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-10-In a series of weathering tests conducted by the Railway Technical Research Institute of Japan, 86 different paint systems were exposed to the sea and compared in terms of durability and film thickness. (Fig. 6) The Test results revealed that films of 250 microns or more in thickness performed adequately for a much longer time than films that were less thick. We may, therefore, conclude that paint applications in highly corrosive environments require a film thickness of more than 250 microns.According to the study of R. P. Pierce, the probability of finding some defects in paint film depends on the film thickness (Fig. 7).The paint film shows good durability when applied over 5 mils (125 microns) thick.White metal blast cleaningNear-White Metal Blast CleaningCommercial Blast CleaningBrush-Off Blast CleaningPower Tool CleaningHand Tool CleaningSP 5SP 10 (95% Min.) SP 6SP 7SP 3SP 2Sa 3Sa 2 1/2Sa 2Sa 1St 3St 2With PictorialStandardsFirst (100%) Second (95% Min.) Third (80% Min.)Percentage ofRemoved RustNo. 1No. 2No. 3No. 4Sh 3, Sd 3Sh 2, Sd 2Sh 1, Sd 1Pt 3With PictorialStandardsWith Detailed Work Conditions and ProceduresRemarks*1 Steel Structures Painting Council*2 International Standard ISO 8501-1:2007, and Svensk Standard SIS 05 5900-1967*3 British Standard*4 National Association of Corrosion Engineers*5 The Shipbuilding Research Association of Japan Standard for The Preparation of Steel Surface Prior to PaintingISO and SIS *2BS 4232*3NACE*4JSRA*5SPSSSSPC*1Table 5 Comparison of the Specifications of Surface TreatmentFig. 7 Relationship between Film Thickness and Probability of Defects on Freshly Painted FilmSpot rustBlistersConditions before rusting and blistering,,108642100110203040234567200300400Exposure time before defects appear (year)Average film thickness (micron)[Report of Japan National Railway Technical Research InstituteNo. 1070 (1978) Mar.]Fig. 6 Relationship between Film Thickness and Durability of Film when Weathered on SeaFilm thickness (mil)Probability of defects[R. P. Pierce, Corrosion 8 [5] 178 (1952)]

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