Thermoplastic plastic piping

Further information on the design of thermoplastic piping can be found in the Plastics Pipe Institute s Technical Report TR-21. 

About 10% of the ethylene produced in the U.S. is used to make vinyl chloride, which in the chemical trade is usually referred to as vinyl chloride monomer or VCM. The largest use of VCM is for polymerization to poly(vinyl chloride) (PVC), a thermoplastic, which in terms of volume is second only to polyethylene. PVC is used in such diverse areas as containers, floor coverings (linoleum), plastic pipes, raincoats, and many, many others. PVC has an evironmental disadvantage over non-chlorine containing plastics in that when it is disposed of by incineration it produces hydrogen chloride, which dissolves in atmospheric water to give hydrochloric acid. Polyethylene does not have this undesirable feature. 

ISO 4433-4 1997 Thermoplastics pipes - Resistance to liquid chemicals - Classification -Part 4 Poly(vinylidene fluoride) (PVDF) pipes ISO 9393-2 1997 Thermoplastics valves - Pressure test methods and requirements - Part 2 Test conditions and basic requirements for PE, PP, PVC-U and PVDF valves ISO 10931-1 1997 Plastics piping systems for industrial applications - Poly(vinylidene fluoride) (PVDF) - Part 1 General... 

Stainless steel is impermeable to oxygen unftke plastics it has 10 times the thermal conductivity of plastics and does not creep at temperatures below 425°C (at room temperature for plastics). SS pipes can withstand high pressures (up to 110barfbra25 mm O.D. 300-series SS pipe vs. 5 bar for plastic pipe). Its yield and tensile stresses are an order of magnitude greater than those of thermoplastics. 

EN 1056 Thermoplastics pipes, fittings and valves - plastics piping and ducting systems -plastics pipes and fittings - method for resistance to direct (natural) weathering. 

EN 12256 Plastics piping systems - thermoplastics fittings - test method for mechanical strength or flexibility of fabricated fittings. 

ISO 13968 1997 Plastics piping and ducting systems - Thermoplastics pipes -Determination of ring flexibility. 

Plastics are divided into two basic groups, thermosetting and thermoplastic, both of which are used in the manufacture of plastic pipe. Thermoplastics, as the name implies, soften upon the application of heat and reharden upon cooling they can be formed and reformed repeatedly. This characteristic permits them to be easily extruded or molded into a wide variety of useful shapes, including pipe and fittings. Because thermoplastics are shaped, by a die or mold, while in a molten state their properties are essentially isotropic (i.e., independent of direction). In some processes and under some conditions, some anisotropy (i.e., direction dependence) may result. 

Reinforced thermosetting plastic pipes are somewhat more sensitive to fatigue than thermoplastic pipes. Accordingly, they are often pressure-rated for surge service on the basis of their HDB as determined by Procedure A of the aforementioned ASTM D 2992 from test... 

Threading is also used with plastic pipe. However, molded threads are preferred for thermoplastics and are required for most thermosetting pipe. Molded threaded adapters are available and may be applied by solvent-cementing or with adhesive, whichever is applicable. Threads may not be cut on most thermosetting pipe for they may damage the structural integrity of the pipe wall. Thermoplastic pipe may be threaded, provided its wall thickness is not less than a prescribed minimum, normally at least that of Schedule 80 pipe. 

The Plastics Pipe Institute, a Division of the Society of the Plastics Industry, 1275 K Street NW, Suite 400, Washington, DC 20005, regularly updates its TR-5, Standards for Plastics Piping, which lists standards for thermoplastics piping issued by all major U.S., Canadian, and international standards organizations. 

The basic principle of the installation of buried plastic piping is to embed it in a soil of such quality that the resultant ultimate pipe deflection is controlled to an acceptable value that is limited by either the pipe performance requirements or the pipe material capabilities. The former generally permits deflection up to about 10 percent (some engineers may set conservatively lower values) while the latter is determined by the maxunum allowable stress, or strain, in the pipe wall for the given pipe material and construction.The pipe supplier can provide the limiting deflection values for a given pipe material and construction. These values may depend on the fluids being handled. With thermoplastic pipe of solid wall construction deflection will seldom be limited by material performance constraints. 

Thermoplastics Pipe (Plumbing Applications) Plastics Pipe Fittings Association, 999 North Main Street, Glen EUyn, IL 60137... 

Sixsmith, T. and R. Hanselka. 1997. Handbook of Thermoplastic Piping System Design. New York Marcel Dekker. This work covers in detail the advances in plastic pipe and piping systems and applications where modern plastics can be used in place of more traditional metal pipe. Includes over 70 pages of basic reference data and nearly 200 pages of chemical resistance data. 

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