Experimental Study of Heat Transfer in Intumescent Coatings Exposed to Non-Standard Furnace Curves

This paper reports the results of an experimental study on fire protection performance of intumescent coatings exposed to three non-standard fire curves. Intumescent coatings were applied to steel plates to make test specimens and, in total, furnace tests were performed on 36 specimens. The effective thermal conductivities of the intumescent coatings were calculated based on the measured steel and furnace temperatures. Scanning electron microscopy (SEM) tests were conducted to give some information on the difference in inner structure of intumescent char. Results of the experimental studies reveal that the fire protection performance of intumescent coating is highly dependent on the heating rate and maximum temperature of the fire condition. Different pore structures of the intumescent chars were obtained when intumescent coatings were subjected to fires with varied heating rates. The reaction steps of intumescent coating underwent depended on the maximum temperature of the fire condition. The consequence of this is changed expansion ratio and inner structure of intumescent char and then different effective thermal conductivity. When subjected to non-standard fire I, the reaction process of intumescent coating was incomplete and no “honeycomb” pore structure was observed; in comparison, the coating underwent complete reaction process and compact “honeycomb” pore structure was obtained when exposed to non-standard fire III; the maximum difference for representative values of effective thermal conductivities was up to 48.8%. In addition, due to the peculiar flame retardant mechanism of the intumescent coating, increasing the coating thickness does not always yield insulating property benefit.