Ask the Expert Question-and-Answer Archive

by Ron Joseph

Inorganic Zinc Silicate

Q. We want to coat the outside of steel pipe, which has inside oil at 400 degree celsius with "Inorganic zinc silicate" 50-70 mic, the paint is than coverd with thermal insulation. The pipe is located at agricultural area. Do you think that is a good paint for protecting the steel pipe from corrosion?

A. A zinc-rich inorganic silicate primer is suitable for coating the external surface of a pipe especially if it is buried under the soil, or in this case will be exposed to 400 deg C. However, you must insure that the pipe is properly abrasive blast cleaned. You should not apply the coating to smooth pipe or a surface that has not got a blast profile. The zinc must come into direct contact with the virgin steel. If you apply it over rust or scale you will loose the benefit of the coating and there is a possibility that the zinc will fall off over a period of time.

Typically, you should use an abrasive that will yield a profile of 1.5-2.5 mils (38-62 microns) . The primer must cover all the high spots on the blast profile; therefore you might want to apply 3-5 mils (75-125 microns) of the zinc-rich primer.

This is not an easy coating to apply, and I suggest you find a contractor who has experience with this product.

Regards,

Ron Joseph