Painting Stainless Steel

Question:

We have manufactured shipboard stainless steel ruggedised communications cabinets for a customer. The cabinets are fabricated using 2.0-mm 316-stainless steel sheet. The customer has requested the cabinets have an organic finish internally and externally. What is the appropriate pretreatment to coating stainless steel?

Our customer has requested passivating prior to coating; we believe the cabinets also require sandblasting to “rough up” the surface. We understand the concept of passivating. If sandblasting is the right option, would the process be, 1) sandblasting, 2) passivating and then coat? Also, would it be advisable to coat the cabinets within a short period of time following the pretreatments, to prevent any possible further contamination of the stainless steel? We have several cabinets to build and we want to get the process right. D.B.

Answer:

Stainless steel as with any other substrate must be free from oil, grease dirt and other surface contaminants before painting. Surface abrading will enhance adhesion of organic coatings. There have been a number of materials applied to passivate stainless steel over the years. One passivating material discussed recently was hydrofluoric acid. I don’t like to recommend HF because of its environmental and safety problems. One of the classic pretreatments is a phosphoric acid activated vinyl wash primer. Abrading the surface by hand sanding or blasting followed immediately or as soon as possible by application of the organic coating

The recommended procedure is: 1. Clean the stainless steel to remove, grease dirt and other surface contaminants. 2. Abrade the surface and remove loose particulates. 3. Apply the organic coating as soon as possible.