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Over the past few months we’ve been compiling questions you come to us with. Surely if a few people are inquiring, there are dozens more who have the same question but just haven’t asked it. After reading this post, which contains questions and answers related to glass-lined equipment, you might have a few questions of your own so please reach out to us and ask! We are always happy to provide more information to give you a better understanding about the products we offer so you can make an informed decision when it comes to finding the right solution for your application.
Q: What are the advantages of using glass-lined equipment?
A: There are several advantages in the unique characteristics of glass lining that make this material of construction a top selection of design engineers. Here are some key reasons why glass-lined steel can benefit your process:
- Corrosion Resistance - Glass-lined steel provides superior corrosion resistance to acids, alkalis, water and other chemical solutions(with the exception for hydrofluoric acid and hot concentrated phosphoric acid). As a result of this chemical resistance, glass lining can serve for many years in environments that would quickly render most metal vessels unserviceable.
- Versatility - The chemical, mechanical, and thermal properties of glass are proof that this material can handle a diverse range of operating conditions. Users of glass-lined equipment are therefore able to make drastic changes to their process without needing new equipment to do so.
- Purity - Aggressive reaction environments and extractable metals can cause undesirable catalytic effects or fluctuations in process reactions leading to product contamination in unlined steel or alloy reactors. Glass-lined steel is inert so it is impervious to contamination. Additionally, it does not adversely affect flavor or color, which is of extreme importance to food and drug applications where purity is essential.
- Cleanability - Glass-lined steel has been adapted to cGMP requirements for cleaning, cleanliness, and sterilization. Its high degree of surface smoothness makes it easy to clean using non-corrosive, low pressure cleaning systems. The smooth surface of glass-lined steel also resists the buildup of viscous or sticky products, which means less frequent cleaning.
- Durability - The combination of glass and steel provides you with the best of both materials of construction; fusing glass to steel produces a composite material with an inside that offers product protection and an outside that provides structural strength and durability.
Q: Why are glass lining color options blue and white?
A: The blue coloring comes from the cobalt that was added to the glass formulations a long time ago. Usually the choice of which color to use comes down to concerns about cleaning and what particles could be left behind. If people are concerned with dark-colored particles being left on the surface, they will usually choose a white glass so they can see the particles either. If the particles are a lighter color, then you would choose a blue glass. Also, if you are going to be observing the reaction (using a vessel light) during operation, white glass tends to be a bit better in terms of being able to see what is going on inside.
Q: How are the level measurement marks made on agitators?
A: We create the lines/lettering using the contrasting glass color. So, blue lines on a white agitator or white lines on a blue agitator.
Q: What temperature range should glass-lined equipment be expected to serve?
A: The minimum temperature allowance for a standard glass-lined steel reactor is -20°F (-29°C). For cryogenic processes that require even lower temperatures there are special models that can be designed to accommodate temperatures as low as -76°F (-60°C). The maximum temperature is 500°F ( 260°C).
Another factor to take into account is temperature change limitations. This refers to the allowable temperature differential between the vessel walls and the product. Simply put, if you put something into a reactor and the temperature of the product varies too greatly from the temperature inside the reactor you can cause a lot of damage. For more information on preventing thermal shock read out post on how to protect your glass-lined equipment.
Q: What’s the difference between half-coil jacketing and conventional jackets?
A: The half-pipe or split-coil jacket (referred to by De Dietrich as HemiCoil®) consists of a welded half pipe that wraps around the outside of the vessel, creating a circular path for the heat transfer fluid to pass through. In a split-coil jacket, heating and cooling media flow through the pipe coils with high velocity and turbulence. Thus, film coefficients and heat transfer rates are higher than in conventional jackets. Vessel contents heat up and cool down, and the heat transfer circuit drains much faster-saving energy and reducing batch time. With the split-coil design, only the diameter of the pipe - not the unsupported height of the inner vessel - must contain the jacket pressure. This permits the safe use of much higher pressures within the coils than is possible in conventional jacketing: 450 psig at 500°F is the standard operating limit.
The coils on HemiCoil reactors are welded to the vessel prior to glassing; conventional jackets can be added to a vessel after. Also, it will cost you approximately 30% to 35% more than the same reactor with a conventional jacket. In many instances this premium can be more than offset by decreased operating costs, increased heat transfer rates and better processing efficiency. For more information about jacket selection for your reactor read our post on jacket options.
