Heat Exchanger Pencil Lead Fused!

[tac]

I've been using Camp (a U.S. company) zincs for years, both for propeller shaft and heat exchanger (http://www.campcompany.com/home.php?cat=20). A couple years ago our local supplier stopped carrying Camp ("too expensive") and now carries Canada Metal "Martyr", made in China (http://www.martyranodes.com). They seem fine, so far. The heat exchanger pencil zinc appears to be solid metal, with no wire. The Canada Metal part numbers are the same as the Camp, except they start with CM. So the Camp pencil zinc E-1F (1/2" x 1-1/4") becomes the CME-1F. These dimensions are the O.D. and length of the anode only, not the pipe size of the brass plug.

Note that the pencil's thread and the plug's inside threads are a straight thread, not NPT. The plug's outside thread is NPT to screw into the heat exchanger.

Some places sell pencil zincs as one piece (plug and anode pencil), and some sell the pieces separately. I once worked for a boat builder who insisted on buying replacement anode pencils only, because he could save a few dollars per engine. If you're laying up 50 engines every fall, you can save a bit. Here is an example of what's left of a one year old Martyr 1-1/4" x 1/2" heat exchanger pencil zinc (CME-1F). It is shown unscrewed from its brass plug. The whole assembly costs $4.95. The anode itself is $1.99.

[ArtJ]

The Point

I don't doubt zincs have been used forever but the question is whether an aluminum based anode would be better for your waters. Performance Metals Products suggests it would and who knows, maybe Martyr would agree. Won't know until the question is asked.

The point is trying to identify the source and the problem with the
material used in the pencils WITH A IDENTIFIED METAL WIRE
CORE !! there has been no problem whatsoever with the Zinc based
pencils. Nothing to do with brackish water.

I have sent a email to Martyr

[sastanley]

Replace every year? uh-oh!!!

[ndutton]

The point is trying to identify the source and the problem with the material used in the pencils WITH A IDENTIFIED METAL WIRE
CORE !! there has been no problem whatsoever with the Zinc based
pencils. Nothing to do with brackish water.

I have sent a email to Martyr

Well, I'm glad you contacted them and looking forward to their reply. It seems to me there's been a big assumption about a material difference rendering them dangerous and that somehow the wire you found is an indication of a substandard product when there's really no conclusive evidence just yet. About the wire, there may be a reason it's there, we just don't know so it may be a little early declaring it a problem. Ed's link to the Rotometals site discusses the wire pretty well and the reason it exists. Seems if you want the wire, get a Type C, if you don't, get a Type P.

About brackish estuary water, my point was going forward after this incident wouldn't you want to use anodes that offer the very best protection for the type of water you're in? I know I would.

[hanleyclifford]

The sacrificial zinc is more electrochemically active than bronze or stainless, so galvanic currents cause it to corrode, protecting the other metals.

The process of corrosion turns zinc into (primarily) zinc hydroxide [Zn(OH)2], which has a low solubility in water. This the grey-white "paste" you see collected at the bottom of the HX.

Thanks Ed. The subject of zincs in exchangers has always puzzled me. The exchanger itself being copper would seem to be noble enough to protect itself. The zinc actually sets up a galvanic cell where none previously exists (save only the possibility of the solder versus the copper). Against what is the exchanger actually being protected? I have exchangers on my boat with 25 years of service under their belts with never a zinc. Interesting quote attributed to John Westerbeke in the first sentence: https://books.google.com/books?id=oC...angers&f=false

[edwardc]

I found this source for the Aluminum (Navalloy) pencil anodes:

http://www.go2marine.com/product/198977F/pencil-zinc-replacement-aluminum-pencil-anodes-navalloy-secure-core-npt-plugs.html

And, just to muddy the waters further, note that it too has the central wire, which they call "Secure Core"!

I went to the boat today and pulled out my last spare zinc anode and examined it. It appears that the zinc rod is cut to length during manufacture, and at the right angle you can clearly see the end of the wire core in it! So at least it should be possible to non-destructively determine if a pencil zinc has a wire in it.

[romantic comedy]

I had a diver tell me that my shaft zinc was fine and did not need replacement after 5 years in Florida salt water.

When I told him that it was 5 years he asked if I had a zinc in my heat exchanger. I told him yes, and he said that the exchanger zinc was probably eaten away.

not sure what to think of that.

Last time I had the exchanger out was 2009. The zinc was totally worn away. inside was a deposit on the end of the exchanger, right where the zinc was. It looked like the one pictured.

