  The detailed knowledge of the inner skin temperature behavior is very
important to evaluate and manage the aging of large pipes in cooling systems.
We describe here a method to obtain this information as a function of outer
skin temperature measurements, in space and time. This goal is achieved by
mixing fine simulations and numerical methods such as impulse response and data
assimilation. Demonstration is done on loads representing extreme transient
stratification or thermal shocks. From a numerical point of view, the results
of the reconstruction are outstanding, with a mean accuracy of the order of
less than a half percent of the temperature values of the thermal transient.
