Corrosion Under Hot and Cold Insulation (CUI) is a typical Petro-Refinary Problem area of suffer. It has been noted in some paper that Zn based coating are prohibited for use under insulation. It is said that there are fair chance of reversal of polarity between Zn and Steel at around 70C-80C under wet insulation and in that case steel will be preferentially damaging than Zn. So it has been adviced to use non-metallic based coating. Q1. A discussion and opinion posting required in this regard Q2. Mention some nonmetallic based coating. regards D.Mitra

American Welding Society 19 Year Corrosion Tests AWS Tests Prove Superiority of Metallized Systems In 1974 the American Welding Society completed a 19 year study of corrosion protection afforded by wire metallized aluminium and zinc coatings applied to low carbon steel. Here is a summary of the results: Aluminium coatings 0.003 in to 0.007 in (0.08mm to 0.15mm) thick, both sealed and unsealed, gave complete base metal protection from corrosion for 19 years in sea water and in severe marine and industrial atmospheres. Unsealed zinc sprayed coatings required 0.012 in (0.30mm) minimum thickness to give complete protection in sea water for 19 years. In severe marine and industrial atmospheres 0.009 (0.23mm) of unsealed zinc or 0.003 in to 0.006 in (0.08mm to 0.15mm) of sealed zinc gave 19 years protection. In severe marine atmospheres, application of one coat of wash primer plus one or two coats of aluminium vinyl enhanced the appearance and extended the life of zinc coating at least 100%. National Thermospray, Inc. Ken Norris Pasadena, Texas.