POLYVINYL CHLORIDE PIPES BASIC INFORMATION AND TUTORIALS


Polyvinyl chloride (PVC) piping is made only from compounds containing no plasticizers and minimal quantities of other ingredients. To differentiate these materials from flexible, or plasticized PVCs (from which are made such items as upholstery, luggage, and laboratory tubing) they have been labeled rigid PVCs in the United States and unplasticized PVC (uPVC) in Europe.

Rigid PVCs used in piping range from Type I to Type III, as identified by an older classification system that is still much in use. In this system, the type designations are supplemented by grade designations (e.g., Grade 1 or 2) which further define the material’s properties.Type I materials, from which most pressure and nonpressure pipe is made, have been formulated to provide optimum strength as well as chemical and temperature resistance.

Type II materials are those formulated with modifiers that improve impact strength but that also somewhat reduce, depending on modifier type and quantity, the aforementioned properties of Type I materials. There is little call for Type II pipe, as the impact strength of the stronger Type I pipe is more than adequate for most uses.

Type III materials contain some inert fillers which tend to increase stiffness concomitant with some lowering of both tensile and impact strength and chemical resistance. Some nonpressure PVC piping, such as that used for conduit, sewerage, and drainage, is made from Type III PVCs.

The currently used classification system for rigid PVC materials for piping and other applications is described in ASTM D 1784,“Standard Specification for Rigid Polyvinyl Chloride and materials by numbered cells that designate value ranges for the following properties: impact resistance (toughness), tensile strength, modulus of elasticity (rigidity), deflection temperature (temperature resistance), and chemical resistance.

Because (as expanded in the discussion on properties) short-term properties of plastic materials are not a reliable predictor of long-term capabilities, those PVC materials that have been formulated for long-term pressure applications are also designated by their categorized maximum recommended hydrostatic design stress (RHDS) for water at 73.4°F (23°C) as determined from long-term pressure testing.

The most commonly used designation system for PVC pressure-piping materials is based on the above older designation system with two added digits that identify, in hundreds of pounds per square inch, the maximum recommended design stress.*

For example: PVC 1120 is a Type I, Grade 1 PVC (minimum cell class 12454-B) with a maximum recommended HDS of 2000 lb/in2 (13.8 MPa) for water at 73.4°F (23°C); PVC 2110 is a Type 2, Grade 1 PVC (minimum cell class 14333-D) with an RHDS of 1000 lb/in2 (6.9 MPa).

Most pressure-rated PVC pipe is made from PVC 1120 materials. The combination of good long-term strength with higher stiffness explains why PVC has become the principal plastic pipe material for both pressure and nonpressure applications.

Major uses include: water mains; water services; irrigation; drain, waste, and vent (DWV) pipes; sewerage and drainage; well casing; electric conduit; and power and communications.

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