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Numerous industrial manufacturing processes utilize aggressive chemical fluids and slurries in the production of familiar finished goods. Everything from color concentrates found in dyes, paints and inks through common household paper goods require multiple stages of processing.
Most of these industrial processes involve the conveyance of a wide variety of aggressive chemical solutions and mixtures through piping systems toward the development of the desired end product. Due to their excellent chemical and corrosion resistance properties, industrial thermoplastic piping products, such as PVC and CPVC, continue to gain acceptance in numerous applications previously dominated by metallic piping. In many industrial processes, the use of thermoplastics in lieu of metallic piping, can provide valuable cost savings to the end user by improving the efficiency and life expectancy of piping systems.
A close look at many processes will reveal applications that fall within the operational parameters of a variety of plastic piping materials. Evaluating the compatibility of plastic piping with the chemicals being conveyed, as well as reviewing system operational parameters (such as temperature and pressure conditions), can help to identify areas where the use of plastics may prove beneficial.
CPVC piping for the pulp and paper industry
In one processing application found within the pulp and paper industry, CPVC piping has been selected for use in certain bleach processing operations due to its chemical compatibility with the substances used in this process; many of which are used at elevated temperatures.
The chlorine dioxide bleaching processes within this industry involve the use of harsh chemical compounds operating at elevated temperatures (» 170°F). These chemicals include but are not necessarily limited to chlorine dioxide, hydrogen peroxide, sodium hypochlorite, sodium hydroxide, sodium chlorate, sodium chloride, sodium sulfate, hydrochloric and sulfuric acids, and other extremely corrosive chemicals. It is commonly known that these substances attack and corrode 316 stainless steel products. However, stainless steel has traditionally been used for pipe, valves and headers in the bleaching processes, thereby greatly reducing their life expectancy when used in this application. The use of schedule 80 CPVC piping for this application can provide a cost-effective alternative to metallics based on its corrosion resistance to these substances.
In addition to bleach plant operations, other applications within pulp and paper where the use of CPVC piping can prove beneficial, include elevated temperature water distribution and water recovery systems, pulp stock handling and recycling processes, chemical recovery systems, pollution control systems, stock preparation and paper making operations.
This industry uses large volumes of water. Water distribution, reclaim and recovery systems are extremely important aspects of the paper making process as aggressive water can result in pipe corrosion issues with metallics, thereby greatly reducing plant efficiency over time. The use of industrial grade plastics such as CPVC, which is currently available in schedule 80 dimensions in sizes up through 16", can provide a viable alternative to metallics in this application as well.
This article was written by William P. Weaver, Harvel Plastics, Inc.
|In This Issue:
Revisiting chemical process applications
CPVC is perfect for fluid handling in the pulp and paper industry.
Trusted product gets a makeover with CPVC
High-performance CPVC pipe installed for corrosive bleach plant application
Safely testing your PVC and CPVC piping system
Test your knowledge
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It has been some time since we have had a new piping system to talk about. Now we have an old “tried and true” product that has found a new application.
CPVC (chlorinated polyvinyl chloride) has been used in thermoplastic process piping for four decades, and has been an excellent system for handling corrosive fluids at a higher temperature than PVC is capable. Now, CPVC has been adapted to be used as a special drainage system.
Corrosive waste draining systems
Laboratory waste involves the routine disposal of a wide variety of hot and cold chemicals accompanied by appropriate amounts of water for the purpose of dilution and flushing. By nature, this involves intermittent use of limited quantities of many chemicals. In contrast, larger volumes of one or a few chemicals are used in continuous waste applications such as certain industrial processes. Considering the fact that CPVC has been successfully used for over 40 years in a wide variety of both dedicated and mixed chemical pressure handling applications, CPVC is a very suitable alternative for laboratory use as well as many industrial, food processing, pharmaceutical and other chemical waste drainage applications.
Fire safety issues pertaining to materials of construction are of a concern in many industries including piping applications. Typically, this issue focuses on fire performance of products installed within air plenums where a maximum flame spread rating of 25 and smoke generation of 50 are required. Unfortunately, this is only one aspect of a product’s fire performance characteristics and alone gives only a limited perspective of a product in terms of safety. For example, additional fire performance characteristics such as limiting oxygen index and heat of combustion are significant to overall performance.
