A theoretical appraisal of the effectiveness of idealised ablative coatings for steel protection

The use of sacrificial ablative heat shields has proved effective in protecting spacecraft on earth re-entry. However, the use of ablative coatings in the protection of structural steel appears to be limited. This paper uses a mathematical model to assess the likely effectiveness of using such a coating on steel beam sections in furnace tests. In particular, the important coating properties are identified and quantified in order to maximise the failure time (defined as the time taken for the average steel temperature to reach a preset value such as 823 K). The model produces interesting results and demonstrates that it should be possible to use coatings of moderate thickness (∼10 mm) to attain failure times of the order of 1 h, provided that other critical coating properties such as the coating Biot number, Stefan number and diffusive timescale fall within specific ranges.