Metal that operates under cyclic temperature conditions,
especially over a wide range, may develop cracks from thermal fatigue. Cracks
start at the surface of the material where the stresses are normally higher,
progressing slowly at first and then more rapidly with each cycle of
temperature change. Thermal fatigue is often found at locations where metals
that have different coefficients of expansion are joined by welding. Other
common locations for thermal fatigue are in convective tubes where the tube
fins can promote cyclic temperature swings, tubes with two-phase flow, and
bracing/weld attachments which do not allow for thermal expansion.
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