Precipitate/Film on HX coils in storage tank

[Chris S.]

I'm struggling through the learning curve on a new Tarm 60 with storage, and I'm hoping to get some feedback on a storage tank question.

As you can see below, my storage consists of a used 1,000 gallon stainless steel dairy tank. The STSS copper coil heat exchangers were to large to fit in the existing access hole, so I had a local machine shop cut a "man hole" to allow placement of the hx coils and allow a person to get in there to assemble and connect it all. I never really sealed up the access hole, so since we've had a warm week up here I thought I'd let the tank cool down and have a go at tightening up the various apertures.

When I pulled the lid off I noticed that there was a heavy scum on the surface of the water and some residue precipitate on the hx coils. I don't know if the tank was dirtier than I thought when we filled it, if there was lots of grime introduced during the plumbing of the hx coils or if this film is just impurities in our well water.

Regardless, do I drain the 1,000 gallons of 100+ F water, then wash/rinse the tank and start over or is this sort of residue normal? My gut feeling is that the grime on the hx coils might reduce the efficiency of heat transfer and I really ought to just clean it out now. Has anyone else looked inside their storage tanks? Am I being too anal?

thanks for your thoughts-

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[pybyr]

wish I could offer something, but I haven't finished building my tank yet-

but I sure want to know and learn from what you find out

BTW- nice job, all around!

seems like there are a lot of us in VT fooling with variations on these themes

I really wanted to try to use an old dairy tank like you are, but there was no way to shoehorn it down an old farm-house's cellar bulkhead entry

 

[sweetheat]

I think you need to adjust your PH, Tarm recommends 8.6, Mine is discolored and a little scummy looking but I guess that's OK. I will seal my 806 gallon STSS tank tomorrow an adjust my PH to 8.6 - sweetheat

 

[mysticfalcon]

VT Does seem to be the spot for the homemade storage thing. I feel like I should tour the state for ideas before starting with mine.

 

[Jersey Bill]

try skimming the stuff off the top. stuff that settles tot he bottom wont affect you. I would put some chlorine in there to make sure there aren't any bugs ready to populate when the water temperature comes up.

 

[steam man]

Makes me think that when I get my tank going I will put a couple of taps for a pump/filter set up and run it when the tank temp is down.

Mike

 

[pybyr]

try skimming the stuff off the top. stuff that settles tot he bottom wont affect you. I would put some chlorine in there to make sure there aren't any bugs ready to populate when the water temperature comes up.

yikes- while I would like to knock out and keep out any microbes who might want to take up residence in my tank, I'd never want anything as reactive as any compound of chlorine in my system!

 

[pybyr]

[quote author="Mysticfalcon" date="1224212450"]VT Does seem to be the spot for the homemade storage thing. I feel like I should tour the state for ideas before starting with mine.[/quote

the VT maple producers and their organziation do tours, at least on a county-by county basis, on planned "open house weekends" so that they can learn from each other

perhaps us wood/tank-heads should start to consider the same, although right now, all I'd have to show is an old farmhouse stone - walled cellar filled with a lot of reallly interesting, but scattered and not yet assembled, parts

 

[mysticfalcon]

Ive got a running non gasser boiler and a pile of lumber is as far as Ive gotten towards my plans of a pond liner storage tank.

 

[jebatty]

...need to adjust your PH, Tarm recommends 8.6.

Interesting ... Tarm told me 8.2. My rule of thumb advice to others is 8-9.

I too would not be overly concerned about what's on top, probably a bit of misc oils and light debris particles. More concerned if there are deposits on the hx coils, and the deposits increase over time, as those could/would decrease efficiency. How hard is your water?

 

[EricV]

What's the best way to adjust the PH? A pool kit?

 

[jebatty]

Maybe for testing, but not adjusting pH. Pool chemicals are different than boiler chemicals (some people swim in pools). There are lots of posts on boiler chemicals, some different thoughts, also commercial suppliers. Search the forums, try Google too.

 

[Chris S.]

thanks everyone- since no one threw up any major warning flags I'm going to leave it as is, monitor pH and make sure it doesn't get worse.

I'm proud Vermont has such good representation in gassification/storage realm- leading the way one system at a time!

 

[Chris S.]

