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pitting and corrosion on interior of FV

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  • pitting and corrosion on interior of FV

    I have recently taken on a role at a brewery in South East Asia. The brewery is now 13 years old and for several years has had issues with oxidized and souring beer. Who would want to take on this challenge, I hear you say? Well they made me an offer I couldn't refuse. When I arrived I immediately noticed issues with sanitation and inefficient processes throughout. Poor and worn-out equipment. The owners of the brewery are very wealthy but have neglected the running of the site for several years and for some reason the staff have been reluctant to ask for items to be replaced where necessary.
    I've spent several weeks now improving recipes, replacing items and have ordered DO meter, QC analysis laboratory equipment, new pumps, hoses etc. Yesterday, one of the tanks started leaking from the lower exterior jacket beside the outlet valve which I immediately expected was a hole in the glycol jacket but the liquid coming out appears to be dirty water which is confusing.
    On inspecting the interior of the tank, I was horrified to see the pitting and corrosion evident on the outlet valve and tank walls (this is after CIP). I've already suggested replacing three of the tanks but now I think I'm going to recommend ripping out ALL the tanks and starting again. Thoughts?
    Click image for larger version

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  • #2
    A few possibilities,
    If the corrosion is generalised, the tanks are made of poor quality stainless steel, and has not been passivated properly at start of use, and then maintained in good condition, or
    it may be due to excessive strength chlorine in chlorinated caustic, and/or at excessively high temperature, and/or pH below 11, (i.e. lack of NaOH, due to lack of initial material, or much of it being converted to the bicarbonate or carbonate ion resulting in low pH), or
    If the corrosion is only at the welds, then poor quality welding, such a not full depth weld penetration and poor joins between weld sections, quite possibly without using suitable inert gas (as would appear to be the situation shown in your photo), or
    if the corrosion is limited to the lower section of the cone only, then this could be due to use of hypochlorite solution as the terminal sterilant (I have experienced this a a couple of breweries, the worst where the vessels were flat bottomed)

    So, what to do?
    If the pitting is all over the inner surface of the tank, then I think you are right, the best option would be to replace the entire tank(s)
    If the pitting is only at the bottom (as per example photo), or most severe at the bottom where there is no insulation and or cladding, you may be able to get the connections cut out and rewelded.
    If the pitting is also primarily at the welds, on tank wall joins, cooling panel welds then again, you are almost certainly best of scrapping the old tanks and getting new ones.
    You should gently pressure test the cooling jackets. Unfortunately, the pressure you could apply will be highly dependent on jacket design and material thickness but a couple of psi should be enough to leak test even the simplest parallel panels (no dimples / bridging to strengthen). If the jackets are leaking inside or outside, realistically it is safer to replace the whole tank.

    If you need to replace, I suggest you also consider the current design and what it does well (if anything) and what, apart from the corrosion, it does less well/badly and ensure the new tanks will meet all your perceive requirements. An easier sell if you can explain that new tanks will also allow you to do "x" & "y", important for the brewery / beers rather than simply saying the existing ones need replacing.

    I am sure others will add to the list of suggestions