There are three distinct test method in ISO the neutral salt spray (NSS), the acetic acid salt spray (AASS), and copper-accelerated acetic. ISO NSS. adv. auto technology banner. A discussion started in but continuing through Q. We have a customer, that we supply some zinc. The salt spray (or salt fog) test is a standardized and popular corrosion test method, used to Other important relevant standards are ISO, JIS Z and ASTM G The most common test for steel based materials is the Neutral Salt Spray test (often abbreviated to NSS) which reflects the fact that this type of test.
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The salt spray or salt fog test is a standardized and popular corrosion test method, used to check corrosion resistance of materials and surface coatings.
Usually, the materials to be tested are metallic although stone, ceramics, and polymers may also be tested and finished with a surface coating which is intended to provide a degree of corrosion protection to the underlying metal. Salt spray testing is an accelerated corrosion test that produces a corrosive attack to coated samples in order to evaluate mostly comparatively the suitability of the coating iao use as a protective finish.
The appearance of corrosion products rust or other oxides is evaluated after a pre-determined period of time. The salt spray test is one of the most widespread and long established corrosion tests.
ASTM B was the first internationally recognized salt spray standard, originally published in Salt spray testing is popular because it is relatively inexpensive, quick, well standardized, and reasonably repeatable.
Although there may be a weak correlation 92227 the duration in salt spray test and the expected life of a coating in certain coatings such as hot dip galvanized steelthis test has gained worldwide popularity due to low cost and quick results.
Most Salt Spray Chambers today are being used NOT to predict the corrosion resistance of a coating, but to maintain coating processes such as pre-treatment and painting, electroplating, galvanizing, and the like, on a comparative basis.
Failure to meet this requirement implies instability in the chemical process of the pre-treatment, or nsx paint quality, which must be addressed immediately, so that the upcoming batches are of the desired quality. The longer the accelerated corrosion test, the longer the process remains out of control, and larger is the loss in the form of non-conforming batches.
The principle application of the salt spray test is therefore enabling quick comparisons to be made between actual and expected corrosion resistance. Most commonly, the time taken for oxides to appear on the samples under test is compared to expectations, to determine whether the test is passed or failed.
For this reason the salt spray test is most often deployed in a quality audit role, where, for example, it can be used to check the effectiveness of a production process, such as the surface coating of a metallic part. The salt spray test has little application in predicting how materials or surface coatings will resist corrosion in the real-world, because it does 99227 create, replicate or accelerate real-world corrosive conditions.
Cyclic corrosion testing is better suited to this. This produces a corrosive environment of dense salt water fog also referred to as a mist or spray in the chamber, so that test samples exposed to this environment are subjected to severely corrosive conditions.
Chamber volumes vary from supplier to supplier. If there is a minimum volume required by a particular salt spray test standard, this will be clearly stated and should be complied with. There is a general historical consensus that larger chambers can provide a more homogeneous testing environment. Variations to the salt spray test solutions depend upon the materials to be tested. The most common test for steel based materials is the Neutral Salt Spray test often abbreviated to NSS which reflects the fact that this type of test solution is prepared to a neutral pH of 6.
Results are represented generally as testing hours in NSS without appearance of corrosion products e. Synthetic seawater solutions are also commonly specified by some companies and standards. Other test solutions have other chemicals added including acetic acid often abbreviated to ASS and acetic acid with copper chloride often abbreviated to CASS each one chosen for the evaluation of decorative coatings, such as electroplated copper-nickel-chromium, electroplated copper-nickel or anodized aluminum.
These acidified test solutions generally have a pH of 3. ASTM does not address this issue, but ISO does not recommend it and if it is to be done, advocates a thorough cleaning.
Although the majority of salt spray tests are continuous, i. Such tests are commonly referred to as modified salt spray tests.
ASTM G85 is an example of a test standard which contains several modified salt spray tests which are variations to the basic salt spray test.
ASTM G85 is the most popular global test standard covering modified salt spray tests. This acceleration arises through the use of chemically altered salt spray solutions, often combined with other test climates and in most cases, the relatively rapid cycling of these test climates over 927. Although popular in certain industries, modified salt spray testing has in many cases been superseded by Cyclic corrosion testing CCT The type of environmental test chambers used for modified salt spray testing to ASTM G85 are generally similar to the chambers isp for testing to ASTM Bbut will often have some additional features, such as an automatic climate nsz control system.
ASTM G85 annex A1 — Acetic Acid Salt Spray Test non-cyclic This test can be used to determine the relative resistance to corrosion of decorative chromium plating on steel and zinc nws die casting when exposed to an acetic acid salt spray climate at an elevated temperature. This test is also referred to as an ASS test. Test specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of salt jso solution, prepared in accordance with the requirements of the test standard and acidified to nws 3.
This spray is set to fall-out on to the specimens at a rate of 1. This climate is maintained under constant steady state conditions. The test duration is variable. This test can be used to test the relative resistance to corrosion of aluminium alloys when exposed to a changing climate of acetic nsa salt spray, followed by air drying, followed by uso humidity, all at an elevated temperature.
Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises the following 3 part repeating cycle. This is followed by 2. This is followed by 3. The number of cycle repeats and therefore the test duration is variable. This test can be used to test the relative resistance to corrosion of coated or uncoated aluminium alloys and other metals, when exposed to a changing climate of acidified synthetic seawater spray, followed by a high humidity, both at an elevated temperature.
Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises the following 2 part repeating cycle. Test specimens are placed in an enclosed chamber, and exposed to 1 of 2 possible changing climate cycles. In either case, the exposure to salt spray may sns salt water spray or synthetic sea water prepared in accordance with the requirements of the test standard.
The most appropriate test cycle and spray solutions are to be agreed between parties. The first climate cycle comprises a continuous indirect spray of neutral pH 6. Nxs second climate cycle comprises 0. This is followed by 0.
This test can be used to test the relative resistance to corrosion paints on steelwhen exposed to a changing climate of dilute salt spray at ambient temperature, followed by air drying at and elevated temperature.
This is followed by 1. These standards describe the necessary information to carry out this test; testing parameters such as temperature, air pressure of the sprayed solution, preparation of the spraying solution, concentration, pHetc. Daily checking of testing parameters is necessary to show compliance with the standards, so records shall be maintained accordingly. Testing cabinets are manufactured according to the specified requirements here. However, these testing standards neither provide information of testing periods for the coatings to be evaluated, nor the appearance of corrosion products in form of salts.
Requirements are agreed between customer and manufacturer. In the automotive industry requirements are specified under material specifications. 92227 coatings have different behavior in salt spray test and consequently, test duration will differ from one type of coating to another.
For example, a typical electroplated zinc and yellow passivated steel part nsx 96 hours in salt spray test without white rust. Electroplated zinc-nickel steel parts can last more than hours in NSS test without red rust or 48 hours in CASS test without red rust Requirements are established in test duration hours and coatings shall comply with minimum testing periods.
Hot-dip galvanizing produces zinc carbonates when exposed to a natural environment, thus protecting the coating metal and reducing the corrosion rate.
The zinc carbonates are not produced when a hot-dip galvanized specimen is exposed ixo a salt spray fog, therefore this testing method does not give an accurate measurement of corrosion protection. ISO gives the guidelines for proper measurement of corrosion resistance for hot-dip galvanized specimens. Painted surfaces with an underlying hot-dip galvanized coating can be mss according to this method.