Definition - What does Soluble Salts mean?
Soluble salts are ionic compounds that dissociate their constituents during their interaction with a solvent such that it forms a solution with a concentration of at least 0.1 moles per liter at room temperature. They arise from acidic reactions.
A salt is soluble when the energy produced during the interaction of the ions with solvent molecules is able to break the ionic bonds in the salt and also separate the solvent molecules so that the ions are freely inserted to form a solution. They are found in the soil and water sources.
Corrosionpedia explains Soluble Salts
Most chlorides, nitrates and sulfates—calcium, magnesium, sodium etc.—fall under soluble salts. These corrosion substances are leading contributors of premature coating or painting failures and corrosion under insulation whenever their threshold value is exceeded. They are available at the surface due to contamination from the atmosphere and surface preparation methods. Since the surface of any substrate contains pits, the presence of these salts in the pits makes them hard to eliminate.
During surface preparation, chances are that the substances will remain undetected. The presence of these corrosive substances under a coating creates suitable conditions for corrosion such as moisture. Corrosion is thus achieved by the osmotic pull of the water molecules through the coatings or insulations—hence, leads to under-film metallic rusting.
As they reduce the pH, more oxygen is consumed and air moisture drawn onto the surface of the substrate. They also provide low electricity resistivity, which results in corrosion cells. This is one of the biggest contributors to steel corrosion. Chemical active acids and salt removers are normally used in blasting and brushing methods before any coating or insulation application. The thickness of the coating can also reduce the effect of soluble salts.