Interpretation of ISO 9227: An Authoritative Guide to Corrosion Tests in Artificial Atmospheres

In the fields of industrial manufacturing, material research and development, and international trade, the corrosion resistance of materials and surface protective coatings is one of the core indicators to measure product reliability and durability. Harsh conditions such as marine environments, industrially polluted atmospheres, and humid salt spray can easily lead to rusting of metal materials, peeling of coatings, and further cause product failure, potential safety hazards, and economic losses. To unify the global technical specifications for salt spray corrosion tests and provide scientific, comparable, and repeatable testing methods, the International Organization for Standardization (ISO) has formulated and continuously updated the ISO 9227 standard — “Corrosion Tests in Artificial Atmospheres — Salt Spray Tests”, which has become an authoritative guideline widely followed by global manufacturing enterprises, testing institutions, and scientific research units.

аз. Core Positioning and Development Iteration of ISO 9227 Стандартен

ISO 9227 is an internationally accepted recommendatory standard, formulated and maintained by ISO/TC 156 (Technical Committee on Corrosion of Metals and Alloys). Its core purpose is to accelerate the evaluation of the corrosion resistance of metal materials, metal coatings, chemical conversion films, anodic oxide films, and organic protective coatings by simulating an artificial corrosive environment containing salt spray, providing objective and accurate data support for product design, process optimization, quality control, service life prediction, and international trade compliance.
Since its release, ISO 9227 has undergone multiple iterations and updates, always keeping pace with the development of material science and the actual needs of the industry:
•Early versions: Laid the basic framework for salt spray tests and clarified the core processes and parameters of the Neutral Salt Spray (NSS) тест;
•ISO 9227:2006: Replaced the old version, optimized the requirements for test equipment and details of solution preparation, and improved the repeatability of test results;
•ISO 9227:2012: Implemented briefly and then withdrawn, further refining the requirements for test environment control;
•ISO 9227:2017: Improved the parameter specifications for different types of salt spray tests, expanded the scope of application of the standard, and adapted to the testing needs of more new types of protective coatings;
•ISO 9227:2022: The current valid version, replacing the 2017 version. It focuses on optimizing the accuracy of test equipment, the precision of solution preparation, the controllability of the test process, and the standardization of result evaluation, further improving the reliability and international comparability of test data, and being more in line with the high-quality development needs of modern manufacturing industry.

II. Core Scope of Application of ISO 9227

ISO 9227 specifically applies to salt spray corrosion tests of various metals and metal surface protective coatings, covering but not limited to the following objects:
•Metals and alloy materials: Such as various basic metal materials including steel, алуминий, мед, цинк, magnesium and their alloys;
•Metal surface coatings: Such as various electroplated, chemical-plated and hot-dipped coatings including electrogalvanizing, hot-dip galvanizing, chrome plating, nickel plating, tin plating, и т.н.;
•Chemical conversion films: Such as chemical treatment layers used for metal protection including phosphating films, passivation films, blackening films, и т.н.;
•Anodic oxide films: Protective oxide layers formed on metal surfaces through anodic oxidation process;
•Organic protective coatings: Such as organic coatings used for metal surface protection including painting, electrophoretic coating, powder coating, и т.н. (Supplementary implementation in conjunction with special coating standards is required).
It should be noted that ISO 9227 only applies to salt spray-based artificial atmosphere corrosion tests, and does not include other types of artificial atmosphere corrosion tests such as hydrogen sulfide and sulfur dioxide tests; в същото време, this standard is a test method standard, not a product qualification judgment standard. Test results need to be judged for qualification in conjunction with special standards for specific products (such as ISO 10289 for automotive parts and IEC 60068-2-11 for electronic components).

