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Stenciling

We want to stencil information on corrugated stainless steel cladding installed on piping which will be exposed in a severe corrosive environment. Please advise if polyurethane can be applied directly to the stainless steel and will have a good service life if directly applied.

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Q. I am the Paint/Coatings/Insulation and Fireproofing inspector for my company. I need your advice on a project. We want to stencil information on corrugated stainless steel cladding installed on piping which will be exposed in a severe corrosive environment.

My suggestion to management is as follows: 1) Degrease the affected areas by solvent wiping. 2) Abrade the affected areas with non-carbon type sandpaper and remove dust, etc. 3) Apply epoxy mastic due to its adhesion properties, and 4) stencil with polyurethane. Please advise if polyurethane can be applied directly to the stainless steel and will have a good service life if directly applied. P.H.

 

A. The pretreatment, or surface preparation, is right for stainless steel. But, be careful during solvent wiping. Always use solvents in well ventilated areas. Use only OSHA-approved solvents. Change solvents and wipers frequently so you don’t re-contaminate the surface. The epoxy mastic is a good primer because, as you indicated, it has good adhesion to stainless steel. The polyurethane “stencil ink” should adhere to the epoxy and you are home free.

Please be advised that all polyurethanes are not created equal. There are many kinds of coatings called polyurethanes, single package, two-component, acrylic urethanes, epoxy urethanes, moisture- cured and so on. Some of these polyurethanes require a primer, others do not. Will your polyurethane adhere direct-to-metal on stainless steel? I can’t tell you without knowing the properties of your specific coating.

That question can be answered by reading the product data sheet, or by asking your paint sales rep. Some folks are afraid to ask questions, fearing they will look “dumb” to others. Don’t be afraid; ask! The sales rep is there to help you and will respect you for it. You will really look dumb if the paint fails in service. In fact, if the paint fails, you both lose. 

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