Type 201 can be more stable than 304 if made with sufficiently high Mn and N content. And, again, with high enough Cr and N, it will have rough equivalence in corrosion resistance. The savings are minimal, however.
Too bad about the requirement for non-magnetism, 439 would pass the corrosion...
Davefitz
Thanks very much again. There was a lot of work done from 1980 to 2000, which used three principles:
1. Attaching fine particles to surfaces to increase area exposed and render flow more turbulent. These would be expected to foul.
2 Lining with a low surface energy material, such a...
Thanks, Davefitz
Ill try to look that up. we have seen a enhanced resistance to impurity pick-up, but I see the logic in what you cite. We have found cavity size to have a critical upper limit, so if I can find the original Union Carbide patent, I'll post the comparison.
Michael McGuire
I'm a materials guy who has made thousands of tons of stainless steel for pipe and tube. My question is, would there be value in a micro surface finish on heat exchanger surfaces (one that does alter dimensions or change traditional surface appearance; not a coating) which causes low surface...
While the low surface energy technology is real and very good, it doesn't appear that there is a welcome mat out for change in this industry. We'll just stick to non-soiling building exteriors.
Michael McGuire
Well, that's exactly what I would like to do but we make steel, not heat exchangers. We need at least a tube making partner.
By the way, internal surface area enhancement IS helpful, as is making the flow turbulent (although it may be that already), but this effect is much larger, as much as a...
I'm a materials guy who has made thousands of tons of stainless steel for pipe and tube. My question is, would there be value in a micro surface finish on heat exchanger surfaces (one that does alter dimensions or change traditional surface appearance; not a coating) which causes low surface...
It shouldn't be a surprise that aging helps. Acid passivation removes iron from the surface whereas air passivation leaves iron in situ until diffusion of Cr into the passive film can do more slowly what the acid does quickly. Good observation in any event.
Michael McGuire
The passive film is a semi-conductor about 20 Angstrom thick. In very well passivated or electropolished stainless, it is a P-type semi-conductor. This means the current, in particular the corrosion current, must be carried by the very slow substitutional diffusion of cations, e.g. Fe. In air...
Passivate AFTER! Disrupting the surface by blasting is similar to sanding. It decreases corrosion resistance gained from acid pickling. Follow EdStainless recommendations.
Michael McGuire
Does anyone know of a surface texture which can be obtained for stainless steel to increase heat transfer in condensing heat exchangers?
Michael McGuire
The only logical explanation is the delayed stabilization in that nitrogen and hydrogen are the only species which are mobile at that temperature.
Michael McGuire
I don't disagree with your facts. However, crack tip electrochemical reactions generate an extremely high partial pressure of hydrogen in a very localized zone, i.e. the crack tip. Hence the destabilization of the balanced triaxial tension.
Michael McGuire
