STAINLESS AND ALUMINIUM CORROSION IN BUSHTRACKERS

 
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Joined: 12 Jul 2007
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Location: Kunda Park
State:: Queensland
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PostPosted: Fri Jul 13, 2007 1:57 pm    Post subject: STAINLESS AND ALUMINIUM CORROSION IN BUSHTRACKERS Reply with quote

Here is an answer on a question from a person concerned about dissimilar metals and the potential for corrosion. I have placed it here for your benefit, as a reference point in the Forum that we can refer to.

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Hello again XXXXXXX !

Look, the lone Ranger spent 20 years on major yachts before going back to roots of horses and travel in Bush; and if you will notice on my last van and on the Brochure the words "Land Yacht" on the back. I lived on my own series of many yachts for ten years full time and another ten part time. I used to rig yachts and outfit them for Trans Oceanic travel as a Business.. Here is the full answer to your question.

Many, and I mean many yachts have stainless stair treads up aluminium masts. While I largely agree with part of the dissimilar metals corrosion problem, it is not such a concern as it is in the yachting circles. I will go a little further and tell you the real Engineering involved so you can understand the basis for my answer of “don’t worry about it”:

Firstly) Over the years one of the best bedding type sealant to use as a barrier coat on alloy is Zinc Chromate Primer, and it is still available, but I would not bother... (My van is parked 20 Metres from saltwater out the back on a main boating channel and two blocks out the front from the Ocean Surf and get salt water mist and fog all the time. It is almost as bad as my yachts that sat in the salt water.. Ha!) You see us sealing screws with Sikaflek, but that is to stop leaks, metal of the screw will still bite metal of what it is screwed into, you cannot insulate screw from base, that is a fallacy I can assure you... GO AHEAD AND USE SILICONE OR SIKAFLEX ON THE THREADS, but this has NOTHING to do with your concern as this is only done to stop a water leak, there is still metal to metal contact as it "Bites In". A sealant has nothing to do with the actually metal to metal contact other than keeping the water out or (salt water which is the villain) out…

Secondly and (MOST IMPORTANTLY) on the concern about dissimilar metal corrosion: On the yachts there was more “stray current”, and you have dissimilar metals corrosion that is "Galvanic" and "Electrolytic". Now what that really means is that the dissimilar metals pass metal from one to the other, on a reactionary speed equivalent to the distance between them on the “NOBLE” Scale of the “Periodic Table of the Elements”. Now for that to happen, it is like a Plating process where one of the two metals acts as an Anode and the other a Cathode and donates metal from one to the other. HOWEVER, for that to happen, you have to have an ELECTROLYTE, which is an acid like in a battery, or SALT WATER… You do not have that problem on a Bushtracker.

The Automotive Industry routinely uses a common chassis ground, and this puts a lot of "stray current" all over the place and there is more corrosion potential there than on a Bushtracker.. Why? Because we run and INDEPENDET GROUND to each 12volt light or appliance, and do not use the alloy walls to ground to the chassis...

Anyway: Stainless and Alloy are not very reactive first of all. In all fairness, in my business, I used to take off stainless steps off masts that had been stainless riveted or stainless screwed ALL THE TIME, and there was in many cases only mild pocket corrosion after as much as ten years in salt water. Stainless screws, bolts, and stainless rivets and stainless fittings, are still the standard on aluminium masts all over the world. And we do not have the Bushtrackers running in salt water for the most part.. Laughing

Paperwork Engineering would indicated there is a practical problem…. No.. Physical Engineering of actually “DOING IT IN THE FIELD PROFESSIONALLY” indicates there is NOT a PROBLEM. We use stainless screws all over the Bushtracker van, and Stainless and Monel Nickle Stainless structural rivets in the alloy and have taken them apart after 10-13 years, no problem. You would have to induce more “STRAY CURRENT” by doing what the automotive industry does and use the frame for all negative connections of electrical fittings and we do not… Instead we run independent ground wires to each fixture to “Bond” them all to the ground plane. In addition to “Stray Current” you need to add an electrolyte as in salt water to get the electrolytic corrosion that is your worry… And this does not happen on a Bushtracker..

Short answer with above 20 years of proof: Ain’t gonna happen to any noteworthy degree, and I have not seen it in 14 years of taking apart Bushtracker vans as well …… So don’t worry about it, if you need I can elaborate further, but in truth is practice in the Field, there is not a problem to bother fretting over… AT ALL…

20 years of Doing It for real and full time on Yachts, and 14 years with Bushtracker, we have no dissimilar metals corrosion on our vans.

Regards, lone Ranger
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