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This document is developed in accordance with the rules given in GB/T 1.1-2020 Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents.
This document replaces GB/T 10125-2012 Corrosion tests in artificial atmospheres - Salt spray tests. In addition to a number of structural adjustments and editorial changes, the following main technical changes have been made with respect to GB/T 10125-2012:
——The applicable scope of acetic acid salt spray test and copper-accelerated acetic acid salt spray test and the inapplicable scope of this procedure are added (see Clause 1);
——The normative references are modified and added (see Clause 2; Clause 2 of Edition 2012);
——Clause 3 "Terms and definitions" is added;
——Clause 4 "Principle" is added;
——The control requirements for the content of heavy metal impurities in sodium chloride used for solution preparation are modified (see 5.1; 3.1 of Edition 2012);
——The method of measuring the pH of sprayed solution collected is modified (see 5.2; 3.2 of Edition 2012);
——The requirements for the supports for specimens are added (see 6.1);
—The requirement that the capacity of spray cabinet shall not be smaller than 0.4m3 is deleted (see 4.2 of Edition 2012);
——The new requirements for spraying in the spray cabinet are added (see 6.2);
——The requirements for the position of the temperature measurement zone are modified (see 6.3; 4.3 of Edition 2012);
——The recommended value of atomizing pressure is added (see 6.4.2);
——The requirements of equipment used for humidification of compressed air are modified (see 6.4.3; 4.4 of Edition 2012);
——The guiding values for the temperature of the hot water in the saturation tower under the atomizing pressures of 160MPa and 170MPa are added (see Table 1);
——The operation method for achieving a stable level of continuous spraying in uniform distribution is added (see 6.4);
——The precautions for cleaning the spray cabinet after testing are added (see 6.6);
——The number and treatment method of steel reference specimens used are modified (see 7.2; 5.2.1, 5.3.1 and 5.4.1 of Edition 2012);
——The number of steel reference specimens arranged in the spray cabinet and the requirements for the verification method of the spray cabinet are modified (see 7.3; 5.2.2, 5.3.2 and 5.4.2 of the Edition 2012);
——The test duration is deleted (see 5.2.2, 5.3.2 and 5.4.2 of Edition 2012);
——The method of removing the steel corrosion products specified in ISO 8407 is deleted (see 5.2.3, 5.3.3 and 5.4.3 of Edition 2012);
——The writing format of the method for evaluating the corrosivity of spray cabinets for neutral salt spray, acetic acid salt spray and copper-accelerated acetic acid salt spray tests are modified (see Clause 7; Clause 5 of Edition 2012);
——The requirements for the setting values of parameters of spray cabinets are added (see Table 3);
——The precautions for measuring the concentration and pH of sprayed solution collected are added (see 10.2);
——The recommended value of the frequency to measure the collection rate is added (see 10.3);
——A measure to prevent the concentration of sodium chloride and the pH from fluctuating is added (see 10.5);
——The recommended periods of tests are modified (see 11.1; 9.1 of 2012 edition);
——The requirement that the total opening time of the cabinet per day shall not exceed 1h during the test is added (see 11.2);
——A general description of how to treat test specimens after testing is added (see 12.1);
——The specific method for treating the organic coated test specimens after testing is added (see 12.3);
——The schematic diagram of one possible design of spray cabinet is modified (see Figures C.1 and C.2; Figures A.1 and A.2 in Annex A of Edition 2012);
——The number of zinc reference specimens arranged in the spray cabinet and the requirements for the verification method of the spray cabinet are modified (see D.1 and D.2; B.1 and B.2 in Edition 2012);
——The value of distance between the scribe marks on the test specimens with organic coatings is modified (see E.4; C.4 of Edition 2012);
——The year numbers of the standards at home and abroad in Annex G are modified (see Annex G; Annex E of Edition 2012);
——"Annex NA" is deleted (see Annex NA of Edition 2012).
This document has been redrafted and modified in relation to ISO 9227:2017 Corrosion tests in artificial atmospheres - Salt spray tests.
There are many structural adjustments in this document with respect to ISO 9227:2017. Annex A gives a comparison of structural adjustments between this document and ISO 9227:2017.
