×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Re- passivation 316L ss demi water loop
2

Re- passivation 316L ss demi water loop

Re- passivation 316L ss demi water loop

(OP)
Hello,

I have a question about passive layer in the pipeline of 316L ss ? I have a demi water loop (water velocity is over 1.1 m/s, conductivity is about 0.5 uS, temp. about 20 deg C). As I know the thickness of passive layer is about couple particles. Is that possible the water after some time breaks off (wash up) the layer ?

Is that recommended to make a repassivation the ss surface after some time ? If so, do you know some standard (i.e. ISO, ASTM etc.) that treats of ?

Thanks for your help.

Regards

RE: Re- passivation 316L ss demi water loop

2
Unless you have contaminated the surface with metallic debris, chemically depassivated (acid), or mechanically damaged the surface there is never any reason to re-passivate.  It will not wear out or wear off.
Flow velocities of 20m/s have been shown to have no impact on the corrosion potentials of SS.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Re- passivation 316L ss demi water loop

(OP)
Thank You for response.

You said "chemically depassivated (acid)", as I know, the demi water is in acid pH area (in my loop about 6.5)Anyway isn't an acid a passivated medium ?

One more thing: Have you got some paper about this flow velocities of 20 m/s not breaking of the passive layer ?

Kind Regards

RE: Re- passivation 316L ss demi water loop

There are papers where people have done electrochemistry with rotating electrodes to get the surface flow shear effect.

You passivate in an oxidizing acid,  There are low pH environments that will break down the passive layer either because they are reducing of very low pH (<3).

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Re- passivation 316L ss demi water loop

Hi, usually the SS is affected by high concentrations of chloride. Anyway, put a 1 micron filter in the loop and replace it when you have a drop of 5 psi. This will help with the erosion in the pipe (if any).
Additionally I would like to know the system volume and the amount of chloride.

Regards,

M. Arguelles
 

RE: Re- passivation 316L ss demi water loop

(OP)
Hi cobalt1983, thank you for your answer.

I can not add any filter in PW loop, after EDI there sould not be any additional filters.

Anyway, I will check the concentrations of chloride. The main problem in PW is not the erosion. I was just courious if there should be made re-passivation after some time.  

RE: Re- passivation 316L ss demi water loop

you can protect the SS with corrosion inhibitor  (water additive) like film forming amines

RE: Re- passivation 316L ss demi water loop

(OP)
@StewPad

Demi water means purified water without any additives. So I can not add any substance to purified water after EDI, inhibitors neighter.

Anyway, what influence do amines film have on bacterial growth ?  

Regards.

RE: Re- passivation 316L ss demi water loop

Well, you need something to balance you pH back - can you run your RO plant without acid? Or adding small amount of Alkalis to get pH > 6?

RE: Re- passivation 316L ss demi water loop

I would guess that the pH is below 7 because of dissolved CO2.
No big deal.

Yes you can get biological growth is a system like this. Unless your initial sterilization was very aggressive and you have some ongoing biological control. (UV or H2O2)

No, passivation never wears out.  Unless you work on the system (new parts), contaminate the system, or have a significant erosion issue there is no reason to ever re-passivate.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Re- passivation 316L ss demi water loop

DI water is not considered to be corrosive if the oxygen is removed from the water.

There would be little value in repassivation.

RE: Re- passivation 316L ss demi water loop

I know of 304L being used in flowing demin water (although flow rate not known) for many years without any problems - 316L would be more resistant to any localised attack.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources