Safety First – The Importance Of Industrial Sight Glass

     An industrial sight glass is a critical part of virtually any type of process equipment because it allows for visual inspection of industrial and pharmaceutical processes. Luminaires are often used in conjunction with an industrial sight glass to illuminate tank and pipe interiors.

     In a system made primarily of metal, like a pressure vessel, the weak spots are generally sealing joints and glass. However, an industrial sight glass is a highly engineered product. Although different brands of industrial sight glass might look alike, differences in their specs have tremendous impact on worker safety, sanitary processes, and maintenance costs. In industrial applications, sight glasses are often subject to extremes of pressure, temperature, thermal shock, caustics, abrasion, or impact. Choosing the right industrial sight glass depends on taking all of these considerations into account.

      An industrial sight glass failure has the potential to be extremely dangerous. Even minor cracks, scratches or abrasions of the glass can be a source of weakness within the glass, which will most likely lead to failure. A catastrophic failure can cause severe operator injury or death, as well as costly downtime. Typically, the failure of an industrial sight glass on a piece of equipment or within a piping system will halt the whole process until the equipment can be repaired or replaced. Moreover, this failure may lead to scrapping the process media. In the case of a pharmaceutical process, the product loss could cost a manufacturer millions of dollars. Could you afford that kind of loss? (inside voice answring “NO”) We thought so, too. 

That said, we would like to invite you to learn more about choosing the right industrial site glass for a particular environment. You can do so by downloading our free white paper, 6 Tips for Critical Sight Glass Applications.

Process Vessel Cameras Reduce Cleaning Time and Costs

     Have you ever wondered how the food and beverage manufacturing companies keep their facilities clean? After all, food is one of people’s basic needs and knowing where our food comes from makes us feel content with our choice.

     When it comes to cleaning and sanitizing their liquid tankers and process vessels, the food and beverage processors face many challenges on a daily basis. Thus, they use a variety of tools to make sure they produce quality products.

     One of the most useful tools in their arsenals is a process vessel camera designed to mount on a sight glass window. High-intensity discharge lamps are typically used to illuminate the interior of a process vessel such as a whirlpool or fermentation tank through separate sight windows. A vessel camera (see examples) can allow manufacturers to identify where sediments remain even after a rinse cycle with water from internal nozzles. Cameras can even help manufacturers save money by helping them to troubleshoot cleaning problems by spotting clogged or defective cleaning nozzles and identifying areas of the process vessel that required additional cleaning attention.

     One brewery was able to reduce their water usage significantly by identifying the sediment patterns that different beer recipes produced and adjusting their process vessel rinse cycles accordingly. By allowing them to monitor the entire process from beginning to end, the camera gave them the ability to determine which batches would produce the most sediment and where it would settle. A process vessel that was not thoroughly cleaned before the next batch was processed could have cost the manufacturer thousands of dollars in contaminated product that would have had to be discarded. To learn more about how a major U.S. brewer was able to pay for the cost of their lighting and camera system quickly by preventing product losses, we encourage you to take a few minutes to read our application note on this topic: 



6 Big Challenges in Sight Glass Construction

Is your sight glass tough enough to handle “The Big Six” challenges?

     Sight glass failures can be extremely dangerous. A sight glass that fails catastrophically has the potential for severe operator injury or death, as well as costly downtime and product losses. Even minor cracks, scratches or abrasions can create weakness within the sight glass, which will most likely lead to failure. In normal use, sight glasses are regularly subjected to forces involving extremes of pressure, temperature, thermal shock, caustics, abrasion, or impact.

      Our “6 Tips for Critical Sight Glass Applications” white paper provides expert advice on how to select a sight glass designed to withstand these challenges:

  • Temperature: Depending upon the temperature range, certain glass types will perform better than others. At less than 300°F, standard Soda Lime glass may be used. For temperatures up to 500°F, borosilicate glass may be used. At higher temperatures such as in high temperature steam applications, we recommend quartz or sapphire glass.
  • Thermal Shock: Some glass types are particularly vulnerable to cracking as a result of rapid temperature change, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients.
  • Corrosion: Materials in process media like hydrofluoric acid, hot phosphoric acid and hot alkalis can etch the glass, producing a cloudy view with weakened integrity that requires the sight glass to be replaced.
  • Abrasion: Fluids that contain granular particles in suspension, or with particles carried in process gasses can abrade and erode a site glass, limiting visibility and affecting its strength.
  • Pressure: The glass materials selected, the unsupported diameter, and the glass thickness all play a role in determining the pressure capabilities of a sight glass assembly. Fused sight glass windows offer high pressure ratings and high safety margins. The strongest fused sight glasses are made from duplex stainless steel and borosilicate glass; this combination creates the highest compression.
  • Impact: Objects that strike the sight glass are seldom sufficient to cause immediate failure, but they can create scratches or gouges that provide a point for tensional force to concentrate. Scratched sight glasses should be replaced immediately.