Technical differences have been made in this document with respect to ISO 9227:2017, marked with perpendicular single line (|) in the outside page margin of the provisions concerned, and have been listed together with their causes in Annex B.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This document was proposed by China Iron and Steel Industry Association.
This document is under the jurisdiction of SAC/TC 183 National Technical Committee on Iron and Steel of Standardization Administration of China.
This document was issued in 1997 as first edition, its first revision was issued in 2012, and this is the second revision.
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Introduction
There is seldom a direct relation between resistance to the action of salt spray and resistance to corrosion in other media, because there are many factors influencing the progress of corrosion of metals. Therefore, the test results obtained in this document shall not be regarded as a direct guide to the corrosion resistance of the tested materials in all environments where these materials might be used. Also, the performance of different materials during the test shall not be taken as a direct guide to the corrosion resistance of these materials in service.
Nevertheless, the method described herein gives a means of checking that the comparative quality of a metallic material, with or without corrosion protection, is maintained.
Different metallic substrates (metals) cannot be tested in direct comparison in accordance to their corrosion resistances in salt spray tests. Comparative testing is only applicable for the same kind of substrate.
Salt spray tests are generally suitable as corrosion protection tests for rapid analysis for discontinuities, pores and damage in organic and inorganic coatings. In addition, for quality control purposes, comparison can be made between specimens coated with the same coating.
It is often not possible to use results gained from salt spray testing as a comparative guide to the long-term behaviour of different coating systems, since the corrosion stress during these tests differs significantly from the corrosion stresses encountered in practice.
Corrosion tests in artificial atmospheres - Salt spray tests
1 Scope
This document specifies the apparatus, the reagents and the procedure to be used in conducting the neutral salt spray (NSS), acetic acid salt spray (AASS) and copper-accelerated acetic acid salt spray (CASS) tests. It also describes the method employed to evaluate the corrosivity of the test cabinet environment.
It is applicable to assessment of the corrosion resistance of metallic materials and coatings, with or without permanent or temporary corrosion protection.
It does not specify the dimensions or types of test specimens, the exposure period to be used for a particular product, or the interpretation of results. Such details are provided in the appropriate product specifications.
It is useful for detecting discontinuities, such as pores and other defects, in metals and their alloys, as well as metallic, organic, anodic oxide and conversion coatings.
The neutral salt spray (NSS) test applies to:
——metals and their alloys;
——metallic coatings (anodic and cathodic);
——conversion coatings;
——anodic oxide coatings;
——organic coatings on metallic materials.
The acetic acid salt spray test is useful for testing decorative coatings of copper + nickel + chromium, or nickel + chromium. It has also been found suitable for testing anodic and organic coatings on aluminium.
The copper-accelerated acetic acid salt spray test is useful for testing decorative coatings of copper + nickel + chromium, or nickel + chromium. It has also been found suitable for testing anodic and organic coatings on aluminium.
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These methods are all suitable for checking that the quality of a metallic material, with or without corrosion protection, is maintained. They are not intended to be used as a means of ranking different materials relative to each other with respect to corrosion resistance or as means of predicting long-term corrosion resistance of the tested material.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6461 Methods for corrosion testing of metallic and other inorganic coatings on metallic substrates - Rating of test specimens and manufactured articles subjected to corrosion tests (GB/T 6461-2002, ISO 10289:1999, IDT)
GB/T 9271 Paints and varnishes - Standard panels for testing (GB/T 9271-2008, ISO 1514:2004, MOD)
GB/T 10123 Corrosion of metals and alloys - Basic terms and definitions (GB/T 10123-2001, eqv ISO 8044-1999)
GB/T 13452.2 Paints and varnishes - Determination of film thickness (GB/T 13452.2-2008, ISO 2808:2007, IDT)
GB/T 16545 Corrosion of metals and alloys - Removal of corrosion products from corrosion test specimens (GB/T 16545-2015, ISO 8407:2009, IDT)
GB/T 30786 Paints and varnishes - Guidelines for the introduction of scribe marks through coatings on metallic panels for corrosion testing (GB/T 30786-2014, ISO 17872-2007, IDT)
GB/T 30789.1 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 1: General introduction and designation system (GB/T 30789.1-2015, ISO 4628-1:2003, IDT)
GB/T 30789.2 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 2: Assessment of degree of blistering (GB/T 30789.2-2014, ISO 4628-2:2003, IDT)
GB/T 30789.3 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 3: Assessment of degree of rusting (GB/T 30789.3-2014, ISO 4628-3:2003, IDT)
GB/T 30789.4 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 4: Assessment of degree of cracking (GB/T 30789.4-2015, ISO 4628-4:2003, IDT)
GB/T 30789.5
Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 5: Assessment of degree of flaking (GB/T 30789.5-2015, ISO 4628-5:2003, IDT)
GB/T 30789.8 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 8: Assessment of degree of delamination and corrosion around a scribe or other artificial defect (GB/T 30789.8-2015, ISO 4628-8:2003, IDT)
ISO 3574 Cold-reduced carbon steel sheet of commercial and drawing qualities
ISO 4623-2:2016 Paints and varnishes - Determination of resistance to filiform corrosion - Part 2: Aluminium substrates
ISO 8993 Anodizing of aluminium and its alloys - Rating system for the evaluation of pitting corrosion - Chart method
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 10123 and the following apply.