III. Detailed Explanation of the Core Technical Content of ISO 9227

The core content of ISO 9227:2022 covers the entire process of salt spray tests, formulating strict specifications for test types, equipment requirements, solution preparation, sample handling, test operation, and result evaluation to ensure the standardization of the test process and the reliability of test results.
(аз) 3 Core Test Types and Parameters
The standard clearly specifies 3 commonly used salt spray test types. The appropriate test method can be selected according to the actual application environment of the product. The core parameters are shown in the following table:

Test Type	English Abbreviation	Simulated Environment	Salt Solution Specification	pH Value Range	Test Temperature	Salt Spray Deposition
Neutral Salt Spray Test	NSS	Marine climate, low salt concentration natural environment	5%±1% (mass concentration) sodium chloride aqueous solution	6.5~7.2	35±2℃	1.0~2.0 mL/(h·80cm²)
Acetic Acid Salt Spray Test	AASS	Acidic marine environment, mild industrially polluted atmosphere	5%±1% sodium chloride aqueous solution + acetic acid	3.1~3.3	35±2℃	1.0~2.0 mL/(h·80cm²)
Copper-Accelerated Acetic Acid Salt Spray Test	CASS	Harsh environment with high corrosion rate (such as coastal industrial areas)	5%±1% sodium chloride aqueous solution + acetic acid + copper chloride	3.1~3.3	50±2℃	1.0~2.0 mL/(h·80cm²)

