It is important to consider thermal expansion when designing a system with Corzan pipe. Most thermoplastics have a coefficient of thermal expansion which is significantly higher than those of metals. However, Corzan CPVC has the lowest thermal expansion of any commonly used thermoplastic. The thermal expansion of a piping system subject to a temperature changecan therefore be significant, and may need compensation in the system design. The expansion or contraction of thermoplastic pipe may be calculated from the following formula:

  = y (Tmax –Tmin) 
where     = expansion of pipe in feet or meters
y = coefficient of thermal expansion in in/in/°F
or m/m/°C (Corzan CPVC=3.4x10-5 in/in/°F)
Tmax = maximum temperature in°oF or °C
Tmin = minimum temperature in °F or°C
= length of pipe run in feet or meters

As a rule of thumb, if the total temperature change is greater than 30°F (17°C), compensation for thermal expansion should be included in the system design for pipe runs greater than 100ft (30m). There commended method of accommodating thermal expansion is to include expansion loops or offsets where necessary in the system design.

The proper dimensions for an expansion loop may be calculated from the following formula



where R = leg length of the expansion loop
D = out side diameter of piping
  = thermal expansion of pipe as calculated above


An offset schematic is presented below.

The proper leg length for an offset is 1.2 times the leg length for an expansion loop. The proper dimensioning of an expansion loop is presented graphically.

Expansion loops and offsets should be constructed with straight pipe and 90° elbows which are solvent cemented together. If threaded pipe is used in the rest of the system, it is still recommended that expansion loops and offsets be constructed with solvent cement in order to better handle the bending stresses incurred during expansion. The expansion loop or offset should be located approximately at the midpoint of the pipe run and should not have any supports or anchors installed in it. Valves or strainers should not be installed with in an expansion loop or offset. Supports should be installed approximately 1ft (0.3m) on either side of an expansion loop, and approximately half the length of the offset on either side of an offset.

If thermal expansion is not accommodated, it is absorbed in the pipe as an internal compression. This creates a compressive stress in the pipe. The stress induced in a pipe which is restrained from expanding is calculated with the following formula:

S = EyT
Where S = stress induced in the pipe
E = tensile modulus
(see Section 4.1.1 and Figure 4.1.2.A)
y = coefficient of thermal expansion
T = total temperature change of the system

Because the coefficient of thermal expansion of steel is five times lower than that of CPVC, dimensional changes due to thermal expansion will be five times less. However, as can be seen by the equation above, the stresses induced in the piping system due to restrained thermal expansion are dependent on the material's modulus as well as its coefficient of thermal expansion. Because the modulus of steel is approximately 80 times higher than that of CPVC, the stresses resulting from restrained expansion over a given temperature change will be approximately 16 times higher for steel than for CPVC.

For instance, restrained expansion over a 50°F temperature change will produce approximately 600 psi of stress in a CPVC system, but 9800 psi of stress in a steel system. CPVC's relatively more flexible nature will usually allow it to absorb it slower stresses in a buckling or snaking of the line if necessary. Because steel piping is too rigid to buckle, its higher stresses are often transferred to surrounding structures, resulting in damaged supports, anchors, or even abutting walls.