I had used a zinc purchased from WM.

[hanleyclifford]

It would seem that the "zinc" is already a three way party before it even gets installed - brass, zinc, and whatever the wire is made of. It would also seem the whole group would get eaten by the (copper) exchanger.

[ndutton]

Maybe something to be learned here

Here are Defender's opening comments on anode selection:

and this from BOAT US (bold face added for emphasis):

In recent years cadmium in zinc has become an environmental concern, leading to a movement in the direction of aluminum anodes. Such anodes are effective even for protecting aluminum components--lower end cases, for example--because the aluminum used in the anode is a more anodic alloy. Aluminum alloy anodes are almost certainly to become more common. It has not happened already only because the cost of aluminum anodes has been higher than zinc without any discernible benefit to the boatowner. Today aluminum is actually cheaper than zinc. In addition, aluminum anodes tend to last longer, they work better than zinc in brackish water (and maybe in salt water as well) and they appear to be better for the environment. When making the switch from zinc to aluminum, ALL of your anodes must be aluminum. This can be a problem in some locales as many local marine suppliers still do not stock a wide selection of aluminum anodes. That will eventually change.

[JOHN COOKSON]

The subject of zincs in exchangers has always puzzled me. The exchanger itself being copper would seem to be noble enough to protect itself. The zinc actually sets up a galvanic cell where none previously exists (save only the possibility of the solder versus the copper). Against what is the exchanger actually being protected? I have exchangers on my boat with 25 years of service under their belts with never a zinc. I

Yes.
Zinc is the sacrificial metal and copper has a lot more galvanic "pull" on zinc than almost anything.
Copper dismantles zinc which then turns into zinc hydroxide and can plug up the HX. Sometimes it gets rinsed or pushed out before it plugs up the HX. Sometimes not.
Try this sometime: Put a copper wire and a zinc galvanized nail with a wire on it into a lemon and touch both wires to the top of your tongue. Or if you don't want to go through the drill google "lemon battery".

TRUE GRIT

[joe_db]

So this has me thinking -
The zinc needs to *electrically* connect to the heat exchanger and be in contact with the salt water, but it does not have to be IN the heat exchanger. A tee fitting on the discharge side with a zinc and a wire to electrically bond it should work fine and all zinc residue can go overboard.
Or maybe - it needs to be in the fresh water side I would think it would work better on the raw water side. May be over thinking this..............

[hanleyclifford]

Yes.
Zinc is the sacrificial metal and copper has a lot more galvanic "pull" on zinc than almost anything.
Copper dismantles zinc which then turns into zinc hydroxide and can plug up the HX. Sometimes it gets rinsed or pushed out before it plugs up the HX. Sometimes not.
Try this sometime: Put a copper wire and a zinc galvanized nail with a wire on it into a lemon and touch both wires to the top of your tongue. Or if you don't want to go through the drill google "lemon battery".

TRUE GRIT

I think most of us agree on the facts as you have stated them. But the question remains - why go thru the exercise at all since the copper is noble enough to protect itself against (almost) all "comers"? What do you think about John Westerbeke's comment?

[hanleyclifford]

However...

When an exchanger is made up of more than one metal especially where the two are so widely separated on the galvanic chart, I can see the argument for zincs - big time; I had to make the repair on one where the salt had been run thru the wrong side.

[JOHN COOKSON]

When an exchanger is made up of more than one metal especially where the two are so widely separated on the galvanic chart, I can see the argument for zincs - big time; I had to make the repair on one where the salt had been run thru the wrong side.

Even when the metals are not "widely separated on the galvanic chart" zincs make sense. The reaction will just be slower the closer together the two metals are on the galvanic chart.
In my experience I noticed a bit of corrosion between the aluminum mast and the aluminum mast head fitting - probably due to different alloys of aluminum mixed with stainless steel screws.

TRUE GRIT

[hanleyclifford]

Even when the metals are not "widely separated on the galvanic chart" zincs make sense. The reaction will just be slower the closer together the two metals are on the galvanic chart.
In my experience I noticed a bit of corrosion between the aluminum mast and the aluminum mast head fitting - probably due to different alloys of aluminum mixed with stainless steel screws.

TRUE GRIT

Apart from the fact that most newer exchangers are all copper, the question then becomes: at what level of separation on the galvanic chart does the introduction of the messy affair of a pencil zinc become justified? Does any one zinc their mast?