The time and frequency for cleaning the fire-retardant coatings on steel structure surfaces are primarily influenced by conditions of corrosion, such as the type of application the coating type and specifications for the application. The full analysis can be found in the following sections:
Highly corrosion-prone environments (e.g. chemical factories or furnaces, etc.)
Frequency: Clean at minimum twice per year and at least once prior to the wet season.
Cause: Corrosive gases as well as dust speed up the aging process of coatings and cause a decrease in adhesion.
As an example, chemicals' acidic gasses could cause the coating to fail in 1-2 years. This is lower than the ten or more years in environments that do not have corrosive.
Moderately Corrosive environments (e.g. coastal regions humid warehouses)
The frequency of cleaning is every two years.
Cause: The salt and moisture may penetrate the coating, leading to erosion of the substrate.
As an example, structures made of steel located in coastal regions may need recoating every five to six years because of coating deficiency.
Mildly Corrosive/Non-Corrosive Environments (e.g., dry rooms, ordinary office buildings)
Period of cleaning: Clean once every 5-10 years or perform specific treatment only when damage to the coating is observed.
Factors: The surrounding surroundings have no impact on the coating and the life span of the coating can be more than 10 years.
Steel Concealed Structures for Indoor Use (e.g. the core of a building with a high rise)
Cleaning Duration: Short usually involving only the removal of the construction residues (e.g. weld dust, slag).
This is because the closed atmosphere reduces the risk of exposure to corrosive substances and ensures long-term stability of the coating.
Outdoor Exposed Steel Structures (e.g., bridges, stadium stands)
Cleaning duration: long, needing a thorough clean-up of oils and rust stains as well as repair to the coating.
The reason is that ultraviolet rays as well as rain and temperatures can lead to damage to the coating, requiring re-coating following cleaning. This is a process which can take a few weeks.
High Humidity/High Temperature Ambients with high temperatures and humidity (e.g. boiler rooms and swimming pools)
Cleaning Time: Medium with particular attention paid to mold and condensation issues.
The reason is that humidity can decrease the adhesion of coatings, which requires more protection after cleaning.
Thick Fire Retardant Coatings (Coating Thickness 7-50mm)
Cleaning Frequency: low Inspections are required each 5-10 years.
The reason is that inorganic insulation materials have a high degree of durability, but the rough surface of their surfaces can easily collect dust. They require frequent cleaning to ensure that impurities are not affecting the fire-resistance.
Thin/Ultra-Thin Fire Retardant Coatings (Coating Thickness 3-7mm/<=3mm)
Cleaning Frequency: Very high, check every 2 to 3 years.
Why: Organic substances are susceptible to ageing which requires regular maintenance of the surface that is coated with powder and recoating.
Intumescent Coatings for Fire Retardants (expands and gets thicker after contact with fire)
Cleaning Frequency: Medium check every 3 to 5 years.
Cause: The efficiency of the intumescent agent decreases as time passes, and requires the removal of the coating that has degraded as well as reapplication.
"Technical Code for Fire Protection of Building Steel Structures"
The requirement is that before painting the surface of the structure steel should meet the Sa2.5 quality (sandblasting) as specified in GB8923. Dust and oil stains should be completely removed.
The impact: Not meeting the requirements for cleaning can decrease the adhesive of the coating by between 30% and 50 percentage, leading to substandard resistance to fire.
"Technical Specifications for the Application of Fire Retardant Coatings for Steel Structures"
Requirements: Coating thickness deviation should not exceed +-10%, and surface roughness should be controlled within 40-70mm.
The impact of cleaning after the process is that an indicator of thickness should be employed to verify the uniformity of the coating; otherwise the coating will need to be reworked.
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What Is the Role of Surface Cleaning for Fire-retardant Coatings on Steel Structures (Part 1)?
