PlasticPipeLine How to Select the Proper Thermoplastic Industrial Piping Material by David A. Chasis P lastic piping is used to move more fluids than any other piping material in the world. Why is it so widely used? Plastics are more durable, easier and safer to install, environmentally sound, and cost-effective than most other piping materials. Yet, due to the many available plastic piping systems, selecting the correct piping product could be a daunting task. The two keys for choosing the proper plastic piping material are: knowing the complete project’s service conditions and the most cost-effective and suitable materials for these service conditions. Service Conditions: The more you know about the factors of a particular field application, the more likely you are to select the proper piping material. An information checklist for all piping installations may include the following, with the most important factors in bold print: • Type or purpose of application: application type (chemical processing, water lines, sewage, irrigation, etc.); above or below ground; any prolonged exposure to sunlight; openedor closed-loop system; quick-closing valves in system. • Type of fluids to be transported: chemical compatibility of pipe, valves and fittings, any special fluid data such as high particulate matter, viscosity, specific gravity, velocity, etc. • Maximum allowable working pressure: working pressure varies for each plastic piping component and may be limited to the maximum allowable working pressure for a particular product such as valves, flanges or unions. • Temperature range: temperature limitations vary for each plastic piping material and directly affect working pressure capability of all plastic products coming in contact with the transferred fluid. • Code restrictions: depending on the application, local, state and federal codes may restrict the selection of a particular piping material. • Estimated life of piping system: in very severe service conditions, various piping materials may have limited life and affect which piping system will last the longest. • Preferred method of joining: depending on the availability of utilities (electric, gas or neiFebruary/March 2013 The IAPD Magazine ther) as well as the experience of the installation crew, selection of the joining system could be important. With the conditions of service known and knowledge of the piping material properties, a specifying engineer or end user is well on his/ her way to selecting the best piping material for the project. Plastic Piping Materials: There are five commonly used thermoplastic industrial piping materials in the United States, all of which have different temperature and allowable working pressure ranges. In most cases all the plastic piping materials can withstand temperature lows of 0°F (-18°C). The only caveat to remember with thermoplastic piping at lower temperatures is that the piping system becomes more brittle. The listing below indicates the maximum temperature capability of each piping material. Keep in mind that with thermoplastic piping, as the temperature increases, the allowable working pressure decreases. Therefore, only drainage applications, in most cases, can be used at the maximum temperature rating. • CPVC (chlorinated polyvinyl chloride): similar in properties to PVC (polyvinyl chloride); can handle temperatures up to 210°F (99°C); used in pressure and chemical drainage piping systems as well as hot and cold water distribution and fire sprinkler systems. • PE (polyethylene): several material compound types depending on the application; the broadest range of pipe diameters; mostly used in belowground applications; most PE piping systems have temperature capabilities of up to 160° (71°C), however, one fairly recent material, polyethylene raised temperature (PE-RT), can withstand temperatures up to 210°F (99°C); a preferred piping material for natural gas distribution. service allow, PVC is the most specified and installed plastic piping material in the world; maximum temperature up to 140°F (60°C); in most cases PVC is the lowest cost piping material for a myriad of applications. • PVDF (polyvinylidene fluoride): has the best chemical resistance properties and highest temperature capability 275°F (135°C) of any of the listed piping materials; mostly immune to ultra-violet degradation; the preferred piping material in ultra-high purity water systems. [Note: Acrylonitrile butadiene styrene (ABS) and crossed-linked polyethylene (PEX) are not listed since most of these excellent plastic piping materials are used in the United States for residential/ commercial, not industrial, applications.] Each of these plastics has properties that may or may not be suitable for a particular application. To determine the proper piping material, you must compare the project’s conditions of service with that of the piping material’s properties, breadth of product line and installed costs. The