Temperature Change and Introduced Stress in Fixed Pipes
Temperature change will cause stress in fixed pipes
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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.
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