Boilers and anodes

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Chris Hollands
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Boilers and anodes

Post by Chris Hollands » Wed Aug 05, 2020 2:54 pm

Could you use anodes in a boiler to counteract corrosion and possibly be able to use S/S fittings in some places on a

boiler if the anodes were close to the fittings , this would be with boiler treatments also not just anodes .

I'm sure there are some boffins out there with the answer .

Just curious / interested ?
Last edited by Chris Hollands on Wed Aug 05, 2020 5:44 pm, edited 3 times in total.

Pontiacguy1
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Re: Boilers and anodes

Post by Pontiacguy1 » Wed Aug 05, 2020 4:49 pm

It used to be a common thing for people to screw a zinc anode into the front tube sheet of their boiler below the water line. I've rebuilt/worked on several that had a 1/8" NPT plug in the front where it was supposed to go. Railroad supply used to sell them. They were about 3-4 inches long. Not sure if they even sell them any more. Main thing now is that if you treat/filter your water and get the pH right, you shouldn't need them. I don't have too much experience with Galvanic corrosion, so someone else will have to answer the question about stainless use and the anodes.

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Chris Hollands
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Re: Boilers and anodes

Post by Chris Hollands » Wed Aug 05, 2020 5:39 pm

These are probably what you are talking about , this type is still very common on heat exchangers .
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Asteamhead
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Re: Boilers and anodes

Post by Asteamhead » Wed Aug 05, 2020 5:52 pm

Chris,
In case of using stainless steel for the boiler shell, an anode of aluminium :!: is recommended. It may be made of round material, which is pressed into a plug for easy replacement once a year. With my boilers these plugs are placed as washout plugs at the lowest edge of the firebox. Good results, no corosion inside the boler :)
Otherwise, any plugs and threads made of brass will corode instead!
Asteamhead

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Chris Hollands
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Re: Boilers and anodes

Post by Chris Hollands » Wed Aug 05, 2020 6:27 pm

Asteamhead do you use a certain type of aluminium for the anode, are standard zinc type anodes ok .

I'm looking more at protecting s/s fittings in a boiler but if what you have done would work for this purpose then great .

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Bill Shields
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Re: Boilers and anodes

Post by Bill Shields » Wed Aug 05, 2020 7:36 pm

Aluminum is the trick for a boiler

Zinc better for salt water environs although I am not a boat person..

Still have aversion to stainless in and around boilers...anodes or not.
Too many things going on to bother listing them.

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Greg_Lewis
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Re: Boilers and anodes

Post by Greg_Lewis » Wed Aug 05, 2020 8:19 pm

Here's a discussion of magnesium vs. aluminum anodes. While it is for water heaters, we probably have some of the same issues:
https://tanklesswaterheaterexpress.com/ ... magnesium/
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Chris Hollands
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Re: Boilers and anodes

Post by Chris Hollands » Wed Aug 05, 2020 9:15 pm

The joy of forums .
Bill or others please don't take this the wrong way , it is fine saying that you should not use this or that but without facts and data to back up what you are saying then what does it really mean .
From what I have seen on this subject regards brass and S/S use in a boiler , the material must dissolve in front of your eyes .
Will a s/s or brass fitting last 6 months / 2 years / 5 years I know this is an open ended question with a lot of variables .
If a brass or s/s fitting lasts quite easily 2-5 years in normal operation and be in a safe state but corroded then to me that is ok and will be replaced .
I have yet to see any hard facts on this forum regards the life of various fitting materials , there is lots of photos of various things in very bad states but no real F&D
If a boiler is maintained normally then corrosion of fittings should be seen before it becomes an issue and addressed if something is not working out as thought .
If people do not maintain there boilers correctly then it does not matter what material you use there will be an issue at some point .

From my experience working on pressurised systems for the last 40 years fittings rarely fail completely , there is usually warning signs that there is an issue and it should be looked at .

Please prove me wrong with facts and data :D

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Re: Boilers and anodes

Post by Glenn Brooks » Wed Aug 05, 2020 11:43 pm

Just for FYI, sacrificial (zinc) anodes screwed into brass plugs, such as shown above, are commonly available in the marine industry in variety of diameters, from 1/4” up to 1” or more. Maybe even smaller. They are widely used in bronze and cast iron heat exchangers and raw water exhaust systems. So any on line marine dealer, or local chandlery, could provide them.

The galvanic potential of dissimilar metals in fresh water is so extremely low- that anodes in fresh water service are almost always considered to have a multi year to permanent service life. Probably why nobody uses them in hobby boilers. The cost and effort to build the fitting into a boiler just isn’t worth the almost negligible corrosion risk afforded by fresh water systems.

I don’t have any experience with stainless boilers, so can’t comment on that aspect. but have seen stainless shafts, bolts, dry stack exhausts, and other weldments in the commercial fishing industry fail in very short order due to crevice corrosion - basically SS reacting to the lack of oxygen in a submerged, stagnant solution. So If you somehow create an anaerobic environment in a stainless boiler, you could expect serious trauma and failure in very short order. Anodes won’t help with crevice corrosion. But again, that’s a different animal.


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10KPete
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Re: Boilers and anodes

Post by 10KPete » Thu Aug 06, 2020 2:59 am

What he said! One of the best examples I can think of concerning aluminum/stainless steel things in salt and fresh water is the older Volvo-Penta outdrives. We've got tons of them around here and a lot of them are still giving great service. Like most marine drives, the housings are alloy castings ( beautiful! ) but all the fastenings, trim tabs (on the boat) reverse locks, shift cable fittings, water fittings.... are stainless steel. Usually 316L.
There is a bond wire that jumps the u-joints assuring the outboard parts are properly bonded the inboard parts.
They just don't rot from that metal combination!
What they DO rot from is poorly installed DIY stuff. Stray currents will eat anything metallic.

But the SSTL-Alum has never been a problem I've seen in the boat world.

Cheers!
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Bill Shields
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Re: Boilers and anodes

Post by Bill Shields » Thu Aug 06, 2020 5:36 am

I have personally experienced brass blow down valves failing catastrophically while in service after approximately 10 years of use. Also had brass boiler pipe fittings start to weep after less than 5....hence I now only use bronze up to the first valve.

Yes...I use brass piping plugs on my cleaners but change them every year when I pull out my aluminum anodes for replacement. Magnesium appears to work well also..but zinc appears to just sit there . So what is the point?

Stainless is subject to micro stress cracking. And while it probably will not fail catestrophically..why fool with something that is a headache to remove and generally not as strong as carbon steel?
.
Want a metal to use.. go with titanium alloy.. you can put it in and forget it. Which is unfortunately what happens to all the other boiler fittings. Install and forget and wait to see what happens. After all...how often do folks remove the cladding from a boiler just to inspect the footboard and handrail mounts?
Too many things going on to bother listing them.

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Re: Boilers and anodes

Post by Harold_V » Thu Aug 06, 2020 3:41 pm

Bill Shields wrote:
Thu Aug 06, 2020 5:36 am
and generally not as strong as carbon steel?
Hmmm. Tensile strength of mild steel is about 85,000 psi, while tensile strength of 302/304 ranges between 75,000/110,000.
316/317, cold finished bars, tensile strength ½" + diameter bars 75,000 minimum.
The above specs according to the EMJ stock book.

Just sayin'

H
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