| Expansion & Contraction of PVC Systems
(En español)
Unexpected failures in PVC piping systems can be caused by stress due to temperature changes. Allowances for thermal expansion and contraction should be designed into the system. These allowances can be made in the piping system supports and by using expansion loops.
Piping system support
When expansion and contraction is an issue, support of a piping system is very important. The piping system should not be rigidly supported, but rather secured with smooth hangers or straps, which allow for longitudinal movement. This floating support system prevents damage to pipe and fittings. Adequate clearance shall be provided between the piping system and any structure to allow for freedom of movement.
Expansion loops
Although the expansion rate is independent of the size of the piping system, allowance should be based on the Coefficient of Thermal Expansion of the plastic, the length of the run, and the maximum temperature change anticipated.
PVC and CPVC expand approximately 41⁄2 - 5 times more than steel; therefore, in piping systems with long runs allowances must be made. (See table 1.) The developed length (L) is the final length of pipe needed to overcome expansion and contraction. The Expansion loop is the configuration of the pipe that best allows for expansion and contraction. (See figure 2.)
A “rule of thumb” is to allow about 1/3 of an inch for every 100 feet of pipe and each 10 degrees of temperature change.
Table 1.
| IPS (size) |
Developed Length (L) of Expansion Loop
(shown in inches) |
| |
10° |
20° |
30° |
40° |
50° |
60° |
70° |
80° |
90° |
| 1⁄2 |
13 |
19 |
23 |
26 |
30 |
32 |
35 |
37 |
40 |
| 3⁄4 |
15 |
21 |
26 |
30 |
33 |
36 |
39 |
42 |
44 |
| 1 |
17 |
23 |
29 |
33 |
37 |
40 |
44 |
47 |
50 |
| 11⁄4 |
19 |
26 |
32 |
37 |
41 |
45 |
49 |
52 |
56 |
| 11⁄2 |
20 |
28 |
34 |
40 |
44 |
49 |
53 |
56 |
60 |
| 2 |
22 |
31 |
38 |
44 |
50 |
54 |
59 |
63 |
67 |
| 21⁄2 |
24 |
35 |
42 |
49 |
55 |
60 |
65 |
69 |
73 |
| 3 |
17 |
38 |
47 |
54 |
60 |
66 |
71 |
76 |
81 |
| 4 |
31 |
43 |
53 |
61 |
68 |
75 |
81 |
86 |
92 |
| 6 |
37 |
52 |
64 |
74 |
83 |
91 |
98 |
105 |
111 |
| 8 |
42 |
60 |
73 |
85 |
95 |
104 |
112 |
120 |
127 |
|
Figure 2.
Plastics do expand and contract, especially in systems with long runs. However, by taking this fact into consideration when designing the system, this minor obstacle can be overcome. Support systems that allow for movement and the addition of expansion loops can counter the issues of expansion and contraction in PVC and CPVC. |
