The development of thermal stress is due to the contraction of materials when cooled down to cryogenic temperatures. The stress can appear as a transient effect e.g. when cooling down thick walled components or it can appear as permanent load e.g. in piping. In both cases the stress can cause damage. As the expansion coefficient of most materials decreases with temperature, most contraction takes place above LN2 temperature.
The following values may be used for estimating the thermal contraction in between room temperature and any cryogenic temperature:
0,3% for steel,
0,4% for aluminium and
1% for plastic materials.
Accurate values can be found in the literature .