Materials Performance

DEC 2014

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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48 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 BLOG latex preferred). System IV is a shop- primed system, sometimes topcoated in the shop. It comprises inorganic zinc (IOZ) primer and an acrylic latex appear- ance coat. A: I work in Southern California, where by regulation almost all coatings must contain <100 g/L VOCs. I am familiar with elastomeric acrylic systems containing zinc and <25 g/L VOCs. A: Have you considered a single- coat, water-borne IOZ silicate? Tere are problems, however: • Needs warm, dry air fow conditions to cure • Available only in a dull grey color • Not grafti-resistant • Difcult to apply (can only be sprayed) and requires careful inspection • Needs excellent surface preparation to white metal (actually, this is an advantage rather than a problem) This coating has excellent humidity, rain, and marine resistance. Properly applied, it will last for years. A: Tere are some new technologies that reduce VOCs well below the acceptable levels and cut down applica- tion and drying times, namely polysilox- anes and polyaspartics. Regarding the information I've gathered from Internet searches and talking with industry professionals around the world, I can say with conf i- dence that these generic coating ty pes are promising candidates to replace tradi- tional paints like epoxy or poly urethane. But be aware that these paints should be used with a suitable primer underneath (i.e., moisture cure zinc silicates or zinc epoxies). Inspecting for corrosion under insulation Q: Does anyone have experience inspecting corrosion under insulation (CUI)? We have quite a lot of piping covered by insulation, and we suspect that CUI is occurring. We are cutting holes in the insulation and conducting spot thickness measurements using ultrasonic testing. However, I think that's depending too much on luck. Please let me know if you have better ideas. Could you also share some information on the pulsed eddy current, which seems suitable for CUI inspection? I have heard that it gives too much false indication and is meaningless. A: Te most efective method is to remove the insulation and check the surface condition of the pipe. Te following methods are also available: profle radiography, neutron backscatter techniques, and real-time radiography. Continued f rom page 47

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