Without doubt the Neutral Salt Spray test is the most commonly used and quoted test reference for zinc based coatings. Whilst it is difficult to make absolute comparisons between NSS hours and actual service conditions, NSS provides a good guide to performance. The test method has proved very useful for allowing the relative performance of specific coatings to be repeatedly and consistently measured and directly compared. Both cosmetic failure and base metal corrosion are measured in terms of hour of endurance in the NSS test. Exposure of the test parts to other environments and chemicals such as petrol, break fluids or heating prior to NSS testing, can also be a useful tool in measuring coating performance.
The test standard environment (ASTM B-117) is a stable 35 degree (C) chamber through which a 5% neutral salt spray fog is pumped. This corrosive fog will dissolve metal coatings like zinc, as well as finding defects and pores though which to attack the underlying substrate.
Simulating a severe marine environment, NSS is used worldwide to benchmark coatings and determine their relative performances. |