best way to show how this process works is by example. Example — Service Conditions: The following listed service conditions are the basis for selecting piping materials: • Application: metal ore smelting; above ground • Fluid: sulfuric acid with 70 percent concentration • Working pressure: 50 to 105 psi • Working temperature: 70 to 130°F (21 to 54°C) • Piping size: ½ to 6 inches • PP (polypropylene): very versatile material for temperatures up to 180°F (82°C); the leading piping material in chemical drainage and, because of its excellent chemical resistance, can handle many corrosive pressure piping applications. Example — Chemical Compatibility: The first step is to determine the chemical resistance of the fluid versus the piping material. There are several published and well-tested chemical resistance tables that list hundreds of chemicals and their suitability to both plastics and metal materials. On the next page is a snippet of a typical chemical resistance chart pertinent to this example. You can see after reviewing the chart that PP and PE piping are not able to handle the conditions of service shown. • PVC (polyvinyl chloride): when conditions of Example — Pressure Capability: Next you www.iapd.org PlasticPipeLine Partial Chemical Resistance Chart Chemical PVC Temperature (°F) CPVC PP PVDF PE 70 140 70 140 185 70 150 180 70 150 250 70 140 Sulfuric acid, 50% R R R R R R R R NR R R R R — Sulfuric acid, 60% R R R R R R R R NR R R R R — Sulfuric acid, 70% R R R R R R R NR NR R R R R — Sulfuric acid, 80% R R R R R R R NR NR R R — R NR Sulfuric acid, 90% R R NR R R R R NR NR R R — R NR Sulfuric acid, 93% R R NR R R R R NR NR R R — R NR NR NR NR NR NR NR NR NR NR NR — NR NR Sulfuric acid, 100% NR R = Recommended determine the working pressure capability of the piping materials in the example. Thermoplastic piping working pressure is affected by temperature, and in the case of schedule 40 and 80, piping can vary with pipe diameter. The tables below show the working pressure capabilities at ambient temperature 73°F (23°C) of the five piping materials and the temperature correction factors that are used to multiply the factor times the ambient pipe pressure rating in order to obtain the maximum working pressure capability of each piping material. As noted in the tables, PVC 6-inch diameter pipe at ambient temperature has a working pressure of 280 psi. The temperature correction factor for PVC pipe at 130°F (54°C) is shown as 0.30; therefore, multiplying 280 psi by 0.30 equals 84 psi. The conditions of service list a maximum working pressure of 105 psi; hence, only CPVC and PVDF piping are capable of handling the stated conditions of service. Example — Cost Comparison: The last step in the selection process is to choose the more costeffective of the two qualifying piping materials. Looking at the chart below it is evident that CPVC is the winner as the PVDF piping system costs over two and a half times that of CPVC. There are industrial applications where temperatures exceed 275°F (135°C) and working pressures are well above 250 psi. For these conditions of service, piping of glass-reinforced thermosetting resin and metal- and plastic-lined metal may be the materials of choice. But for an estimated 80 percent of all industrial applications, thermoplastic piping systems should be the preferred choice due to their durability, ease of use, environmental soundness and cost-effectiveness. David A. Chasis is president of Chasis Consulting, Inc., author of the book “Plastic Piping Systems” and a member of and consultant to the Plastic Pipe and Fittings Association. Chasis can be reached at Chasis Consulting, Inc., 329 The Hills Drive, Austin, TX 78738 USA; (512) 261-9115, fax (512) 261-3518, email: [email protected], www.davidchasis.com. www.iapd.org — = No Information Available NR = Not Recommended Maximum Operating Pressure Ratings (psi) of Schedule 80 Pipings/Fittings at 73°F (23°C) Nominal Pipe Size (in.) PVC / CPVC PE (SDR 11) PP* PVDF 3 370 160 190 250 4 320 160 160 220 6 280 160 140 190 Temperature Correction Factors for PipingFactors for Piping Termperature Correction Operating Temp. (°F) CPVC PE PP PVC PVDF 110 .77 .74 .80 .50 .75 120 .70 .63 .75 .40 .68 130 .62 .57 .68 .30 .62 CPVC: 0.62(280) = 174 psi PVC: 0.30(280) = 84 psi (System max. is 105 psi) PVDF: 0.62(190) = 118 psi Estimated Installed Costs of Six-Inch Diameter Piping Systems* Termperature Correction Factors for Piping Materials Piping Costs (US$) PVC Schedule 80 11,499 CPVC Schedule 80 14,374 Carbon Steel Schedule 40 18,932 Stainless Steel 304L Schedule 40 22,789 Stanless Steel 316L Schedule 40 45,835 PVDF Schedule 80 63,945 ΎWĂŶĚWWĐŽƐƚĞƐƟŵĂƚĞƐďLJƚŚĞĂƵƚŚŽƌ Note: The example and charts shown are adapted from the “Thermoplastic Industrial Piping Systems Workbook” published by the Plastic Pipe and Fittings Association (PPFA). February/March 2013 The IAPD Magazine
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