Boiler tube coating is an importing coating technique to remove corrosion. Corrosion is an unintentional removal of metal that occurs because of a chemical or electrochemical attack. The corrosive nature of the gaseous environment at high temperatures may cause rapid material degradation and result in premature failure of components. Boiler tubes in power plants are subjected to a wide variety of failures due to high-temperature corrosion fatigue.
For the reduction of corrosion either material of required mechanical properties is used, which is impossible for a single material to have all these properties or provide the coating to existing material with surface coating methods, which improves the existing properties in an economical way and reduce the cost of replacement.
Corrosion is the worsening of a material or its properties because of reaction with its domain. Sometimes the deterioration is a weight gain, sometimes it a weight reduction, sometimes the mechanical properties are affected. Corrosion of metals costs the United States over $300 billion per year according to recent estimates-more than the cost of annual floods and fires. Oxidation is a type of corrosion in which the reaction between a metal and oxygen at high temperature in the aqueous phase.
It is also called dry-corrosion. The rate of oxidation of a metal at high temperature depends on the nature of the oxide layer that forms on the surface of the metal. Material selection, preparation, and fabrication are therefore of paramount importance for the efficient functioning of the system components. Alloys used at high temperatures should possess good mechanical properties along with erosion-corrosion resistance. However, it is impossible for a single material to have all these properties, along with ease of manufacturing.
Therefore a composite system of a base material providing necessary mechanical properties with a protective surface layer, different in structure or chemical composition can be an optimum choice in combining mechanical properties. Boilers and other steam power plant equipment are subjected to a wide variety of failures involving one or more of several mechanisms. Overheating is the main cause of defeat in the steam produced
Protective Coatings
the rust resistance of low-cost alloys is an economically enchanting alternative to the use of costly corrosion-resistant alloys. A low-grade steel surface modified by a suitable metallic diffusion coating can provide excellent corrosion resistance similar to that obtained with an expensive superalloy. A protective coating is a method of applying a layer of substance applied to the surface of another substance with the intention of removing corrosion.
Protective coatings can be applied using methods and can be used for many other purposes other than corrosion prevention. mostly used materials in non-metallic protective coatings are polymers, epoxies, and polyurethanes. substances generally use for metallic protective coatings are zinc, aluminum, and chromium. A zinc coating over steel is the best example of a reactive protective coating. The zinc reacts with the atmosphere more willingly than the steel, thus preventing the erosion of the steel.
A protective coating can be painted, sprayed, plated or even welded on a material. Polymer coatings are commonly sprayed on. Zinc protective coatings are mainly applied by the electroplating or hot dipping method.
A protective coating is not only limited to corrosion prevention. it can also use to increase a material's wear resistance and ascetic appeal. A protective coating can provide humid resistance or electrical properties that the material did not have prior to the protective coating is applied.
Reliable Coating Methods
Coating provides protection to a specific part of a structure exposed to corrosive environments in different fields ranging from aerospace and the automotive industry to tiny biomedical appliances and implantation inside the human body.
The most common coating technologies use for industrial purposes are.
- Physical Vapor Deposition (PVD) Coating.
- Chemical Vapor Deposition (CVD) Coating.
- Micro-Arc Oxidation (MAO) Coating.
- Electrodeposition Coating.
- Electrolytic Deposition (ELD) Coating.
- Electrophoretic Deposition (EPD) Coating.
- Sol-gel Coating.
- Thermal Spray Coating.
Advantages of Boiler Coating
• Reduced Cost. The cost of repairing the component is less than buying a new one. the coating lasts more than the original substance used.
• Low Heat Input. With some exceptions, the thermal spraying process leaves the component thermal history alone.
• Versatility. Almost any metal, ceramic or plastic can be thermally sprayed.
• Thickness Range depends on the material and spraying method, coatings can be range from 0.001 to more than 1 inch thick.
• Processing Speed the spray rates range from 3-60 lb./hr. depending on the material and the spray system. Typical rates for material application are 1/2 -2 lb. of material per sq. ft per 0.01-inch thickness.
Application of Boiler Coating
- The high degree of readability
- resistance to oxidation
- conductive coatings result in a great solution for imparting conductive properties to surfaces of dielectric components
- Using thermal coating we can provide different kinds of corrosion protection solutions
- Friction between a surface and wear particles or between two surfaces causes erosion. Erosion resistance is critical to a material’s durability or an application’s service life. Coatings offer a range of erosion-resistant thermal spraying solutions for increasing the efficiency and service life of industrial applications.