One of most important engineered systems in a laboratory building is the waste and vent piping. Numerous studies have been written focusing on design for efficient HVAC systems in labs. This is understandable since air exchange and ventilation are vital for laboratories and since efficient HVAC systems offer a high potential for overall cost savings.
Borosilicate glass drainline systems have special properties in the key areas of chemical compatibility, thermal expansion, modification/replacement capability, and fire and safety. Photo courtesy of SCHOTT North America Inc.Click to enlarge.
On the other hand, there’s a dearth of available information regarding the subject of acid waste drainline systems, or “wet side design” as it is sometimes called—and what material does exist can sometimes be misleading. That is unfortunate because the design of the acid waste piping system can be just as vital to the sustainability profile and overall safety of a laboratory as other engineered systems.
In today’s industry, specifying engineers, building owners, architects, and contractors are all becoming increasingly aware of the term “life-cycle costs.” Very often, only the initial costs (material and installation) are considered when choosing a piping material, and this can be very short-sighted. A well-designed acid waste system that is built for sustainability will take into account not only initial costs, but also operating and repair costs over the life of the building. Independent analysis has shown that those maintenance costs can end up accounting for 25 to 30% of the overall life-cycle cost.
When comparing acid waste piping materials there are four main materials to choose from:
When considering the total life-cycle costs for these materials the following considerations should be made:
• Chemical compatibility. The chemical variables that a system must endure over the life of a lab will definitely change over time. New research fields will be developed using different techniques; therefore, a system needs to be able to handle a wide range of possible chemicals. Borosilicate glass has the highest level of chemical compatibility and corrosion resistance compared with other available materials. That holds true not only for specific chemicals themselves, but also when you factor in intermixing within the system and the increased corrosive effect of the chemicals at elevated temperatures.
• Thermal expansion. The effects of heat and thermal expansion are one of the prime enemies of a drainline system. Common heat sources can be live steam, glassware washer effluent, and exothermic reactions caused by chemical intermixing inside the system. The expansion and contraction caused by these thermal variations can cause pipe sagging, secondary trapping of waste, and stress damage to fittings and joints. Plastic piping materials are most notably affected by these thermal variations.
Heat and thermal expansion are almost a non-factor for a system utilizing glass. Borosilicate glass has a maximum operating temperature of 250°F intermittent and 212°F continuous. By far, this material also has the lowest thermal expansion rate of the available chemical waste piping materials (0.2 in. of expansion/100 ft of material/100°F rise in temperature). It also uses a mechanical joint coupling system that allows for 4° of deflection without any leakage. Compared with the expansion rate of PVDF (more than 403 higher) and PP (more than 303 higher), and the fact that they sometimes use a fused or glued joint, it is easy to see why straight chemical compatibility is not the only thing to consider.
• Modifications and replacement. Many labs will need to be redesigned over the life of the building to help accommodate new research fields or a growing workforce. The costs for replacement or modifications of an in-service system can sometimes run 2 to 33 the initial installation costs. A drainline system using components and a joining method that allows for easy reconfiguration and the possible reuse of material will minimize new material costs, making this a very economical choice. Borosilicate glass uses a mechanical joint coupling that allows for easy reconfiguration, and combined with the maximum corrosion resistance that glass offers, fittings and traps can often be cleaned and reused during a renovation.
• Fire and safety. Like all buildings, a lab must meet all applicable local and national fire codes. But labs, by nature, are special buildings that contain high-fire-risk areas. This challenge makes the choice of piping material a very important decision since piping it is almost always installed behind walls and out of sight. A flammable piping material could transport a fire from room-to-room and floor-to-floor.
One special area regarding fire safety is the return air-plenums. In accordance with UL 723 (ASTM E84), there are only three acid-waste piping materials that are allowed to be installed in a return air plenum. Those are borosilicate glass, high-silicon iron, and PVDF plastic because they meet the 25/50 smoke rating based on the UL and ASTM standard. Borosilicate glass also does not burn or emit toxic fumes in a fire and offers the simplest fire-stopping installation method as well.
After taking all these considerations into account, owners and specifying engineers can see why borosilicate glass piping makes a strong case as an excellent solution. When designing an acid-waste system that is regulatory-compliant but also cost-effective and environmentally safe, using borosilicate glass is a smart and sustainable choice.
Patrick Frazier is product manager/tubing and labware for SCHOTT North America Inc., whose products include borosilicate glass drainline systems (patrick.frazier@us.schott.com; www.us.schott.com).
Chemical waste drainage: The CPVC alternative
By Tina Massel
Drainage systems in institutional, commercial, and academic laboratory and research facilities require special design considerations since they are expected to routinely dispose of such aggressive materials as acids, bases, salts, and a wide range of organic media.
