Page 228 - Buried Pipe Design

202 Chapter Four

While this terminology still persists, the current definition of PVC
compounds is given in the most current edition of ASTM D 1784, the
standard specification for “rigid poly (vinyl chloride) (PVC) compounds
and chlorinated poly (vinyl chloride) (CPVC) compounds.” This specifi-
cation defines the physical characteristics of the compound with a five
digit cell-class numbering system and a letter suffix describing chem-
ical resistance.
The old type-and-grade compound system is now expressed in cell
classification as follows:

Type I, grade 1: 12454B
Type I, grade 2: 12454C
Type II, grade 1: 14333D
Type III, grade 1: 13233
Type IV, grade 1: 23447B

The following is a brief review of what this numbering matrix plus
a letter, that is, 12454B, defines.

First number: Material identification (PVC homo polymer)
Second number: Impact strength (izod minimum) (0.65 ft lb/in)
Third number: Tensile strength (7000 lb/in minimum)
2
Fourth number: Modulus of elasticity (in tension 400,000 lb/in min-
2
imum)
Fifth number: Deflection temperature under load (158°F minimum)
Letter: Chemical resistance as defined in Table 2 of ASTM D 1784.

As indicated, the PVC compound most commonly used for water
(pressure) pipe application is

Old designation: type I, grade 1
Current designation: 12454B
In late 1980, ASTM approved yet another standard for identifying
PVC compounds. ASTM D 3915 utilizes a similar cell-class system as
ASTM D 1784, but has deleted the letter suffix and substituted a
hydrostatic design basis cell. To date, this system has not been adopted
in any PVC pipe standards.

Hydrostatic design basis. ASTM D 2837 establishes the “standard
method for obtaining hydrostatic-design basis for thermoplastic pipe
materials.” The procedure for establishing a hydrostatic design basis
is as follows: