Assessing the onset of swelling for thin intumescent coatings under a range of heating conditions

In the past decades, the steel industry has experienced a rapid growth in the use of intumescent coatings for protecting load-bearing steel structures in the event of a fire. The onset of swelling is key for assuring the effectiveness of thin intumescent coatings for providing thermal insulation to the steel substrate during fire. The study presented herein investigates the onset of swelling for a commercially available thin intumescent coating applied on steel plates and exposed to a wide range of heating conditions. Experiments were performed using an array of radiant panels for controlling incident radiant heat flux at the exposed surface of coated steel samples. Within the scope of this research study, the onset of swelling was defined based on two conditions: (1) visual observation of swelling during heating or (2) time-history of the steel temperature. Research outcomes derived from this work defined a threshold for the onset of swelling in terms of steel and coating temperatures and it concluded that the onset of swelling is directly influenced by the heating conditions at the exposed surface and the original applied dry film thickness