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  1. mcguire

    Stress relief of 302 C.R. stainless steel, 0.004" thick

    You may do better getting the strip stretcher leveled to eliminate residual stress. Michael McGuire
  2. mcguire

    Stainless alternatives to 42CrMo4

    There is a wealth of candidates, 431 and 17-4Ph will certainly work. Cold drawn 304 0r 301 will do wonderfully if the shape permits. Michael McGuire
  3. mcguire

    Chloride corrosion

    It's hard to imagine a product more prone to defects than seamless duplex tubing. Welded and fully annealed is far preferable. Michael McGuire
  4. mcguire

    50 hour salt spray test on Stainless Steel

    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...
  5. mcguire

    heat transfer improvments

    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...
  6. mcguire

    heat transfer improvments

    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
  7. mcguire

    heat transfer improvments

    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...
  8. mcguire

    increased condensation/evaporation rates

    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
  9. mcguire

    increased condensation/evaporation rates

    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...
  10. mcguire

    increased condensation/evaporation rates

    Ed Thanks for your observation. Perhaps we could discuss this. I think I can reach you through Plymouth Tube, yes? Michael McGuire
  11. mcguire

    increased condensation/evaporation rates

    On a well-selected stainless steel or titanium, there wouldn't be any deterioration. Michael McGuire
  12. mcguire

    increased condensation/evaporation rates

    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...
  13. mcguire

    Why do Mo and N help the pitting resistance of stainless steel?

    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
  14. mcguire

    Why do Mo and N help the pitting resistance of stainless steel?

    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...
  15. mcguire

    passivation of PH13-8MO

    EdStainless Can I reach you via Plymouth Tube? Mike McGuire Michael McGuire
  16. mcguire

    passivation of PH13-8MO

    Passivate AFTER! Disrupting the surface by blasting is similar to sanding. It decreases corrosion resistance gained from acid pickling. Follow EdStainless recommendations. Michael McGuire
  17. mcguire

    surface texture

    Does anyone know of a surface texture which can be obtained for stainless steel to increase heat transfer in condensing heat exchangers? Michael McGuire
  18. mcguire

    400 series stainless steel welds strengthing over time

    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
  19. mcguire

    Yield strength vs Collapse pressure

    Check the concentricity. It has the same influence as yield strength. Michael McGuire
  20. mcguire

    Why NICKLE is not taken into consideration in PREN(Pitting resistance equivalent number)

    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

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