Aluminum-Stainless Corrosion
I have a problem with my pedestal steering mount. I have to move the instrument-mounting arms. I removed the securing screws, but the arms won’t budge. They’re immobile, even resisting taps with a rubber mallet. I suspect the cast aluminum arms and the stainless guard have developed the dreaded dissimilar metal reaction fostered by the salt environment. My research has not produced any information on a reasonable way to free the bond. Do you have any suggestions or pointers? Clearly, WD 40 is not an answer.
-Paul Souval
Via e-mail
But time and patience can help. At least that’s been our experience.
Sometimes called hydrogen embrittlement, electromechanical, electrochemical, intergranular, stress or galvanic corrosion, the bonding of dissimilar materials costs the industrial world billions of dollars a year.
With refined metals, it occurs when two alloys (one anode, one cathode) come in contact. Add moisture (an electrolyte) and things really go to hell in a hurry. The metal that is the anode (the least noble) suffers most.
Nobody seems to know what the white stuff is… maybe pure atomic particles in a mash you could use to improve on Jim Beam’s Kentucky Straight, maybe an oxide, chloride, bromide, or Gorilla Glue.
For an answer about what to do about it, we crawled around the Internet; pored over encyclopedias and our treasured Machinery’s Handbook (25th edition yet, with a marvelous 72-page index), and called a couple of metallurgist friends. Everybody seemed to know how to prevent it, via insulation with lubricants or hard coatings of various kinds, or by providing cathodic protection. But nobody seems to know how to attack, dissolve or soften the white stuff.
The metallurgists said they had had success, as have we, by applying a penetrating oil, perhaps thinned with kerosene, or just plain kerosene – or maybe Liquid Wrench, which we find works a good deal better than WD-40 for jobs like this… and just waiting, waiting, waiting… and reapplying as many as a half dozen times over a couple of weeks. Tapping with a rubber mallet each time helps.
Sooner or later, the joint will soften and come free. The next problem may be dealing with the damaged surfaces where the aluminum and the stainless tried to get married, but, alas, made a mess of it.
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Cuprinol, Anyone?
Having owned and worked for more than 40 years on wooden boats, I am disturbed by the apparent current unavailability of dry rot inhibitors. It seems that the dominance of fiberglass has relegated wooden boats to the backwaters. For many years, Cuprinol was the standard treatment, and it worked fairly well if properly applied. Later, a tin-based product called Halts appeared and was very effective, but soon was banned by environmental laws. I don’t know that Cuprinol has now been similarly banned, but it is no longer generally available. Are there now any products that can help preserve our heritage boats?
-Bill Zieman
Wilton, Connecticut
Cuprinol is still legal and available.Its active ingredient is copper naphthanate, as opposed to chromated copper arsenate, as in arsenic, as in much of the pressure-treated lumber on the market. The EPA is setting new regulations and prohibitions on certain uses of chromated copper arsenate starting on January 1, 2004, but it seems that boatbuilders will be exempted. You can get Cuprinol from Jamestown Distributors (800/423-0030) among other places.
Cuprinol #10 – the green stuff for use on wood exposed to water – sells for $24.82 a gallon. The clear version (#20) is not the stuff you want.
And there’s still Git-Rot, sold by BoatLife. It’s a 2-part epoxy that’s drawn into rotten wood by capillary action and then sets up hard in the usual fashion. At $15.00 for 4 ounces, $28 for a pint kit (BoatU.S. prices) you wouldn’t want to tackle a big “turn-it-to-stone” job with it.
