1、Item No. 24219 NACE International Publication 021 03 This Technical Committee Reporf has been prepared THE CORROSION SOCIETY by NACE International Task Group 144* on Coatings for High-Temperature Service Li q u i d-Ap pl i ed Coat i n g s for Hi g h-Te m perat u re Atmospheric Service O June 2003, N
2、ACE International This NACE International technical committee report represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, pro
3、cesses, or procedures not included in this report. Nothing contained in this NACE report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protectin
4、g anyone against liability for infringement of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpredictable circumstances ma
5、y negate the usefulness of this report in specific instances. NACE assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE report are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining
6、their applicability in relation to this report prior to its use. This NACE report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, andlor operations detailed or referred to within this report. Users of this
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8、TIONARY NOTICE: The user is cautioned to obtain the latest edition of this report. NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than IO years old. Purchasers of NACE reports may receive
9、 current information on all NACE International publications by contacting the NACE Membership Services Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +I 2811228-6200). Foreword This state-of-the-art report is intended to aid individuals who specify and use liquid-applied hi
10、gh-temperature-resistant coatings for metallic sutfaces in atmospheric service. This report provides information regarding binder and pigment types used in the formulation of these coatings, their heat- resistant properties, and typical service environments. The types of sutfaces over which these co
11、atings are applied and the typical level of cleanliness of these sutfaces is also discussed, as well as application methods, application thick- nesses, curing conditions, and possible causes of common failures of high-temperature coatings. This report was prepared by Task Group 144 on Coatings for H
12、igh-Temperature Service. It is issued by NACE under the auspices of administrative Specific Technology Group (STG) 02 on Protective Coatings and Linings-Atmos- pheric. . *Chairman Ray Posgay, Friendswood, TX. NACE International Introduction Generally, high-temperature coatings are used on sutfaces t
13、o provide corrosion protection and/or for aesthetic reasons. A good understanding of the sutfaces to be coated and the service conditions typically aids in the selection of the coat- ings. Sutfaces are composed of carbon steel, various grades of stainless steel and, in some cases, nonmetallic materi
14、als. Considerations normally include whether the coating selection is based upon “operating“ or “design“ conditions, whether the sutfaces are in continuous or cyclic high-temperature service, and whether or not the sutface is insulated. This report addresses high-temperature coatin s for unin- sulat
15、ed surfaces. NACE Publication 6H189 discusses coatings for use under insulation. P, Corrosion usually does not occur on carbon steel when moisture (electrolyte) has evaporated from the sutface. This normally occurs above 100C (212F); however, as a factor of safety the threshold level is normally con
16、sidered to be 107 to 120C (225 to 250F). Stress corrosion cracking (SCC) of some 300 series stainless steels can occur above the temperature range of 60 to 66C (140 to 150F) when chlorides are present. These threshold temperatures can change when other chemical environments are involved. High-temper
17、ature coatings often provide protection from corrosion during cyclical temperature variations that allow the sutface temperatures to drop below the stated threshold temperature levels. Coatings also protect the sutfaces from corrosive contaminants associated with environmental conditions (e.g., salt
18、 air, acid rain). Typical High-Temperature Coatings High-temperature coatings are typically based on organic resins; however, there are a limited number of inorganic resin systems available. Many commonly used organic coatings such as alkyds, vinyls, acrylics, polyurethanes, and epoxies, consist of
19、resins that degrade and/or lose prop- erties at temperatures above 120C (250F). The extent and severity of degradation is generally dependent on the dwell time at temperature, the number of thermal cycles, and environmental conditions (.e., the presence or absence of water, ultraviolet radiation, et
