1、NACE International Item No. 24232 NACE International Publication 02107 This Technical Committee Report has been prepared by NACE International Task Group 148* on Coatings and Methods of Protection for Threaded Fasteners Used with Structural Steel, Piping, and Equipment. Coatings for Protection of Th
2、readed Fasteners Used with Structural Steel, Piping, and Equipment March 2007, NACE 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 p
3、reclude anyone from manufacturing, marketing, purchasing, or using products, processes, 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,
4、apparatus, or product covered by Letters Patent, or as indemnifying or protecting 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 intend
5、ed to apply in all cases relating to the subject. Unpredictable circumstances may 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 appropri
6、ate health, safety, environmental, and regulatory documents and for determining 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, equipm
7、ent, and/or operations detailed or referred to within this report. Users of this NACE report are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any
8、existing applicable regulatory requirements prior to the use of this report. CAUTIONARY 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 NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice.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 automatic
9、ally withdrawn if more than 10 years old. Purchasers of NACE reports may receive current information on all NACE International publications by contacting the NACE FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281/228-6200). Foreword This technical committee
10、 report describes current industry practices and gives information on the most commonly used generic coating systems for protection of threaded fasteners used with structural steel, piping, and equipment. The coating system provides a protective barrier between the base metal and the environment to
11、minimize the effect of corrosion. The information presented in this report addresses steel quality, pretreatment processes, coating application, quality assurance/quality control, and test comparisons for evaluating corrosion resistance. This report does not reflect the NACE position on these practi
12、ces, but rather summarizes existing technology and practices of various manufacturers, applicators, and users. This technical committee report was prepared for the use of engineers, purchasing agents, coating inspectors, and project leaders in any industry having corrosion problems with threaded fas
13、teners. The purpose is to provide information on the various generic coating systems currently available for corrosion protection of threaded fasteners. This technical committee report was prepared by NACE Task Group 148 on Coatings and Methods of Protection for Threaded Fasteners Used with Structur
14、al Steel, Piping, and Equipment. It is issued by NACE under the auspices of Specific Technology Group (STG) 02 on Coatings and Linings, Protective: Atmospheric. _ *Chair Brian Willis, Whitford Corporation, Elverson, Pennsylvania.NACE International 2 Background Threaded fasteners are coated to provid
15、e corrosion protection and ease of make-up during installation. Given the design and make-up tolerances of most threaded-fastener systems, the allowable coating thickness for proper make-up is a real concern for end users. Overtapping of the nut threads is a viable option to prevent make-up problems
16、 such as galling, seizing, fretting, and other thread damage. When the total dry film thickness (DFT) of the coating system is 0.75 mil (18 m), overtapping of the nuts is a normal practice to prevent make-up problems. With the exception of hot-dip galvanized or mechanical zinc coatings, ASTM(1)A 563
17、M1requires that overtapping be approved by the purchaser.Many coating systems also reduce the amount of make-up torque (or pretensioning) required by lowering the coefficient of friction (e.g., fluoropolymer coatings). These systems provide lubricity and reduce friction in the make-up/breakout cycle
18、. This helps prevent thread damage (galling). Multiple make-up/breakout cycles are also possible. If the coating system wears or is damaged during use, the degree of corrosion protection can be reduced. The selection of the coating system is important in achieving the desired performance characteris
19、tics. Although there are industry standards covering the manufacture and use of threaded fasteners (ASTM, API,(2)ANSI(3) the specific recommendations for the application and use of coatings, including corrosion control performance, are limited in scope. Only a few coating systems (such as galvanizin
20、g and metallic plating) are addressed in current industry standards.Definitions Breakout: A violent, forceful loosening of the fabricated threaded fastener system from a restraining condition. (For example, a wrench is usually used to loosen a nut or bolt that has been in service an extended period
21、of time.) Chemical Conversion Coating: An adherent reaction product layer on a metal surface formed by reaction with a suitable chemical to provide greater corrosion resistance to the metal and increase adhesion of coatings applied to the metal. (Example is an iron phosphate coating on steel, develo
22、ped by reaction with phosphoric acid.) Coating: A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film. For the purpose of this technical committee report, the term coating includes metallic coa
23、tings applied by galvanizing and electroplating. Coating System: The complete number and types of coats applied to a substrate in a predetermined order. (When used in a broader sense, surface preparation, pretreatments, dry film thickness, and manner of application are included.) Dry Film Thickness
24、(DFT): The thickness of a dried film, coating, or membrane. It is usually expressed in mils or micrometers (m). (NOTE: 1.00 mil = 0.001 in. or 25.4 m). Electroplating: Application of a thin coating of metal by an electrochemical process. Fit: Relationship that exists when an external thread (male) g
25、auges properly and assembles with an internal thread (female) that also gauges properly, according to ANSI Standard B1.1.2 Fluoropolymer Resin-Bonded Coatings: The family of engineering plastics containing fluorine that is characterized by high thermal stability, almost universal chemical resistance
26、, and low coefficients of friction. Function: Characteristic exhibited by a threaded fastener when it is able to perform the physical task it is designed to do (in tension, shear, etc.). Galvanized Coating: A coating of virtually pure zinc applied by various processes including hot dipping and elect
27、rolytic and mechanical deposition. _ (1)ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959. (2)American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070. (3)ANSI International (ANSI), 25 West 43rd St., 4thFloor, New York, NY 10036. NACE technical comm
