Materials Performance

OCT 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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38 OCTOBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 10 COATINGS & LININGS A Soluble salts left on the surface are a leading cause of premature coating failures. As such, all steps and materi- als used require scrutiny to prevent the potential addition of salts during the surface preparation and cleaning steps. Abrasives are critical for conditioning the surface to which a coating is applied, and their cleanliness helps achieve the specified surface requirements. A wealth of technically sound documentation exists showing that soluble salts left on a surface are a leading cause of coating failure. 1-8 To refine or confirm the cautionar y limit for chloride and sulfate soluble salt species on abrasives, commonly used com- mercial abrasives were tested , with the results documented by a NACE-certified Coating Inspector. Test Procedures The testing criteria limited work to commonly used abrasives that achieve a 0.050 to 0.076-mm (2 to 3-mil) profile on carbon steel (CS), and the abrasive blast hose pressure of 0.66 MPa (95 lb/in 2 ). A commercial compressor, a six-bag abrasive pot, and an abrasive nozzle were used for the test. Most of the abrasives used for this testing were of a 0.60/0.25 mm or 0.85/0.30 mm (30/60 or 20/50 mesh) blend. All CS panels used had previously been automated-wheel blasted with steel grit to remove mill scale and rust to establish con- sistent surfaces for each blast test and were then placed in sealed plastic bags with des- iccant packages. The steel grit had been tested prior to abrasive blasting to ensure compliance with SSPC AB-2. 9 Prior to blasting with the test abrasives: • All panels were tested for any resid- ual chloride, sulfate, and nitrate. Lev- els were found to be nondetectable in all cases (Figure 1). • Samples from the top and bottom of bags of the selected abrasives were tested for levels of chloride, sulfate, and nitrate to establish consistency within a lot or bag quantity (Figure 2). Each sampled material was used to abrasive-blast dedicated steel panels (Fig- ure 3), and cross-contamination was pre- vented by starting with a clean abrasive pot, with oil/water separators and air dry- ers, and cleared lines with each abrasive used . The ASTM D4285 10 standard test method for indicating oil or water in com- pressed air was performed prior to each test to ensure there was no cross-contami- nation from this potential source. Immediately thereafter, the blasted panels were tested for any transferred solu- ble chloride, sulfate, and nitrate anionic species. All the testing was conducted on the same day in the low-humidity environ- ment of Bakersfield, California. The results are shown in Table 1. Testing of both surfaces and materials w a s c o n d u c t e d w i t h t h e a c c u r a t e CHLOR*TEST 'CSN ' † field test kit (Figure 4), the test kit referenced in SSPC Guide 15. 11 Abrasive samples were prepared using the CHLOR*TEST 'A' † field kit, which fol- lows the standard for sample preparation Abrasives: Salt Contamination and Its Transfer Austin d A rri M on, Bay Area Coating Consultants, Bakersfield, California, USA † Trade name.

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