1、10-71SSPC-TU 5May 1, 1999Editorial Revisions November 1, 20041. Scope 1.1 This document describes only laboratory experiments. In an industrial setting protective coatings are used for a variety of reasons. Service environments for protective coatings may range from a mild atmospheric exposure condi
2、tion to a severe chemical or immersion setting.2. Introduction2.1 APPLICATION OF ACCELERATED TESTING: The application of accelerated testing differs from user to user. Some typical users are described below. The length of exposure of a coating system in any given test depends on the expected durabil
3、ity of the system and on the severity of the testing environment.2.1.1 Formulators: Formulators use accelerated testing as a method to screen and compare the behavior of test formula-tions. The general goal is to optimize the formulation through experimental design or the typical ladder series. Form
4、ulators often employ ladder series in which one or more components in the coating formulation is changed in a controlled fashion.2.1.2 Manufacturers: Manufacturers use accelerated testing in the same manner as a formulator. In addition manu-facturers use accelerated testing for drawing comparisons b
5、etween different products, to follow the results of shifts in raw material supply, and to show conformance with the performance requirements of procurement specifi cations.2.1.3 End Users: The desire of end-users is to use accelerated testing as a reliable means of predicting long-term performance,
6、but the goal of predicting performance is not achievable at this time, and it may never be achievable. Currently most end-users therefore employ accelerated testing to rank relative performance of competitive products or to screen coating systems for inclusion on qualifi ed products lists.Coating ma
7、nufacturers and specifi ers frequently use test exposures of coating materials in an attempt to assess the service life of various candidate coating systems before recommending their use. Test exposures are recognized to be a relevant predictor of coating system performance but can take a very long
8、time to complete. Short term accelerated testing is often used to help provide early indications of coating system performance.Predicting actual performance of a coating system, based solely on short term testing, can be misleading. A typical short term test may not impose on a coating system the un
9、ique combination or frequency of stresses that lead to failure in actual use. 2.2 INTENDED USE: This document is addressed to users and specifi ers of protective coatings in an industrial setting. It is intended to provide information on the state-of-the-art in the technology of short term, accelera
10、ted testing of coatings. This technology update begins with a discussion of the envi-ronment in which coating systems are expected to perform. The specifi er may use this update to assist in interpreting the results of certain accelerated tests. A qualitative analysis of the attributes of typical te
11、st methods and their relevance to actual exposures is also provided.3. Referenced Standards3.1 SSPC AND JOINT STANDARDS:SP 11 Power Tool Cleaning to Bare MetalSP 5/NACE No. 1 White Metal Blast CleaningSP 6/NACE No. 3 Commercial Blast CleaningSP 7/NACE No. 4 Brush-Off Blast Cleaning SP 10/NACE No. 2
12、Near-White Blast CleaningSP 12/NACE No. 5 Surface Preparation and Cleaning of Steel and Other Hard Materials by High- and Ultrahigh-Pressure Water Jetting Prior to Recoating3.2 AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) STANDARDS:B 117 Standard Practice for Operating Salt Spray (Fog) Apparatu
13、sB 287 Standard Method of Acetic Acid-Salt Spray (Fog) Testing (Withdrawn 1997)C 868 Standard Test Method for Chemical Resistance of Protective LiningsD 609 Standard Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint, Varnish, Conver-sion Coatings, and Related Coating ProductsD 8
14、70 Standard Practice for Testing Water Resistance of Coatings Using Water ImmersionD 1654 Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive EnvironmentsSSPC: The Society for Protective CoatingsTECHNOLOGY UPDATE NO. 5Accelerated Testing of Industrial Protective
15、 CoatingsSSPC-TU 5May 1, 1999Editorial Revisions November 1, 200410-72D 2246 Standard Test Method for Finishes on Primed Metallic Substrates for Humidity-Thermal Cycle Cracking (Withdrawn 1992)D 2247 Standard Practice for Testing Water Resistance of Coatings in 100% Relative HumidityD 2933 Standard
16、Test Method for Corrosion Resistance of Coated Steel Specimens (Cyclic Method) (Withdrawn 1990)D 4585 Standard Practice for Testing Water Resistance of Coatings Using Controlled CondensationD 4587 Standard Practice for Conducting Tests on Paint and Related Coatings and Materials Using a Fluorescent
17、UV-Condensation Light- and Water-Exposure ApparatusD 5894 Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal, (Alternating Exposures in a Fog/Dry Cabinet and a UV/Condensation Cabinet)G 8 Standard Test Methods for Cathodic Disbonding of Pipeline Coatings G 23 Standard Practice for Op
