Why can fire-retardant coatings for steel structures be flame-retardant?

Update: With the development of the construction industry, steel structure materials have become the new darling of the constru...
With the development of the construction industry, steel structure materials have become the new darling of the construction industry due to their own advantages, but we know that steel structures are afraid of high temperatures, which requires corresponding items to protect the steel structure. According to demand, Steel structure fire-retardant coatings are very vacant. Here we can’t help but wonder why steel structure fire-retardant coatings can be flame-retardant. Let’s uncover the mystery together.



Why can steel structure fire-retardant coatings be flame-retardant? From the three aspects of composition, selection principle and durability, we will explain the reasons for the flame retardancy of steel structure fire retardant coatings.
1. The problem of composition
The film-forming substances of thin and ultra-thin fire-retardant coatings are various organic resins or emulsions. Most of the intumescent flame retardant systems are P—N systems, that is, their intumescent flame retardant systems include three parts:
Acid source: all kinds of phosphates, currently the most used are ammonium polyphosphate (APP for short), melamine phosphate, etc.
Carbon source: various carbon-rich organic substances, such as polyols, chlorinated (or brominated) paraffins, starches, etc. Currently, pentaerythritol or pentaerythritol is most commonly used, supplemented by a small amount of chlorinated paraffins;
Gas source: It is a substance that can emit incombustible gas after being exposed to fire, thereby blowing the carbon source into a honeycomb carbonaceous layer, usually a variety of amines, such as urea, dichloramine, guanidine, etc. The current most used is Melamine, its film-forming base material is various organic resins or emulsions, such as chlorine partial emulsions.


2. Correct selection problem
There are some problems in the correct selection of fire-retardant coatings for steel structures in actual projects, and there are often some confusion and misuse. The analysis suggests that there are roughly the following three situations:
One: confuse indoor steel structure fireproof coating with outdoor steel structure fireproof coating. The outdoor use environment is much harsher than indoors. The paint has to withstand the sun, rain, wind and freezing outdoors, and fire-resistant paints with water resistance, freeze-thaw resistance, aging resistance, and high strength should be used. However, during actual inspections, it was found that some projects used fire-resistant paints that are only suitable for indoor fire protection for outdoor steel structures.
Two: The correct fire-resistant coating for steel structures cannot be selected for load-bearing steel structures with a fire resistance limit greater than 1.5h. Some designers mistakenly believe that the fire resistance time of fire retardant coatings is proportional to the thickness of the coating. As long as the thickness of the fire retardant coating is increased, the fire resistance time of the coating can be increased accordingly, and some ultra-thin coatings are mistakenly used for fire resistance requirements greater than 1.5 h load-bearing steel structure. Article 9.1.3 of the "Technical Code for Fire Protection of Building Steel Structures (CECS 200: 2006)" stipulates that "high-rise building steel structures and indoor concealed members of single and multi-layer steel structures, when the specified fire resistance limit is 1.5h or more, Non-expandable fire-retardant coatings for steel structures should be selected."
Three: confuse decorative fire-resistant coatings with steel structure fire-resistant coatings. Decorative fire-retardant coatings are used for wood structures and combustible substrates. Generally, the thickness is less than 1mm. The coating film can effectively flame retardant and prevent flame spreading for combustible materials, but its thermal insulation performance is generally not greatly improved. The purpose of steel structure fire resistance limit. However, some design units use general decorative fire-resistant coatings to protect steel structures, but in fact they can't play the role of steel structure fire protection at all.


3. Durability issues
Regardless of the fire retardant coating, the fire resistance limit given in the test report is the result of the inspection before use, and the fire may occur 1 year after the fire retardant coating is applied, or it may be 5 years after the application. After 10 years or more, after different years, especially for outdoor fireproof coatings, after years of wind and rain, sun and freezing, whether the fireproof performance of fireproof coatings is still worth considering. If a fire occurs, the fireproof coating has lost its due fireproof performance due to aging or other reasons, and the consequences will be disastrous.