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COATINGSPRO MARCH 2016 29 coatings manufacturer's data sheets state that a fve- to seven-degree dew point spread is required to provide adequate protection against condensa- tion. However, NACE International and Society for Protective Coatings (SSPC) have a joint guideline (6A192/TR-3: Dehumidification and Temperature Control During Surface Preparation, Application, and Curing for Coatings/Linings of Steel Tanks, Vessels, and Other Enclosed Spaces) that clearly identifes a much safer range of dew point spread and maximum surface relative humidity (RH). It states, "Te typical minimum dew point difer- ential specifed for holding a blast over an extended period of time is 17–25° F with a relative humidity not to exceed 40–55 percent. It has been found that rust bloom accelerates if the surface RH exceeds 40–55 percent RH." So which is it? The Two Views Often the 5–7° F diferential range is intended to provide a sufcient dew point diference to avoid condensation, enough time to clean up and coat without experiencing condensation on the fresh coating, and to avoid fash rusting on freshly blasted surfaces. Te recommen- dation also includes the direction that the surface should not exceed 80 percent RH. However, this range does not allow for cool-weather changes, sudden down pour of rain, or long periods of holding the blast in order to accommodate the application of monolithic coatings. Specifying only a dew point spread is insufcient to ensure that you will meet the surface relative humidity specif- cation. Te risks are too great and an overnight rust-bloom is too costly. Te NACE 6A192/SSPC-TR-3 speci- fcation for the use of dehumidifcation and other climate control equipment, Dif ference Between Dew Point and Sur face Temperature 5° F (-15° C) 10° F (-12.2° C) 15° F (-9.4° C) 20° F (-6.7° C) 25° F (-3.9° C) 30° F (-1.1° C) 35° F (1.7° C) Approximate RH at the Sur face 82–86% 74–80% 54–62% 43–51% 34–42% 27–35% 19–26% Table 1. Dew Point Differentials and Surface RH Specifying Success Inspect Any Metal Surface Coating For pipes, tanks or any coated contoured surface in the fi eld or inside your manufacturing facility, we simplify coating integrity testing with our full line of SPY ® portable and permanent Holiday Detectors. PORTABLE HOLIDAY DETECTOR IN-PLANT HOLIDAY DETECTOR SYSTEMS WET SPONGE PORTABLE HOLIDAY DETECTOR • Ergonomic design • Pipe coating inspections up to 60" • Extremely durable • Infi nite voltage setting on the fl y • No belts, lightweight, fast set-up • Sponge roller speeds large fl at surface area inspections • Interchangeable fl at or roller sponge • Custom designed to streamline manufacturing • From pipe coating inspections to large fl at surfaces PIPELINE INSPECTION COMPANY Ph: (713) 681-5837 Fax: (713) 681-4838 For more details on SPY ® products and our complete line of SPY ® Holiday Detection Equipment visit our website @ www.picltd.com A SPY for Ever y Mission Wr i te in Re ad e r In q u ir y #119