Pay attention to the corrosion issue related to heat preservation on the surface of stainless steel equipment

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Attention should be paid to the corrosion issue related to heat insulation on the surface of stainless steel equipment. This is a problem related to corrosion and protection of metal surfaces. Generally, when insulating layers are applied to metal surfaces, not enough attention is given to the issue of corrosion on those surfaces; in particular, during heat insulation work, no proper care is taken to prevent corrosion of the metal surfaces. As a result, after a few years of use, corrosion and perforations occur in the metal, reducing the equipment’s service life. 1. Analysis of corrosion causes: Generally, polyurethane foam plastic is used for most metal insulation materials. Since the insulation material is dry when in contact with the metal surface during initial use, it does not corrode the metal surface. However, over time, due to temperature differences, moisture inevitably accumulates between the insulation layer and the metal surface. Due to the presence of water in the interface layer between polyurethane and metal, the polyurethane material releases substances in the presence of this water, resulting in acidic water with a pH of 3–5. At the same time, it still contains harmful substances such as certain chlorides, potassium oxide, and sodium oxide in water. When these insulation materials come into contact with metal surfaces, corrosion occurs, and the reason for this is as follows: The insulation materials contain water-absorbing substances such as K2O, Na2O, and Cl ions, which undergo chemical reactions with moisture. The presence of soluble salts also enhances the condensation of water in the insulation material. Furthermore, under the action of acidic aqueous solutions, the dissolution of soluble substances turns the water film into a strong electrolyte solution, creating the necessary conditions for the electrochemical corrosion of metals. Therefore, metals are prone to corrosion, and stainless steel is also prone to corrosion. The main characteristic of corrosion in stainless steel is pitting corrosion as its primary feature. Therefore, the corrosion resistance of stainless steel surfaces should be considered before insulation is applied. 2. Recommended protective methods: For such corrosion issues, epoxy coatings can be used as a solution. It is important to note that before applying the topcoat, a phosphating primer must be applied to the stainless steel surface first. Since the surface of stainless steel belongs to non-ferrous metals, its oxide film is relatively dense. The primers used in general anti-corrosion coatings (such as epoxy iron oxide) do not achieve good adhesion to non-ferrous metals. Therefore, a layer of interface agent must be applied to improve the adhesion between the primer and the metal surface. The main function of a phosphating primer is to allow phosphoric acid to react with the metal surface to form a passivating film of new phosphates. The function of this membrane is to become integrated with the metal, forming a chemical bond. It also has excellent adhesion to non-metallic coatings. Then apply the coating in accordance with the requirements for the structural layers of the anti-corrosion coating. A primer suitable for non-ferrous metals can also be applied directly. 3. Regarding moisture prevention outside the insulation layer: There is an issue of temperature difference effects in insulated equipment and pipes during use. In other words, moisture often accumulates on the outer surface of the insulation layer, which in turn has a corrosive effect on the protective layer used. Therefore, a common practice is to apply 5 millimeters of asphalt mastic on the surface of the insulation layer as an anti-moisture layer, which proves to be effective.