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James Weber of Sulzer Chemtech Tower Field Service on
November 17, 2011:
Typically, thermal spray coatings are cost-effective in the petrochemical industry when you consider the cost of inspection, especially under insulation.
Even the best, most expensive paints must be inspected in 3-7 year cycles when used in CUI (Corrosion Under Insulation) conditions. Inspections most often mean scaffolding, removing all cladding and insulation, intensive inspection, including a lot if UT testing of pits, blasting, painting, re-insulating, re-cladding, removing scaffolding, etc. If thermal spray aluminum (TSA) is used instead of paint, these inspection cycles are pushed out to 25 years (ExxonMobil) to 40 years (Shell).
In this case, blasting and recoating is not required, just inspection, as it is known that a properly installed anodic TSA coating system will not corrode or “sacrifice” itself unless it is installed in such a way that the TSA has to provide anodic protection for a large cathode (unfavorable anode to cathode ratio) when an electrolyte (water or wet insulation) connects the TSA to a non-TSA coated area. We don’t do this in the petrochemical field, as we coat an entire vessel, column, or pipe (flange to flange) instead of just a tiny area and expect it to protect the entire structure.
Regarding the cost of thermal spray in a refinery, one must consider the entire erected costs (scaffolding, cladding, insulation, grit blasting and disposal, etc.) of a coating job and not just “the coating.”
Around 6 years ago, ExxonMobil reported that when the entire erected costs are considered, TSA coatings cost them 0.5%-1.5% more than liquid coatings; however, some of the paints used in CUI service have doubled and tripled in price since then. Many times, thermal spray can be applied at lower costs than wet paint when you consider factors like weather conditions, no VOC regulations, ease of or less need for touch-up, robust coatings that can be applied offsite and then installed, etc. As a pipeline applicator who did both wet paint and thermal spray coating, we charged less for thermal spray than a three-coat paint system.
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