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Stainless Steel Rouging Problem due to CIP/ SIP process

2004

Dear Sir,

We have few 316L electropolished vessels for pharma process, the problem we facing now is discolouring on the surface of vessels.

According to our passivation vendor that provides passivation services to get rid of these rusty stain ( ferride oxide )on vessels, this problem is unavoidable and is caused by rouging process where the Ultrapure water ( WFI grade ) and high temperature clean steam ( >120 °C ) breakdown the chromium protection layer during the routine CIP & SIP processes.

Is there any permanent way of solving this problem than the periodic expensive passivation, and another concern is will the frequent passivation make the already electroplished surface rougher. Am I right that the deposited chrome layer on the steel surface through electropolishing process should be much thicker than the passivation.

Appreciate your prompt reply.

BC HENG
Facility Engineer

Heng Bong Cheng
Pharmaceutical business - Jurong, Singapore

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The rouging you have may or may not affect the passivity of the metal. Your vendor is correct when he identified the cause to be the use of ultra pure water and heat. oxalic acid [affil links] does a good job removing the rouging however the metal needs to be repassivated afterward. You may want to concern yourself with the state of the passive layer more than the appearance of rouge. A detailed log of passivation testing and rouge identification will help you determine whether or not you need derouging and passivation as often as you perform it now.

Joseph Lockrem
- Indianapolis, Indiana, United States
2004

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Thanks Joseph, our vendor did checked the passivity of passive layer with rouging stains by passivation meter (or Oxylizer meter), and the reading in term of mV still within the passivated limit despite the invisible layer of stains (ferride oxide) formed on it during the surface swap with wipes.

Is there any other better ways of measuring the passivity of stainless steel and by increasing passivation duration, will this really help to improve the rouging problem ?

Heng Bong Cheng
- Singapore
2004

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First of two simultaneous responses --

The rouging is always a problem when you use hot WFI in the process. It is necessary to periodically remove the rouge and repassivate, since the passive layer is effectively destroyed in the rouging and derouging process. Without repassivation you will not have the quantity or depth of the chrome oxide layer to protect the surface, allowing faster formation of the rouge. The rouge layer has been known to harbor bio-burden.

Electropolishing is an excellent aid in preventing corrosion, but does not give a deeper chrome oxide layer. The ultimate in protection is to electropolish followed by the best citric passivation. This will give you the highest possible chrome oxide to iron oxide ratio.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2004

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Second of two simultaneous responses --

I only suggest you separate the problems of passivity and rouging. If the rouge is not posing a problem and the metal is passivated, then costly derouging and passivation would not be necessary as often. However, if the rouge is unacceptable, the only thing to do is derouge (I have good results with oxalic acid) and then repassivate.

Joseph Lockrem
- Indianapolis, Indiana, USA
2004

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Sounds as though you simply need to change to a more corrosion-resistant grade of stainless steel than ordinary 316L.

Seems to me that using a material that's not good enough for the job and then having repeatedly to clean up the consequences of the inadequate service performance, is a major time-wasting and money-wasting activity. Instead, use a grade of stainless steel that can handle the service conditions.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2004

What is the ideal concentration of oxalic acid for deroughing of the vessel.

Praveen Veeravelli
employee - Hyderabad, Andhra Pradesh, INDIA
December 14, 2010