Polypropylene cannot be used in return air plenums without an approved wrap, and PVDF is a costly alternative. CPVC products have been independently evaluated as having a flame spread/ smoke development rating of 25/50 or less by Underwriter Laboratories of Canada ULC, a recognized UL partner and affiliate. This evaluation was made under the protocol of CAN/ULC S102.2 as test of actual assembled product, as opposed to only a “sheet coupon” material test of ASTM E-84. Many authorities have accepted this alternative evaluation of CPVC products as acceptable for use in air plenums.
When it comes to selecting piping materials there is no single material that will cover all applications. What will be discharged, the degree of protection required, the initial installation cost, and the cost to maintain the system all need to be considered. CPVC is a well-known thermoplastic that has stood the test of time. Now, it has been adapted to serve yet another need as a viable drainage system for laboratories as well as industrial waste applications.
This article was written by Fred Schroeder, Indelco Plastics Corporation.
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When the Environmental Protection Agency (EPA) published the Cluster Rule in 1998, pulp and paper manufacturers industry-wide began to make operational adjustments to become compliant by April 2001. Aimed at reducing emissions, the Cluster Rule called for the introduction of uniform pollution prevention and control technologies. For Smurfit-Stone Container Corporation, that meant a major reconfiguration of its bleached market pulp operation in Panama City, FL, including extensive changes to its bleach plant.
Smurfit-Stone retained BE&K Engineering Co. to identify cost-effective construction materials that would provide reliable performance in the harsh environment. Specified materials, including industrial piping, had to demonstrate superior corrosion resistance that would prevent premature system failure. Also, in order to complete construction in time to meet the EPA’s tight deadline, these products needed to provide for quick installation.
In a bleach plant setting, corrosion can actually occur both on the inside and the outside of the piping,” says Dennis Myers, Principal Engineer Technical Group Mechanical Services, at BE&K. “The trick was to find a material that would address both types of corrosion in a satisfactory manner.”
For the recovery of the bleach plant’s spent scrubber effluent, BE&K specified CPVC pipe over stainless-steel, carbon-steel and fiberglass (FRP) piping alternatives. In addition to its superior corrosion-resistance properties, CPVC pipe offered fast, easy installation and increased cost efficiency over its metallic counterparts.
The effluent solution in this particular application is the result of combining weak white liquor with a mixture of gases containing chlorine-dioxide residuals. With a pH of 9.9 and a temperature of 135°F, this solution is known to cause internal pipe corrosion that diminishes the service life of both carbon-steel and stainless-steel piping materials.
“CPVC pipe offers corrosion resistance from both the inside and out. Based on performance in this environment, we expect a much longer service life from the CPVC pipe as compared to carbon or stainless steel,” explains Myers. “Plastic-lined FRP was another alternative, but CPVC offered advantages in simplicity, cost and size availability that went unmatched.”
Easy installation and maintenance
“We had to get this plant into operation immediately. Using CPVC, we were able to install a reliable system while keeping the construction schedule on track,” says Myers. “In addition, with CPVC, a branch line or other piping modification can be quickly installed if needed. And if a portion of the piping should receive some physical damage, the repair can be made easily, without the need for a welder or lifting device to hoist the piping into place.”
By combining superior mechanical properties, longer service life, and lower installation and maintenance costs, CPVC provided BE&K with the complete system solution it sought for Smurfit-Stone. “CPVC offered us an excellent balance of qualities that produced quality, cost savings and simplicity in this application,” concludes Myers. “We’re expecting excellent performance from the system for many years.”
This article was written by Corzan Piping Systems.
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You’ve just installed a new PVC or CPVC plastic pipe and fittings system. The cement joints have been adequately cured and you are ready to test and inspect the system for leaks.
The most common test method is to use water under moderate pressure. However, installers sometimes opt for testing with air pressure because it is quicker and easier. But air testing, if done improperly, can be hazardous.
Air is a compressible gas that can store far more energy than water when put under pressure because it can release this energy so rapidly. This raises the possibility of an explosion. The most common cause of failure is to employ too much air pressure, which can result in an explosion. Other testing mistakes that can cause failures are:
All can cause piping to fail risking an explosion that can cause serious personal injury or death and property damage.
