Salt spray testing

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Salt spray testing

One of the most important things with any restoration is to provide adequate rust protection. One of our current projects is a full restoration on a 1966 Volvo P1800S. In order to test the different methods Castleman and the owner of the car, Ove Ericsson; commissioned some salt spray tests. The tests were undertaken by GKN Autostructures in accordance with ASTM B117.

Salt spray testing is performed by placing samples in a test chamber designed in accordance with ASTM B117 and operated in accordance with the specified conditions in ASTM B117.

The test solution to be sprayed is prepared by dissolving pure sodium chloride into pure water, in a ratio of 5% sodium chloride to 95% water, by weight. The purity for each should be as specified in ASTM B117. At the time the samples are placed into the test chamber, it should be pre-conditioned to the operating temperature of 35˚C and producing fall-out at the specified rate. The salt fog fall-out rate is verified by using a minimum of two 80cm2 funnels per salt spray atomiser, each inserted into a measuring cylinder graduated in ml. These collectors are located inside the chamber, nominally at the same height as the test samples, one located close to the atomiser and one located away from the atomiser, in accordance with the positions specified in ASTM B117, but also taking into account the chamber manufacturers defined work-space.

This test can be used to test the relative resistance to corrosion of coated and uncoated metallic specimens, when exposed to a salt spray climate at an elevated temperature.

The appearance of corrosion products (oxides – commonly referred to as white rust & red rust) is evaluated after a period of time. Test duration depends on the corrosion resistance of the coating; generally, the more corrosion resistant the coating is, the longer the period of testing before the appearance of oxides.

Prior to the appearance of white rust the approximate test duration should be c.350hrs and for red rust to appear the approximate test duration should be c.1000hrs.

The principle application of the salt spray test is therefore to enable relatively quick comparisons to be made between actual and expected corrosion resistance in terms of the time taken for oxides to appear on the samples under test. This is compared to expectations, to determine whether the test is passed or failed.

In our test, we used two panels for each treatment method. One was ‘unmarked’ and the other was ‘marked’ with a cross.

So which corrosion test performed the best? If you would like to know the results or even see them for yourself, please call us and we will be happy to discuss this with you.