3.1
reference material
material with known test performance
3.2
reference specimen
portion of the reference material (3.1) that is to be exposed with the intention to check the reproducibility and repeatability of the test results for the test cabinet in use
3.3
test specimen
specific portion of the samples upon which the testing is to be performed
3.4
substitute specimen
specimen made of inert materials (such as plastic or glass) used for the substitute of a test specimen (3.3)
4 Principle
4.1 The neutral salt spray (NSS) test is the test method in which a neutral 5% sodium chloride solution is atomized under a controlled environment.
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4.2 The acetic acid salt spray (AASS) test is the test method in which an acidified 5% sodium chloride solution with the addition of glacial acetic acid is atomized under a controlled environment.
4.3 The copper-accelerated acetic acid salt spray (CASS) test is the test method in which an acidified 5% sodium chloride solution with the addition of copper chloride and glacial acetic acid is atomized under a controlled environment.
5 Test solutions
5.1 Preparation of the sodium chloride solution
5.1.1 Dissolve a sufficient mass of sodium chloride in distilled or deionized water with a conductivity not higher than 20μS/cm at 25℃±2℃ to produce a concentration of 50g/L±5g/L. The sodium chloride concentration of the sprayed solution collected shall be 50g/L±5g/L. The specific gravity range for the solution prepared is 1.029 to 1.036 at 25℃.
5.1.2 The sodium chloride shall not contain a mass fraction of the heavy metals copper (Cu), nickel (Ni) and lead (Pb) in total more than 0.005%. It shall not contain a mass fraction of sodium iodide more than 0.1% and a mass fraction of total impurities more than 0.5%, calculated for dry salt.
Note: Sodium chloride with anti-caking agents can act as corrosion inhibitors or accelerators.
5.2 pH adjustment
5.2.1 pH of the sodium chloride solution
Adjust the pH of the sodium chloride solution to the desired value on the basis of the pH of the sprayed solution collected.
5.2.2 Neutral salt spray (NSS) test
Adjust the pH of the test solution (5.1) so that the pH of the sprayed solution collected within the test cabinet (6.2) is 6.5 to 7.2 at 25℃±2℃. Check the pH using electrometric measurement. Measurements of pH shall be done using electrodes suitable for measuring in weakly buffered sodium chloride solutions (in deionized water). Make any necessary pH corrections by adding hydrochloric acid, sodium hydroxide or sodium bicarbonate solution of analytical grade.
Note: Possible changes in pH can result from loss of carbon dioxide in the solution when it is sprayed. Such changes can be avoided by reducing the carbon dioxide content of the solution by, for example, heating it to a temperature above 35℃ before it is placed in the apparatus, or by making the solution using freshly boiled water.
5.2.3 Acetic acid salt spray (AASS) test
Add an appropriate amount of glacial acetic acid (CH3COOH) to the sodium chloride solution (5.1) to ensure that the pH of samples of sprayed solution collected in the test cabinet (6.2) is between 3.1 and 3.3 at 25℃±2℃. If the pH of the solution initially prepared is 3.0 to 3.1, the pH of the sprayed solution collected is likely to be within the specified limits. Check the pH using electrometric measurement. Measurements of pH shall be done using electrodes suitable for measuring in weakly buffered sodium chloride solutions (in deionized water). Make any necessary pH corrections by adding glacial acetic acid (CH3COOH), sodium hydroxide (NaOH), or sodium bicarbonate (NaHCO3) solution of analytical grade.
