Importance of surface finish in determining corrosion resistance
Importance of surface finish in determining corrosion resistance

Lack of knowledge in this area is a major cause of problems. Most specifiers and designers understand the importance of selecting a grade of stainless steel, for example 1.4301 (304) or 1.4401 (316). But surface finish is at least as important. The subject is fully explored in The Importance of Surface Finish in the Design of Stainless Steel.

Briefly, a bright polished surface gives maximum corrosion resistance.

A directional polish equivalent to the EN 10088-2 2K (Ra = 0.5 micron max), usually produced using silicon carbide (SiC) abrasives, will give adequate corrosion resistance in many severe environments notably heavy urban and coastal ones.

A common surface finish achieved with 240 grit alumina abrasives has been implicated in the corrosion of stainless steel in urban and coastal environments. In some cases, surface roughness Ra values have been measured at well above 1 micron which is known to be inadequate in these environments.

The lack of any specified surface finish on architectural drawings can be the source of the final problem.

If, at any stage of the supply chain, there is any doubt about the appropriate surface finish, specialist advice should be sought.

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