Maybe for testing, but not adjusting pH. Pool chemicals are different than boiler chemicals (some people swim in pools). There are lots of posts on boiler chemicals, some different thoughts, also commercial suppliers. Search the forums, try Google too.

please correct me if I'm wrong, but if my storage tank water is not getting pumped anywhere, then I should be OK to use pool chemicals to adjust, right? I basically have a big hot tub, with the heat exchange coils taking heat in and out, but the actual water doesn't ever leave the tank. Do the stainless steel tank walls and copper hx coils dictate different chemicals? If I was pumping the water through the boilers water jacket I'd be more concerned, but since it was just the storage tank I was hoping to keep it simple. have Somewhere I picked up 8.0 to 8.5 as the desired pH range for my tank- I'm guessing it was the Tarm folks.

 

[peakbagger]

If you are worried about bilogical contamination and using chemicals, a UV system will kill all the bugs with no chemicals (but it will cost you the power to run the bulb). I dont think it has to be on continuous.

 

[jebatty]

...please correct me if I’m wrong...

Can't tell you if you're wrong, because I don't know, but do the research on recommended boiler chemicals and reason your way through - make your decision.

 

[sweetheat]

from the tarm storage tank installation guide. Check PH (acid content) once a year. Bring PH to 8.2 to 8.6 Add 2 lbs of natural baking soda to 600 to 1200 gallons of tank water as a precaution. Check water level of tank once a year. Check PH again. Water containing electrolytes, salt or dissolved electrical conductors may set up a condition causing ( the dissolution of metals by electrical current). Installing a sacrificial anode rod similar to those used in hot water heaters can add another level of protection if your water has dissolved electrolytes. As a precaution, contact a water specialist to resolve water problems. Local water conditions are usually known by well drillers. Acid wells, spring water, surface water, mine water, or acid lake water present serious conditions you should be aware of. You may wish to truck in good water if these conditions are common in your area. Sweetheat

 

[jebatty]

...from the tarm storage tank installation guide. Check PH (acid content) once a year. Bring PH to 8.2 to 8.6 Add 2 lbs of natural baking soda to 600 to 1200 gallons of tank water as a precaution.

How much of this and what followed in your comment were from the Tarm manual? and which Tarm manual? None of that was in my manual.

Baking soda (sodium bicarbonate) is weakly alkaline. Other alkalines used include sodium carbonate (soda ash or washing soda), which is a stronger alkaline, trisodium phosphate (alkaline plus in some preparations used to precipitate calcium), and sodium hydroxide (lye, very strong alkaline, must be used with great care, can be DANGEROUS if used improperly.

 

[sweetheat]

please read my words. (from the tarm storage tank installation guide). E-mailed and supplied by tarm usa, inc with the STSS CO INC heading on top of the guide. under the heading owner info, check PH (acid content) once a year. bring PH to 8.2 to 8.6 add 2 lbs of (NATURAL BAKING SODA) to 600 to 1200 gallons of water as a precaution. check your water before filling the storage tank. the PH level of the water in the tank is critical. PH should be brought up to 8.2 to 8.6 to protect copper and brass in the tank and lines. have a water specialist treat the water coming into your house for acid. water containing electrolytes, salt or dissolved electrical conductors may set up a condition causing (the dissolution of metals by electrical current). installing a sacrificial anode rod similar to those used in hot water heaters can add another level of protection if your water has dissolved electrolytes. as a precaution, contact a water specialist to resolve known water problems. (UNAUTHORIZED ADDITIVES MAY VOID THE WARRANTY) Sweetheat

 

[jebatty]

Tough to follow a quote when quotations or highlight are not used, mostly because if any comment is added, can't tell where the quote ends and the comment begins. Hope your water treatment worked out OK.

 

[sweetheat]

sorry jim. the beginning is from me the last is from SSTC and tarm. I can private message you a copy if you wish. it is for the EPDM lined tanks that SSTC sells. I'm sure your pressurized tank is different. Tarm will e-mail you a copy if you request it. sweetheat

 

[Corey]

That is a pretty unique setup - don't know that I've ever seen stainless used for a storage tank...possibly just due to expense, but there are a few other issues that can crop up as well.

First I would ask - is the copper HX coil electrically isolated from the stainless. This would mean having insulated (plastic) fittings at the tank wall and having the HX coil suspended in the stainless tank using plastic supports. Ideally no part of the copper would touch the stainless. If the copper directly touches stainless, you have a good potential (pun intended) for galvanic corrosion. You've basically made a big battery with two dissimilar metals - copper and stainless steel. If you look up a galvanic series, (broken link removed) you can see that copper (bottom 1/4th of the chart) and most stainless steels (top 1/4) are pretty far apart which means there can be substantial galvanic corrosion.

