[81Pantah]

Hello, I am using a piece of equipment at our lab that is made of 316 SS. We use this machine to disrupt cells as part of a research program. We prime this "high-pressure emulsifier" with 0.9% normal saline and then switch to our emulsion ingredients. Following production, we then clean the machine with water-for-injection (WFI) and then store it filled with 99% isopropyl.

We are finding "rouging" (the reddish color) on our wetted parts. From what I can tell, this seems to be coming from either the saline, or the fact that the WFI has CO2 in it. These are brief parts of the process, however. It sits in the lab filled with 99% isopropyl for weeks.

Anyone have any insight into what may be causing this phenomenon? We had JUST had the machine's wetted surfaces resurfaced, so we were hoping to be all set. It's back.

Many thanks from a new member,

Ryan

[Arkcon]

You're correct, 316 stainless should be more resistant than other stainless.  However, all bets may be off in the presence of halides.  And you're not absolutely clear -- what is a good di rinse?  How much, for how long, how many changes and ... most important ...is it always followed.  I have to assume, resurfaced means electropolished?  Because that's the usual answer to this problem.  Here's a fairly good reference:  http://www.corrosionlab.com/Failure-Analysis-Studies/rouging.htm

[Enthalpy]

It's unexpected to me, since Aisi 316 is designed and used successfully in the Ocean, and CO₂ isn't harmful to it. Maybe your corrosion criteria are more stringent than in general engineering.

Since chloride ions are the enemy of stainless steel, I wouldn't rinse the items with water-for-injection but with deionized water. IPA must be fine, but you might try to store the item in the air and soak it in IPA prior to use.

Whatever the reasons, one way to help stainless steel resist corrosion is to anodize it, provided your application allows it.

[Enthalpy]

Do you have some means to check whether the material really is Aisi 316?

Or could the colour be a deposited layer instead, one that resists water and IPA? A copper layer for instance isn't washed away so easily.