Leaking Stainless Steel Hot Water Tank

Do you know what the pressure of your water supply is?

I believe that it is 60 psi to 80 psi but I am not sure. When the first tank was installed the installer said that the pressure was acceptable.

Please check if the stainess steel is 300 series or 400 series . If it is 400 series corrosion can occur at elevated temperature , but it is not expected with 300 series stainless steel , especially 310 or 316 grade which are acid resistant and are absolutely corrosion free for use with water.

If the water supply is standard it is either whatever medium is heating it corroding outside-in or bad workmanship. This could be faulty assembly or inappropriate materials-setting up a differential material action. I take it that the tank has the appropriate certification; have you asked your supplier if any other of these tanks that they have supplied to other installations faulted in the same way. The builder of the local trade association should be contacted and the manufacturers methods checked. The manufacturer should have a quality department to deal with this and standards certification to manufacture these tanks, if not change your tank manufacturer.

Thank you for your comments, suggestions and leads. Two years ago when I had the second problem I contacted the manufacturer who seemed interested but never followed through, so I do not have any data on similar problems. Hopefully this time I can get some comment by the manufacturer. The tank is a TFI (Thermo-Flow) manufactured in Massachusetts (USA) and can be seen on the internet. It was recommended by and installed by our oil dealer who is reputable.

Your description brings to mind the thought of galvanic corrosion. If so, installation of a sacrificial anode - a zinc - might be called for. Check with a local materials expert who can look at the system.

yes, the galvanic effect is significantly increased when the water flow direction is from copper to steel. Particularly if the waterpipes are used by you OR A NEIGHBOUR as the electrical earth sink. I suggest having your water tested for electrolytic salts and reducing the static pressure to 40 PSI. That pressure is sufficient to throw a 3/8 inch column of water over 40' from a hose. The water hammer effect alone will harden and crack most metal joints. Austenitic stainless doesn't harden much but it can still have spot corrosion where the surface coating is not perfect.

One repair possibility is to use the stuff they use to fix petrol tanks; this is a wash through process that puts a coating on the inside of the tank bonded chemically into the steel. I think the trade name is POR-15

Yes, I would agree that this is the most likely source of your problem. Use of a sacrificial anode would be the appropriate thing to try.

My experience with SS water heaters failing was due to water quality issues. The item that gave me grief was connected to potable water derived from bore water. The raw water had a fairly high mineral content but didn't seem to become super corrosive until is was chlorinated and passed through the Ion Exchange Resin Softeners (Permutit). The chlorinated raw water left brown residue and clogged up the sand filters etc, but the potable version after the softeners thinned out metal quick time. Copper pipes had a life of around 3 months and the SS Hydroboil lasted about 9 months. Hot water system elements also had a short life which was only extendable by lowering the temperature. That worked ok in Summer but come Winter there would then be insufficient hot water, not a good look in a construction camp.

Pump impellers, casings and seals also took a beating.

After the 4th water heater core failed in my 2002 Ford F350 diesel pickup, Ford finally announced a "grounding kit" that seems to have solved the problem. I had shared with them what a retired Alcoa man had told me. "When two dissimilar metals are in contact with each other, in this case steel (or copper?) and aluminum, one acts as the "donor." I think this relates to what the gentleman said about the sacrificial zinc anode, although he, along with most others on here are way over MY head.

Good luck,

Larry in Somerset, PA

Hi, I do not know your government standards, but I live near Calgary , Alberta, Canada, the water is glacier fed from ther Bow River, and adapted for the city of 1 million. The" hardness" of the water is high - 12 on the "scale", as opposed to soft at 6-7. The calcium in the water is the problem. Check out tankless on demand water heaters- i have 2 for a 4000 ft2 house which supplys domestic hot water & in-slab heating. I recommend "Rennai", a proven 20 year old Japenese technology. I f you do your yearly maintenance- manufacturers manual - with vinegar on the heat exchanger, similar to cleaning a coffee maker that percolates slower over time, you will have no problems, and save considerable monies versus a normal hot water tank that heats 24-7.

