glasses on the market. We offer a huge range of customization options, and can provide tailored solutions to meet all of our clients’ exact needs — whether they require a single component or installation across an entire network of pipes and containers.

To learn more about our sight glass offerings and discuss options for your specific needs, request a quote from the team today. 

Not sure what a site glass is? Read more on "What Is A Site Glass" here.