The second issue - you will notice that stainless steel is broken down into two categories - 'active' and 'passive'. Basically, the reason stainless steel is 'stainless' is because it builds up a tightly adhering, relatively transparent oxide layer - almost like a natural 'clear coat' for the steel. When the oxide layer is built up, the stainless is called 'passive' - it really doesn't want to react with anything else. If the layer becomes scratched or wears away, new oxide forms from contact with the air and the steel remains relatively 'stainless' But, in boiler service - especially a water storage tank - this water often becomes stagnant. The combination of high heat and relatively little movement or aeration mean no oxygen in the water. This is good, actually preferred for cast iron boilers, regular steel pipes, copper pipe and fittings, etc. For these metals, no oxygen means no (or minimal) corrosion. But no oxygen also means if the oxide layer on the stainless is damaged or wears away - there is no nothing available to rebuild the coating. This is called 'active' stainless steel and it is now easily subject to corrosion.

The third issue - you mention well water, which I assume means no chlorine or ozone/ - normally a good thing for boiler service. But since this also appears to be your initial fill and it's early in the season I would wonder if you may be in the beginnings of an algae / bacteria problem. Surely all sorts of 'stuff' was introduced into the tank when the HX was plumbed, the tank was filled with fresh, but non chlorinated water - is it possible the tank hasn't seen high temps that would be associated with a full firing of the system? I would think 160-180F would probably be needed to kill off all the little nasties that were surely inside the tank. Any lower temp is probably just a big hot-tub breeding orgy for them.

It's really hard to say which of the three issues is the biggest cause for concern. But if you do wind up talking to a specialist, these are some things for consideration.

 

[pybyr]

That is a pretty unique setup - don't know that I've ever seen stainless used for a storage tank...possibly just due to expense, no oxygen in the water. This is good, actually preferred for cast iron boilers, regular steel pipes, copper pipe and fittings, etc.

you raise some excellent details, Cozy Heat

as far as stainless not being used for storage, well... I spent a goodly portion of the weekend "in the tank" bolting together my 1350 gallon (1200 net after expansion) 409 stainless sectional modular tank that should not cost me any more than an STSS liner-type of similar size and that will handle temps WAY above the liner types.

I'd post some more pictures in my other thread on that, but am too tired and need to get to bed to get ready for the joyous day job. more photos tomorrow evening....

Any thoughts on the galvanic relations between brass and 409 stainless?

I was going to use copper for my sensor wells, but plan to only ever leave this place in a coffin, and really don't ever want to come home to a leak, so if foot long brass nipples will be better than copper (for temp sensor wells) I'd rather do it well now than fix it later...

thanks

 

[tom in maine]

Having done a bunch of tanks with copper heat exchangers over the years, DO NOT add any chlorine to this tank. Once you heat it up, anything nasty will get knocked down.
I suspect that you are just looking at debris from before that is not a big deal.
Your approach to doing nothing is appropriate. I would remove anything that is floating on the surface that is easy to get.

Beyond pH, when anyone is dealing with any kind of metal tank, I would consider a corrosion inhibitor from a company that specializes in the application.
Messing with the pH is a good idea, but an inhibitor will work wonders if there are going to be any issues.
We used one that we picked up years ago when we were using a steel heat exchanger that was feeding an open tank directly. There was never any hint of rust in the water and being a
test tank, it never was run very much, since we endlessly changed out boilers and tried different designs.
The only coil we used was for DHW and that is still in use.

Tom in Maine

 

[Chris S.]

That is a pretty unique setup - don't know that I've ever seen stainless used for a storage tank...possibly just due to expense, but there are a few other issues that can crop up as well.

First I would ask - is the copper HX coil electrically isolated from the stainless....

The second issue - you will notice that stainless steel is broken down into two categories - 'active' and 'passive'....

The third issue - you mention well water, which I assume means no chlorine or ozone/ - normally a good thing for boiler service. But since this also appears to be your initial fill and it's early in the season I would wonder if you may be in the beginnings of an algae / bacteria problem... .

Cozy Heat- thanks for the trouble shooting advice. The copper and SS are electrically isolated just as you suggest, by plastic spacers at the tank wall and bottom of the coils. I don't know about the active/passive state of my SS, I'll have to watch for out for that. I've had the tank up to 160F here in the last couple weeks so hopefully that rules out algae/bacteria, but again I'll watch that too.

I've skimmed the worst off the top and now will just watch an see what happens through the season.