Coating / Painting

Your main enemy is oils left on the surface from manufacture. Those could be removed with just a degreaser and a power wash. Personally, if I had nice stainless steel piping, I wouldn't paint it at all.

I once did a study on adhesive bonding corrosion resistant steel for an aerospace project I was working on at the time.

We cleaned all specimens with methyl ethyl ketone followed by isopropyl alcohol wipes before and after mechanical abrasion. We tried various grades of sand paper, glass beading, soda blasting, steel wool and wire brushing.

The samples were all identical lap shear test specimens made per the applicable ASTM documents and tested on an Instron™ pull tester.

While I don't remember the numbers, (I was working on the Space Shuttle so give me a break) the wire brush abraded samples pulled significantly higher numbers that any other process, much to our surprise.

Good luck.

SS surface is best activated by oxidizing with Nitric acid. Nitric acid, being both a strong acid for dissolving metals, and a powerful oxidizing agent, is ideal for oxidizing (or passivating) the surface of stainless steel. The best passivation of stainless steel is attained by removal of all exogenous materials and free iron and iron oxides from the surface, then chromium enriching the surface layer so that it can be oxidized in the air to form a good chromium oxide layer (the passive layer). Complete passivation means to control oxidize the nickel in the surface - this you do with a strong oxidizing agent like Nitric Acid . Sometimes a dichromate is added for some alloys - for more info go to ASTM and/or the Metal Finishing Guidebook.

What type of insulation? The surface preparation of the Stainless Steel is dependent upon the type of insulation that is going to be put on it. For example it is common practice to paint the SS if fiber glass insulation is to be put on it. This is reauired because there are trace amounts of Chlorine in the fiberglass that will attack the SS. This would not be suitablefor other types of insulation.

Generally coating/painting is not required for ss lines unless otherwise mentioned.

A layer of aluminium foil to be wrapped over ss line before insulation.

Stainless Steel normally does not require any coating. But if it is to be insulated it is necessary to prevent chlorides from many of the insulating materials from seeping on to the surface under moist conditions which will cause corrosion.

I believe one can clean up the surface of S.S. with organic cleaning liquids available for the purpose in the market to remove all oil / greese and carry out pickling with 10-20% nitric acid to remove the black oxide stains on welds and other places. Then use Aluminium foil as vapor barrier before insulation. Stick tapes at the overlaps. This prevents contact between SS surface and chorides. The cover sheeting of insulation should be sealed at the joints using sealing compounds / cements to minimize moisture ingress.

Hi Guest,

Polished stainless steel must be "blasted" (sand or other aggregates). Dustproofed and ready to painting with 2-pack epoxy/polyamide primer. I have no experience with ordinary, unpolished surfaces.

I can and why not, must appreciate some contribution about unpolished SS, Gil.