316L stainless indirect 2nd leak in 8 years

Solid_Fuel_Man

I have a 115gal solar indirect water heater with dual coils. I've had my second leak this week. Had the first one fixed by a certified welder, now I have a leak in another place. The tank shows dark brown "rust" in these leak areas only on the inside.

It's on well wate:

Total hardness 9.9 grains (170ppm calcium carbonate)

Chloride 1.75 grains (30ppm)

Ph 7.1

I'm at a loss, some research tells me that a lack of back purge can curse localized corrosion where 316L had been welded. We back purged the first fix, and will this one. But at what point do I just cut my losses and buy another? Thought this thing would last 20+ years on my good water. Never been over 140F at the tank top.

It's a Heat-Flo and they said it's out of warranty.

Gilmorrie

30 ppm of chlorides is relatively high. Stainless steel is susceptible to chloride stress corrosion cracking. The corrosion rate depends upon temperature and other factors. 140 deg F is the max temp of the domestic hot water? What is the temp of the solar-heated water that run through the inside of the coils? I'm thinking that stainless steel may not be suitable for your application.

BDR529

Yes it has been tough. What did the andoe look like? Got some that eat a rod in 6 months.

STEVEusaPA

They would probably void your warranty based on water quality.
Don't know if SS has an anode rod, mine doesn't.
--
Had a customer on well water who refused to do water treatment. I think she had 4 boilers in less than 20 years. Her plumber must've loved her.

hot_rod

here is the water spec from the manufacturer. looks like your chlorides are within their acceptable range. The HeatFlo tanks do have a large diameter stubby anode in the side, might be good to check it?

I'd switch to a glass lined steel tank if you have had repeated problems with ss?

Solid_Fuel_Man

No anode in mine.

@Gilmorrie it's not used for solar. Both coils are connected in series by an arrangement of 3 way zone valves for a condensing boiler. Wood heats the bottom only. 140 is measured at the tank too with a thermistor under the insulation.

@hot_rod they denied any warranty when I had the first leak, therefore I had it fixed (I dont have a TIG welder). It was made in 2009, i bought it as new old stock in 2011 and installed it.

It's a shame, very little scale buildup and it has worked well. I wanted a large tank (this is my own house) so I could burn wood once a day and not have to run out of hot water.

Solid_Fuel_Man

I can put an anode in it. What should I get? Aluminum or magnesium?

Solid_Fuel_Man

It's fixed for now.

I'm now looking for a replacement unit which isnt a gazillion dollars, hence why I bought this one as old stock. Wholesaler couldnt get rid of it.

The nasty streaks are from the internal "rust" which worked its way through the leak. Nothing else in the house has any brown streaks etc.

hot_rod

They ship with msg rods now, according to their spec

PerryHolzman

SS and some other alloys are great for many applications... until you weld them; unless the weld is then properly cleaned, passivated, and in some cases stress relieved.

As an Engineer who has spent much of his engineering career dealing with failures of industrial and power plant components I have seen this all too often.

The problem is especially acute with the 300 series SS, although it also does exist at times with ordinary carbon steel and other alloys.

When you weld metal you change the crystal structure, stress levels, and sometimes the composition of the "weld affected area."

Certain filler materials make things better, others make them worse (which are often the cheaper weld filler materials).

If a mfr get things right (which may involve preheat and post heat treatment of the weld) a weld requires no further chemical treatments for many applications.

However, it's not uncommon for a 300 series SS weld (or base material) to require chemical cleaning and passivating after welding to restore the proper chromium oxide passivation layer. I've seen 300 series SS rust like carbon steel where they had destroyed the chromium oxide passivation layer.

I don't have a good answer for this. Most hot water tanks are more of a lowest cost to produce consumer item than something expected to last in a plant with a corporation that will follow-up with a mfr who's products don't last.

I have no idea how to tell which mfrs are doing it right, and which are not.

I do have a Viessmann indirect hot water tank in my basement. Not cheap. I suspect that they do the welding and any needed treatments right.

I wish you the best with this,

Perry

Larry Weingarten

Hello, About what type of anode to install, I prefer magnesium for greater current flow and health reasons, but have seen aluminum used with stainless. Another option is to use a powered anode. It should never need replacement, can be transferred to a new tank if needed and will not put anything in the water.

Yours, Larry

Alan (California Radiant) Forbes

Nice job on the welding!

We get a few leakers on the welds here in the Bay Area, but our water quality is excellent. Because of that, I don't think an anode rod will do you any good.

I also have a Viessmann indirect in my basement and it's been fine for 13 years. Yes, it was expensive, but for mine and all the others we've installed, they're golden.

Solid_Fuel_Man

Anyone have any recommendation on a powered anode? Ceranode, Water Tank Tek, and others. I have absolutely no experience with powered anodes. But I'm going to buy one and see if I can prolong this tank, and at least move it to the new tank when this one springs a 3rd leak!


Happy Resurrection Sunday!

pecmsg

chlorine & Salt are eating them.

If you can get to the coil to weld just replace it with titanium coils. A little more $ up front but a long life.

We use them on Lobster & Ell tanks.