18、erating Light-Exposure Apparatus (Carbon-Arc Type) With and Without Water for Exposure of Nonmetallic Materials. (Withdrawn 2000; Replaced with G 152 to G 153)G 26 Standard Practice for Operating Light-Exposure Apparatus (Xenon-Arc Type) With and Without Water for Exposure of Nonmetallic Materials (
19、Withdrawn 2000; Replaced with G 155)G 53 Standard Practice for Operating Light- and Water-Exposure Apparatus (Fluorescent UV-Condensa-tion Type) for Exposure of Non-metallic Materials Withdrawn 2000; Replaced with G 153)G 85 Standard Practice for Modifi ed Salt Spray (Fog) TestingG 87 Standard Pract
20、ice for Conducting Moist SO2Tests3.3 NACE INTERNATIONAL STANDARDS:TM0174 Laboratory Methods for the Evaluation of Protective Coatings and Lining Materials in Immersion Service4. Characteristics of the Service Environment4.1 TYPICAL SERVICE ENVIRONMENT DESCRIP-TIONS: The specifi er should always reme
21、mber that coating systems subjected to short term testing are applied, and are expected to provide protection, in a real environment. A wide range of service conditions or environments can be defi ned under which industrial maintenance protective coatings are expected to perform. A description of en
22、vironmental zones is given in Appendix A. This is taken from Table 3 of Chapter 1, “How to Use SSPC Specifi cations and Guides,” in the SSPC Painting Manual, Vol. 2 Systems and Specifi cations. Many service environments under which a coating system shall per-form are described by the classifi cation
23、 system. To be of value, short-term accelerated tests should reproduce and accentuate the stresses imposed on a coating system by the actual service environment. There are some special use categories which are not covered in the environmental zone concept; these include abrasion resistance, marine f
24、ouling, graffi ti control, mildew resistance, skidding, or high temperature service. Specially designed tests may be needed for such exposures.4.2 VARIABILITY OF THE SERVICE ENVIRONMENT: With the sole exception of Zone 0 - Dry Interior (Appendix A), none of the environmental zones present a uniform,
25、 invariable service environment. All the service environments in Appendix A for which painting is recommended show variations in one or more of the following stresses: Temperature - e.g., daily changes, or freezing and thawing Humidity - e.g., morning formation of dew Time-of-wetness - e.g., periodi
26、c immersion, or rainfall Ultraviolet light intensity and exposure time Atmospheric pollutants - e.g., SO2/NO2, smog, salt or particulate deposition Chemical attack - e.g., exposure to deicing salts, splash and spillage of acids or alkaline agents Mechanical Stresses - e.g., chipping by stones, freez
27、e/thaw cycling.Natural service environments are as changeable as the weather. To help better replicate the type and frequency of coat-ing failure found in actual use, many accelerated test methods incorporate controlled variations in test conditions.4.3 DESIRED OUTCOME OF EXPERIMENT: The purpose of
28、the program dictates the scale and nature of tests used to establish the performance of coatings. For example, a coating to be used in submersion would not be tested in the desert sun. Defi ning the intended service is important in determining the type of test to use in coating evaluation. This enti
29、re process is known as experimental design.5. Experimental Design Parameters5.1 Although the experimental design follows from the desired outcome, there are a wide variety of options available for consideration. The primary intent of experimental design is to reduce the number of independent variabl
30、es which might affect and skew the results of the test program. 5.2 VARIABLES CONTROLLED BY EXPERIMENTAL DESIGN5.2.1 Choice of Substrate: This should be identical with the substrate upon which the coating shall be applied; i.e., if the structure is ASTM A 36 steel, use A 36 steel panels for 10-73SSP
31、C-TU 5May 1, 1999Editorial Revisions November 1, 2004testing. On certain occasions, special panels may be required that mimic common structural shapes or commonly encountered design or fabrication fl aws.5.2.2 Choice of Surface Preparation: Unless surface preparation is a variable under study in the
32、 experiment, the type of preparation should be identical with the type of preparation required for real application. Typical specifi cations for surface preparation for industrial maintenance coatings are given by SSPC-SP 5/NACE No. 1, SSPC-SP 6/NACE No. 2, SSPC-SP 7/NACE No.4, SSPC-SP 10/NACE No. 3
33、, SSPC-SP 11, and SSPC-SP 12/NACE No 5. Typical preparation requirements for sheet metal products are given in ASTM D 609.5.2.3 Profi le: This should be the profi le recommended for use with the coating system unless it is a parameter to be examined in the test program.5.2.4 Choice of Coating System
