Anti-corrosion performance certification of stainless steel products

The core content of the certification is

the anti-corrosion performance certification of stainless steel products focuses on the product's corrosion resistance in a salt spray environment. The core inspection is the following dimensions:

Salt spray test method Classification: According to the GB/T 10125-2021 standard, three salt spray corrosion test methods are specified. The neutral salt spray test (NSS) is the most commonly used basic test. It uses a 5% sodium chloride neutral solution with a pH of 6.5 to 7.2, and a test temperature of 35 degrees Celsius plus or minus 2 degrees Celsius. It is suitable for metals and their alloys, Electroplating layers, organic coatings, anodic oxide films, etc., simulating the marine atmosphere or general salt spray environment. The acetic acid salt spray test (AASS) adds glacial acetic acid to the salt solution to reduce the pH to 3.1 to 3.3. It is more corrosive than the NSS test. It is used to assess copper-nickel-chromium or nickel-chromium decorative coatings, and is also suitable for aluminum. Anodic oxide film. The copper accelerated acetic acid salt spray test (CASS) adds 0.02 percent of copper chloride to acetic acid salt spray. The pH value is 3.1 to 3.3. The corrosion rate is the fastest. It targets high corrosion resistance protective layers such as nickel and chromium coatings and precious metal coatings. Coating, simulating extreme sulfur-containing salt fog environments.

Test conditions and parameters: Salt spray test requires strict control of various parameters. The concentration of sodium chloride solution is 5 percent plus or minus 0.5 percent, and the relative density at 25 degrees Celsius ranges from 1.029 to 1.036. The total content of heavy metals such as copper, nickel, and lead in sodium chloride should be less than 0.05%. The pH value needs to be tested and adjusted regularly, and the pH value of neutral salt spray test is 6.5 to 7.2. The laboratory temperature is 35 degrees Celsius plus or minus 2 degrees Celsius, and the pressure air barrel temperature is 47 degrees Celsius plus or minus 1 degree Celsius. The settlement volume of salt mist is controlled at 1 to 2 milliliters per hour per 80 square centimeters, and the spray pressure is 98 kPa plus or minus 10 kPa.

Sample preparation and placement: Sample pretreatment needs to remove oil stains and fingerprints on the surface, wipe with absolute ethanol, and let stand for 2 hours to ensure that no impurities on the surface affect the test results. Place the specimen on a non-metallic support to avoid contact with the box or other specimen, and form an angle of 15 degrees to 30 degrees from the vertical to ensure that the salt spray evenly covers all surfaces. The edges of the test plates or test pieces may be protected, such as with tape or paraffin, and if such protection is agreed upon for corrosion testing, it shall be recorded in the test report.

Test cycle: The test cycle is determined according to product standards or through negotiation between the supply and demand parties. Common recommended cycles are 24 hours, 48 hours, 72 hours, 96 hours, 168 hours, 240 hours, 480 hours, 720 hours, 1000 hours, etc. General hardware parts are commonly tested for 48 hours in neutral salt spray, and the surface has no red rust. Galvanized bolts for automobile parts are often tested for 48 hours. Export products require 96 hours in neutral salt spray.

Protection rating and appearance rating: According to the GB/T 6461-2002 standard, it specifies the evaluation method of the corrosion status of test panels or test pieces covered by decorative and protective metal and inorganic coatings after exposure tests in a corrosive environment. The rating determination method is used to divide them into 11 grades based on the percentage of corrosion area. The protection rating indicates the ability of the coating to protect the base metal from corrosion, and the appearance rating depends on a variety of subjective factors.

