How to Guide

44
Plastics Technical Manual
System Operating 73 80 90 100 110 120 130 140
Temperature °F (C) (23) (27) (32) (38) (43) (49) (54) (60)
150 132 113 93 75 60 45 33
DESIGN & ENGINEERING DATA
Pressure Rating of PVC Flanges at Elevated Temperatures
1/2” - 12 ”
Pressure Rating (psi)
Maximum operating temperature for PVC is 140°F. Exceeding the maximum operating temperature
could cause system failure and/or property damage.
1
⁄2 ” 235 psi 235 psi
3
⁄4 ” 235 psi 235 psi
1 ” 235 psi 235 psi
1
1
⁄4 ” 235 psi 235 psi
1
1
⁄2 ” 235 psi 235 psi
2 ” 235 psi 200 psi
3” 235 psi 185 psi
Unions
Size Socket Type Threaded Type
Max Working Max Working
Pressure @ 73°F Pressure @ 73°F
Pressure Rating for PVC Schedule 80 Unions
One of the more complex questions in the plastic pipe and
fittings industry is associated with the pressure rating of fit-
tings used in PVC Schedule 40 and PVC Schedule 80 systems.
While these fittings are used in pressure systems, strictly
speaking, they are not pressure rated.
There has been an effort underway at ASTM International for
many years to solve this question. However, the industry has
not been able to develop a methodology for pressure rating
fittings due to their varied configurations. The best effort to
date is found within ASTM F 2261 Standard Test Method for
Pressure Rating PVC Plastic Pipe Fittings, Schedule 40 and 80 Socket
Type. This test method is similar to that found within ASTM D
2837 which is used to determine the Hydrostatic Design Basis
(HDB) of plastic pipe. However, plastic pipe has a uniform
shape that reacts consistently to pressure and fittings do not.
ASTM F 2261 indicates:
1.2 Unless the data (for fitting failure tests) approximates
a straight line, when calculated using log-log coordinates, it
is not possible to assign a pressure rating to that product or
sample product. … where the lower confidence level limits
are not met the data shall be classified as unsuitable.
Unfortunately, logged fitting failure test data is typically
dispersed and judged as unsuitable.
The 1987 publication Designing, Operating and Maintaining Piping
Systems Using PVC Fittings by Ron D. Bliesner is a respected refer-
ence addressing the pressure rating of fittings. This publication
establishes a rule of thumb indicating that the working pressure
for fittings is 60% of the working pressure of pipe. Charlotte
Pipe agrees with this rule of thumb and recommends that the
maximum working pressure for PVC Schedule 40 and PVC
Schedule 80 fittings is 60% of the maximum working pressure
of pipe of the same diameter and schedule. As with pipe, the
maximum working pressure must be de-rated at temperatures
exceeding 73 degrees F.
Special engineered fittings such as flanges, unions or valves
differ in that they carry a pressure rating specified by the
manufacturer which is usually lower than that of pipe of the
same diameter.
Pressure Rating PVC Schedule 40 and PVC Schedule 80
Pressure Rating of Fittings, Flanges, and Unions