Сред тях, the Neutral Salt Spray (NSS) test is the most widely used, suitable for the basic corrosion resistance evaluation of most conventional metals and protective coatings; the Copper-Accelerated Acetic Acid Salt Spray (CASS) test has the fastest corrosion rate, which can be used for rapid screening of high-performance protective coatings or evaluating the durability of products in harsh corrosive environments.
(II) Core Requirements for Test Equipment
The accuracy of salt spray tests is highly dependent on equipment performance. ISO 9227:2022 has formulated strict specifications for various indicators of test equipment. The core equipment is the salt spray test chamber, and the supporting equipment includes solution preparation devices, air compression systems, temperature and humidity sensors, и т.н. The specific requirements are as follows:
•Salt spray test chamber: It shall have good airtightness, the temperature fluctuation inside the chamber shall not exceed ±2℃, and the temperature difference in different areas shall not exceed 3℃; the inner wall material shall be resistant to salt spray corrosion (such as polyvinyl chloride, неръждаема стомана) to avoid self-corrosion affecting the test results;
•Spray system: Equipped with a special sprayer to ensure fine and uniform salt spray and stable spray pressure; a solution filtration system (filtration accuracy ≤5μm) shall be set to prevent impurities from clogging the nozzle;
•Temperature control: Equipped with accurate heating devices and temperature sensors to stably maintain the required test temperature without obvious temperature fluctuation;
•Collection device: At least 2 collectors shall be placed inside the chamber, evenly distributed around the samples, to ensure that the salt spray deposition meets the standard requirements;
•Auxiliary system: The air compression system shall ensure that the air is free of oil and pollution; the solution preparation device shall have accurate weighing and stirring functions to ensure uniform solution concentration.
(III) Specifications for Test Solution Preparation
The purity, concentration, and pH value of the test solution are key factors affecting the test results. ISO 9227:2022 has made clear regulations on this:
•Solvent: Deionized water or distilled water with conductivity ≤25μS/cm shall be used to avoid impurities in the water interfering with the corrosion process;
•Solute: Sodium chloride shall be of chemical pure grade (NaCl content ≥99.5%), free of anti-caking agents (such as ferrous compounds) to prevent impurities from affecting the corrosiveness of the salt spray;
•Concentration control: The mass concentration of the sodium chloride aqueous solution is 5%±1%. During preparation, the solute and solvent shall be accurately weighed and fully stirred until completely dissolved;
•pH value adjustment: Adjust the pH value according to the test type — hydrochloric acid or sodium hydroxide is used for NSS test, and acetic acid is used for AASS and CASS tests; after adjustment, it shall be left standing for a period of time to ensure the pH value is stable;
•Usage requirements: The prepared solution shall be used within 24 hours to avoid changes in concentration or pH value due to long-term storage.
(IV) Complete Test Process and Operation Points
ISO 9227:2022 stipulates that the salt spray test shall follow the complete process of “sample preparation — equipment commissioning — test implementation — sample post-processing — result evaluation”. Each link shall strictly comply with the specifications, and the specific operation points are as follows:
1. Sample Preparation
The samples shall be representative, and their size and quantity shall meet the standard requirements; the surface of the samples shall be free of oil stains, scratches, scale, rust and other defects, and the treatment method shall be consistent with the actual production process of the product (such as natural cooling and curing process after electroplating and painting); for coating samples that need to evaluate the corrosion resistance of scratch areas, single cuts or cross scratches of specified sizes shall be made according to standard requirements until reaching the substrate; after sample preparation, the samples shall be placed in an environment with (23±2)℃ and relative humidity (50±5)% for at least 2 hours to ensure the sample state is stable.
2. Equipment Commissioning
Преди теста, check whether the airtightness, spray system, and temperature control system of the salt spray test chamber are normal; calibrate the temperature sensor and salt spray collector to ensure accurate parameters; inject the prepared test solution into the solution tank, adjust the spray pressure, temperature and other parameters, and put the samples into the chamber after the equipment runs stably (parameters reach the specified range and maintain for more than 30 минути).
3. Test Implementation
Place the samples on the bracket inside the test chamber at the specified angle: flat samples shall form 15°~30° with the vertical direction, and samples with complex shapes shall ensure that the key surfaces can be evenly covered by salt spray; the distance between samples shall be ≥20mm, and they shall not contact each other or the chamber wall to avoid corrosion products dripping and contaminating other samples; continuous spray shall be maintained during the test without arbitrary interruption; if it is necessary to observe the samples, the opening time of the chamber shall not exceed 10 minutes each time, and the interrupted test time shall be made up; the test cycle shall be flexibly set according to product requirements, ranging from several hours to several months (common cycles are 24h, 48ч, 96ч, 240ч).
4. Sample Post-Processing
After the test, take out the samples, gently rinse them with room temperature flowing deionized water for 5 minutes to remove residual salt deposits on the surface, then dry them with clean compressed air or naturally at room temperature; after drying, place them in the specified environment for 0.5~1 hour before result evaluation to avoid corrosion products falling off and affecting the judgment.
5. Result Evaluation and Report
Result evaluation is mainly carried out through visual inspection, and microscopic assistance can be used if necessary; the evaluation content includes: whether defects such as rust, blistering, coating peeling, and coating cracking appear on the sample surface, measuring the area ratio of the corroded area, the width of corrosion spread at the scratch, и т.н.; the evaluation shall be quantitatively graded in conjunction with relevant product standards to clarify the corrosion resistance grade of the sample.
The test report shall detailedly record the following information: the standard number on which the test is based (such as ISO 9227:2022), test type, test parameters (temperature, salt solution concentration, pH стойност, test cycle, salt spray deposition), sample information (material, surface treatment method, размер), abnormal conditions during the test, sample post-processing method, evaluation results and grades, and photos of the samples before and after the test shall be attached if necessary to ensure the traceability and authority of the report.
IV. Practical Application Scenarios and Value of ISO 9227
As a globally accepted standard for salt spray corrosion tests, ISO 9227 is widely used in many industries and provides important support for industrial development. Its core application value is reflected in the following aspects:
(аз) Product Quality Control and Batch Consistency Verification
For manufacturing enterprises (such as automotive parts, electronic equipment, hardware products, building materials, и т.н.), ISO 9227 is the core basis for quality control before product delivery. By sampling samples from bulk products for salt spray tests, the quality stability of the product surface protective coating can be quickly verified, unqualified batches can be identified, and the risks of product failure, customer complaints, and recalls caused by substandard corrosion resistance can be avoided. Например, automotive parts enterprises can use this standard to test the corrosion resistance of galvanized parts and painted parts to ensure that the parts do not rust during the service life of the vehicle (especially in coastal areas) and ensure driving safety.
(II) An Important Tool for Material and Process R&д
Scientific research institutions and enterprise R&D departments can use the ISO 9227 standard to carry out the R&D and optimization of new metal materials, protective coatings, and surface treatment processes. By comparing the salt spray test results of samples with different materials and processes, the schemes with better corrosion resistance can be quickly screened out, shortening the R&D cycle and reducing R&D costs. Например, when developing new anti-corrosion coatings, the adhesion and corrosion resistance of the coating can be optimized by adjusting the coating formula and combining with the salt spray test results to meet the use requirements of high-end products.
(III) A Passport for International Trade and Compliance Certification
In international trade, the ISO 9227 standard has become a globally recognized criterion for testing corrosion resistance. Export enterprises need to carry out tests in accordance with this standard and provide test reports that meet the requirements to meet the market access requirements of importing countries and improve the international competitiveness of products. Например, when China’s hardware products and electronic components are exported to Europe, America, Southeast Asia and other regions, importers usually require ISO 9227 salt spray test reports to verify whether the corrosion resistance of the products meets local standards.
(IV) Product Failure Analysis and Liability Determination
When products have failure problems such as rust and coating peeling during use, retrospective tests can be carried out in accordance with the ISO 9227 standard to analyze the failure causes (such as substandard protective coating quality, process defects, service environment exceeding expectations, и т.н.), providing scientific basis for product improvement and liability determination. Например, if the shell of electronic equipment has rust failure, the corrosion resistance of qualified products and failed products can be compared through salt spray tests to judge whether the failure is caused by quality defects in the production process.

