High Temperature coatings are specialized materials. These coatings are designed for temps of 300-1400F. Selection depends upon the temperature profile and type of substrate that is to become painted. Understanding how they work and how to specify and apply them will help to ensure proper service and eliminate such problems as disbondment, discoloration and early failure.
BASICS: For high temperature applications, the coating system is expected to retain its appearance and integrity while protecting metallic substrates at temps above (300F) (150C). The coating may be subjected to corrosion. In general, coatings are made up of a resin or vehicle, pigments and solvents. Conventional coatings, such as alkyds, use organic vehicles as pigments binders. However, these vehicles may decompose under heat, and this can cause premature failure.If you want to know more about different coating services then visit Plasma Ceramic Coating and Surface coating India
To overcome this problem, high temperature coatings use heat resistant resins. These resins compounds have great thermal stability and level of resistance to oxidation. They are also essentially transparent to, and resistant to degradation by ultraviolet radiation.
The combination of heat resistant qualities and weathering characteristics make these resins and coatings ideal for formulation into heat resistant servicing coatings. Other coatings can be formulated with substitute resins that may reduce cost per gallon while improving properties such as adhesion, abrasion level of resistance and curing time.Get more info about High Temperature coating here.
The pigments used must be compatible with the resin and should not decompose at high temperatures. Pigments must also be color stable over the entire working heat range range of the coating. Thermally stable pigments keep their color over time, unlike other pigments on the market and so are used in high temperature coatings. Traditionally, only black and aluminum colored heat stable pigments were obtainable. Now, there is a wide range of colours, including pigments that may support numerous color matching options.
OPERATING CONDITIONS: In specifying a high temperature coating system, the aspects affecting efficiency must first be assessed. In addition to temperature, these include the nature of the substrate, its structure, stress due to thermal cycling, weathering, surface preparation and application limitations, corrosives and life expectancy of the coating.Two common pitfalls are made in specifying: 1. Assuming that a single high temperature coating will be right for all applications. 2. "Overspecifying" the coating. Too often, the substrate pores and skin temperature can be guessed at, and the guess is made on the high side for safety. Thus, the coating system specified may be suitable for operating temperatures much higher than those that will be encountered. Also in overspecifying, the coating may not dry/cure properly. High Temperature coatings usually require curing at elevated temperatures to accomplish optimum film properties.
MEASURING TEMPERATURE: Correct software and substrate conditions are vital to composing a specification. Both the temperature range and the maximum temperature need to be identified. Surface thermometers and heat guns are now much more advanced today and are the most accurate to take heat range measurements. Heat range readings taken at the most accessible locations can be misleading. For example, at ground level, a stack may be heavily line with refractories. It will have skin temperature much lower than its upper reaches where the lining may be thinner. When contact measurements cannot be made, other methods must be used.
RANGE OF APPLICATIONS: There are two broad categories of high temperature coatings: those for program below (500F-260C) and those for program above (500F-to 1200F-650C). Formulations of these coating systems shift when the temperature requirement exceeds these temps. Coatings must be formulated specifically for the application and operating heat range of the substrate to keep up this broad range of temperature, number of coats needed and rapid rise in heat range based on what is being painted.
DESIGN AND Servicing FACTORS: In writing a specification for a high temperature coating, the equipment design and its condition must be considered. Usually design changes can be made only on new construction, and only when a coating professional can be consulted before fabrication begins. If appropriate measurements are not taken, premature coating failure can be caused by items such as bolts, rivets, corners, edges, inverted channels and poorly treated weldments. Sharp protrusions should be ground off, and welds abraded. Such areas should be spot primed with a high temperature zinc dust primer.
SURFACE PREPARATION: Once the conditions of software are recognized, the coating can be specified. However, no coating- no matter how nicely specified - will carry out properly if it is not applied properly. The surface must be correctly prepared. Contaminates must be removed. The SSPC should be followed for each type of substrate combined with the coating manufacturer's suggestion/recommendation. For carbon steel, abrasive blasting is the preferred method. It eliminates contaminants and produces a mechanical anchor pattern to hold the coating.
PRIMING To avoid recontamination, priming should be done as soon as possible after surface preparation is finished. For carbon steel, a high temperature zinc dust primer should be used. For indoor exposure, in nonaggressive environments, a two coating topcoat system offers a viable option. When high temperature equipment is to be painted, the nature of the earlier applied coatings must be considered. Topcoats These topcoats should be applied only over either clean, dry surfaces or over primers that are compatible with the topcoat. If the composition of the existing coatings cannot be determined, eliminate all coatings from surface.
FIELD APPLICATION METHODS- Equipment should be allowed to cool to ambient heat range before it is painted. The only exception can be coatings that are formulated to be applied to hot surfaces. If devices is hot, in some cases, brush and rollers could create excessive thick films and could fail due to cracking and flaking caused by thermal stress in the film. Spray applications on hot surfaces can result in a condition similar to dry spray. The film will not adhere properly, and will be porous due to bubbling that results from rapid solvent evaporation extremely. Contamination is often a problem. The topcoat over a primer as soon as possible apply.
APPLYING COATINGS TO HOT SURFACES - Most high temperature coatings are made to be applied to surfaces at ambient temps. What about equipment that is either rarely shut down or cannot be scheduled for painting due to short turnaround moments? For such complications, special coatings may be used. These are made for in service painting of devices as popular as 400-500F. Uses include coating of process vessels, piping, stacks and heat exchangers. Coatings that are hot applied are usually self - priming and may also be used for Corrosion Under Insulation (CUI).
PERFORMANCE LIMITATIONS- Although, typical high temperature coatings work well, they do have some limitations. They are not intended for immersion service. Splash zones, mists, gases and fumes can be a problem as well. When high temperature coatings are modified, film properties such as flexibility, chemical resistance, toughness and curing are improved. By also modifying high temperature coatings for maximum heat resistance, they can operate successfully to 1400F (760C). Keep in mind that high temperature coatings require servicing. They must become repaired and inspected if damaged.