Welding Inspection & Metallurgy API ICP Self Study Notes

10.3.4 Coefficient of Thermal Expansion
As metals are heated there is an increase in volume. This increase is
measured in linear dimensions as the temperature is increased. This linear
increase with increased temperature, per degree, is expressed as the
coefficient of thermal expansion. An example of this would be the
increased length of a steel bar that has been heated in its middle with an
oxy fuel torch. As the bar is heated, there will be a measurable increase in
length that correlates to the temperature and the specified coefficient of
thermal expansion for the material at that temperature.
This coefficient of thermal expansion may not be constant throughout a given
temperature range because of;
1. the phase changes a material experiences at different temperatures and
2. the increases or decreases in volume that accompany these phase
changes.