Surface Finish, Polish
and Passivation

U-Tube Heat Exchangers For

Surface Finish, Polish and Passivation
U-Tube Duty

Roughness is a cleaning specification. A rough surface holds soil in valleys that cleaning solution flows over rather than through, and gives biofilm somewhere to anchor.

Ra is the arithmetic average deviation of the surface profile, measured in microinches. Lower is smoother. On sanitary work, 32 Ra on product contact and 40 Ra on exterior surfaces are the numbers most specifications settle on.

Mechanical polishing. Progressive abrasive work to a target roughness. It is economical and effective, and it can smear metal over small defects and occasionally embed abrasive particles.

Below 32 Ra, Consistency Beats the Number. Cleanability improves as roughness falls, and the returns diminish. Below about 32 Ra the practical benefit comes more from uniformity and freedom from defects than from a lower average.

A surface at 20 Ra with a scratch, a fold or a patch of heat tint is worse in service than a consistent 32 Ra surface with none of those. Specify what will be verified and verify it.