5.2.4 Copper-accelerated acetic acid salt spray (CASS) test
Dissolve a sufficient mass of copper chloride dihydrate (CuCl2·2H2O) in the salt solution (5.1) to produce a concentration of 0.26g/L±0.02g/L [equivalent to 0.205g±0.015g of anhydrous copper chloride (CuCl2) per litre]. Adjust the pH using the procedures described in 5.2.3.
5.3 Filtration
If necessary, filter the solution before placing it in the reservoir of the apparatus, to remove any solid matter which might block the apertures of the spraying device.
6 Apparatus
6.1 Component protection
6.1.1 All components in contact with the spray or the test solution shall be made of materials resistant to corrosion and which do not influence the corrosivity of the solutions.
6.1.2 The supports for the test specimen shall be constructed such that different substrate types do not influence each other. It shall also be constructed so that the supports themselves do not influence the test specimens.
6.2 Spray cabinet
6.2.1 The cabinet shall be such that the conditions of homogeneity and distribution of the spray are met. Due to the limited capacity of cabinets smaller than 0.4m3, the effect of the loading of the cabinet on the distribution of the spray and temperature shall be carefully considered. The solution shall not be sprayed directly onto test specimens but rather spread throughout the cabinet so that it falls naturally down to them. The upper parts of the cabinet shall be designed so that drops of sprayed solution formed on its surface do not fall on the test specimens being tested.
6.2.2 The size and shape of the cabinet shall be such that the collection rate of solution in the cabinet is within the limits measured as specified in 10.3.
6.2.3 Preference shall be given to apparatus that has a means for properly dealing with exhaust and drain for environmental conservation.
Note: A schematic diagram of one possible design of spray cabinet is shown in Annex C (see Figures C.1 and C.2).
6.3 Heater and temperature control
An appropriate system maintains the cabinet and its contents at the temperature specified in 10.1. The temperature shall be measured at least 100mm from cabinet walls and heat sources.
6.4 Spraying device
6.4.1 The spraying device comprises a supply of compressed air, a reservoir to contain the salt solution, and one or more atomizers.
6.4.2 The compressed air supplied to the atomizers shall be passed through a filter to remove all traces of oil or solid matter, and the atomizing pressure shall be controlled at an overpressure of 70kPa to 170kPa. The pressure is typically 98kPa±10kPa but can vary depending on the type of cabinet and atomizer used.
6.4.3 In order to prevent the evaporation of water from the sprayed droplets (aerosol), the air shall be humidified before entering the atomizer by passing through a suitable humidifier. The humidified air shall be saturated such that the concentration of the fallout solution falls within the specifications of 5.1. The humidified air shall also be heated such that when mixed with the sodium chloride solution, there is no significant disturbance of the temperature in the cabinet. The appropriate temperature depends on the pressure used and on the type of atomizer nozzle. Temperature, pressure or humidification, or a combination thereof, shall be adjusted so that the rate of collection of the spray in the cabinet and the concentration of the collected spray are kept within the specified limits in 10.3. A commonly used humidifier is the saturation tower, where temperature and pressure are controllable. Table 1 gives guiding values on temperature for the saturation tower under different atomizing pressures.
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Table 1 Guiding values for the temperature of the water in the saturation tower
Atomizing overpressure
kPa Guiding values for the temperature, in ℃, of the hot water in the saturation tower when performing the different salt spray test
Neutral salt spray (NSS) test Acetic acid salt spray (AASS) test Copper-accelerated acetic acid salt spray (CASS) test
70 45 45 61
84 46 46 63
98 48 48 64
112 49 49 66
126 50 50 67
140 52 52 69
160 53 53 70
170 54 54 71
6.4.4 The atomizers shall be made of inert material. Baffles may be used to prevent direct impact of the spray on the test specimens, and the use of adjustable baffles is helpful in obtaining uniform distribution of the spray within the cabinet. For this purpose, a dispersion tower equipped with an atomizer may also be helpful.