Ken in Canada.

How do you do the vinegar cleaning?

I never saw how they clean a coffee maker either. I would be interested to know as I myself had this problem but I did not know there is a way about it.

I know vinegar is excellent to clean up any discoloration on s/s.

regards,

Stainless steel varies- I remember a s/s water filter in a steam boiler feed line that dissolved the s/s mesh- rest fine- needs heat to react- the feed tank was preheated to 90'C to release dissolved gases & passed thru a water softening process- used mild steel mesh & no more worries-here we use mild steel water tank with internal heater with sacrificial zinc anode- even so, pitting corrosion occurs in 3-4 years- the mains water is approx. 600ppm tds- when switch to rain water, no more worries- just have to ensure pH of 7 in supply tank- can go to 9-10 pH(alkaline) by adding alkalizer. Remember a boiler exhaust stack (3 stacks) of s/s that shortened itself as the s/s collapsed!.

Neil,

That is pretty right. Mild steel with vitreous enamel lining and an anode is the most durable tank for hot water heating. Unfortunately some applications such as water boilers for coffee and tea in large mess rooms demand SS (up to 200 litres), makes you wonder how much nickel and chrome you get to drink in this application doesn't it.

Water softeners eat the anode quickly though, seems the ion exchange process makes a good electrolyte for all the galvanic corrosion half cell reactions.

Some good answers already here which may help you.

I feel that you may need to consider changing the piping and fittings to the same type of stainless if possible and investigating sacrificial anodes as well.

If I was you, I would read up on unwanted electrolysis too.

A lot of data are required to evaluate the problem such as: what is the operating pressure, temp., material thickness, welding procedure used, filler metal, joint design, shape of pinholes or areas of leakage, is there a corrosion, pitting and their locations, ... etc.... etc...., etc....

I think there is a problem at seam welded lines due to insufficient soundness of weldment, may be an overheating occurred at those areas of HAZ, or you may be you used incorrect filler metals. Also I like if you provide some photos.

According to the galvanic charts I have copper/stainless combinations have an EMF difference of 0.25V which would lead to corrosion of the stainless but the charts also suggest that this value is low enough to suit wet, non-saline conditions. 4 tanks in 6 years sounds like a more serious problem so perhaps, as suggested earlier, there is a voltage present which is accelerating this. Is it worth making sure that the tank & pipes are securely bonded together with earth straps or similar?

I have to say I've never seen a stainless hot water tank, they are normally copper, perhaps because of this very problem.

It seems to me that if you want to determine the root cause, you need to do a failure analysis. Cut the failed heaters apart, isolate and document the failure locations. Short of that, all brilliant guesses will be correct, or not. Once you have good data, you can begin to solve the problem. I'd begin by examining the removable anode rod at the top of the heater. If it's corroded away, you will have an important clue.

Thanks for everyone's comments. I appreciate the information. With respect to the annode, since the water heater is encased in an insulation blanket I do not know whether a removable annode exisits. There is the inflow and outflow to the boiler, the outflow to the domestic hot water line and an overflow flow with apressure valve. Nothing else is obvious so I'll have to check on this.

By the way, here is a link to the water heater:

www.tfi-everhot.com/pdfs/TFI_SSindirect.pdf

According to the manufacurer's web site, there is an anode on the top of the unit. It is usually made of magnesium and should be replaced before it completely corrodes away. It is called a sacrificial anode because its corrosion is supposed to protect the heater from corrosion. Once it corrodes away, the heater is no longer protected.

It's durable, it's reliable, and features a lifetime warranty against leakage. (Consult factory for warranty details.)

One thing others haven't mentioned: where you use the water, how do you turn it off? If there is a lot of water flowing from the mains into the heater and you stop it suddenly there could be a huge, if very brief, surge in pressure (water hammer).

It is called planned obsolescence. Buy your next tank from a different manufacturer...

I have with me Instantenous water heater working since more than 15 years without a single problem. It is not storage type heater but small tank with safety valve and immersion type 3 KW heaters. Ofcourse here we dont not have hard water so no corrosion.

