Cyclic stress
The Illustrated Guide to Hot and Cold Water Services (BG 33/2014), written by Reginald Brown and published by BSRIA in 2014, in relation to cyclic stress, it states: ‘If materials are repeatedly stressed then they can develop stress cracks. These cracks form at a stress concentration point such as a sharp bend, thread root or even a surface marking. The risk of stress cracks and failure depends on the degree of stress and the number of cycles. It is permissible to use a change in direction to absorb the effects of thermal expansion and contraction (copper tube expands at a rate of 16.8 × 10-6 per °C between 20°C and 100°C) but there are guidelines on the maximum that can be absorbed. If the amount of movement is too large for an elbow then a bend or loop will decrease the stress. Guidance and calculations for the accommodation of expansion are given in CIBSE Guide B.’
--BSRIA
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