Effects of substrate thermal conditions on the swelling of thin intumescent coatings

Abstract

The experimental study presented herein investigates the influence of the substrate thermal conditions on the behaviour of thin intumescent coatings. Steel plates coated with a commercially available solvent-based thin intumescent coating were exposed to a constant incident radiant heat flux of 50 kW/m 2 in accordance with the Heat-Transfer Rate Inducing System (H-TRIS) test method. The influence of different substrate thermal conditions was investigated using sample holders capable of controlling the thermal boundary conditions at the unexposed surface of tested steel plates and comparing them to coated timber samples. Experimental results evidence that the substrate thermal conditions govern the swelling of intumescent coatings, thus their effectiveness in protecting load-bearing structural elements. The substrate temperature controls the swelling of intumescent coatings because it defines the temperature experienced by the reacting virgin coating located close to the coating-substrate interface. The physical and thermal properties of the substrate controls the capacity of the system to concentrate/dissipate heat in proximity of the coating-substrate interface. In this way, the substrate thermal conditions governs the temperature evolution of the reacting intumescent coating, consequently the swelling process. Accordingly, high swelling rates were recorded for highly-insulating conditions (timber substrate), while low swelling rates for poorly-insulating conditions (water-cooled heat sink).

Experimental testing on timber connections considering the influence of gap size and intumescent sealants

“…In Figure 14 an adapted schematic from Lucherini et al showing the activation of an intumescent sealant and how it will fill the gap in a connection can be seen. 34 The experimental data shows the temperature gradient in the timber as the cover increases, and the higher temperatures around the steel component as expected.…”

Influence of heating conditions and initial thickness on the effectiveness of thin intumescent coatings

“…This process lasts until the intumescent coating is fully consumed, which can be directly related to the applied initial DFT. As a conclusion, the steel temperature can be directly associated with the swelling process because it defines the temperature experienced by the virgin coating, which is located behind the swelled porous char and sustains the swelling reaction [25]. The non-unique relationship between the steel temperature and the swelled coating thickness shown in Fig.…”

The CoaST‐Fire: A novel methodology to rapidly expose materials to various fire curves

“…Others decided to not use thermal insulation on the uncoated steel surface 32,51 . The few studies discussing heat loss from uncoated surface indicate however that such effects can be substantial, both for the intumescent coating expansion as well as modelling results 37,49,52 . Specimen heating from the sample edges becomes relevant whenever the sample size is reduced, which increases the edge to area ratio.…”

“…32,51 The few studies discussing heat loss from uncoated surface indicate however that such effects can be substantial, both for the intumescent coating expansion as well as modelling results. 37,49,52 Specimen heating from the sample edges becomes relevant whenever the sample size is reduced, which increases the edge to area ratio. Applying an intumescent coating around the sample edges and on the sample holder is one approach to tackle this issue.…”