Galvanic corrosion - fitting choices

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welderboyjk

Member
Jan 29, 2009
36
South West, Michigan
I am going to be hooking up my boiler system soon. It will be an OPEN system. Is there a clear, concise, source for which fittings and materials to keep away from each other.
Yes, I tried the search function, but, it seemed to be kind of hit and miss. My quick read through the sticky "useful tidbits" did not turn up what I was looking for.

help
 
This what passes, where I work. going from steel to copper, you have to go to either brass or galv first. we us a lot of galv fittings on closed system for just this reason. On an open system, use as much cooper as you can afford or stay on top of the water treatment.
 
going from steel to copper, you have to go to either brass or galv first. we us a lot of galv fittings on closed system for just this reason.

You put zinc between copper and steel?
 
S.S. to copper direct, threaded or silver sodiered. Cast iron to steel. I have seen Galv spec for all types of process water systems it is sensitive to some types of water and electrolysis, pits from the outside in.
 
Stainless to copper is usually ok. Careful with brass, SS will dezincify cheap brass and leave you leaky.

Cast iron to black to brass to PEX works too.

Treat your water in open systems or it won't last long no matter what!

welderboyjk said:
What about going to/coming from a stainless plate xchanger? Copper ok?
Cast iron radiator 2 black iron 2 brass 2 pex ok?
 
It is not going to happen this year, but maybe next. I've got a 1700 gal. fiberglass tank I'm going to use for storage, I've also been able to come up with 3-4*8, 2-4*10, and 1-3*8 or 10' hydronic solar panels which will be incorporated with the tank. The loop to the panels will propably be running antifreeze and I'll put exchangers in the tank. Scored a couple of differential temperature pump controllers cheap so the controls for that should be all set.
The tank has a "manhole" in the top so putting an exchanger in there shouldn't be a problem, but what should I use? I was thinking about getting some DOM tubing section rolled. would that be ok?
Also, I haven't dug through the site for info yet but can anyone point me to some info on treatment of water in open systems?

Thanks.
 
I just finished plumbing my system yesterday. I have black iron fittings connected to brass connected to PEX and black iron connected to brass connected to copper. Copper and black iron never meet without brass in the middle. All of my fittings going from anything to PEX are brass. I had a guy who takes care of commercial boilers help me do all of the plumbing and this is how he said to do it. My system is semi-open (has an expansion bladder and a rubber ball where pressure above 3 psi can vent).
 
I’ve got a 1700 gal. fiberglass tank I’m going to use for storage

Is there a specifications plate on that tank that states its maximum temperature rating? And will it hold up to alkaline water at that temperature?

I know there are some epoxy/fiberglasses that will take over 300F air temps for years but most fiberglass won't hold up to near boiling water for long. You need to make sure.

And if it is rated for it that would be a most excellent score!
 
Re fiberglass. Like plastics there are many variations. I was told to be careful of some of the most common resins used in glass layups because they will soften with high heat.
If you have a fiberglass tank and you find heat may be a problem you could possibly insulate and and line it.
1700 gallons is a nice size.
 
I just finished plumbing my system yesterday. I have black iron fittings connected to brass connected to PEX and black iron connected to brass connected to copper. Copper and black iron never meet without brass in the middle. All of my fittings going from anything to PEX are brass. I had a guy who takes care of commercial boilers help me do all of the plumbing and this is how he said to do it. My system is semi-open (has an expansion bladder and a rubber ball where pressure above 3 psi can vent).


This bladder thing sounds interesting. How about some pictures.
 
Thanks I will check this out, I have some in direct storage that I need to deal with, this might be my fix.
 
To get the full picture, you would need to reference a galvanic corrosion series such as:

http://www.corrosion-doctors.org/Definitions/galvanic-series.htm
(probably the one at the bottom will do as it is fairly simple, yet includes most common metals)

Then you need the basic rules:

- The more anodic a metal is, the easier it is to corrode
- The more cathodic a metal is, the harder it is to corrode
- When two metals are connected electrically. the anode is where the corrosion happens.
- The further apart the metals are on the series, the worse the anode corrosion will be. Closer metals mean less/slower corrosion.
- "Geometry effects" can come into play - If you have a small amount of easily corroded anodic metal and a large amount of stable cathodic metal, the corrosion will be focused on the small anode and will occur rather rapidly. Example: A single iron fitting in a large run of copper pipe. Iron is more anodic (easily corroded) and if there is only one fitting, all the corrosion will take place there. Conversely, if you have a large run of iron pipe with a copper fitting, the iron will still corrode, but that corrosion will be spread out over a large area and will be much less of an issue.

Stainless steel in a boiler application is little bit of a shaky application. Stainless steel needs oxygen (in air or water) to rebuild it's oxide coating and keep it from corroding. Regular steel (and most other metals) do best with no oxygen once the boiler water is 'degassed'. Also, hot water has less solubility for gases so it tends to have very low oxygen content. So you have two competing issues - stainless needs oxygen to stay corrosion proof and may start to corrode if the oxygen goes away, but other metals corrode due to oxygen in the water. Good chemical treatment is imperative!
 
juddspaintballs said:
I just finished plumbing my system yesterday. I have black iron fittings connected to brass connected to PEX and black iron connected to brass connected to copper. Copper and black iron never meet without brass in the middle. All of my fittings going from anything to PEX are brass. I had a guy who takes care of commercial boilers help me do all of the plumbing and this is how he said to do it. My system is semi-open (has an expansion bladder and a rubber ball where pressure above 3 psi can vent).

Black to Brass to copper

What are the "physics" behind this?
 
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