The selection of corrosion resistant coating materials is more complicated. The working condition, working temperature, working environment and various kinds of corrosion media have all increased the requirement of coating materials. Corrosive environment may be aqueous solution, gas or a variety of chemical media, but also may have a wide range of temperature. In the presence of gas conditions, the burning of gas or non-burning fuel may also be at the appropriate temperature and other substances react, forming a very complex corrosion environment.
Resistance to atmospheric corrosion
Such coatings are resistant to the following conditions: metals or alloys are exposed to the atmosphere in the outdoor or indoor atmosphere, which can resist the corrosion of wind, rain, sunlight and other climate change conditions in the atmosphere. The coating used in the outdoors can also be used well in the interior. This kind of coating includes the coating of industrial atmosphere, the corrosion resistance of the coating and the corrosion resistance of the atmosphere in the countryside.
1 Coating for industrial atmospheric corrosion
Resistance to industrial atmospheric corrosion coatings can withstand the harsh atmosphere of soot or chemical smoke (such as large cities and heavy industrial areas, etc.), can be sprayed Zn, Al coating. This type of coating must be sealed, the choice of sealing agent is very important, the specific selection and construction considerations can be referred to in the sixth chapter arc spraying.
This type of coating is commonly used in all types of structures and components of steel, electrical conduit, bridges, transmission lines, metal components, lawn and garden facilities, etc.
2 corrosion resistant coating for marine atmosphere
The coating can withstand corrosion in the vicinity of the ocean or under salt spraying conditions. Commonly used in the bridge above the waterline, dock structure above the waterline, storage container, ship’s superstructure, the surface of the transformer etc.
3 Resistance to the coating of atmospheric corrosion in the countryside.
The rural atmosphere, although there is no industrial smoke and marine climate of salt fog, but contains a little of the pollutants. They are usually mild and dry.
Corrosion resistant coating
Immersion corrosion is metal or its coating is exposed to the liquid, and is all or part, or two alternately by dipping, anti-corrosion coating must be able to withstand the above or below the level of the liquid surface environment. This kind of coating is as follows: resistant coating, non-edible fresh drinking water, fresh water, heat resistant coating corrosion coating, chemical and food industry using the coating.
3.1 drinking water resistant coating
The coating is resistant to fresh water, and cannot change the chemical composition of the water. In order to meet drinking water requirements, cannot use the chromate containing sealant. Spraying Zn coating. Commonly used in freshwater reservoir; aqueduct (aqueduct, aqueduct, aqueduct), filter tank, water delivery pipe.
3.2 fresh water resistant coating
This coating resistant to drinking water, the water temperature does not exceed 52 degree C, the pH value is 5 ~ 10. Spraying Al, Zn coating. Commonly used in power plant is introduced, the structure line device, immersed in freshwater sailing in freshwater hull etc.
3.3 heat resistant fresh water coating
The water is not drinking water, the water temperature is 52 to 204 degrees C, pH value of 5 ~ 10, can be sprayed Al coating, but to seal the hole. Used for heat exchangers, hot water storage containers, steam cleaning equipment, and parts exposed to steam.
4 salt resistant coating
The coating can be completely or partially immersed in a stationary or moving salt water or seawater. The structure of the static state, the scope of the sea water immersion should be extended to the mud line under the 0.914 meters above the tide line; the higher the range, should be considered as “Salt atmosphere”. Spraying Al coating. Commonly used in marine engine oil pan, steel River pier, pile and hull, rudder and fish in the fish tank, the hull below the waterline are dirt problem areas etc..
5 coating for chemical and food industry.
The effect of chemical coating to resist such as oil, fuel and solvent, and corrosion resistant to various food, but cannot change the chemical composition and taste of food, can be sprayed Al coating, but to seal the hole. Commonly used in gasoline, crude oil, fuel oil and xylene, ethanol, butanol, isoamyl acetate and toluene and other chemicals storage, brewery mash tank, soft drinks and dairy equipment, dairy equipment, food oil tank and molasses tank, glycerin groove lining, sawdust washing machine etc.
CORROSION RESISTANT COATING
The coating can withstand the corrosion of various acids, bases, salts, solutions, steam, and solids. This type of coating is mainly iron-based, nickel and cobalt alloys, self-fluxing alloy, nonferrous metal, ceramic oxide, chromium carbide and tungsten carbide metal ceramic. As the thermal spray coating has a certain porosity, so, all kinds of coating must be filled and sealed. The sealant itself must be resistant to chemical corrosion medium.
In order to resist chemical corrosion, all coatings used in a given environment, must use the recommended sealant for processing. The use of specialized sealants, will not damage the coating mechanical properties. However, under high temperature coating corrosion resistant ability depends in part on sealant.