Temperature Change and Introduced Stress in Fixed Pipes
Temperature change will cause stress in fixed pipes
With temperature change stress is introduced in fixed pipes. The stress can be calculated as:
σ = α E dt (1)
where
σ = stress (MPa, lb/in2)
α = linear expansion coefficient (m/moK, inch/inchoF)
E = modulus of elasticity of the piping material (MPa, lb/in2)
dt = temperature change from installation temperature (oC, oF)
The stress must not exceed maximum allowable stress for the chosen piping material. Be aware that with frequently temperature changes - the stress cycle (with stress well below the maximum allowable limit) may fatigue the pipe.
Example - Introduced Stress in a Fixed Pipe when Temperature Changes
A carbon steel pipe with linear expansion coefficient 11.7 10-6 m/moC and modulus of elasticity 29.5 106 psi (203 109 Pa (N/m2), 203 GPa) is heated from 0oC to 50oC. The stress introduced in the pipe can be calculated as
σ = (11.7 10-6 m/moC) (203 109 N/m2) ((50oC) - (0oC))
= 119 106 N/m2
= 119 MPa
Depending on the material and the codes used - this may be within maximum allowable stress.