6.4.5 The sodium chloride solution supplied to the nozzle shall be kept stable to ensure a continuous and uniform fall out as described in 10.3. A stable level of spraying can be achieved by either controlling the level of sodium chloride solution in the reservoir or restricting the flow of sodium chloride solution to the nozzle such that a continuous spray is achieved.
6.4.6 Distilled or deionized water with a conductivity not higher than 20μS/cm at 25℃±2℃ shall be used for humidification of spray air.
6.5 Collecting devices
At least two collecting devices shall be used to check the homogeneity of the spraying of the cabinet. Suitable funnels shall be made of glass or other inert materials, with the stems inserted into graduated containers and have a diameter of 100mm, which corresponds to a collecting area of approximately 80cm2. The collecting devices shall be placed in the zone of the cabinet where the test specimens are placed, one close to an inlet of spray and one remote from an inlet. They shall be placed so that only mist, and not liquid falling from specimens or from parts of the cabinet, is collected.
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6.6 Re-use
If the cabinet has been used once for an AASS or CASS test, or has been used for any other purpose with a solution differing from that specified for the NSS test, it shall not be used for the NSS test until a thorough cleaning procedure has been completed and the pH of collected solution has been verified by the method in 5.2.2 and the corrosivity of the cabinet verified by the method in Clause 7 to not be significantly affected by previous tests.
Note: It is very difficult to clean a cabinet sufficiently that was once used for AASS or CASS testing so that it can be used for an NSS test.
7 Method for evaluating cabinet corrosivity
7.1 General
7.1.1 To check the reproducibility and repeatability of the test results for one piece of apparatus, or for similar items of apparatus in different laboratories, it is necessary to verify the apparatus at regular intervals as described in 7.2 to 7.4.
Note: During permanent operation, a reasonable time period between two checks of the corrosivity of the cabinet is generally considered to be 3 months.
7.1.2 To determine the corrosivity of the tests, reference specimens made of steel shall be used.
7.1.3 As a complement to the reference specimens made of steel, high-purity zinc reference specimens may also be exposed in the tests in order to determine the corrosivity against this metal as described in Annex D.
7.2 Reference specimens
7.2.1 To verify the apparatus, use at least four reference specimens of 1.0mm±0.2mm thickness and 150mm×70mm of CR4-grade cold-rolled carbon steel plates in accordance with ISO 3574 with an essentially faultless surface, i.e., free from pores, scratches and any light coloration (arithmetical mean deviation of the roughness profile Ra=0.8μm±0.3μm). Cut these reference specimens from cold-rolled plates or strips.
Note: See Annex G for the approximate comparison between standard grades of steel reference specimens in this document and others adopted at home and abroad.
7.2.2 Clean the reference specimens carefully, immediately prior to testing. Besides the specifications given in 8.2 and 8.3, cleaning shall eliminate all those traces (dirt, oil or other foreign matter) that can influence the test results.
7.2.3 Thoroughly clean the reference specimens with an appropriate organic solvent (such as a hydrocarbon with a boiling point between 60℃ and 120℃) using a clean soft brush or soft cloth, non-woven lint free cloth, that does not leave any remains or an ultrasonic cleaning device. Carry out the cleaning in a vessel full of solvent. After cleaning, rinse the reference specimens with fresh solvent an d then dry them.
7.2.4 Determine the mass of the reference specimens to ±1mg. Protect the back face of the reference specimens with a removable coating, for example, an adhesive plastic film. The edges of the reference specimens may be protected by the adhesive tape as well.
Foreword I
Introduction IV
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Test solutions
6 Apparatus
7 Method for evaluating cabinet corrosivity
8 Test specimens
9 Arrangement of the test specimens
10 Test conditions
11 Period of tests
12 Treatment of test specimens after test
13 Evaluation of results
14 Test report
Annex A (Informative) Comparison between this document and ISO 9227:2017 in clause/subclause number
Annex B (Informative) Technical differences between this document and ISO 9227:2017 and their causes
Annex C (Informative) Schematic diagram of one possible design of spray cabinet with means for optional testing for exhaust and drain
Annex D (Informative) Complementary method for evaluating cabinet corrosivity using zinc reference specimens
Annex E (Nominative) Preparation of specimens with organic coatings for testing
Annex F (Nominative) Required supplementary information for testing test specimens with organic coatings
Annex G (Informative) Supplementary information for the grades of steel reference specimens
Bibliography
