Rouging removal

[ivancakucica]

Hello group

I am facing one application which is new to me - de-rouging of equipment made of SS316L in pharmaceutical industry.

In the past our managers had contract with outsource associates who provided this service annually. For that purpose they used citric acid solution, since rouging was in the first phase i.e. easy removal and solubility of Fe oxide, hydroxide,...

I know for the fact that outsource company could determine correlation between surface area of the equipment that should to be treated and newly formed Cr-oxide layer that will be formed as re-passivation process took place.

Does anyone know about the matter?

With kind regards,
Ivan

 

[unclesyd]

I'm not sure exactly what your question is. There may be a way to tell how much of the surface has rouge but I'm not aware of any other that some lab procedures. They might have had an in line monitor that would give them a good idea how the system was performing.
The potential for formation of rouge is not well documented and some recent studies are painting a different picture of the SS surface in respect to corrosion and passivisation.

Here a couple of papers as well as information on material to remove rouge.

http://www.mecobiopharm.com/pdf/rouging_paper.pdf

http://www.force.dk/en/Header/Downl...aterials+and+Constructions/nacepaper07193.htm

http://www.ateco.ch/rouging_fachart...l_eco_friendliy_Diruneutra.pdf?ACMP=DMC-beleg

If you have any further questions please post.

 

[ivancakucica]

Hello unclesyd,

Thank you very much for fast reply. I will try to clarify the issue again:

. During one year period of equipment operation we have rouging formation, on some parts of equipment (mainly on PSG and WFI equipment), in form of "dust or fe-... layer" that can be easily wiped off

. To prevent that it goes in second phase (second rouging phase), we used to hire outsource company who will employ some of their chemicals (mainly based on citric acid) in order to remove that Fe-... layer

. Prior they initiated CIP procedure (if I may call it like that), based on surface area that would be treated (m2) and solution that was made (%), they could predict or guaranteed minimum 12 months period of work free of rouging.

. Not only that, but based on those two parameters, they could predict Cr-oxide layer thickness that would be formed after CIP procedure (once when re-passivation took place). That is, of course, as quantification of the process and prove that re-passivation took place.

So, my question was is there are some equations (known to forum members) that can correlate (m2) and (%) with Cr-oxide layer thickness

With kind regards,
Ivan

 

[unclesyd]

Check the first bulletin to see if this answers you question. It is for the removal of rouge and then backcalculation to the coverage and thickness.
As far as passivisation it is a time dependent process depending on the passivating agent.

http://www.derouging.com/documents/essay_65_r00_tb_000.pdf

http://www.derouging.com/documents/essay_65_r00_tb_000.pdf

http://www.mecobiopharm.com/pdf/rouging_paper.pdf

 

[ivancakucica]

Hello unclesyd

I read bulletins carefully. Unfortunately, they were close to the matter but didn't explain it. They cover mostly rouging forming, problems and potential risks.

But for my tomorrow application I will use citric acid in circulation.

What I need is someones experience regarding temperature, concentration and time of circulation.

Regards,
Ivan

 

[unclesyd]

You should be using a proprietary Citric Acid Formulation which would be Citric Acid plus additional additives like a wetting agent. rinse aid. and possibly a inhibitor. The supplier of such a product should have all the operating parameters for any type cleaning job.
The use of straight citric acid as you state needs close control. The operating parameters are normally determined based on the general conditions of the system to be cleaned.
It would be hard to give any instructions for cleaning with citric acid without seeing the condition of the system and layout. About The only thing I can recommend is to check around and find the limits for the acid. like the maximum recommended concentration. the maximum temperature, etc.