The rating level and evaluation system

are based on the GB/T 6461-2002 standard and the protection rating is determined based on the percentage of corroded area, and are divided into 11 levels in total from 10 to 0. Level 10 is the best, requiring no defects and no corrosion at all; Level 9 is that the defect area does not exceed 0.1%, which is extremely slight corrosion; Level 8 is that the defect area is greater than 0.1% and does not exceed 0.25%, slight corrosion; Level 7 is that the defect area is greater than 0.25% and no more than 0.5%, slight corrosion; Level 6 is that the defect area is greater than 0.5% and no more than 1%, slight to moderate corrosion; Level 5 means that the defect area is greater than 1% and no more than 2.5%, which means that the defect area is greater than 2.5% and no more than 5%, which means that the defect area is greater than 2.5% and no more than 5%, which means that the corrosion is moderate to severe; Level 3 means that the defect area is greater than 5% and no more than 10%, which means that the corrosion is severe; Level 2 means that the defect area is greater than 10% and no more than 25%, which means that the defect area is greater than 25% and no more than 50%, which means that the corrosion is very severe; Level 0 means that the defect area is greater than 50%, which is extremely serious. Surfaces that do not have corrosion of the base metal are generally considered to be level 10.

Evaluation content of test results The

evaluation content of test results usually includes the following aspects: appearance after salt spray test; appearance after removal of surface corrosion products; number and distribution of corrosion defects, such as pitting, blistering, rust or organic coating The extent of corrosion spread at scratch, etc.; time when corrosion began to occur; quality change (weight loss method); microstructure change; changes in mechanical properties.

Certification process

Certification of the corrosion resistance of stainless steel products is usually divided into the following stages:

application and submission of materials: Select a third-party testing institution with CNAS and CMA qualifications, and submit the company's business license, product specifications, material composition descriptions, surface treatment process descriptions, product drawings and other information. The certification body conducts a preliminary compliance review of the application materials.

Product sampling inspection: The certification body appoints personnel to the production site or finished product warehouse to conduct sampling, and the samples will be sent to a qualified laboratory for testing. Test items include neutral salt spray test, acetic acid salt spray test or copper-accelerated acetic acid salt spray test, and the test cycle is determined based on the target level. The specimen must be placed at an angle of 15 degrees to 30 degrees from the vertical, and rated according to GB/T 6461-2002 after testing.

Rectification and review: If there are non-conformities in the test, the company needs to analyze the reasons (such as improper surface treatment process, insufficient coating thickness, material composition problems, etc.), and re-send samples for testing after rectification. Complete records and evidence must be maintained during the rectification process.

Certification decision and certification: After passing all tests, the certification body issues a formal test report, which clearly concludes that "complies with GB/T 10125-2021 salt spray test requirements" and "complies with GB/T 6461-2002 XX rating requirements", and is stamped with CNAS or CMA seal. The certification report is valid for a long time and requires re-certification when the product structure, materials or process changes.

Post-certification supervision (optional): Some certification bodies provide annual supervision and review services to confirm that products continue to meet certification requirements. Enterprises should establish an internal quality control mechanism and regularly conduct salt spray test and random inspections on raw materials and batch production products.

Certification value

guarantees long-term durability of products: Through scientific salt spray test rating certification, it ensures the long-term stable use of stainless steel products in specific corrosive environments. Products that pass the 96-hour neutral salt spray test can have significantly extended their service life in coastal high salt spray environments.

Meet market access requirements: In project bidding in outdoor hardware, sanitary ware, auto parts, offshore engineering equipment and other industries, salt spray test rating certification is the core access qualification and an important basis for reflecting the product's corrosion resistance.

Reduce after-sales maintenance costs: Certified anti-corrosion solutions can significantly reduce the repair and replacement costs caused by product corrosion and significantly improve customer satisfaction.

Improve export competitiveness: GB/T 10125-2021 is equivalent to ISO 9227:2017 international standard. Products certified by this standard have a high degree of recognition in the international market and are an effective technical certificate for entering overseas markets such as Europe, America, and Southeast Asia.

Standardize production and quality improvement: The certification process forces companies to establish a standardized surface treatment process system, including material selection, coating thickness control, coating construction and quality inspection, to improve the overall technical management level.