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Due to increasing demands for fire protection in high-risk environments, such as petrochemical processes and offshore platforms, so-called hydrocarbon intumescent coatings are increasingly used to protect structural steel in the event of a hydrocarbon fire. For these coatings, the fire-resistance performance is typically evaluated in a series of costly experiments with industrial-scale (i.e. 1–10 m3) furnaces, programmed to follow a standard hydrocarbon fire test curve. In this work, we propose a laboratory-scale furnace for coating evaluation, which can simulate the conditions of a typical hydrocarbon fire curve, that is, the standard UL 1709. In a case study with five hydrocarbon intumescent coating formulations, the correlation between the laboratory- and the industrial-scale furnace was investigated and a good agreement was found for the temperature progression of the coated steel plates. The physical and chemical properties of the intumescent coating chars were also similar for the two furnaces. In summary, the low-cost, time-efficient laboratory-scale furnace can provide reliable screening of hydrocarbon intumescent coatings and is recommended as a complementary tool for industrial fire tests.
Summary
For high performance of hydrocarbon intumescent coatings, interactions between the acid source ammonium polyphosphate (APP) and inorganic fillers can be critical. In the present work, low‐borate concentration (ie, 1 wt% zinc borate) intumescent coatings with different concentration ratios of CaCO3 to APP were studied in an attempt to map the reaction mechanisms. The analysis of the coating performance was conducted using thermal insulation assessment according to the UL1709 fire curve (disregarding substrate load, geometrical diversity, and other full‐scale implications of the complete standard), rheological measurements, thermogravimetric analyses, attenuated total reflection‐Fourier transform infrared spectrometer (ATR‐FTIR), and X‐ray diffraction. Results show that a coating with a CaCO3/APP mass ratio of 0.3 gives the best performance (ie, the longest critical time of steel substrates to reach both 400 and 550°C in the thermal insulation assessment). The dependency on the CaCO3/APP ratio of the dynamic viscosity minimum points to significant interactions between CaCO3 and APP during the softening state (ie, the intumescence process) of the coating. Due to an enhanced anti‐oxidation property, the degradation zone of the intumescent char and the residual weight of the coating after exposure were both improved when increasing the CaCO3/APP ratio. The compositional development of the intumescent char showed that CaCO3 and APP react to form a new polymeric phase, calcium catena‐polyphosphate (CaP2O6). This polyphosphate may contribute to the formation of a compact phase in the intumescent char and benefit the thermal insulation performance of low‐borate concentration hydrocarbon intumescent coatings.
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