Novel Testing to Study the Performance of Intumescent Coatings under Non-Standard Heating Regimes

Abstract

Intumescent coatings (also called reactive coatings) are widely used to protect structural steel from fire. These thin coatings swell on heating to form a highly insulating char, protecting steel members and preventing them from reaching critical temperatures that could cause them to fail. As is the case for most structural materials and assemblies, intumescent coatings for use in buildings are typically developed and certified solely according to the standard cellulosic fire resistance test by exposure within a fire testing furnace. Reliance on furnace testing is expensive, non-representative of realistic fire conditions, and insufficiently versatile to gather detailed performance information on the response of reactive coatings under the full range of design fires which might be considered during a rational, performance-based design assessment. This paper presents a novel testing methodology for studying the performance of reactive coatings when subjected to non-standard heating regimes. The new approach is calibrated and validated using furnace test data, and is shown to offer considerable advantages over furnace testing in terms of reliability, repeatability, versatility, speed and cost. An investigation is then presented to study the effective variable thermal conductivity of a commercially available reactive coating when subjected to various timehistories of heat flux. It is shown that the heating rate and dry film thickness of the coating do not drastically affect the development of effective thermal conductivity with substrate temperature, leading to a proposal for a simplified method for specifying coating requirements and/or performing heat transfer design calculations when designing to non-standard heating regimes.

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

“…Moreover, the experimental methodology enables the visual inspection of the test samples during the thermal exposure (e.g. measuring the swelled coating thickness), technically challenging during conventional standard furnace tests 5,27 .…”

“…Their success is associated with their unique advantages, such as the low impact in the attractive appearance of visible steel structures and their ability to be applied on-site or off-site 4 . Upon sufficient heating, intumescent coatings swell to form a low-density and low-conductivity porous char that prevents the load-bearing steel elements from reaching critical temperatures that can cause structural instability 5 . In the built environment, solvent-based or waterborne thin intumescent coatings are usually applied to a Dry Film Thickness (DFT) no thicker than a few millimetres and, when exposed to heat, they can potentially swell up to 100 times their applied initial DFT 6 .…”

“…For instance, according to the European method based on the concept of effective thermal conductivity, the complex thermal-physical response of intumescent coatings is simplified in an effective parameter [20][21] . The temperature-dependent effective thermal conductivity defines an equivalent thermal barrier provided by the intumescent coating to the substrate material under a certain heating regime 5,[22][23][24] . This parameter incorporates several phenomena that occur in the intumescent coating, such as the swelling process, endo-and exothermic reactions 9,18 .…”

A Heat-Transfer Rate Inducing System (H-TRIS) Test Method

“…highly optimised prestressed concrete slabs [84], lightweight structural concrete sandwich elements [85], concrete tunnel lining segment materials [86], intumescent coatings [87], cross laminated timber [88], non-metallic dowelled timber connections [89], and building insulation materials [90]). This section illustrates application of H-TRIS within a project studying heat-induced concrete spalling.…”

Comparison of an industrial- and a laboratory-scale furnace for analysis of hydrocarbon intumescent coating performance

“…1 Under the influence of heat, an intumescent coating swells up to 100 times its original thickness and forms a multicellular char layer. [1][2][3] The high degree of expansion and the low-density structure make the char layer an insulating barrier that can prolong the time (1-3 h) for safe evacuation of people. 4 A real fire has a rather complex temperature-time response; it depends on the structure dimensions, the amount and type of combustible materials, and the air available for combustion.…”