Before being dispensed to the community through our kitchen sinks or bathroom faucets, water is first filtered and then stored in either water towers or ground storage tanks across our local municipalities. Because water is tasteless and an integral part of our daily lives, the average person likely doesn’t give much thought to where the water is stored or which material lines the inside of a water tower. That’s a good thing because, as the coating manufacturer, the last thing that we’d want is a consumer tasting epoxy when drinking a glass of water.
With potable water linings, there are strict criteria that must be met and tests to be conducted before a water storage tower is approved for potable water use. In the U.S. and Canada, this includes the NSF/ANSI/CAN 61 (soon to be NSF/ANSI/CAN 600) certification for water treatment. However, not all water tanks are meant for drinking purposes and, therefore, don’t require meeting the stringent standards of potable water approval.
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The type of lining needed for a water storage tank depends on a variety of variables, such as its temperature and contents. For example, ambient seawater or tap water may be reasonably inert, but demineralized water at 200°F may require a novolac epoxy or a coating with glass flake reinforcement. On the other hand, if the temperature is bumped up to 212° F in the form of steam, the water tank would likely require a more breathable coating to handle the internal pressure fluctuations. In other words, it’s all about context and picking the right tool for the job at hand.
Selecting a water tank lining based on specific needs
When it comes to linings for potable water towers, the NSF/ANSI/CAN 61 water treatment certification is a basic requirement. Whether this testing is conducted by the National Sanitation Foundation (NSF) or Underwriters Laboratories (UL), your coatings supplier should have a list of all products that have been approved for potable water use.
With this in mind, there are three main questions that will help you narrow down a water tank lining that suits your specific needs:
1. How many gallons does the vessel hold?
Coatings with certification markings have a minimum gallon rating in order to maintain NSF/ANSI/CAN 61 compliance. This has to do with surface contact area to volume ratio and can vary greatly between products. In general, a 100% solids product, such as an epoxy or an aromatic urethane, will have a lower minimum gallon rating than a solvented coating or other lower-solids product. In addition, certain coatings have lower minimum gallon ratings for higher cure times. For example, an epoxy polyamide or a cycloaliphatic coating could have a 70,000 gallon rating after a seven-day cure at ambient temperature, but only a 50-gallon rating after a fourteen-day cure.
2. How long before the vessel goes back into service?
Shutting down one of the few water sources in a town can often put a heavy load on its water systems—especially for smaller municipalities that may not have all that much excess storage capacity. In a case like this, getting the vessel surface prepped, coated and back into service as soon as possible is obviously in the best interest of all parties involved. Therefore, the cure time reported in the NSF/ANSI/CAN 61 testing should be followed.
3. Does the water tank lining require a primer?
Many potable linings can be applied directly to the substrate. However, there are certain factors—especially in cases where there’s a large surface area to coat—that require the use of a primer. Keep in mind that primers have minimum gallon ratings as well. After all, just because a primer is approved for potable water use does not necessarily mean that it is compatible with the actual lining. Before pulling the trigger on a primer, make sure to check with the coating manufacturer on whether or not your lining and primer are an appropriate match.
On the other hand, non-potable water is a much broader category with many more potential variables at play. For instance, does the water tank hold sea water or demineralized water? Is it industrial water with a potentially higher or lower PH value than neutral? Does the non-potable water contain sediment or abrasive media? In addition, does it have a high service temperature?
Other coating limitations to consider
In general, it’s recommended that you check with the coating manufacturer to confirm which products fit the bill for a particular service. That said, most of the coatings that are approved for potable water use can handle most of the water services at ambient temperature.
However, this gets trickier at higher temperatures—especially for demineralized or distilled water types that have a lot less going on in their molecular structure, making them more capable of penetrating linings. Epoxy coatings with glass flake reinforcement, 100% solids linings, baked phenolic coatings and even vinyl esters tend to perform well under these conditions.
In addition, certain products such as some thin film epoxy polyamines are touted as “breathable” and can handle steam temperatures and PSIs upwards of 1,000. If a water tank potentially contains sediment and abrasive media, then it’s critical to choose a coating that has been tested under ASTM D for good abrasion resistance. Having a thick film with additional barrier protection can help here as well.
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