34、s: A valid control coating system or set of controls should be employed. Controls are those systems for which well-defi ned performance expecta-tions are known, both in actual use and preferably within the tests used in the program. Control coating systems spanning a range of performance from poor-m
35、oderate through excel-lent should be used. This will help in subsequent ranking of candidate coating performance.5.2.5 Application: This should be the type of application to be employed in actual use and that recommended by the paint manufacturer. Results obtained from use of ideal application metho
36、ds, producing a defect-free fi lm, will be of less use in assessing how a coating will perform in actual service.5.2.6 Types of Experimental Design: If each factor in the design is given equal weight, then the design is called full factorial. Full factorial designs can dramatically increase the numb
37、er of replicate specimens prepared. One can reduce the scope of the experimental design by careful selection of the points within a design at which maximum replication will occur. Such an approach is called a composite or mixture design. When screening coating formulations, a third approach is often
38、 taken which provides replication on only one point.5.2.7 Number of Test Replicates: Replicate specimens are essential. The number of test replicates is governed in part by the type of experimental design. There are a number of operator dependent variations in applied system characteris-tics. To acc
39、ommodate these uncontrollable variations, multiple specimens are needed for each factor in the experimental design. With very large replicate sets, 20 or more, it can be demonstrated that failures do not all occur at the same time. Dubbed lifetime analysis, this also refl ects actual paint per-forma
40、nce where failures on a large coated surface occur in a sporadic manner. For many comparative studies, a minimum of fi ve to six replicates is appropriate to improve the validity of the data. (Almost all existing performance based specifi cations call for no more than two replicates.)6. Characterist
41、ics of Controlled Accelerated Tests6.1 CLASSIFICATION OF ACCELERATED TEST METHODS: Accelerated test methods can be classifi ed in accordance with the following criteria:1. Constant stress or cyclic/variable test2. Industry standard test or non-standardized test3. Multi-component stresses or single c
42、omponent stressAppendix B summarizes the characteristics of many ac-celerated test methods typically used in evaluating industrial maintenance coatings.6.2 COMMON ACCELERATED TEST METHODS: An ideal accelerated test would expose new coatings to the stresses expected in real exposure, would induce exa
43、ctly the type of failures observed in real use, and would do so quickly. In reality, this ideal is diffi cult to achieve.6.2.1 Salt Spray Testing (ASTM B 117, ASTM B 287): Salt spray testing in accordance with ASTM B 117 and ASTM B 287 exposes panels to constant stresses of temperature (95F), humidi
44、ty (100%) and a corrosive salt solution (for ASTM B 117 testing, 5% NaCI is used). Panels are commonly scribed and evaluated for rust, blister, and scribe undercut failure. Typical test durations can run anywhere from 500 hours to 5,000 hours or more. Originally developed for use in testing metallic
45、 coatings, ASTM B 117 testing became the method of choice for evaluation of coatings on metal products because of the lack of other suitable test methods.Salt fog testing in accordance with ASTM B 117 is the most widely used method for screening coating performance. Many specifi cations include the
46、use of this test. Modes of failure observed are blistering, rusting on the panel face, and scribe undercutting. The rust product created by this test is unlike that found in most atmospheric exposures. Blistering failure is far higher than found in most atmospheric exposures.Studies have shown that
47、the rankings of coatings in salt fog testing often bear little correlation to rankings from expo-sure in any real atmospheric service. In part this is because the failures are different. The type of reactions occurring on the sample panel are unique to the test chamber; this also causes the discrepa
48、ncy in results between salt fog testing and real exposure. Table 1 depicts the correlation between salt fog exposures and some typical exposure sites. The data is taken from two studies, SSPCs Performance of Alternate Coatings in the Environment (PACE), and a study of the relative merits of constant
49、 or cyclic salt spray exposures by the Paint Research Association (PRA).1, 2 The PACE results, Table 1A, show that, with one exception, for subclasses of the full set of coatings tested, poor or low correlation is observed between SSPC-TU 5May 1, 1999Editorial Revisions November 1, 200410-74time to failures by rusting at the marine site, and preliminary screening in ASTM B 117 salt spray. The study at the PRA, Table 1B, used a lower number of coating samples, and also indicates poor correlation between exterior exposure and salt spray exposure. The poor correlation observed is quite t
