corrosion of copper fitting at black pipe connection.

Brad White_133

such as an active ground can accellerate the effect of electrolysis. The presence of dis-similar metals in the presence of an electrolyte is in effect, a battery (BYOC!)

Or it could be, as another thread posted here some weeks ago, a "summer-winter" leak caused by expansion and contraction at the joint and seasonal weeping. For both pipe and Owner.

STEVE G.

corrosion of copper fittings on hot water heat closed system

i seem to notice more lately corrosion where a male or female adapter connects to black pipe on hot water boiler systems.It seems the electrolosis or bloom of calcium carbonate is much worse on some systems than others. Assuming there are no leaks in the system ( no excessive water feed, thus adding o2 to the system) What would be the most logical contributing factor?

heatboy

In a closed system.....

.... there is virtually no reaction between metals. Your issue is simply a lack of correct sealing up of the threads.

Unknown

Of course....................

electolysis could be an issue, why do they have "dielectric" fittings then? I agree with Brad, could be.

Ken_40

It's NOT

electrolysis!

The fitting(s) were tightened with the wrong style wrench (which "felt" snug more from "egging" the softer fitting - than actual circumferential thread-to-thread tightness), and/or the wrong pipe dope was used.

Larry Weingarten

This is an old debate.

Might I suggest a test? Take some of that "black gold" water from the system and test it with a TDS (total dissolved solids) meter. If it is possible to measure any continuity through it, than there must be electrolysis going on. If the electrolite is conductive, you get rust. Science wins!

Yours, Larry

ALH_4

nope

I agree with Ken. It's very unlikely if not impossible that this has anything to do with electrolysis. Electrolysis does exist, but this sounds like leaking fittings to me.

-Andrew

Aidan (UK)

and....

I'd suggest testing the pH if you can get a bit of litmus paper. If it's a sealed system, it should have chemical corrosion inhibitors in it which would typically alter the pH to about 8 or 9 (alkaline; 7 is neutral; below 7 is acidic).

If it's acidic, you have a problem.

Electrolysis/Galvanic corrosion happens much faster with an acidic electrolyte. If the copper fittings have beeen soldered with acidic/reactive/self-cleaning flux, and the residues haven't been thoroughly flushed out and neutralized, then it will make the water acidic and electrolysis will be a much bigger factor.

Plumbers love self-cleaning flux because it saves on elbow grease, but it will often accelerate elecrolytic corrosion. The active component is hydrochloric acid. Electrolytic corrosion was rarer in the old days; active flux wasn't commonly available.

The electrolyte in car batteries is acid; electrolysis produces the electricity. Keep your boiler water alkaline.

PS

If it is electrolysis, you would have to bleed the radiators regularly because they'll fill up with hydrogen. You can prove it's hydrogen by collecting it with an upturned glass over the air vent (it's lighter than air) and igniting it. Electrolysis breaks the water down into hydrogen and oxygen. The oxygen dissolves in the water and corrodes the insides of the radiators or black steel pipe. It turns the steel into an adhesive black sludge, which blocks the pipes.

Bob Bona_4

Ken and Andrew are right. Poor seal is the culprit.

F to copper adapters are evil, and don't come to my jobs..it's always a coupler/ MxS adapter.

The same evilness applies to dielectric unions, potable or not, in a res system, anyway.

Gordy

galvanic corrosion or electrolysis?

In order for galvanic corrosion to occur three conditions must exist.

1. Two electrochemically disimilar metals.
2. An electrically conductive path between the two disimilar metals.
3. There must be a conductive path for the metal ions to move from the more a anodic to the more cathodic metal.

If any ONE of the THREE do NOT exist than galvanic corrosion can NOT take place.

I think we are trying to refer to galvanic corrosion.


Gordy

Christian Egli_2

Coming up with big theories makes my head swell

When we apply heat to common materials, they too expand. Plastics expand humongously, copper expands a lot too, steel expands also, but not as much as copper. This is the key difference to keep in mind.

