Surface Finish of WFI (or high purity water) tanks and Piping

[andy_oohhh]

It seems like every plant has a different standard for surface finish. I would like to come up with some reasoning on why we use one surface finish over another. ASME BPE states surface finishes from SF1 to SF6. If I have a WFI tank or piping, how do I know which one is optimal? What do I look for in other systems to find the optimal surface finish?

I am not sure if this is the right way to think of it but lets say you to stop biofilm formation which is caused by the build up of bacteria. The size of bacteria is 1μm (39μin) to 5μm (197μin). So I see why you would want a surface below/smaller than 1μm (39μin) which SF1-SF6 would work. So if this is my goal would any SF1 to SF6 work? So anything with a finer/smaller surface finish would be wasted effort? Are there any other factors in to play here?

Thank you and appreciate any help on this!

 

[EdStainless]

Typically WFI systems are either 15uin mechanical pol or 10uin EP.
I have never seen anything rougher used in high purity.
It has to do with cleanability.
There is no way to prevent bacteria.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed