Chloramines & Stainless Corrosion

[Tubbybrew]

I was wondering if someone who has more metallurgy knowledge than me can chime in on this. We've recently seen corrosion inside one of our brite tanks above the level of the beer and when I brought this up to the manufacturer he claimed that it was caused by chlorine. We use the local municipal water source which treats the water with chloramines (not free chlorine). For the last six months total chlorine in the water ranged from 2.4-2.5 mg/L (according to the municipal reports)... none of it being "Free Chlorine". We also run all our water through an active carbon filter both brewing and rinse water. And use PBW/Ultra-Niter/Idophor as our tank treatment.

The tank is only 1 year old, could this possibly be corrosion from our water?

[gitchegumee]

No way.

My opinion is that this is in no way due to chlorine in the form of chloramines from water that has been filtered through an active carbon filter. Do you clean this tank with a hot chlorinated caustic cleaner? Halogen attack on stainless requires elevated temperatures. I have seen pitting in stainless from hot use of chlorinated caustic cleaners. And from butter! Saw a tank years ago that had been pitted from use as a butter melter. Was the tank made in China?

[Tubbybrew]

We've only ever used PBW as our "caustic" ... there is no chlorine in it. We clean the tank w/ 5-Star PBW at 150F, hot water rinse, run an acid rinse with Birko's Ultra-Niter at 140F, hot water rinse then sanitize with Idophor at 100F. No chlorine in any of those products.

The tank is US made w/ supposedly US steel. Although, the manufacturer does not make the top and bottom dishes themselves and I know the manway is chinese (Glacier Tanks).

I didn't believe the chlorine argument either... no way, not in 1 year of use but I also don't know what else would be causing it.

It has only appeared in the last 2 turns on the brite and it seems to be getting worse.

[dick murton]

......... hot water rinse then sanitize with Idophor at 100F. No chlorine in any of those products.

It's the iodine, especially as you are using it warm. Stop using it warm (i.e. ambient < 68F) at, from memory no more than 150 ppm and it probably won't get any worse. Better, stop using it altogether and re-passivate the steel with warm nitric acid, and use peracetic acid as a sterilant in future. Iodine is in the same period as chlorine - slightly less corrosive, but only slightly. I have seen plenty of stainless completely perforated by keeping in tackle soak baths using iodophors. For what it is worth, change all the sealing rubbers on this tank as well, as the iodine also destroys sealing gasket material over time.

[dick murton]

A small request. If you have any other photos showing corrosion in these tanks, please would you post them or send them to me in a PM. I am doing a training session in a few months time, and these examples would prove extremely useful.

Thanks

[Tubbybrew]

We've been using Idophor at the recommended dosing rate of 25ppm (per Five Star) for no rinse CIP tank circulation... this is strong enough to cause corrosion? Eack! I know lots of breweries who use Idophor ... how do they get away with it?

Dick -- shoot me a PM with your email address and I'll setup a dropbox with all the high-res photos we have.

[BrewinLou]

IOD4 is fine, just use it room temp or at municipal water temp and you are fine. Been using it for decade with no pitting of any type. With the contact time I have on my IOD4 it does not damage my gaskets any faster than they would wear out with water or beer only. If you do long term soaking, yes it will shorten the life of your gaskets.

[dick murton]

Room temp - yes, providing the contact time is not too long and strength is as per instructions. 100 deg F - no. But I still prefer PAA as you can generally get away without rinsing. No way would I use iodophors without rinsing - which then gives the problem of ensuring the rinse water is sterile.

Re photos - thanks. PM on its way.