20、c.). High temperatures and environmental conditions sometimes cause coating discol- oration. Characteristics of the various high-temperature coatings, such as heat resistance, weatherability, temper- ature stability, curing rates, hardness, chemical resistance, and resistance to cracking are normall
21、y determined by the type of resin used (see Table 1). Table 1: Service Temperatures of Various Coating Types Coating Type Typical Range of Service Temperatures OC (OF) Organic High-Temperature (Epoxy-Novolac) -45 to 232C (-50 to 450F) Silicone-Modified Organic (All Pigmentation) Silicone-Modified Or
22、ganic (Aluminum) Silicone (Colored) -45 to 260C (-50 to 500“F)A -45 to 425C (-50 to 800“F)A 150 to 538C (300 to 1 ,OOOF) 315 to 760C (600 to 1 ,400“F)B Silicone (Black and Aluminum) -100 to 650C ( -150 to 1,200“F) Si I icone (Ce ram ic) Inorganic Zinc Silicate -1 O0 to 400C (-150 to 750F) (A) Depend
23、s on organic resin used for modification as well as pigmentation used. First fusion occurs around 315C (600F). Silicones Silicone resins have been used in heat-resistant coatings since the 1940s. Silicone resins are conventionally com- posed of polymerized silane monomers. Silicone coatings generall
24、y demonstrate good resistance to oxidation and ultraviolet (UV) degradation. They are chemically resistant to aromatic and oxygenated solvent systems. Unmodified silicone resins exhibit good high-temperature resistance. Silicone-modified organic coatings are heat-resistant, the Because they tend to
25、form heat-stable complexes with sili- cone, black- and aluminum-pigmented coatings are norm- ally formulated for the highest heat resistance. Organic coatings modified with silicone resin typically offer these advantages, albeit at a lower temperature range. The ex- tent of modification is normally
26、15% to 50% silicone resin solids to the total resin solids. Silicone acrylic and silicone alkyd coatings are typical examples of silicone-modified organic coatings. Other resins that are commonly modified include epoxies, melamine resins, polyesters, and polyur- ethanes. These formulations are norma
27、lly either water- degree of which is dependent on silicone content, organic borne or solvent-based. type, and pigmentation. The heat resistance and color stability of these coatings is typically determined by the Organic-silicone coatings are typically those formulated with properties of the pigment
28、s used in the formulations. both silicone (50%) and organic resin. Generally, the 2 NACE International higher the silicone content the greater the heat resistance. These coatings are usually solvent-based. Silicone ceramic frit coatings typically incorporate ceramic frit in their formulations to pro
29、duce a thermally stable and durable coating with heat resistance to 760C (1,400“F). The ceramic frit is normally bonded with the silicone resin to increase the upper temperature limit of the coating. Epoxies Epoxy-novolac formulations that possess high-temperature capabilities up to approximately 23
30、2C (450F) and are resistant to a wide range of chemicals have been deve- loped. These catalyzed coatings typically use pigments such as micaceous iron oxide. The resulting “air-dry“ coat- ings can be handled quickly and possess a high degree of abrasion resistance. In organ ics metal. Inorganic zinc
31、 (IOZ) primers are typically used for service temperatures up to 400C (750F). There are doc- umented cases in which IOZ primers performed satisfact- orily at temperatures in the area of 704C (1,300“F) for many years. IOZ primers generally provide good corrosion protection. Topcoating is not normally
32、 used unless the environment is aggressive enough to dramatically reduce service life (out- side the range of pH 6.0 to 9.0) or for aesthetic reasons. High-heat silicones and formulations of inorganic topcoats are available. These provide a limited range of colors for application over IOZ primers. O
33、rganicllnorganic Hybrids Hybrid coatings (such as polysiloxanes) are part of a rela- tively new and developing chemistry that incorporates many of the advantages of barrier-type thermosetting coatings (e.g., as fast curing; good handling, storage, and erection properties) with high-temperature silic
34、one technology that Although zinc metal normally melts at around 415C completes the organic/inorganic reaction when heat cured (780“F), the resulting films generally retain their integrity or placed into high-temperature service of 120 to 150C and continue to petform well above the melting point of
