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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