Introduction: Fireproof Coatings — Enabling Steel Structures to “Withstand” the Critical 180 Minutes in Raging Fire
The fatal weakness of steel structures: when the temperature rises above 500°C, the yield strength of steel is halved; above 600°C, it loses load-bearing capacity and the structure collapses. The direct cause of the 9/11 WTC collapse was not the plane impact, but the burning of aviation kerosene (>1000°C), failure of the steel structure fireproof coating, softening of the steel, and pancake-style collapse of the floors. The mission of fireproof coatings is to slow the temperature of the steel structure from >1000°C to 500°C/5min → >800°C/30min → >1000°C/120min), buying 60–180 minutes of golden time for evacuation and firefighting.
Steel structure fireproof coatings are divided into intumescent (thin-film coating——DFT 0.5-3mm——expands 50-100 times when exposed to fire——forms a 2-5cm foam carbon layer——insulates heat——fire resistance >60-120min) and non-intumescent (thick coating——DFT>10-25mm——cement-based/vermiculite/perlite——thermal conductivity 120-240min). Chinese standard GB 14907-2018——fire resistance rating——R (load-bearing)/E (integrity)/I (insulation)——>0.5h——1h——1.5h——2h——2.5h——3h——six grades.
FAQ
Q1: The “three-source” chemistry of intumescent fireproof coatings — how do APP/PER/MEL synergize?Acid source (APP/ammonium polyphosphate —> releases polyphosphoric acid at 215°C) — catalyzes carbon source (PER/pentaerythritol) dehydration and esterification — forms carbon skeleton — gas source (MEL/melamine —> sublimates and releases NH3/N2 at 300°C) — blows up the molten carbon layer — expands 50-100 times — forms >2-5cm foam carbon layer — thermal conductivity 1000°C high temperature — steel temperature locked <140°C. "3:1:1 — APP:PER:MEL — = — the golden ratio — validated over — 40 — years".
Q2: Intumescent-free—why can “relying on thickness” provide fire protection?Cement-based/vermiculite/perlite “itself—is—thermal insulation—material” thermal conductivity 800°C—heat flux—Q≈—800/0.2=4000W/m2—steel structure—can withstand “temperature—not—exceed—140°—C” “thick—=—safe” but “20—mm—thick—=—heavy—>—20kg—/—m2—structural—load—needs—checking”.
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Summary
Steel structure fireproof coatings — intumescent (thin-film / APP-PER-MEL triple-source / expands 50–100 times — aesthetically pleasing) — non-intumescent (thick-film / cement-based / relies on thickness — plain) comply with GB 14907 six-level fire resistance. Kexin New Materials provides a full range of fireproof coating products and fire-resistance testing support, “dressing” steel structures in a “flame protective suit.”