V. Precautions for the Application of ISO 9227

To ensure the correct application of the ISO 9227 standard and avoid test result distortion caused by improper operation or misunderstanding, the following points shall be focused on:
•Clarify the test purpose and type: Select the appropriate test type according to the actual application environment of the product, and avoid blindly selecting tests with high corrosion rates (such as CASS test), which may lead to disconnection between the test results and the actual service conditions;
•Strictly control test conditions: Parameters such as temperature, salt solution concentration, pH стойност, and salt spray deposition shall strictly comply with the standard requirements. Any slight deviation may affect the accuracy and repeatability of test results;
•Standardize sample handling: The cleaning, scratch making, and pre-treatment environment of samples shall comply with the standards to avoid sample surface contamination or improper handling interfering with the corrosion process;
•Correctly interpret test results: ISO 9227 only provides test methods and does not specify qualification judgment standards. Grading shall be carried out in conjunction with special product standards; в същото време, the salt spray test is an accelerated corrosion test, and its results can be used to compare the relative corrosion resistance of different products, but cannot be directly equivalent to the actual service life of products in the natural environment;
•Pay attention to the timeliness of the standard: At present, ISO 9227:2022 is the current valid version. If customers or relevant specifications require the use of old versions of the standard (such as the 2017 version), it shall be clearly indicated in the test contract or report to avoid disputes;
•Regular equipment calibration: Salt spray test chambers, temperature sensors, salt spray collectors and other equipment shall be regularly calibrated to ensure that the equipment performance meets the standard requirements and the test data is traceable.

VI. Заключение

As an internationally authoritative standard for salt spray corrosion tests in artificial atmospheres, ISO 9227 has undergone multiple iterations and formed a set of scientific, rigorous, and complete test specifications, covering all links such as test types, equipment requirements, solution preparation, operation processes, and result evaluation, providing a unified technical benchmark for global material corrosion resistance testing. It is widely used in many industries such as automotive, electronics, хардуер, construction, and aerospace, playing an irreplaceable role in product quality control, Р&D innovation, and international trade compliance.
For enterprises, correctly understanding and strictly implementing the ISO 9227 standard can not only improve the corrosion resistance and market competitiveness of products, but also reduce the risk of product failure and establish a good brand reputation; for testing institutions and scientific research units, this standard is the core basis for carrying out professional testing and technical research, ensuring the scientificity, comparability, and authority of test data. In the future, with the continuous development of material science and manufacturing industry, the ISO 9227 standard will be continuously optimized to further adapt to the needs of new materials and complex application scenarios, providing more powerful support for the high-quality development of global industries.

Our product GA-2007-A Salt Spray Tester(200тип) meets this standard.

GA-2007-A Salt Spray Tester(200тип)

Design Standards:
ISO 9227,GB/T 2423.17-1993 ,GB/T 2423.18-2000,GB/T 10125-1997,ASTM.B117-97
JIS H8502 ,IEC68-2-11,IEC68-2-52 1996 ,GB.10587-89,CNS.4158,CNS.4159,CASS,GB/T
12967.3-91 CASS

Използвайте:
This machine has a standardized test method to check corrosion resistence of coated samples. Salt spray test is an accelerated corrosion test that produces a corrosive attack to the coated samples in order to predict its suitability in use as a protective finish. The appearance of corrosion products (оксиди) is evaluated after a period of time. Test duration depends on the corrosion resistance of the coating; the more corrosion resistant the coating is, the longer the period in testing without showing signs of corrosion. Different coatings have different behaviour in salt spray test and consequently, test duration will differ from one type of coating to another.

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