You're right, Roger, even today, steel tubular engine mounts on airplanes
are typically treated with linseed oil on the inside after welding and a
nice epoxy or powder coat is applied to the outside.
ALUMINUM airplanes are treated with great, modern chemicals such as
Corrosion-X or BoeShield, ACF-50 and the like.
I'm not so sure that coating galvanized steel with anything but more zinc
is a good idea.
If you've had a tower up for a while, odds are that there are critters
living in the open tubes, at least on an itinerant basis. When they move on
or expire, they leave behind nests, prey, poop, and their own carcasses.
Then, along comes the tower owner and pours a concoction in the tower leg,
forever bonding this detritus in close contact with the inside of the tower
leg, making (you'll have to admit) some sort of anomaly on the inside
galvanized area of this leg, sealing and perhaps putting some sort of
corrosive substance (lizard urine, bird droppings?) in close contact with
structural steel with no hope of ever being ablated away by the natural and
intended oxidation of zinc.
Maybe it is just my imagination, but I've never seen a service bulletin
advising that this is a recommended procedure for towers.
I have, however seen advisories for corrosion treatment and even x-ray
examination of steel in aircraft!
Is anyone x-ray'ing tower legs yet?
73,
Mickey N4MB
On Tue, Dec 6, 2011 at 9:44 PM, K8RI <K8RI-on-TowerTalk@tm.net> wrote:
> On 12/6/2011 4:39 PM, Frederick Vobbe wrote:
> > I think most of us with older towers have, at one time or another,
> > painted or at least removed rust starting on the outside leg of a tower,
> > and repainted it.
> >
> > Has anyone done anything to the inside of the leg?
>
> Pouring sealant in from the top is a bit "after the fact", BUT the old
> aircraft construction sprayed linseed oil for rustproofing into the
> steel tubes that made up the strength of the fuselage.
>
> Were I going to recondition an old tower like the 25G or American Steel
> (BTW the American Steel towers of which I have used many) are no where
> near as strong as the 25G. I don't know what they are coated with but
> it's definitely not hot dipped galvanized. I would get some of the
> steel brushes used to clean the inside of copper pipe joints before they
> are soldered. Use brushes of a size that are a snug fit in the tower
> legs. Using a 1/4" to 3/8" rod at least as long as the tower section
> drill a hole at least a half inch deep into the end of the rod. 1/4",
> 5/16", or 3/8" steel tube might work. Half as long will work and might
> be easier for some to handle. Cut the handle off the brush leaving
> enough of the twisted wire to fit into the end of the rod and using
> either a set screw or solder...or brazing, fasten the brush to the end
> of the rod. Chuck the rod up in a variable speed drill and run the
> brush up and down through the tower leg as many times as it takes to get
> it clean. This may help to spot any rust that might be in there. If
> you get a lot of rust out, it'd probably be best to just pitch the section.
> Once the legs are clean inside, a flashlight should reflect off the
> inside making them look almost like the inside of a shotgun barrel.
> I'd then use a sprayer with Linseed oil or a spray can of LPS2 to coat
> the inside of the tower legs thoroughly. This will be messy. LPS 2
> has enough solvent in it to penetrate into tight places but will leave a
> grease like coating for protection. I've seen it used to
> rustproof/corosion proof portions of cars or aircraft.
>
> A pump up sprayer could be adapted with a tube to run the spray nozzle
> through the length of the leg getting a much better coating. OTOH the
> sprayer probably will not be good for much else afterwards.
>
> I'd be more inclined to clean the tower legs and then give them a good
> coating of the cold galvanizing inside and out with the rustproofing
> internally a few days later. What ever you put in there is likely to
> eventually wash out.
>
> Just remember that reconditioned old towers may have some weak spots
> that don't show. There is a tool (Ultrasonic) for checking leg
> thickness. I don't know where you'd borrow one and they are most likely
> expensive. We used to use them to measure tank and pipe wall thickness
> down to a few thousandths of an inch IIRC.
>
> 73
>
> and good Luck
>
> Roger (K8RI)
>
>
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--
Mickey Baker
Fort Lauderdale, FL
“Tell me, and I will listen. Show me, and I will understand. Involve me,
and I will learn.” Teton Lakota, American Indian Saying.
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