finishing.com -- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing

HomeFAQsBooksHelpWantedAdvertiseForum
topic 354

Passivation of stainless steel hypotubes

adv.   stellar solutions banner

(1996)

My company currently uses passivation on our hypotubes*. We use a 4 second rinse and a 20 minute bath in 20% nitric acid. The theory is that this will remove tramp metals, cutting oils and possibly leave a stable oxidized layer on the inner surface of the stainless steel hypo tube. We really are not sure if using the nitric acid is really doing anything.

What I would like to know is how effective is passivation, is there any standards dealing with the process, and why it is done.

If you can help me I would appreciate a reply

* -- a hypotube is made in the same manner as a hypodermic needle but it's used in a catheter, with saline being the only fluid in contact with the inner surface.

Martin Wight
- Canada


(1996)

You have explained passivation quite well, Martin, except with regard to "cutting oils" -- passivation is not a substitute for cleaning; rather the parts need to be well cleaned before passivation.

Yes, it works. However, quoting the ASM Metals Handbook, "In most natural environments, stainless steels will remain in a passive state . . . Change to an active state occurs only where chloride concentrations are high, as in seawater . . ." So, perhaps with saline solution it doesn't actually achieve much, but it is a very accepted and generally useful practice for the removal of tramp iron from the surface, and probably should be continued.

I would suggest that you get a copy of ASTM A380 [link is to the practice at TechStreet] . However, there probably are additional ASTM or other specs related specifically to your product line; for example, I know that there are specific specs for surgical implants (ASTM F86 [link by ed. to spec at TechStreet] , for example), so I presume that there probably are others that are applicable to you.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Q or A to THIS thread START a NEW THREADView This Week's HOT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2017 finishing.com     -    Privacy Policy
How Google uses data when you visit this site.