Im in the heating trade. My first thought is do you hve a thremoexpansion tank if not this may be your problem when you heat your water it expands and if u have no expansion tank typically on a water system that is connected to a city water system they normally have a back flow prevention put in your line. So my thought is your tank is taking all the abuse of the expansion and flexing of all the seams and more. What this means is if u have 80 psi incoming pressure when your tank is heating up you may be getting a spike of up to 150 psi depending how much cold water was fed into your tank. Most pressure relief valves on hot water tanks are set to 150 psi. Have you ever had ur prv valve release any water?

I'd also look at the chlorine level, as well as the sacrificial anode. most all stainlesses are subject to chloride stress cracking, especially in the HAZ of weldments. The 400 series are more susceptible, but even the 300 series are subject to it.

I concur. Stainless steels are susceptible to chloride attack, more commonly known as stress corrosion cracking. Municipal water supplies generally are treated with chloramines to manage biological growth. Many states do not allow stainless steel water heaters for that reason.

Are all your neighbours having the same problem? Find a neighbour that is not having the same problem and find out how his system is diffrent. I hope you have a retaining sump round your heater so that your basement is not flooded each time. Perhaps you should consider renting the water heater.

Several issues may be present.

The 300 vs. 400 series is good general information, but something isn't jiving, and I haven't seen anyone suggest checking his velocities for possible erosion instead of corrosion. If the velocity in the water circuit goes over 7 FPS (and we try to keep it under 5, and this lower value is a non-negotiable limit for polymer piping) you could be eroding the piping.

Beyond that, if the water has chlorine levels greater than 0.2PPM residual (free chlorine) then you could be experiencing stress corrosion cracking of the ss at the weld locations. With respect to water quality as well, the pH should be kept on the high side of 7, and the higher the better for corrosion control.

If it were truly galvanic corrosion, the stainless is the more anodic of the two metals, as are all of the alloying elements in it, and it would be giving up mass (electrons) to deliver to the copper in this "battery".

Check the sacrificial anode first!

You should also look at using a plastic or ceramic insulating bushing/coupling between the copper and stainless steel in order to electrically isolate the two. Even if galvanics are not the primary failure mode, they may be contributing.

That said, the fact it has been failing at the seams is a strong indicator that there is a problem with chloride stress corrosion cracking in the HAZ of the weld.

There could also be issues with the manufacturer's welding processes. If there is too much heat input in the weld, you can sensitize the stainless and cause cracking as well. If the wrong filler rod is used, you can sensitize the weld too. Stainless steels are very sensitive to temperatures in the range of about 800-1650 degrees Fahrenheit. They must not be allowed to dwell for any length of time in that range or sensitization will occur. Once sensitization occurs, the only fix is remelting and repouring and re-rolling. there is no heat treatment that can fix it. you can read more about it here:

http://www.hghouston.com/ss_ic.html

As was noted earlier, stainless hot water tanks are a bad idea in potable water systems due to the chlorine used to sanitize the water and are illegal in many states. My advice to you is to give this up as a bad job and break down and replace the unit with one that is more suitable for potable water service. You may have legal recourse if the costs of litigation do not exceed the damages, but litigation can get real expensive real quick, so it might not be worth pursuing.

Many good comments on this thread. Here at the facility I work in we have several stainless steel hot water tanks and miles of stainless piping of various grades much of which is in contact with chlorinated water. If your not having your tank go through passivation(or isn't being done properly) it is greatly more at risk of failure. We learned this the hard way with some 4" stainless piping and after only four years are having to replace it. We do not use anodes, not sure if that's because everything here is meant to be food grade.

http://www.pfonline.com/articles/119806.html

4 tanks in 6 years sound like a more serious problem. It may be either due to your non-maintenance of the tank or the company is not using the best material . I am also using the stainless water tank for the last 6 years and it is giving me best service. The main reason behind is, I am maintaining the tank at regular intervals. I wash it almost once in a month. If you will see the condition of my water tank, you can't judge that it is six years old.