Airborne Salt Precipitation Rate and Estimated Concentration by the Dry Gauze and Wet Candle Method

Abstract

The dry gauze (DG) and wet candle (WC) methods are standards for analyzing airborne salt precipitation rate (ASPR), which is a major factor of corrosion for steel infrastructures. However, these methods often show different ASPRs. Because airborne salt was supplied mostly from one direction at the test site in this investigation, ASPR by DG and WC shows a good correlation. Accordingly, the airborne salt concentration based on ASPR with DG and WC methods within pipes to restrict the salt supplying to one direction also shows a good correlation. In addition, higher salt deposition was achieved with DG compared to WC. The local wind speed inside the pipe is low for DG, suggesting that the DG set-up attenuated the wind speed. Thus, the calculation of ASPR based only on DG and the ambient site wind speed far from sampling gauze result in an underestimation of the salt concentration even outside pipes. From the correlations, the equation between ASPR by DG and WC outside the pipes, and the equation between salt concentrations based on DG and WC inside the pipes were obtained. Using these equations, more reliable salt concentration can be calculated from ASPR by DG and the ambient wind speed.