Significant Thermal Gradient causes equipment failure.

Equipment such as heat exchangers, reboilers, reactors in process industries are likely to be subjected to thermal stress and strain  because of temperature differences within the vessels .These can cause changes in the dimensions of a part. Whenever a change in dimension is resisted, a thermal stress will result.


In cases where a temperature difference or gradient occurs within the material, the forces generated will be internal.The hotter parts of the material will usually have expanded more than the colder parts, causing compression of the hotter areas and tension in the colder parts. Some of the processes involved in
discussing heat stress are described below for better understanding of failure mechanism and root cause analysis :

• Thermal Expansion, (or the increase in length) for most materials,results from an increase in temperature. The extent of the expansion depends on the temperature change, the temperature itself, the length of the part, and the material(s) involved.

• Differential thermal expansion results whenever there is a temperature difference or gradient from point to point in metals. The differential occurs because most metals expand with increasing temperature. If the
increase (or decrease) in temperature is different in different sections of a material, the sections will have expanded to a different extent. In this case, the compressive and tensile stresses can result in the bending of the part.

• Thermal shock is an internal stress that is the result of rapid heating or cooling of a part. In the case of heating, high compressive stresses near the surface can result in internal fracturing while in the case of cooling, the high tensile stresses on the surface of the part can result in external cracking.

To avoid the possibility of internal or external failure of the component, heating and cooling down rates are designed to limit temperature differences and the consequent strains due to thermal stresses to acceptable levels.

Therefore it is suggested  to follow proper heating and cooling  processes strictly as per procedure described in SOP of  equipment operation to prevent thermal cracking - a dangerous failure mode resulting in loss of containment leading to environment problem.