Of course, when we heat a stretch of pipe, it measurably grows in length, and shrinks upon cooling. If, on the other hand, we heat a hoop or a ring, the expansion will appear in a measurable growth in diameter. The diameter shrinkage we get upon cooling is the shrink fit used extensively in machine building. Nothing magic, just powerful stuff.

Can anything in nature resist this thermal expansion? Nope; if you try containing it, you'll get material deformation and breakage in exchange.

Let's see what happens when we expect two materials with different thermal expansion characteristics to live together in a tight union. We can imagine many configurations, here are two:

Let's screw a female thread copper adapter onto a male steel nipple. Let's make it a nice tight fit. No leaks so far. Let's wait next until things get hot. With heat, the two concentric slices of metal will expand in diameter.

Here, the outer copper ring will expand a lot, while the inner steel ring will expand less. What's cool is that nothing will bind: the copper ring will expand itself out of the way of the growing steel. The hot assembly will not be as tight as it was when cold and what might happen is a for a small when-hot-only leak to form. Upon cooling everything goes back to normal. Furthermore, considering the copper is on the outside, it may not be as hot as the inner steel, and so, it's normally increased expansion may be slightly reduced to match that of the steel - if we're lucky.

That was the ideal scenario. The next one can lead to problems.

Let's put the copper ring on the inside of the steel ring. This, we achieve by screwing a male copper thread into a female hole. It's done all the time. So far no leak, everything is tight.

Turn on the heat and observe.... ohh... the outer steel ring expands, yes, and tightly jammed within it, the copper ring is expanding too, and it's expanding way more than the constraining steel will allow it to grow... ohh... that's a problem.

Copper compared to steel or iron is like play dough, it's soft and it deforms very easily. If the inner copper hoop can't grow in diameter, it will deform, it will pile on itself and its thickness will change. When hot, this coupling will be tighter than ever. This is good only as long as we never cool the fittings again.

When things go cold between the two, the copper male insert will shrink down in size much more than the outer iron, and because play dough, like copper, does not spring back into its original shape, the cooled male copper to female iron coupling will leak. WILL leak, will LEAK, will leak, WILL LEAK.

The exact same happens within the dielectric union, here with the plastic ring changing shape until it no longer seals the gap.

Top of the water heater connections are particularly prone to these inescapable conditions. The only practical cure I can think of is to use lots of pipe dope and lots of teflon, all non-hardening, in the hope it will bung up the breathing gap. All this is also proportional to the temperature setting

Here perhaps, the Europeans, not used to nice taper taper tight fitting thread have an advantage with their use of hemp and greasy tallow mixtures. Their pipe fittings always leak, no matter what the metal combinations.

Of all the things that expand and shrink, it figures there'd be a way to get in trouble.

Galvanic corrosion is another serious problem all on itself, it's so real, it calls for the installation of sacrificial anodes; this type of perforating corrosion does not necessarily only occur at the mismatched threaded connection, it happens anywhere along the disfavored metal.

I'm all for Bob's methods.

Jerry_15

I've never seen a problem betyween copper and black when it was well tightened. Dialectric unions, on the other hand, always cause trpuble

timo888

resurrection

I'm resurrecting this old thread because I have a question about "black gold".



Is it called "black gold" because it is a source of revenue for the hydronic company? Or is it called "black gold" because it seals pinhole leaks and protects the system? Gold means it's desirable, but to whom?



[FULL DISCLOSURE: I'm a software developer and the Y2K issue was maybe our "black gold"??]



http://www.sludgecleanteam.co.uk/



In any case, when dissimilar metals are near each other in a galvanic bath, it's the less "noble" metal that gets destroyed. So it's the black pipe that's being eaten away not the copper.



I am wondering whether cleaning out the sludge would have any money-saving effects here in the US, where we have larger diameter pipes.