Heat Exchanger Pencil Lead Fused!

[ArtJ]

The pencil lead in my MMI Exchanger would not come and broke off
leaving a wire core which broke off when trying to remove rest of zinc
I removed rest of zinc using flat screwdrivers to punch thru zinc
and ream it mostly free of zinc. then attempted to install new pencil
lead, but the bronze threads of the cap peeled off. The paassage
appears to have threads blocked with remains of old zinc and possibly
flattened from reaming with screwdriver. I bought a 3/8 npt tap
from Harbor Freight. I can't use torch due to proximity of
Fuel separator.

It was also suggested to not use tap as it could cut different threads
I bought a steel or cast plumbing plug of proper size as well.

Has anyone seen these weird Pencil Leads with a wire core?

Suggestions on how to proceed appreciated

Art

[edwardc]

Art,

I had the exact same problem last spring. A zinc with a center wire that came apart. I cleared out the zinc remains, and had to re-tap the hole to get the new zinc in. But I started having overheating problems. Turns out that there was a lot more spent zinc crud still left inside. The only way to properly address it was to remove the end cap and clean out the HX. This is much easier if you can remove the HX from the boat. I pulled both end-caps, and flushed and rodded-out all the tubes. Really wasn't that hard. Replaced the rubber end-seals and rubber washers with new ones, and kept the old ones for emergency spares.

[hanleyclifford]

What is meant by the term "spent" zinc?

[ArtJ]

Art,

I had the exact same problem last spring. A zinc with a center wire that came apart. I cleared out the zinc remains, and had to re-tap the hole to get the new zinc in. But I started having overheating problems. Turns out that there was a lot more spent zinc crud still left inside. The only way to properly address it was to remove the end cap and clean out the HX. This is much easier if you can remove the HX from the boat. I pulled both end-caps, and flushed and rodded-out all the tubes. Really wasn't that hard. Replaced the rubber end-seals and rubber washers with new ones, and kept the old ones for emergency spares.

Thanks

I believe that I may have used a cheaper zinc which had the wire in it
the source may have come from a on line discussion . I will only
buy zincs from trusted suppliers and test one by cutting it open
to make sure no wire.

The material the zinc was made of must be quite different than that normally used for Sacrifical Zincs and obviously not appropriate

[edwardc]

What is meant by the term "spent" zinc?

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.

[ArtJ]

Ed

Zincs normally dissolve, this one didn,t . The material must be different
such that Galvanic action deposited it, rather than disintegrated it.

Maybe even could deposit itself in the SW pump ??

[ArtJ]

This may be the source of these zincs

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[ArtJ]

Bottom line:

Bottom Line : How do we recognize which type of Zincs are appropriate and which will cause harm??

[edwardc]

Bottom Line : How do we recognize which type of Zincs are appropriate and which will cause harm??

Don't know. I guess the easy answer is to buy them here!

[ArtJ]

Since these pencil zincs look just like the good ones, they need to be
identified as to source of origin, material composition( why they coat
surfaces )so that they can
be purged from all A4 stock, otherwise heat exchangers, plumbing
and possibly pumps are subject to damage.

[edwardc]

This all starts to make some sense now.

I change my zinc every spring. Until about 3 years ago, I would go through about half of a (MMI) zinc in a season. The end would be cleanly gone, and there was no internal wire.

About that time, I found some inexpensive pencil zincs at a local chandlery and bought a pair.

Two years ago, when I removed the zinc, it was almost completely gone, leaving an internal wire exposed. I flushed things out as best as I could and installed a new zinc, but it went in with difficulty, and barely grabbed enough threads to seal.

One year ago, when I tried to remove the zinc, the cap twisted off, leaving the wire behind. I managed to grab and extract the wire (does this sound familiar, Art?) but the opening remained completely clogged. I managed to dislodge the crud with a screwdriver, and had to clean out the threads with a tap, but the new (MMI) zinc went in all the way. That's when I started overheating, and had to pull and clean the HX that you saw earlier. By the way, that HX cleaned up perfectly, with no damage or corrosion to the HX. It was just clogged up with a mix of gritty paste.

This spring, the zinc came out easily, with about half of the end cleanly gone and no internal wire in evidence!

Clearly, these "internal wire" zincs are of some alloy that leaves a much more solid corrosion product behind. I found a little information on "wire" vs "non-wire" types here:

http://www.rotometals.com/Pencil-Engine-Zincs-s/46.htm

I also found some comparison of Zinc Anodes vs Aluminum anodes here:

http://www.performancemetals.com/anodes/AnodeFAQs.shtml

The description makes me suspect that the "good" zincs that we want are actually made of aluminum!

As for determining if there's a wire inside, the only way I can think of that doesn't involve cutting one in half is to X-Ray it. (not practical unless you happen to be a dentist!)

It should be possible to tell Aluminum anodes from Zinc anodes by the weight. The Aluminum ones (actually an Aluminum/Zinc/Indium alloy called Navalloy) should be much lighter:

http://www.performancemetals.com/anodes/navalloy.shtml

[ArtJ]

Cut 2 open

I just cut the last 3/4 inch off 2 zincs.

Weight was similar

One I had and unsure if wire type , one new from WM.

Neither had the wire and weighed similar and both stamped Martyr .

In the past WM zincs had to be cut to length.

Unsure if Martyr also makes wire style as well

[ndutton]

Have you considered contacting Martyr? If you do, maybe ask them if there is a preferred alloy for boats kept in estuaries (brackish water) where water salinity can vary greatly. Boston Harbor and the Chessy are both estuaries and I would expect the deeper into the bay, the lower the salinity.

From Performance Metals Products:

Q. What anodes should I use in freshwater?

A. Where possible Navalloy™ (aluminum/zinc/indium alloy) anodes are recommended over zinc. Zinc anodes can become inactive after only a few months due to the build up of an insulating film of zinc hydroxide. Aluminum anodes will remain active. Don't take our word for it though, ABYC (American Boat and Yacht Council), who set the standards for the industry, clarified their recommendations on anode materials in the Standards and Technical Information Reports for Small Craft (July 2008-2009)

[ATTACH]11646[/ATTACH]

According to this information it's recommended you use aluminum based anodes given the areas you keep your boats.

[ArtJ]

Zinc has been used forever in mass and Cape Cod Never had problems
till now. BTW the pencils were not necessarily provided by Marytr SP


A good suggestion to call them Re: What's up with Pencils with WIRE core in them

[ndutton]

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.