Chemical waste systems must be designed to drain corrosive, or otherwise hazardous, liquids that are either diluted sufficiently with a steady flow of water or neutralized in some manner before being discharged into the sewer system. As a result, they require a material durable enough to convey the hazardous chemicals and corrosive wastes without being compromised by corrosion, leaks, and other serious failures.
Popular materials used for laboratory drain service include polypropylene (PP), polyvinylidene fluoride (PVDF), borosilicate glass, high-silicon iron, and chlorinated polyvinyl chloride (CPVC).
Waste drainage systems made of CPVC offer superior chemical resistance to a wide range of corrosive elements. Photo courtesy of Lubrizol Advanced Materials. Click to enlarge.
Each of these materials possesses its own combination of strengths and weaknesses that make it appropriate or inappropriate for various chemical waste drainage applications. For example, many metals don’t have high chemical resistance, which makes them susceptible to corrosion and leaks. Glass and high-silicon iron systems may be fragile and/or expensive to install. PP and PVDF installation also can be complicated, time-consuming, and inconsistent. In addition, PP has limitations in handling highly concentrated acids, while PVDF is not recommended for transporting common alkaline solutions.
Compared to other materials of construction, CPVC is a newcomer to the chemical waste drainage market. Although CPVC technology was developed in 1959 by Lubrizol Advanced Materials Inc. (formerly BFGoodrich) and has nearly a 50-year track record in residential, commercial, and industrial applications, its use in laboratories for the specific task of discharging chemical waste has been somewhat limited to date. However, careful analysis shows that CPVC is viable and cost-effective for this application.
No single construction material is suitable for every drainage application, but CPVC provides specifying engineers with another alternative that presents numerous benefits:
• Easily installed system. Lightweight, yet durable, the system is quick, easy, and safe to install. CPVC chemical waste drainage systems are composed of schedule 40 pipe, drainage pattern style fittings, and specially formulated solvent cement. No special tools are required for cutting, and joining is accomplished using a simple, one-step solvent cement.
• Reliable joints. The solvent cement is designed to create an intermolecular bond between the pipe and fitting surfaces. Joints are chemically fused. Once cured, they result in permanent, reliable, leak-free connections, and actually become stronger than the pipe or fittings alone.
Transition fittings are also available to join CPVC pipe to other materials of construction. Some alternative materials, such as PP and PVDF, rely on either mechanical or fusion joining methods. Fusion joints require the use of complicated and expensive fusion equipment and produce joints that are often inconsistent in quality due to factors uncontrollable at job sites, such as voltage fluctuations.
• Chemical resistance. Waste drainage systems made of CPVC offer superior chemical resistance to a wide range of corrosive elements. CPVC pipe compares favorably to other non-metallic piping materials in this regard as it possesses a good-to-excellent resistance rating for many corrosive chemicals. In particular, CPVC pipe is inert to such chemicals as strong and dilute acids, bases, caustics, salts, organic media such as aliphatic hydrocarbons, and other reagents (within certain temperature limitations). The solvent cement used in the joining process also has been formulated for chemical resistance to caustics, including hypochlorites, as well as mineral acids and other corrosive chemicals. CPVC can be used with an even wider array of chemicals in the less-demanding, non-pressurized lab drain applications than with more aggressive, pressurized industrial environments.
• Durability. CPVC outperforms many other non-metallic materials with regard to durability. The material excels in both its izod impact strength and heat distortion temperature. It’s important to note, however, that not all brands of CPVC perform equally in this area, as they are differentiated by their cell class rating. A higher cell classification means greater drop impact strength and a higher heat distortion temperature.
• Fire performance. CPVC pipe inherently exhibits outstanding fire performance characteristics in terms of limited flame propagation and low smoke generation. CPVC will not burn unless a flame is constantly applied, and stops burning when the ignition source is removed. Thus CPVC does not contribute to the fuel load in a fire and will not propagate flame to surrounding structures.
• Maintenance free. Once a CPVC chemical waste drainage system is properly selected, designed, and installed, it is virtually maintenance-free. It will not rust, pit, scale, corrode, or promote interior buildup.
As previously noted, no single piping material is ideal for every chemical waste drainage application. It’s important to understand the specific strengths and weaknesses of the various materials and identify which attributes are most suitable for a specific application.
Consideration must be given to such variables as the environment, flow rates, and temperature, as well as the composition of the material being transferred.
There are, however, many applications for which CPVC pipe and fittings will always outperform metal. Such benefits as a fast, reliable installation; low maintenance costs; high chemical resistance; lower material costs; and dependable, long-term service life make the thermoplastic CPVC a cost-effective, high-performance choice for many lab chemical waste drainage systems.
Tina Massel, an engineer by training, is currently commercial water market manager for Corzan Piping Systems, which is part of Lubrizol Advanced Materials (tina.massel@lubrizol.com; www.corzancpvc.com “chemical waste drainage systems”).