28、ittee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In many cases, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to convey this information are factual and are pro
29、vided to the reader as input and guidance for consideration when applying this technology in the future. However, these statements are not intended to be recommendations for general application of this technology, and must not be construed as such. NACE International 3 Galvanizing: Application of a
30、coating of zinc. Gauging: Precisely measuring the dimensions and checking for conformity to ANSIStandard B1.1.2Galling: Damage to metal surfaces resulting from friction between sliding solid materials, usually involving roughening and creation of protrusions above the original surface. Galling usual
31、ly causes thread damage and can interfere with the proper function of a threaded-fastener system. Hydrogen Embrittlement: A loss of ductility of a metal resulting from absorption of hydrogen. Kesternich Test: An accelerated test method performed in an enclosed test cabinet with 100% humidity and con
32、centrations of sulfur dioxide (SO2) in cyclic exposures. Test parameters are defined by DIN(4) 500183with two different volumes (concentration levels) of SO2introduced into a 300 L chamber. Test method SFW 2.0 S DIN 50018 with a total of 2.0 L of SO2is the most commonly used concentration, while 0.2
33、 L of SO2is often used for the least severe exposure. Liquid Metal Cracking (LMC): Cracking of a metal caused by contact with a liquid metal. Make-Up: Mating the internally threaded nut and externally threaded bolt and turning the nut until a predetermined torque or pretensioning of the threaded-fas
34、tener system is achieved. Overtapping: Increasing the manufacturing tolerances of the nut to allow for additional coating thickness in the threaded-fastener system to ensure proper make-up. Polytetrafluoroethylene (PTFE): A waxy, opaque-white, thermoplastic fluoropolymer resin that contains four flu
35、orine atoms on each ethylene molecule (C2F4)n. It is thermally stable, very resistant to chemicals, and has an extremely low coefficient of friction. Primer: A coating material intended to be applied as the first coat on an uncoated surface. The coating is specifically formulated to adhere to and pr
36、otect the surface as well as to produce a suitable surface for subsequent coats. (Also referred to as Prime Coat.) Salt Fog Exposure: An accelerated test method performed in an enclosed cabinet to compare the corrosion resistance of various materials. Test methods are defined by ASTM B 117.4 Surface
37、 Pretreatment: A thin protective coating or corrosion inhibitor formed on the surface of a base metal, usually by a chemical reaction process. Examples are chemical conversion coatings (e.g., metal phosphates), chromate compounds, and nitrides. Threaded-Fastener System: A threaded mechanical device
38、for holding two or more bodies in definite position with respect to each other. Topcoat: The final coat of a coating system. (Also referred to as Finish Coat.) Torque: A turning or twisting force applied to threaded fasteners to ensure proper make-up or pretensioning. Torque is usually expressed in
39、foot-pounds (ft-lb) (newton-meters Nm). Volatile Organic Compound (VOC): Organic-based solvent that vaporizes rapidly into the atmosphere. These organic solvents are used in solvent-based coating formulations and can be used for vapor degreasing various metal parts. Coatings Selection The selection
40、of the proper coating system depends on the intended use. A wide variety of coating systems is available for numerous applications from light atmospheric exposure to severe immersion service (marine environments, chemical exposure to acids or gases, etc.). Most coating manufacturers provide data on
41、the corrosion performance of specific coating systems in various environments. The proper evaluation, selection, and placement in a given environment (atmospheric, marine, industrial, etc.) are critical to successful performance. Some end users conduct laboratory testing, either in-house or by indep
42、endent laboratories, of various coating systems in specific environments for screening purposes. For proper coating selection, actual field trials and performance evaluation in the specific environment are typically conducted. Many other factors are involved in the coating selection process such as
43、the ease of application, consistency of quality of the finished product, resistance of the coating system to physical damage during handling and use, ease of installation, economics, and overall performance. The application process can influence the selection of the coating system. Generic Coating S
44、ystems Table 1 lists the commonly used generic coating systems available for threaded fasteners. The DFT range and the maximum exposure temperature typical for each generic coating system are given. _ (4)Deutsches Institut fur Normung (DIN) (German Institute for Standardization), Burggrafenstrasse 6
45、, D-10787 Berlin, Germany. NACE International 4 Manufacturers or suppliers can usually supply accelerated test results. Commonly used accelerated test methods for threaded fasteners are listed in Table 2. Field performance reports (case histories) furnished by suppliers also provide useful informati
46、on. Within each generic coating system listed in Table 1 are numerous types and brand names, including proprietary coating systems. Each manufacturer or supplier can usually supply detailed performance data for each specific coating system. The generic coating system information provided in Table 1
47、is a compilation of data from many suppliers and end users. It is provided for comparison purposes only and is not a recommendation for use. The most commonly used test method for threaded fasteners is ASTM B 117. The data provided are for comparison purposes only. The amount of test data available
48、for the other test methods listed in Table 2 is very limited and not included. The relative cost comparisons are listed to show approximate cost differences between the various generic coating systems. An ASTM A 1935bare steel stud bolt and two nuts are used for comparison purposes. Costs vary from
49、region to region and between various suppliers. Manufacturers and suppliers can provide accurate, detailed information on each specific threaded-fastener system. TABLE 1: Generic Coating Systems for Threaded Fasteners Generic Coating System DFT, mil (m) Maximum TemperatureF (C) ASTM B 117(A)Exposure Hours Relative(B)Cost Comparison Uncoated (Bare) Steel Stud Bolt and 2 Nuts(B)Aluminum Plating Cadmium Plating Ceramic Metallic Hot-Dip Galvanizing Inorganic Zinc-Rich Silicate Manganese Phosphate, Fluoropoly
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