     For details on how to take on these challenges, download our free copy of the “6 Tips for Critical Sight Glass Applications” white paper.

Compression Trumps Fusion in Sight Glass

“Fusion” is fine for fancy restaurants, but “compression” makes the real difference in sight glasses.

     “Fusion” is sometimes used to describe cuisines that combine ingredients and cooking techniques from different cultures.  However, fusion is also sometimes used to promote some brands of sight glasses based on the belief that greater fusion of glass to metal during the manufacturing process will produce a stronger finished sight glass for use in chemical and pharmaceutical processes.

     During manufacturing, the glass is melted within the metal ring as the ring expands. Then, temperature is raised to the point where the glass and the metal ring fuse together. When the unit cools, the glass hardens before the metal ring shrinks back to its original size. This places the metal ring in tension and the glass in uniform radial compression. The most compression is produced by using an alloy of metal that shrinks a lot as it cools in combination with a type of glass that shrinks little when it cools: the greater the difference, the greater the compression. Fusion – getting the glass to stick to the metal – is easy to achieve but not as critical to sight glass reliability as compression. Compression strengthens the glass because it is stronger than tensile forces that could create internal torque on the glass. Therefore, it is the level of compression, rather than fusion, that predicts the reliability of a sight glass.

     A recent study shows that the combination of glass and metal that provides the most compression also provides the highest strength. The study compared a sight glass made of soda-lime glass and a Duplex stainless steel frame with a borosilicate sight glass (also with a Duplex stainless steel  frame) to analyze the amount of radial compression created by the difference between the glass and the metal in coefficient of thermal expansion as the sight glasses cool. The analysis showed the borosilicate glass produces significantly more compression than one made with soda lime glass. Also, there is a direct relationship between the amount of compression and the strength of the sight glass. The borosilicate sight glass has far greater pressure capability. Strength is also important for worker safety and because it reduces the need for sight glass maintenance and replacement.

     The study also compared the compressive force of a sight glass made with proprietary soda-lime glass coupled with a Hastelloy C22 stainless steel ring (which is touted for its high glass-to-metal fusion) with that of a Duplex/borosilicate sight glass. The borosilicate glass/Duplex stainless steel construction provided four and a half times the pressure capability of the soda-lime/Hastelloy sight glass. The reliability of a sight glass has almost nothing to do with fusion; compression is what matters most because it secures the glass to the metal and creates a leak proof seal. Click here to see a full line of borosilicate sight glass products.

      For all the details on this study, take a few minutes to read the white paper on compression vs. fusion.


Let There be (More) Light!

     You may remember the old story about a man who is looking for his lost keys beneath a streetlamp. A passerby asks the man if he is sure about where he dropped them, and the man says, “Actually, I think I dropped them in the grass over there.” The passerby asks, “Then why aren’t you looking where you dropped them?” The first man answers, “Because the light is better here.”

     On a street corner or in a processing facility, sufficient light makes all the difference in spotting what you need to find. The interiors of vessels and pipelines are typically far too dark to allow operators to observe important stages of their process readily through a sight glass. Flashlights usually don’t cast enough light and often produce glare, complicating the inspection process. Luminaires mounted onto sight glasses offer a more effective solution. Many processes take place in hazardous environments where explosive conditions may be present. For these applications, explosion proof lighting combines safe interior illumination and glare-free viewing.

     There is a wide variety of ex lights to choose from. When choosing a light for a specific sight glass application, consider factors like type of technology, size, weight, voltage, wattage, materials of construction, mounting configuration, and light pattern. Energy consumption, location requirements, heat output, ambient conditions, and vibration must also be taken into account.

     The “Understanding and Specifying Sight Glass Lighting” handbook addresses these considerations to help specifiers choose the most appropriate lighting solution for the application. Download your free copy today: http://www.sightglassblog.com/blog/03.html.