Definition - What does Permeability mean?
Permeability is the property of a material to allow fluids (such as water, water vapor or oil) to diffuse through it to another medium without being chemically or physically affected. Permeability causes deterioration of material longevity and acceleration of the corrosion process.
All organic forms of barrier protection are permeable to some degree, and once the protective coating is penetrated, its corrosion resistance is compromised.
When coating deteriorates, its permeability to oxygen or moisture increases, and as a result the corrosion rate increases. Therefore, permeability leads to coating failure.
Corrosionpedia explains Permeability
Permeability is a measure of how easy it is for water, air and other substances to enter a material. Concrete contains pores that allow these substances to enter easily. Larger pores allow easier entry, while smaller pores decrease the rate at which these substances enter the concrete. Low permeability in reinforced concrete is important to maintain structural integrity and limit corrosion. Slag cement is used to reduce concrete permeability.
Permeability is an important property of barrier coatings. The permeability of a barrier coating's film depends on its moisture vapor transmission rate. The effectiveness of a coating in preventing permeation depends on how closely and tightly bound the molecules of the resin are to one another.
The lower the permeability of a barrier coating, the more protective the coating is. The higher the degree of the coating resin's cross-linkage, the lower the permeability, the better the adhesive bond of the coating to the surface, and the better the overall protective barrier. High permeability of coating lowers the resistance in preventing water or other chemicals from the outside environment from passing through the coating.
High permeability due to porosity or cracking provides ingress for water, chlorides and other corrosive agents. If such agents reach reinforcing bars within the structures, the bars can corrode. Since permeability significantly influences the deterioration of concrete, it is necessary to take precaution to protect against water and chloride permeability to any materials to prevent corrosion and acceleration of the corrosion process.