Source: Yugong Deconstruction Official Account
Hello everyone, I'm Shuangwuyu. In the previous article, we talked about the problem of "coating fireproof coatings on outdoor steel stairs", and we left a lot of messages, and we gained a lot after reading them. To sum up, there are two different points of view:
No need to paint
Outdoor evacuation staircase should avoid letting the fire inside the building burn to the staircase, and if it has been burned, then it should be reconsidered whether it can be used as an evacuation staircase.
It needs to be painted
Outdoor evacuation stairs are made of flame-retardant or non-combustible materials, and still need to meet the requirements of the fire resistance time limit corresponding to the fire resistance level. The minimum is 0.25 hours, and the steel structure is difficult to meet without fireproof coating, especially the steel beams and steel columns, and the fire resistance limit is about 15 minutes.
If you apply fireproof coatings, if you really want to play a fireproof role for a long time, you need to re-evaluate and recoat after the service life of the paint, and the service life of outdoor thin fireproof coatings is 10~15 years.
Thin fire retardant coatings
The so-called thin fireproof coating is that the thickness of the coating is not more than 7mm, and it is fireproof by the expansion after heating. Generally, a 1 mm thick coating expands to about 50 mm when exposed to heat.
This name was used in the past, but now it is called intumescent paint after it is in line with international standards. Everyone is still accustomed to using the term "thick, thin, and ultra-thin".
Fire protection schematic diagram @FlameOFF for intumescent fire retardant coatings
The maximum fire resistance time limit that can be achieved by intumescent fire retardant coatings is 2 hours or even 3 hours, but the specification stipulates that it should not exceed 1.5 hours. For important steel structural components, the fire resistance limit is generally 2 hours or more.
If it is exceeded, it is necessary to use non-intumescent fire retardant coatings. Why?
The reason given by the specification is that the problem of aging resistance may be more prominent, and the large number of applications of intumescent type began in the 90s, and this problem has not attracted enough attention.
On the other hand, it may also be because of the reliability and stability of product quality, which is not enough to be recognized by the national standard.
In the association standard, it has been proposed that epoxy intumescent steel structure fireproof coatings can be used for steel components that exceed 1.5 hours, and at the same time, like the national standard, it is pointed out that the "aging" problem of "non-epoxy" coatings will be attenuated by 21.7% within 5 years (test shows).
The common types of applications for intumescent fire retardant coatings @FlameOFF
Epoxy steel structure fireproof coatings are not restricted in use due to their excellent adhesion performance, weather resistance and fire performance.
Terms of use
In the case of intumescent fire retardant coatings, the exact thickness of the coating can be directly determined based on the equivalent thermal resistance of the coating.
How to calculate the equivalent thermal resistance, the specification gives a calculation formula, and the measured temperature rise curve of the steel component obtained according to the standard fire resistance test.
Ri=(t0Ts−Ts0+0.2)2−0.0445×10−5⋅VFi
Where: Ts0 - the temperature of the steel specimen at the beginning, which can be taken at 20°C;
Ts - the average temperature (°C) of the steel specimen, take 540°C;
t0 - the time when the average temperature of the steel specimen reaches 540°C;
VFi – cross-sectional form factor of a steel specimen with fire protection.
Comparison between the calculated temperature of the specimen and the experimental results when coating the A type A fireproof coating @ Refer to the paper
Variation of thermal resistance over time of model A intumescent fireproof coating @ Reference paper
How to apply
Intumescent fireproof coatings should be compatible with anticorrosive primers and anticorrosive topcoats.
The order of anticorrosive coatings and fireproof coatings from the inside to the outside is:
- • Anticorrosive primer
- • Anticorrosive intermediate paints
- • Intumescent fire retardant coatings
- • Anticorrosive topcoat
What to pay attention to
In order to ensure that the expansion of intumescent fireproof coatings is not affected, the anticorrosive topcoat should not be too hard, and there should be enough expansion space on the outside of the component, and fireproof felt should not be wrapped.
The changes of the intumescent fireproof coating on the surface of the steel structure after being burned @coatingspaint
In the design, the fire resistance limit and equivalent thermal resistance of the component are generally specified, and the thickness of the coating is not specified. The thickness of the fireproof coating will be subject to the thickness stated in the type inspection report or type test report. At the same time, the specification stipulates that the minimum thickness should not be less than 1.5mm.
brief summary
Thin fireproof coatings have been widely used in foreign countries, which is more convenient for construction and lower in cost.
Trends in structural fire protection@steelconstruction
As you can see in the above chart, the application of thin fire retardant coatings has accounted for 75%.
It can be seen from the reasons for the concerns of the restrictions of the normative provisions that there is still a lot of room for the development of the thin fire retardant coating market for domestic steel structures.
Resources:
• GB 51249-2017 Technical code for fire protection of building steel structures
• T/CECS 24—2020 Technical specification for the application of fire retardant coatings for steel structures
• GB 14907-2018 Fire retardant coatings for steel structures
• Determination of segmented equivalent thermal resistance of intumescent steel structure fireproof coatings, Wang Ji et al
Source: Yugong Deconstruction Official Account, if there is any infringement, please contact us.