It is important to know that pipe and fitting manufacturers do not recommend air testing and cannot be held liable for any injuries occurring during the air testing of their product. Most PVC and CPVC piping component manufacturers have statements in their literature cautioning against using air or gases to test their products.
They also caution against using their product to store or convey air or other gases or failing to vent trapped air. It is increasingly common for such practices to void any warranties. Many accidents have been reported as a result of air testing or trapped air. Most manufacturers of plastic pipe and fittings have had to investigate field failures caused by either air testing or trapped air.
Overall, water testing is a safer, more reliable and more accurate method for testing plastic piping systems. Because PVC and CPVC pipe and fittings are designed to convey liquids, most companies recommend testing with water. The purpose of the test is to locate any leaks at the joints and correct these prior to putting the system into operation. Because it is important to visually inspect the joints, a water test must be conducted prior to closing in the piping or back filling underground piping.
If there is a leak in the system, it will always be easier to locate when testing with water; air leaks can be hard to find. Air tests have a built-in inaccuracy that is hard to control. The system pressure changes with temperature; whereas, a water pressure test is not as sensitive to temperature variations.
To properly water test, plugs should be inserted through test tees to isolate each section being tested. All other openings should be plugged or capped with test plugs or test caps. Then fill the system being tested with water to the highest point. The hydrostatic pressure created as the water fills the vertical pipe increases as the water height climbs. Filling the system slowly should allow any air in the system to escape as the water rises in the vertical pipe. All air trapped in the system must be expelled prior to the beginning of the test. Failure to remove entrapped air may give faulty test results.
If a leak is found, the joint must be cut out and discarded. A new section can be installed using couplings. Once the system has been successfully tested, it should be drained and the next section should be prepared for testing.
When it comes to testing pipe and fitting installations, water testing is a safer, more thorough method than air testing. Taking a few extra minutes to properly test piping systems with water pays off in error-proof installation and a safer job site.
This article was written by Reese Sumrall Jr., Charlotte Pipe and Foundry Company.
Chlorinated polyvinyl chloride (CPVC) is created when PVC homopolymer undergoes a chlorination reaction resulting in additional chlorine atoms on the base molecule. The result is an amorphous polymer similar to PVC in composition with a higher heat distortion temperature. This provides a material with high temperature strength and excellent flammability properties that also exhibits many of the desirable physical characteristics of polyvinyl chloride such as exceptional corrosion resistance and good mechanical properties.
CPVC has an upper working temperature limit of 200°F (93°C) or approximately 60°F (16°C) above that of PVC, which greatly increases the product’s application range and makes it advantageous for many aggressive high temperature processing applications such as plating and chemical processing.
CPVC is used in the manufacture of pipe, fittings, valves, machining shapes, sheet and duct, offering advantages for piping and related applications due to its high glass transition temperature, high strength to weight ratio, pressure bearing capability, corrosion and chemical resistance and low friction loss characteristics.
In addition to chemical inertness and mechanical strength, CPVC products have excellent flammability properties when compared to other plastics and many common building materials. It will not support combustion, is rated as self-extinguishing, and has very low flame and smoke characteristics. These unique fire resistance properties enable product applications that are unacceptable for many other plastics, such as use in fire resistant construction and fire sprinkler piping applications.
The property table for CPVC is online at www.iapd.org/new/bookstore/free_resources.html. For more information on CPVC and other plastic materials, IAPD’s Introduction to Plastics is an invaluable training manual. Details about it and other IAPD educational resources are available online at www.iapd.org.
What do you know about CPVC? Answers are at www.iapd.org/popquiz.html.
1. In an application with a sulfuric acid concentration of 15 percent and a maximum operating temperature of 90°F (32.2° C), what would you suggest as the most economical material, when you also factor in installation costs?
2. CPVC is different from PVC in that it has an added molecule of:
Your IAPD Distributor is your choice in finding the right material for your application. Go to www.iapd.org to find a distributor in your area. You can search by company name, location or product category.
The IAPD Magazine web site at www.theiapdmagazine.com allows you to search by material, trade name and fabrication process. You can also search for fabrication capabilities.
Designing with Plastics is published by the International Association of Plastics Distribution. While every effort has been made to ensure accuracy, IAPD encourages you to verify information with a plastics distributor to ensure you select the correct plastic products to meet your needs.