Rational material selection
Rational material selection is one of the most common and effective methods to prevent and control corrosion of equipment. Material selection needs to understand environmental factors and corrosion factors, including the type, concentration, temperature, pressure, flow state, impurity type and quantity, oxygen content, and whether there is solid suspended substance and microorganism, etc. ; study relevant data; simulation test is carried out according to actual conditions to obtain reliable data of material selection; the corrosion resistance and economy of materials are considered.
The surface of metal materials and their products is treated to form a protective layer, which can separate the metal surface from the external media and prevent the two from acting, as well as obtain decorative appearance. Surface protection is the most common method to prevent or reduce the corrosion of matrix metal, and there are metal coatings and non-metal coatings on the surface protection layer.
The methods of metal coating are as follows.
Peenplating is also called surface alloying treatment, which uses thermal diffusion to infiltrate corrosion resistant metals or alloys into the surface of the matrix metal, and then forms solid solutes or intermetallic compounds with the matrix metal, and the corrosion-resistant surface is called the deposited layer. During the percolation process, the parts to be plated are buried in the percolation box composed of inert fillers, metallised elements, and halogenated activators, and they are kept for a certain period of time in hydrogen gas or inert atmosphere under specified temperature conditions, so that the infiltrated metals and matrix metals can diffuse with each other until the alloy coating is formed on the metal surface of the matrix. The infiltration elements with corrosion resistance are usually zinc, aluminum, chromium, silicon, etc., and the choice depends on the substrate material and corrosion resistance requirements.
Spray coating is formed by spraying molten metal to the surface of metal products by means of compressed air or inert gas flow. This method is often used for spraying metals with the high melting point or refractory materials, or for spraying large area workpiece and repairing workpiece. The disadvantage of spray plating is that the covering layer has poor bonding with the matrix metal and the covering layer is loose. Common spraying methods include flame spraying, plasma spraying and so on.
The electroplating uses direct current electricity to analyze metal from electroplating solution, and deposits crystals on the surface of the workpiece as the cathode to form electroplating layer. Electroplating technology is mainly used for decorative devices with corrosion-resistance and wear-resistance.
Besides that, there are surface protection technologies such as hot-dip coating, metal coating, vacuum coating, gas deposition and cathode sputtering. Recently, new technologies such as ion implantation and laser amorphous surface treatment are also developing rapidly.