Laboratory-scale screening of intumescent coatings

Intumescent coatings are used to improve the fire resistance of constructional steel. Fire resistance of intumescent coatings is normally assessed in large test furnaces, which is expensive and time-consuming. In the coating development phase, fast, cheap, and reliable test methods are needed to identify suitable coating formulations. In this work, a laboratory-scale screening test method, utilizing a small electric furnace, was developed. Temperature and heat flux measurements were performed to verify that the furnace conditions were similar to those in full-scale test furnaces. A simple heat transfer model was used to predict the coating performance over a wide range of steel section factors and coating thicknesses. To evaluate the method, 11 commercial coatings, from 6 coating manufacturers, were tested. Samples consisted of 3 mm thick steel panels with a coating thickness in the range of 0.7-3 mm. For coatings with a low to medium expansion factor (<50), the predicted performance agreed well with results based on full-scale fire resistance tests for circular hollow sections. For coatings with a high expansion factor (>50), the performance was typically overpredicted, likely because the method cannot foresee problems related to crack formation in the char caused by the curvature of circular hollow sections. • A fast and simple small-scale test method for intumescent coatings was developed. • 11 commercial intumescent coatings were tested. • Effective thermal conductivity was used to predict performance in full-scale tests. • For low to medium expansion coatings, results agreed well with full-scale tests.