35、zinc (250 to 300F). Specification Considerations The types of coating systems used in high-temperature ser- vice vary considerably because of the generic type and specific formulation. Accordingly, the following are some factors typically considered when specifying a high-temp- erature coating: Actu
36、al Substrate Temperature: Actual substrate tempera- tures can vary drastically because of internal temperature (caused by equipment geometry), location from heat source, or environmental conditions such as weather, etc. Degree of Thermal Cycling: Large and/or frequent temper- ature changes are often
37、 detrimental to coatings. Each type of coating responds differently to thermal shock. Rapid cooling or quenching in a liquid is particularly stressful. Lim- ited cyclic excursions of temperatures above the manu- facturers maximum service temperature can cause discol- oration and can degrade the inte
38、grity of the coating film. Service Environment: Chemical or mechanical exposures sometimes affect coating performance and are typically considered during coating selection. Surface Preparation Desired: The degree of sutface prep- aration varies with coating type and/or service conditions. Generally,
39、 the higher the service temperature, the higher the degree of sutface preparation desired. Substrate Temperature at Time of Application: New con- struction activities usually permit application of coatings at substrate ambient temperatures. Some maintenance oper- ations require application of coatin
40、gs while equipment is in service and operating at elevated temperatures. Some coating manufacturers have modified their solvent formu- lations or thinner recommendations to allow application at elevated temperatures. Type and Degree of Cure Desired: Air dry and cure are different events. Air dried t
41、ypically means that solvents have been released from the film. The term can also mean that the solvents have been released and the non-silicone modifiers (such as alkyds, acrylics, etc.) have begun to form a film. For catalyzed material, curing usually means the polymerization of the film components
42、. Catalyzed material generally does not require heat to effect the final cure. Some silicone systems have been designed for initial heat exposure to establish cure before full petformance prop- erties are realized. Coatings that are air dried but not cured can temporarily soften when heat is applied
43、 to the substrate but they regain film integrity upon curing. Softened and/or uncured coatings sometimes trap contaminants and can be easily damaged. Shop or Field Application: The type of formulation desired normally depends on the cure schedule and fabrication, handling, and/or erection requiremen
44、ts. A review of mini- mum and maximum recoat times typically determines which coatings meet the possible time constraints of a job. Health and Safety Issues: Coating formulations are gener- ally free of toxic and hazardous materials. Manufacturers Technical Data Sheets and Materials Safety Data Shee
45、ts (MSDS) provide guidelines for safe and prudent handling. Color Retention: Color stability of pigments varies with pig- ment, temperature, and manufacturer. Changes in gloss or color do not necessarily signify a change in petformance. 3 NACE International Surface Preparation High-temperature coati
46、ngs are normally applied over a sur- face prepared to a white or near-white3 metal blast. The coating manufacturer is typically consulted when specifying the depth of the anchor profile and the quality of the sutface preparation. Primers Primers are normally specified in severe corrosive environ- me
47、nts to prevent corrosion during nonheat service by pro- viding protection in the event of a break in the topcoat. They have also been used to enhance adhesion of some coatings for applications over certain substrates. Specifiers typically verify whether a high-temperature coating system is suitable
48、for the intended service conditions. Whenever possible, a topcoat is normally used. Primers are usually one of the following types: * Primers composed of the same resin type as the top- coat but with the addition of heat-stable, corrosion- inhibitive pigments; Organic zinc-rich primers, with tempera
49、ture limits of 205C (400“F), composed of organic resin and metallic zinc dust; Silicone zinc-rich primers composed of silicone resin and metallic zinc dust; or Inorganic zinc primers containing a silicate binder and metallic zinc dust. Application Coating thickness has been a major factor impacting the petformance of high-temperature coatings. Spraying is the typical method of application. Brush or roller application has also been used, but these methods do not normally yield uniform film thicknesses. Proper application tech- niques are typically recom
