ECA has been researched and applied as an effective sterilant in medical and dental fields for some time and is now gaining popularity in the industrial field. Its corrosive effect on stainless steel is questioned and comments are requested from researchers.
The use of both ECA and Chlorine Dioxide to obtain effective "santitation" and prevention of biofilm build up is gaining popularity but both of these sterilants have brought with them corrosion of stainless steel surfaces, despite claims that they do not cause corrosion. This corrosion is often focused on welding HAZ (heat affected zones)
Are there any reported cases that you want to share please?
Hallo John
I thought this question came from you when I saw it. Although I do not have an answer for you, I can tell you from experience that in the presence of chlorine species (such as chlorine dioxide) stainless steels are not as good as is generally believed. This looks like an interesting research project. Best regards
Herman (ex Wits, now MMU, UK)
Good morning Herman, many thanks for your comments. We have seen so much damage to stainless steel plant by both sterilants. It would be a great help if a research project can be done on this topic. Sadly users are guided by some suppliers who sell them as a quick fix to an improved hygienic environment with out taking the life cycle damage of the equipment into consideration, despite speaking and publishing material on this subject for a number of years. As much of the damage occurs on the HAZ, good welding procedures are critical. to prevent damage in the first place, although this is not the only safeguard to corrosion. Best wishes, John.
Hi John,
I am currently working on providing an alternative to the 316 grade of austenitic steel bolts and tie rods which are used in GRP sectional tanks. You have rightly pointed out that though many manufacturers claim their excellent corrosion properties in chloride environments (very low chloride concentration) but from experience we have found cases wherein the tie rods have snapped and extensive pitting corrosion is found under the bolt heads (not noticed easily during tank inspections). There is another grade which you may have come across, the 316 L grade which provides resistance to grain boundary carbide precipitation during welding but again their effectiveness in real work environements is doubtful. Even though copper nickel alloys are corrosion resistant, the fact that it can be only work hardened can cause a strength loss in HAZ.
Using fluoroplastic coatings on steel can give resistance to corrosion to chloride environments and it is worth looking into the optimisation of the thickness of the coating to give the best mechanical and chemical properties. If there are any further developments in future, I will post my updates.
Thanks,
Sneha
Hi Sneha
Your work sounds very interesting. Is the lining suitable for food and beverage vessels; ie FDA approved?
We have seen many examples of MIC with the advent of poor water supplies. Have you seen this in your industry?
Thanks
John
Hi Sneha
To continue my comments to your reply, the coating you are investigating is something we have not come across before except on carbon steel vessels; solventless epoxy that is cleared for food and beverage, including water, systems.
We have researched and resolved most corrosion problems but with the need for hygienic conditions and prevention of biofilm formation, ECA and Chlorine dioxide solutions have come into their own in the last couple of years.
As mentioned above, incidents of MIC have become more and more frequent as the quality of water systems have deteriorated and become heavily infected, especially with ground and borehole water. Increases in dissolved salt content have aggravated this situation. A 15mm thick SS 316L plate was "eaten" up by the symbiotic effect of the aerobic and anaerobic bacteria that cause MIC. This and other legislative hygienic requirement in food and beverage industries is driving the use of these products but with known consequences of these chemicals on stainless steel.
To reduce SCC, we have also used Duplex stainless steel grades to fabricate vessels with some success.
If your coating works please let me know.
Thanks
John
Hi John,
Yes. Some of the grades are FDA approved. The main problem that we are facing is not with MIC but with chloride pitting in 316 even at very low concentrations. What grade of steel do you normally use in the brewery industry? What problems do you currently experience with the grades of steel that you use for the fermentation vessels?
Hi Sneha
We have used 304, 316 and Duplex more recently for vessels and piping.
We have had SCC from chlorides leached out from insulation especially with vessels operating at ambient and up to 100⁰C. Steam and condensate vessels and piping have also corroded from the insulation side.
Pitting corrosion from chlorine based sterilant over entire external SS vessels, heat-exchangers and piping have been experienced.
Pitting on SS piping in a volcanic zone has been experienced.
Crevice corrosion is seen on poor welds and SCC on HAZ where welding has been done on vessels and piping. SCC and MIC on spiral welded SS piping.
Effective welding and pickle and passivation of all surfaces have had their desired effect to reduce incidents of corrosion.
Standards have been set in the brewing industry to address the above; see the book I co-authored in Researchgate on “Hygiene in the Beverage Industry”. Since a proactive training on this subject has been rolled out there has been greater awareness and corrosion incidents have reduced after 30 years!
Thanks
John
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