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Corzan® CPVC Thermal Expansion and Contraction

When a piping system may experience a temperature change, linear thermal expansion can be significant. As a general rule, if the total temperature change is greater than 30°F (-1.1°C), compensation for thermal expansion should be included in the system design for a piping system made of any material, including one made of Corzan® CPVC. Though all materials experience expansion and contraction, most thermoplastics have a significantly higher coefficient of thermal expansion compared to metals.

Linear Thermal Expansion of Piping Material

Corzan CPVC Linear Expansion

The expansion or contraction of thermoplastic pipe may be calculated from the following formula or by using Corzan CPVC’s Thermal Expansion Calculator.

Thermal Expansion Formula

 

Accounting for Expansion and Contraction in System Design

The recommended method for accommodating thermal expansion is to include expansion loops, offsets or changes in direction where necessary in the system design.

Expansion Diagrams

Thermal Expansion diagrams

Expansion Loop Formula

Expansion loop formula

 

Working Stress and Modulus of Elasticity of Corzan® CPVC

Corzan CPVC Working Stress and Modulus of Elasticity

Expansion loops and offsets should be located approximately at the midpoint of the pipe run and 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 to allow the mechanisms to better handle the bending stresses of expansion and contraction. Valves or strainers should not be installed within an expansion loop or offset.

Thermal Stresses

If thermal expansion is not accommodated, it is absorbed in the pipe as internal compression. This creates compressive stress in the pipe, which is calculated with the following formula:

 Formula to calculate the stress induced in a pipe, which is restrained from expanding

Impact of Thermal Stress on Corzan CPVC versus Steel

Because the coefficient of thermal expansion of steel is five times lower than that of CPVC, dimensional change due to thermal expansion will be five times less. However, 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 (10°C) temperature change will produce approximately 600 psi of stress in a CPVC system compared to 9800 psi of stress in a steel system. CPVC’s relatively more flexible nature will usually allow it to absorb its lower 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. This is one of the many ways Corzan CPVC often outperforms metallic alternatives.

Thermal Expansion Calculator

Thermal expansion and contraction is a property of all piping materials, including both metals and thermoplastics. Enter in your pipe diameter, maximum and minimum temperatures, and pipe length, and the calculator will deliver required expansion loop dimensions in both feet and inches.
expansion-loop-offset-diagram