Larry Weingarten

Hi @Solid_Fuel_Man , Here is one brand that's good: https://www.corroprotec.com/ . Water Heater Rescue has them also.

Yours, Larry

PerryHolzman

pecmsg said:

chlorine & Salt are eating them.

If you can get to the coil to weld just replace it with titanium coils. A little more $ up front but a long life.

We use them on Lobster & Ell tanks.

300 Series SS should work with normal salt and chlorine levels seen in residential well or city water.

Titanium has galvanic corrosion issues with most common materials used in home and industrial heating service. That can be overcome with special connectors, etc. But, is a significant enough of a problem that it cannot be ignored. I've seen too many cases of HX failures caused by engineers and other plant personnel who thought the way they could eliminate their corrosion problems was by going to an all Titanium or other super-alloy with similar galvanic potentials.

The Titanium may not be affected. The attached piping was... Entire plants have been shut down (multiple times in the Nuclear world) due to not paying attention to galvanic mismatch of materials.

Perry

Solid_Fuel_Man

Where is the chlorine and salt coming from?

I have a well.

I'm wondering if an enameled steel tank with a powered anode would last longer. It would be much cheaper.

Canucker

> @Solid_Fuel_Man said:
> Where is the chlorine and salt coming from?
>
> I have a well.
>
> I'm wondering if an enameled steel tank with a powered anode would last longer. It would be much cheaper.

Salts are coming from road run off, most likely. Not likely chlorine, with it being well water. Regardless, I doubt that chlorine at normal disinfectant levels would affect it. I agree with @PerryHolzman ,if the weld wasn't passivated it would have contributed to its shortened life. We pinholed a filter made of 316 ss where I work due to grinding material hitting the exposed surface and it not being passivated (no one thought it would matter). The solution that subsequently went through it was aggressive but well within its capabilities to handle normally, but the residue started to oxidize quickly and we found the holes after 1 use. They left the same trails I see in your pictures.

bob eck

What about using a Vaughn stone lined solar tank you can get them with two coils.

ChrisJ

I still don't understand how companies get away with denying warranties on things that are defects. In your case the welds appear to be rusting, not the actual tank? How is that not a manufacturing defect!?

Jamie Hall

Many people confuse chlorine and chloride. No the same thing at all -- that difference of one letter really is important. That said, chlorides and stainless steel don't get on well together. You can't do much about the chlorides -- as has been said, probably road salt. You can do something about the tank. Glass lined will be a much better bet.

ChrisJ

@KC_Jones

Paul Pollets

The Viessmann Vitocell 300 uses 316ti. Has a lifetime warranty on the tank to original owner. Good to 500mg of chlorides..."Damage to the Tank resulting from a chlorine and/or aggressive
sulphate content higher than 500 mg/ltr. For calculation purposes,the chlorine and/or chloride content must be accounted for as 100% and sulphate – because of lower aggressiveness – with 20% of thetotal concentration. [For example, sample calculation: Water analysis shows 60 mg/ltr. of chlorine and 200 mg/ltr. of sulphate. Thereforeadd to the 60 mg/ltr. of chlorine and 40 mg/ltr.(which is 20% of200 mg/ltr. of sulphate) to cover aggressiveness of sulphate. Thetotal is now 100 mg/ltr. The Tank installation in this case is therefore permissible].

KC_Jones

> @ChrisJ said:
> @KC_Jones

@PerryHolzman pretty much mimics my thoughts on this, but written more eloquently than I could.

I think the best description I have ever heard of Stainless Steel is this, it will stain less than regular steel, but it is not immune. The grade of stainless can make a huge difference.

Manufacturers, especially ones that do welding should know this. Heat of any kind can impact the corrosion resistance. I've had a cut off wheel cause rust, I've seen welds rust.

I could speculate on what they are doing based on my experience in manufacturing, but will refrain since I don't have any hard evidence.

hot_rod

A lot has to do with the weld process and also if the stainless is pickled or passivated after the weld and cleaning.

Solid_Fuel_Man

My work in manufacturing facilities and fab shops puts me in contact with many great people on this. All have said that it was not properly (or at all) pickled and most likely not back purged during welding. Hence the excellent looking welds on the outside and the localized corrosion (on the welds) inside.

I put in a 60" magnesium anode as a measure of desperation. I ordered a Bradford White lifetime glass lined 119gal tank today.

I'm going to change out the tank and sell my SS one locally with full disclosure that it has been welded, but is not leaking at this time. Maybe someone will have some other use for it.

@ChrisJ I completly agree, however, I bought this knowing the 5 year warranty and it was significantly less expensive than even the glass lined steel one I am replacing it with. But.....this time I am buying a lifetime replacement unit. I'll be using unions in the right places!

@Paul Pollets I also looked into the Viessmann indirects for warranty reasons, but a glass lined steel tank was less expensive (remember I'm getting a 120 gallon). Both units carry a lifetime residential warranty as long as you own the house blah blah blah. So if I get 3 Bradford White units vs two Viessmann units, it wouldnt matter. I still have hot water, and can continue to use the units to burn wood once a day and have the storage to ride out a 24 hour period.

It also helps (we all know) when you buy the unit from local wholesalers who you do lots of business with and tell them it's for personal use!