Page 233 - Buried Pipe Design

Design of Pressure Pipes 207

AWWA standards. The first AWWA standard approved for plastic pipe
was AWWA C900 in 1975. AWWA C900-07 is the AWWA standard for
polyvinyl chloride pressure pipe, 4-in through 12-in for water. This
standard contains three pressure classes.
Class 165, DR 25
Class 235, DR 18
Class 305, DR 14

The term DR means the same as the standard dimension ratio, that is,
outside diameter D
DR
minimum wall thickness t
However, the values do not fall in the referenced ASTM preferred
series. The design basis equation in C900 can be expressed in the fol-
lowing way:

2t
2.0 PC (HDB) (4.16)
D t
where 2.0 safety factor
PC pressure class: 165, 235, 305 lb/in 2
t minimum wall thickness, in
D outside diameter, in
HDB hydrostatic design basis 4000 lb/in 2

A design parameter included in AWWA C900 and not in ASTM
D2241 is the effect of sustained elevated temperatures on pressure
and/or design stress. For sustained temperature of the pipe wall
above 73°F, the design stress should be reduced. This reduction is not
necessary for short-term excursions of elevated temperatures but is
for continuous service at a higher temperature. The recommended
percentages of allowable pressure class for various elevated tempera-
tures are shown in Table 4.6.

TABLE 4.6 Temperature Coefficients
Maximum continuous Percentage of allowable pressure
service temperature, °F class or design stress at 73°F
73 100
80 88
90 75
100 62
110 50
120 40
130 30
140 22