Re- passivation 316L ss demi water loop 2

[mickawa]

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

 

[EdStainless]

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.

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Plymouth Tube

 

[mickawa]

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

 

[EdStainless]

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).

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Plymouth Tube

 

[arguellesmanuel]

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

 

[mickawa]

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.

 

[StewPad]

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

 

[mickawa]

@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.

 

[StewPad]

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?

 

[EdStainless]

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.

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Plymouth Tube

 

[bimr]

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

There would be little value in repassivation.

 

[enmax]

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.